The engine makes a lot of EM interference, it’s beneficial to place it as far away from the sensors are possible so it ends up at the back. Also convenient if you wanna look forwards without a prop in your way.
Still good.
They damaged an irreplaceable plane.
We can make a million more drones.
US Military Industrial Complex moment.
(I still think we should put ATAS on drones even if that's a bit accelerationist)
A much heavier plane sturdy enough for supersonic flight and high-G maneuvers hit a much lighter subsonic drone on the tail - I doubt there was much damage to the plane.
Anyway for them the main thing is that the Clumsy Ivan maneuver got the drone out of the sky with enough plausible deniability.
Counter measures.. eject volcanic ash into the airstream mixed with ball bearings and wait Come closer IVAN...pft pft....ingest some of that...Turmansky
Seriously surprised no one does this instead of flares and chaff...Volcanic Ash and Ball Bearings into the airstream especially for Chinese pilots who get too close
I've always thought this.
Could also be detonated to destroy any sensitive tech if there's a mechanical failure where the drone is going down over contested territory.
Is that any different than ground crews handling GBUs, missiles and other ordnance on manned aircraft?
But yeah, there might be an issue with overflying other friendly nation's territory.
Human brains are largely unaffected by propellers in the field of view and vibrations. On the other hand, there are advantages to tractor configuration.
The latter is more correct If you have an engine in any location, then the sensors move. Puller? Put the antennas in the back. Pusher? Front.
But yes, a radar in the front would def. need a pusher. Now....why a prop and not a jet?
Props are more efficient for low-speed loitering, which is the majority of what these types of UAVs do, as well as being cheaper and less complex.
UAVs where jets would be appropriate, such as high-speed drones or larger craft that need to remain stealthy (a propeller has a large and not-very-disguisable radar signature) do use jets - see RQ-170, S-70 Okhotnik, MQ-28.
Isn't it also just practical to not have the engine in the way when you try to find a place for all the sensors? From what i know of aviation many planes have their configurations to make sure that the airplane is balanced and just it being able to fit in the fuselage right?
A state trooper drives up to a drunk man pulling a chain up a hill, puts on his lights and gets out of the car. The trooper walks up to the drunk man and says "Hey you! Why are you pulling a chain up this hill?" The drunk, looks to the trooper and ponders for a moment before saying "Would you rather I push it?"
\-My dad, telling me this joke while helping me replace the water pump on a Saab 900, absolutely blitzed.\*
\*Honorable mention for "Just don't be a bitch about it" and "Sometimes it works, and sometimes it don't"
On the ground, yes. In the air it's less obvious. The terrestrial effect is because if you push at the back of a load on a frictional surface, you generate some moment that tends to drive the front end of the load into the ground. But in an aircraft, other than on the ground, you can easily compensate for any pitch down moment through design by doing something like changing the angle of attack of the elevator very slightly, since the elevator is already intended to create a pitch down moment.
There is a mixed bag of effects of pusher versus puller props and it's not necessarily clear that one is inherently more efficient than the other. Wing mounted pullers enable greater lift at lower speed because the engine is generating some of the necessary air flow over the wings, but simultaneously that means they're disturbing the airflow incident on the wing in a way that might not be great for efficiency. And single engine pullers basically don't benefit from that effect at all, but they still disturb the airflow.
Only where the fuselage is bulky enough that propeller blanking effects negate the gains from reduce tail loading, aerodynamic improvements over the body and control input reductions due to torque and wash effects of a puller configuration. All factors that profoundly effect modern, sleek drones.
> laminar flo not being disrupted
I'm extremely skeptical that there is ever any actual laminar flow over any surface of an aircraft. Just the presence of the boundary condition of zero flow at the mating of the airplane surface and air surface will necessitate the condition of turbulent flow, especially at any aircraft speeds.
Yeah only bits of it. You really only get laminar flow over a limited part of the whole airframe. "laminar" being a gradual velocity gradient from zero at the skin surface to the local airspeed of the aircraft (or any body moving through a fluid). For a wing section flow may only be laminar over the first 25% of the chord, or less. For subsonic flow, making maximum thickness further aft as possible helps. Look at a more laminar Mustang wing section vs, say, a Spitfire. (obsolete Aero degree here...)
Laminar flow is critical to flight and a huge part of efficiency: https://blogs.nasa.gov/armstrong/2011/02/11/post_1296777084480/#:~:text=Laminar%20flow%20is%20essentially%20the,of%20their%20shape%20and%20size.
There are plenty of examples of whole airframe laminar flow: https://www.popsci.com/story/technology/otto-aviation-celera-500l-explained/
I think you may be misunderstanding laminar flow over the aircraft and turbulence throughout the atmosphere.
>Sailplanes operate in a speed range where both laminar and
turbulent flow regions exist on the surface
[source](http://ak-ptuj.com/e107_files/public/1511726405_5_FT3170_393-1486-1-pb.pdf)
So even in the most optimal case there is a mixed bag. The most they can get is a managed area of conversion from laminar to turbulent flow.
It depends. As long as you have a laminar boundary layer you can have laminar flow over your aircraft. Only when the required pressure gradient gets too large, the boundary layer switches to a turbulent one. The conditions for laminar flow on a plane are very specific though. Most Gliders these days feature full laminar flow on the underside of their wings and almost full laminar flow on the upper side of the wing. It all depends on the wing profile, speed, size and atmospheric conditions.
The velocity of the fluid at the surface is zero this is due to no slip boundary condition. So yes you will have but the boundary layer increases along a 2d plate. And the vorticity increase as it moves downstream due to Stokes theorem. At a certain distance in fluids called Delta that no longer grows if I remember correctly it is sqrt of 1/re. From there the flow is laminar.
You are correct there isn't! However there are sections where it gets close enough. At those points there are static ports that are used to measure the outside air pressure for altitude. For aircraft that fly in heavily congested airspace with reduced spacing (RVSM, reduced vertical separation minimums) there are tables set up in the air data computers that take into account the variances from speed that affect the reading of the actual outside pressure. It's aptly enough called the SSEC (static source error curve). If you have any questions let me know! I do avionics engineering and testing.
I'm afraid it doesn't work that way. The wings are out of the way of a prop airflow with a front prop, but a rear prop is in the way of the disturbed airflow going round the fuselage. Rear props are a bit less efficient.
It's for other reasons, like balance or needing to fit a forward-looking sensor suite up front.
It's because it's the first thing to touch the air. You don't have anything in the way that might restrict airflow or generate turbulence.
There are also stability reasons. To be controllable, a plane should be slightly nose-heavy, and since the engine is the heaviest component of the aircraft, it just makes sense to put it in the nose. It also helps stability to keep the center of thrust ahead of the center of mass. Think of it like trying to pull a trailer vs push a trailer.
The last part about stability doesn't check out
Trailers are a totally different setup in terms of the dynamics. Any way you perturb the attitude of an aircraft the thrust line moves with it. You won't get a stabilizing or destabilizing effect from what you're describing
Now prop position can affect stability in other ways, especially with pitch dampening or speed interactions if it is above or below, but that's different and unrelated
Yep, and putting them on the wing would increase cost by at least two and for a system that’s not performance but survivability centric it makes sense.
The engine in the MQ-9 pictured is a turboprop, i.e. the same amount of maintenance as the jet + the gearbox for the prop. The MQ-1 had a 4-cylinder piston engine.
The reason they used a prop is efficiency at the speed and altitude the drone is operating, not cost or maintenance.
Efficiency. Drones fly relatively slow and low (at least the ones with propellers yes chicken and egg) and that is where propellers work best. They fly low because mostly they work with cameras so you can’t be too far or you will not see details due to weather and vibration. Then you also don’t want to be too fast because that is in efficient and makes it harder to stay around whatever you are looking at.
Jets want to fly at least twice as fast as a propeller plane, they also want to fly high where the air is thin and there is less drag. If you use them low and slow then they suck up gas at a very fast rate and that is not good for persistent surveillance.
20 year UAS operator here:
There are a few different reasons why pushers are the predominant design choice but there's not a specific reason since there are quite a few pullers and even multi engine UAS out there. In no particular order:
1) Weight and Balance. The entire purpose for a UAS to fly is to collect intelligence, and every other mission is secondary. That means payloads, payloads, payloads. There's no cockpit or crew to throw off your CG, so imagery payloads tend to go as far forward in the fuselage as possible to give good line of sight, synthetic payloads and retrans radio systems go on wing stations, so the only logical location left to put the engine is aft.
2) Efficiency. Take a look at any American UAS and what do you see? Antennas. Lots of them. Pretty much every type of parasitic drag you can think of. So you may as well go to a pusher configuration to minimize drag coming from the engine.
3) Launch systems. In the early days of UAS a lot of the tactical systems were put in the air by using some type of launcher system, either hydraulic or tension. That meant the aircraft would be static and oriented at an upward angle. To make crew access to the engine easier, the engines were placed aft to make them lower to the ground. And since most tactical systems don't have the ability to self start, you need the crew to be able to access the engine in order to start it.
4) Safety. Contrary to popular belief (or assumption) with the exception of the Air Force all of the services use enlisted personnel to fly and operate UAS, not officers. In the army it is not uncommon, and usually quite ordinary, to have an aircraft operator and aircraft crew chief both below the rank of SPC/E4. The conventional wisdom is that a dumbass junior enlisted soldier is less likely to walk into a propeller if you put a boom or a tail surface on either side of it. But, shocker, they still do.
5) Packaging. Similar to number 1. UAS tend to be smaller than manned platforms but they still require a shit ton of avionics and radios to keep them going. And being military systems they tend to be quite portly. So again, putting the power plant aft helps with weight and balance.
I say that with all the love in world because I was an enlisted operator before going into contracting and government work. But when I was a 21 year old specialist I was a fucking idiot.
Civilian here - I was once working/volunteering with a bunch of ROTC cadets on a project. Show up, start unpacking gear & tools from my car, couple of cadets come over to help. I hand one a fire extinguisher. "What's this for?" He asked. "I've worked with cadets before." I believe #4.
They are. Last Gray Eagle flight I observed had a PFC flying it, a SPC working the payloads, and a SSG crew chief.
There are officers and warrant officers in every UAS unit, but they typically don't do any flying at all. Every once in a while you'll find a warrant officer who will stay current and keep flying UAS, but I have never once seen or heard of a commissioned army officer flying one.
In addition to many great answers above, I'd like to add an educated guess that it also ensures engine exhaust doesn't pass over cameras and sensors which would degrade their performance.
Very likely it saves a lot of problems and cross sectional area ducting the hot air away from an engine that has IR sensors right behind it trying to look forward.
I was just about to say the same thing. I'm no drone expert, but a lot of the footage we see on TV is infer red and that would be messed up if the engine and its exhausts were at the front.
UAS Operator here. I have flown the Hunter RQ-5A/MQ-5B, which has a push/pull configuration, as well as the Aerosonde and ScanEagle systems, which are both pushers. The presence of the prop in the front of the aircraft makes no difference on our ability to collect on a target, as most of the time you're looking down and to the left. What does have an impact though is when your front engine expels some oil all over your payload lens. All the systems I've flown have had oil seepage for one reason or another, and while that's considered normal and accounted for, it's a pretty bad reason to have to break off a target.
Does it have to do with takeoff rotation? I thought most props on manned aircraft are up front because they’d hit the runway during takeoff rotation. Maybe these drones have small enough props so they don’t need to worry about hitting the runway?
When MQ-9s take off, they don't so much as rotate as they just start lifting off the runway. They have an incredible amount of lift compared to their weight, so they're pretty much level at takeoff, and only barely pitching up for landing
When MQ-9s take off, they don't so much as rotate as they just start lifting off the runway. They have an incredible amount of lift compared to their weight, so they're pretty much level at takeoff, and only barely pitching up for landing
nah, they sit pretty high up. [https://media.defense.gov/2023/Apr/25/2003207934/-1/-1/0/230421-F-TY635-1245.JPG](https://media.defense.gov/2023/apr/25/2003207934/-1/-1/0/230421-f-ty635-1245.jpg)
One thing folk aren't mentioning: CoM/CoL. Most of the weight in a cleanly configured drone (aside from the engine) is the sensor suite. Which is at the front. Makes sense to stick the other heavy bit at the other end from a basic aero perspective.
Outside of obscuring view of sensors as others have mentioned, all the electronics that control the sensors are in the front since that's where the sensors are. There is also all the mechanical assemblies like the camera gimbal that have large portions inside.
There would also be a large vibration and EMI source directly by your sensors.
I think on this scale, they glide better. When it's in loiter mode it will glide and finds currents in the air. The prop itself will fold in when it stops spinning to create a better gliding profile.
I could be wrong but that's what makes sense to me.
I fly RC planes and have both pushers and tractors. Tractors are very quiet because the prop is hitting clean air. Pushers tend to be very noisy because the prop is constantly chopping through two separated air masses. They can be made more quiet by moving the prop farther back from the trailing edges, but I've still never experienced a pusher that was actually quiet.
Would you maybe be able to add a duct to help the airflow be less turbulent? Not sure if it would work better or not, or if merging the airflow before the prop helps.
Not sure if a duct, but in the first drone pic, which I went back and looked at, they have made a lot of effort to taper the tail and move the prop out back. It's also a decent distance from the wings, which would make the most turbulence. So, I would think that one would not be loud... still not quieter than a tractor, but not bad.
I'll bet that 2nd drone is loud though.
Of course with these, it's a piston engine, so there's noise from that already. The difference between tractor/puller is very noticeable on electrics where the motor is silent.
What? Completely wrong!
Crosswind susceptibility only applies to takeoff and landing and is more based on landing gear configuration (nose wheel or tail wheel, how wide the main gear track is, whether the gear casters or can land with side loads); how long the wings are, how low they are, and if there are things (like engine pods, ordnance, or fuel tanks) hanging underneath that will limit slip angle; and the takeoff and landing speeds of the aircraft (faster means crosswinds affect them less).
Pushers require MORE vertical stab area. The centre of gravity is further back meaning that to counter the increased surface area ahead of it.. you have to add more behind it.
Acoustic footprint is awful because the prop has to cut through disturbed air rather than the clean air. That’s why planes like the Piaggio Avanti sound so loud.
Rearward CG can be compensated by a giant pile of sensors up front. On most drones the front boom is significantly longer, so it will easily counteract the CG of the prop.
It’s not about compensating for a rear CG, it’s the distance between the CG and the vertical stabilizing surfaces.
Take a look at the Reaper in the picture at the top of the thread. The CG almost certainly lives about a quarter of the way from the leading edge to the trailing edge of the wing, give or take perhaps 10%. The wing is - to my eyes - just a little bit offset to the aft of the midpoint of the tip of the nose to the tip of the spinner. So we can surmise the thing flies with the CG at pretty much the halfway point of its total length. But the stabs and associated ruddervators aren’t even at the very back of the aircraft length, so the arm on those surfaces is maybe 40% of the total aircraft length?
To have equivalent stability and control, you need a hell of a lot more vertical stabilizer and rudder area when their arm is less than half the length of the aircraft, than say something like a Cessna 172 where the relationship is probably more like 70%.
This is likely at least partly why canted stabilizers are a common feature in drones with this configuration. Get a bit of drag relief because while your stabilizers are relatively huge, you at least don’t need three full sized ones.
I also understand that pushers aren’t ideal for single-engine pax aircraft because in the event of a forced landing or crash, that engine may continue through the cabin and cause greater injury or death. Which isn’t an issue with single engines in the front.
Depends on the drone and mission. You showed a couple that are meant for medium altitude and slow.
Global Hawk, MQ-25, Avenger, XQ-58 are all full jet so no propeller.
I keep seeing posts asking seemingly innocent questions about military technology. MOD doesn’t this seem a little suspicious? Like phishing for classified info?
They're seemingly innocent because they are. These are very, very basic questions that all but the most decrepit and embarrassing military would quickly and easily figure out for themselves with only a quick round of testing and experimentation, the answers here might advance Sudan's military R&D efforts by like a week tops. I mean, maybe it's fishing for *something* special but it's also plausible that more wars = more people interested in stuff about fighting wars. Occam's razor and all that.
If somebody starts asking a bunch of highly detailed questions about the arrangement of the layers of molecular structure of the radar absorbing materials, or the sequences and methodologies used to encrypt the command links and secure them against jamming and hijacking, then I might be a little more alarmed.
Picture two is a Raytheon RQ7B legacy, it is a pusher with a rotary engine! Loud little fucker on the ground but the exhaust points up with no muffler, in the air it sounds like it’s 100 miles away if you can hear it at all! I operated these my last few years in the army! It uses a catapult to launch and lands on any flat and semi hard surface. Definitely a bad ass little platform for what it is
Sensors for the military are heavy, emf resistant cages and as much hardware that can not be knocked out with any kind of energy weapon, usually has old school relays and circuit breakers, it all adds up for sure. Not to mention mission specific payloads.
PT6 engine is backwards. Intake in front and exhaust in the back, just in front of the prop. Makes maintenance easy to have rear power section which can easily split off from forward gas gen section.
Prop wash distorts the camera view which is positioned in the nose or belly. Putting the prop in the back removes prop wash all together. Spoke to some pilots a few weeks ago and had same question.
More viewing angle for sensors, better thrust angle for the engine, in other words none, it also looks pretty badass probably the number one feature. Also if it's a terrible prop there should be almost no em interference, the military does not care about carbon emissions.
There are many aerodynamic advantages of pusher configuration over tractor. No prop wash over the wings, more compact fuselage with less wetted area and hence less drag and less weight. They are generally more stable because less wash, so they need less control/stabilising surfaces which has a number of benefits such as cross wind performance.
The main disadvantages are they are structurally more complex and maybe more difficult to design. Look at the second drones twin boom configuration for example. One of the reasons tractor configuration is common in ww2 monoplane fighters is because these planes were designed to be produced in mass.
I think why you see these more interesting configurations with drones are because they are unmanned and because of this fact the designers are more liberal and can take more risk in the design and hence often produce something more innovative.
The engine makes a lot of EM interference, it’s beneficial to place it as far away from the sensors are possible so it ends up at the back. Also convenient if you wanna look forwards without a prop in your way.
EM and probably just vibrations too. I work with civilian aerial survey equipment and vibrations can really make data hard to work with.
All good until you have a Russian ~~Mig~~ SU buzzing you over the Black Sea, from behind ;) Edit: Correction, as it was a Flanker
> buzzing If that’s the Russian idea of a buzz I would hate to see their version of a ram!
He had only had a pint of vodka prior to take off so he wasn't as sharp as usual.
Define "usual"...
Usually it's 2 pints.
One pint Vasily, 1 pint only - to be read in Sean Conery's voice. 😃
Ah, my favorite Russian accent
Five sheets to the wind
Don’t say that in a Sean Connery accent.
r/shubreddit ? ETA: seems to be gone :(
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Supply Chain Failures...
Your thought of ruzzian army is too far from reality. Vodka is for generals only, any person below that rank drinks defrosting liquid
No no comrade, his in-flight vodka ran dry.
Just a bit buzzed
Hah, you don’t know Russians use ethanol for antifreeze in cooling system. Na Zdorovia!
Alcoholics needs more to stay clear in the head, probably had a hangover ;p
OH YES HAHA RUSSIA WEAK RUSSIA NO HAVE TECHNOLOGY RUSSIA DRUNK HA HA EASY TO BEAT
With their accuracy I’d be more worried about a buzz, since that might mean they actually hit something
It's called a баран Hahaha thanks I'll show myself out
Still good. They damaged an irreplaceable plane. We can make a million more drones. US Military Industrial Complex moment. (I still think we should put ATAS on drones even if that's a bit accelerationist)
A much heavier plane sturdy enough for supersonic flight and high-G maneuvers hit a much lighter subsonic drone on the tail - I doubt there was much damage to the plane. Anyway for them the main thing is that the Clumsy Ivan maneuver got the drone out of the sky with enough plausible deniability.
Counter measures.. eject volcanic ash into the airstream mixed with ball bearings and wait Come closer IVAN...pft pft....ingest some of that...Turmansky
I was thinking “Spy Hunter “
Nice job, James Bond.
Seriously surprised no one does this instead of flares and chaff...Volcanic Ash and Ball Bearings into the airstream especially for Chinese pilots who get too close
Dumping fuel on you.
Drones like this kind aren't meant to be very survivable.
USAF should have slapped a bomb on it and command detonate it. Oops, did you SU blow up too ? Well, shouldn't fly so dangerously then.
I've always thought this. Could also be detonated to destroy any sensitive tech if there's a mechanical failure where the drone is going down over contested territory.
Sounds fun but in reality makes it pretty dangerous for ground crews and brings a myriad of other issues.
Is that any different than ground crews handling GBUs, missiles and other ordnance on manned aircraft? But yeah, there might be an issue with overflying other friendly nation's territory.
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Pretty good way to spin it TBF, as long as no one from FSB is within earshot. Pro tip, they are.
Flanker*
Wasn't a MiG hehe
Aren't those things true for a manned aircraft as well?
Human brains are largely unaffected by propellers in the field of view and vibrations. On the other hand, there are advantages to tractor configuration.
and that's the correct answer good show
The latter is more correct If you have an engine in any location, then the sensors move. Puller? Put the antennas in the back. Pusher? Front. But yes, a radar in the front would def. need a pusher. Now....why a prop and not a jet?
Props are more efficient for low-speed loitering, which is the majority of what these types of UAVs do, as well as being cheaper and less complex. UAVs where jets would be appropriate, such as high-speed drones or larger craft that need to remain stealthy (a propeller has a large and not-very-disguisable radar signature) do use jets - see RQ-170, S-70 Okhotnik, MQ-28.
Also RQ-4
That wasn't meant to be an exhaustive list. There are a lot of jet UAVs.
Flight time endurance. Jets use more fuel for that kind of flight regime.
Id also guess having a prop in front of the camera blowing any dirt right into it is less favourable.
Exhaust can be an in issue also with front engine. The heat can distort images
Isn't it also just practical to not have the engine in the way when you try to find a place for all the sensors? From what i know of aviation many planes have their configurations to make sure that the airplane is balanced and just it being able to fit in the fuselage right?
So, it's the same reasoning as the ship in 2001: A Space Odyssey.
I’m guessing better sensor space up front. Plus a lot of countries copy designs of existing ones.
Also if the heavy sensors are up front putting a heavy engine in the back can help with weight balance.
Same as if a heavy engine is in the front it will be balanced by heavy sensors in the back ;)
I suspect only being to see backwards would make flying the aircraft slightly more difficult
I'm guessing it's more efficient due to less drag due to laminar flo not being disrupted
Pushing is less efficient than pulling unfortunately
A state trooper drives up to a drunk man pulling a chain up a hill, puts on his lights and gets out of the car. The trooper walks up to the drunk man and says "Hey you! Why are you pulling a chain up this hill?" The drunk, looks to the trooper and ponders for a moment before saying "Would you rather I push it?" \-My dad, telling me this joke while helping me replace the water pump on a Saab 900, absolutely blitzed.\* \*Honorable mention for "Just don't be a bitch about it" and "Sometimes it works, and sometimes it don't"
Upvote for Saab 900!
Why was he pulling the chain up the hill? I wanna know the back story
I appreciate this little read c:
"Fuck 'em if they can't take a joke"
I MISS MY SAAB 900S 😭😭😭😭
On the ground, yes. In the air it's less obvious. The terrestrial effect is because if you push at the back of a load on a frictional surface, you generate some moment that tends to drive the front end of the load into the ground. But in an aircraft, other than on the ground, you can easily compensate for any pitch down moment through design by doing something like changing the angle of attack of the elevator very slightly, since the elevator is already intended to create a pitch down moment. There is a mixed bag of effects of pusher versus puller props and it's not necessarily clear that one is inherently more efficient than the other. Wing mounted pullers enable greater lift at lower speed because the engine is generating some of the necessary air flow over the wings, but simultaneously that means they're disturbing the airflow incident on the wing in a way that might not be great for efficiency. And single engine pullers basically don't benefit from that effect at all, but they still disturb the airflow.
Only where the fuselage is bulky enough that propeller blanking effects negate the gains from reduce tail loading, aerodynamic improvements over the body and control input reductions due to torque and wash effects of a puller configuration. All factors that profoundly effect modern, sleek drones.
it depends on a lot of factors really.
Source? That's a bold claim sir.
https://www.google.com/search
Mm the stock response from the baseless claim artist. Can't back up your own argument.
> laminar flo not being disrupted I'm extremely skeptical that there is ever any actual laminar flow over any surface of an aircraft. Just the presence of the boundary condition of zero flow at the mating of the airplane surface and air surface will necessitate the condition of turbulent flow, especially at any aircraft speeds.
Yeah only bits of it. You really only get laminar flow over a limited part of the whole airframe. "laminar" being a gradual velocity gradient from zero at the skin surface to the local airspeed of the aircraft (or any body moving through a fluid). For a wing section flow may only be laminar over the first 25% of the chord, or less. For subsonic flow, making maximum thickness further aft as possible helps. Look at a more laminar Mustang wing section vs, say, a Spitfire. (obsolete Aero degree here...)
I had to read that five times. I think I figured out what it means. I'm serious. And thank you
Laminar flow is critical to flight and a huge part of efficiency: https://blogs.nasa.gov/armstrong/2011/02/11/post_1296777084480/#:~:text=Laminar%20flow%20is%20essentially%20the,of%20their%20shape%20and%20size. There are plenty of examples of whole airframe laminar flow: https://www.popsci.com/story/technology/otto-aviation-celera-500l-explained/ I think you may be misunderstanding laminar flow over the aircraft and turbulence throughout the atmosphere.
>Sailplanes operate in a speed range where both laminar and turbulent flow regions exist on the surface [source](http://ak-ptuj.com/e107_files/public/1511726405_5_FT3170_393-1486-1-pb.pdf) So even in the most optimal case there is a mixed bag. The most they can get is a managed area of conversion from laminar to turbulent flow.
It depends. As long as you have a laminar boundary layer you can have laminar flow over your aircraft. Only when the required pressure gradient gets too large, the boundary layer switches to a turbulent one. The conditions for laminar flow on a plane are very specific though. Most Gliders these days feature full laminar flow on the underside of their wings and almost full laminar flow on the upper side of the wing. It all depends on the wing profile, speed, size and atmospheric conditions.
...and this is why I'm not an engineer, I guess. Ok, yeah, I follow you...at a safe distance...
The velocity of the fluid at the surface is zero this is due to no slip boundary condition. So yes you will have but the boundary layer increases along a 2d plate. And the vorticity increase as it moves downstream due to Stokes theorem. At a certain distance in fluids called Delta that no longer grows if I remember correctly it is sqrt of 1/re. From there the flow is laminar.
You are correct there isn't! However there are sections where it gets close enough. At those points there are static ports that are used to measure the outside air pressure for altitude. For aircraft that fly in heavily congested airspace with reduced spacing (RVSM, reduced vertical separation minimums) there are tables set up in the air data computers that take into account the variances from speed that affect the reading of the actual outside pressure. It's aptly enough called the SSEC (static source error curve). If you have any questions let me know! I do avionics engineering and testing.
I'm afraid it doesn't work that way. The wings are out of the way of a prop airflow with a front prop, but a rear prop is in the way of the disturbed airflow going round the fuselage. Rear props are a bit less efficient. It's for other reasons, like balance or needing to fit a forward-looking sensor suite up front.
If it came out the shape was just "the one the boss liked the look of" I wouldn't be that surprised
Kind of looks like a Burt Rutan VariEasy.
Propellers are cheaper and works better in alow speed compared to jets. Pusher propellers are not in the way for radar, cameras and other instruments.
Ok so reverse question, why is the prop in front for every other plane?
Because it’s more efficient
Is it because it blows more air over the wings to generate lift?
Mostly due to undisturbed airflow around the prop.
It's because it's the first thing to touch the air. You don't have anything in the way that might restrict airflow or generate turbulence. There are also stability reasons. To be controllable, a plane should be slightly nose-heavy, and since the engine is the heaviest component of the aircraft, it just makes sense to put it in the nose. It also helps stability to keep the center of thrust ahead of the center of mass. Think of it like trying to pull a trailer vs push a trailer.
The last part about stability doesn't check out Trailers are a totally different setup in terms of the dynamics. Any way you perturb the attitude of an aircraft the thrust line moves with it. You won't get a stabilizing or destabilizing effect from what you're describing Now prop position can affect stability in other ways, especially with pitch dampening or speed interactions if it is above or below, but that's different and unrelated
Pushers make sense bc the sensors will be looking forward or down, not backwards. So, you don’t get interference from the prop.
Yep, and putting them on the wing would increase cost by at least two and for a system that’s not performance but survivability centric it makes sense.
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Jet powered drones like Global Hawk also have their engine and intake in the aft. More space for sensors up front.
Jets are more expensiv and require a lot more maintanance. So if you do not need the soeed, stick with a prop
The engine in the MQ-9 pictured is a turboprop, i.e. the same amount of maintenance as the jet + the gearbox for the prop. The MQ-1 had a 4-cylinder piston engine. The reason they used a prop is efficiency at the speed and altitude the drone is operating, not cost or maintenance.
Also these kind of drones typically operate at (relatively) low altitudes where jet engines aren’t very efficient.
Efficiency. Drones fly relatively slow and low (at least the ones with propellers yes chicken and egg) and that is where propellers work best. They fly low because mostly they work with cameras so you can’t be too far or you will not see details due to weather and vibration. Then you also don’t want to be too fast because that is in efficient and makes it harder to stay around whatever you are looking at. Jets want to fly at least twice as fast as a propeller plane, they also want to fly high where the air is thin and there is less drag. If you use them low and slow then they suck up gas at a very fast rate and that is not good for persistent surveillance.
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Lol if all you have is a very expensive hammer then every problem has to be a nail.
No pilot to keep cool so it doesn’t have to be in the front.
Lol. The classic joke of when the big fan in the front quits, the pilot starts to sweat.
That’s golden 💀
The pilot still needs air conditioning.
20 year UAS operator here: There are a few different reasons why pushers are the predominant design choice but there's not a specific reason since there are quite a few pullers and even multi engine UAS out there. In no particular order: 1) Weight and Balance. The entire purpose for a UAS to fly is to collect intelligence, and every other mission is secondary. That means payloads, payloads, payloads. There's no cockpit or crew to throw off your CG, so imagery payloads tend to go as far forward in the fuselage as possible to give good line of sight, synthetic payloads and retrans radio systems go on wing stations, so the only logical location left to put the engine is aft. 2) Efficiency. Take a look at any American UAS and what do you see? Antennas. Lots of them. Pretty much every type of parasitic drag you can think of. So you may as well go to a pusher configuration to minimize drag coming from the engine. 3) Launch systems. In the early days of UAS a lot of the tactical systems were put in the air by using some type of launcher system, either hydraulic or tension. That meant the aircraft would be static and oriented at an upward angle. To make crew access to the engine easier, the engines were placed aft to make them lower to the ground. And since most tactical systems don't have the ability to self start, you need the crew to be able to access the engine in order to start it. 4) Safety. Contrary to popular belief (or assumption) with the exception of the Air Force all of the services use enlisted personnel to fly and operate UAS, not officers. In the army it is not uncommon, and usually quite ordinary, to have an aircraft operator and aircraft crew chief both below the rank of SPC/E4. The conventional wisdom is that a dumbass junior enlisted soldier is less likely to walk into a propeller if you put a boom or a tail surface on either side of it. But, shocker, they still do. 5) Packaging. Similar to number 1. UAS tend to be smaller than manned platforms but they still require a shit ton of avionics and radios to keep them going. And being military systems they tend to be quite portly. So again, putting the power plant aft helps with weight and balance.
I like answer #4. Lol
I say that with all the love in world because I was an enlisted operator before going into contracting and government work. But when I was a 21 year old specialist I was a fucking idiot.
Most of us are. I count myself in that category. The statement was funny because I never considered that. I have a b.s. in aerospace engineering.
Civilian here - I was once working/volunteering with a bunch of ROTC cadets on a project. Show up, start unpacking gear & tools from my car, couple of cadets come over to help. I hand one a fire extinguisher. "What's this for?" He asked. "I've worked with cadets before." I believe #4.
Current 13 year UAS avionics technician, I concur with your synopsis.
Thank you!
Are Army Gray Eagles flown by enlisted Soldiers?
They are. Last Gray Eagle flight I observed had a PFC flying it, a SPC working the payloads, and a SSG crew chief. There are officers and warrant officers in every UAS unit, but they typically don't do any flying at all. Every once in a while you'll find a warrant officer who will stay current and keep flying UAS, but I have never once seen or heard of a commissioned army officer flying one.
In addition to many great answers above, I'd like to add an educated guess that it also ensures engine exhaust doesn't pass over cameras and sensors which would degrade their performance.
Very likely it saves a lot of problems and cross sectional area ducting the hot air away from an engine that has IR sensors right behind it trying to look forward.
I was just about to say the same thing. I'm no drone expert, but a lot of the footage we see on TV is infer red and that would be messed up if the engine and its exhausts were at the front.
Because the sensors would like to be able to see forward.
UAS Operator here. I have flown the Hunter RQ-5A/MQ-5B, which has a push/pull configuration, as well as the Aerosonde and ScanEagle systems, which are both pushers. The presence of the prop in the front of the aircraft makes no difference on our ability to collect on a target, as most of the time you're looking down and to the left. What does have an impact though is when your front engine expels some oil all over your payload lens. All the systems I've flown have had oil seepage for one reason or another, and while that's considered normal and accounted for, it's a pretty bad reason to have to break off a target.
It keeps the spinny bit as far away from the looky bit as possible.
Cameras and sensors are mostly upfront. A front facing prop is going to interfere with the camera
The exhaust is a problem too. Cessnas fitted as camera platforms often have extended exhaust pipes to reduce that problem
Because forward looking sensors go BRRR! Forward looking sensors no like when prop in front go BRRR!
They are in the back so that people looking at them get confused in which direction they are flying…
Spilt all the beans man
No exhaust and oil mess on the sensors when the engine is in the back.
Does it have to do with takeoff rotation? I thought most props on manned aircraft are up front because they’d hit the runway during takeoff rotation. Maybe these drones have small enough props so they don’t need to worry about hitting the runway?
When MQ-9s take off, they don't so much as rotate as they just start lifting off the runway. They have an incredible amount of lift compared to their weight, so they're pretty much level at takeoff, and only barely pitching up for landing
It sits quite high with long landing gear.
When MQ-9s take off, they don't so much as rotate as they just start lifting off the runway. They have an incredible amount of lift compared to their weight, so they're pretty much level at takeoff, and only barely pitching up for landing
nah, they sit pretty high up. [https://media.defense.gov/2023/Apr/25/2003207934/-1/-1/0/230421-F-TY635-1245.JPG](https://media.defense.gov/2023/apr/25/2003207934/-1/-1/0/230421-f-ty635-1245.jpg)
Because, if the propeller of these drones is replaced with pulling one, they will fly backwards.
Unobstructed views
One thing folk aren't mentioning: CoM/CoL. Most of the weight in a cleanly configured drone (aside from the engine) is the sensor suite. Which is at the front. Makes sense to stick the other heavy bit at the other end from a basic aero perspective.
Just the same as you could put the engine in the front and the sensors at the back.
Outside of obscuring view of sensors as others have mentioned, all the electronics that control the sensors are in the front since that's where the sensors are. There is also all the mechanical assemblies like the camera gimbal that have large portions inside. There would also be a large vibration and EMI source directly by your sensors.
Interference drag is greatly reduced with pushers. You only need to be able to cool the engine properly.
I think on this scale, they glide better. When it's in loiter mode it will glide and finds currents in the air. The prop itself will fold in when it stops spinning to create a better gliding profile. I could be wrong but that's what makes sense to me.
It's about control. Pushers are less susceptible to crosswinds and require less vert stab area for stability. Acoustic footprint is reduced as well.
I fly RC planes and have both pushers and tractors. Tractors are very quiet because the prop is hitting clean air. Pushers tend to be very noisy because the prop is constantly chopping through two separated air masses. They can be made more quiet by moving the prop farther back from the trailing edges, but I've still never experienced a pusher that was actually quiet.
Would you maybe be able to add a duct to help the airflow be less turbulent? Not sure if it would work better or not, or if merging the airflow before the prop helps.
Not sure if a duct, but in the first drone pic, which I went back and looked at, they have made a lot of effort to taper the tail and move the prop out back. It's also a decent distance from the wings, which would make the most turbulence. So, I would think that one would not be loud... still not quieter than a tractor, but not bad. I'll bet that 2nd drone is loud though. Of course with these, it's a piston engine, so there's noise from that already. The difference between tractor/puller is very noticeable on electrics where the motor is silent.
Have you heard a Piaggio P180 compared to a King Air flyover?
This guy pushes
That aircraft and the similar Beechcraft Starship have a VERY distinctive sound.
What? Completely wrong! Crosswind susceptibility only applies to takeoff and landing and is more based on landing gear configuration (nose wheel or tail wheel, how wide the main gear track is, whether the gear casters or can land with side loads); how long the wings are, how low they are, and if there are things (like engine pods, ordnance, or fuel tanks) hanging underneath that will limit slip angle; and the takeoff and landing speeds of the aircraft (faster means crosswinds affect them less). Pushers require MORE vertical stab area. The centre of gravity is further back meaning that to counter the increased surface area ahead of it.. you have to add more behind it. Acoustic footprint is awful because the prop has to cut through disturbed air rather than the clean air. That’s why planes like the Piaggio Avanti sound so loud.
Rearward CG can be compensated by a giant pile of sensors up front. On most drones the front boom is significantly longer, so it will easily counteract the CG of the prop.
It’s not about compensating for a rear CG, it’s the distance between the CG and the vertical stabilizing surfaces. Take a look at the Reaper in the picture at the top of the thread. The CG almost certainly lives about a quarter of the way from the leading edge to the trailing edge of the wing, give or take perhaps 10%. The wing is - to my eyes - just a little bit offset to the aft of the midpoint of the tip of the nose to the tip of the spinner. So we can surmise the thing flies with the CG at pretty much the halfway point of its total length. But the stabs and associated ruddervators aren’t even at the very back of the aircraft length, so the arm on those surfaces is maybe 40% of the total aircraft length? To have equivalent stability and control, you need a hell of a lot more vertical stabilizer and rudder area when their arm is less than half the length of the aircraft, than say something like a Cessna 172 where the relationship is probably more like 70%. This is likely at least partly why canted stabilizers are a common feature in drones with this configuration. Get a bit of drag relief because while your stabilizers are relatively huge, you at least don’t need three full sized ones.
Why wouldn’t that be an advantage in human bearing planes?
Greater frontal lobe area for nav equipment
Sensor location and handling. Especially the ones from Insitu/Boeing.
They have cameras, sensors looking in feont
A human eye can See trough a Propeller, a camera has a Problem.
Safer for ground handling?
i think it helps with loiter time and as a lot of other people said, sensor placement.
The nose has to fit the avionics and communication
Sensors in the front, looking forward... Engine and prop at the back providing thrust... Simple.
Better view for front facing sensors/cameras. Wouldn't want them looking through a prop.
Saves fuel, increases control, helps with stealth
Also the left yawing tendency is reduced.
I also understand that pushers aren’t ideal for single-engine pax aircraft because in the event of a forced landing or crash, that engine may continue through the cabin and cause greater injury or death. Which isn’t an issue with single engines in the front.
Getting rear ended by your own prop is a hell of an image!
Depends on the drone and mission. You showed a couple that are meant for medium altitude and slow. Global Hawk, MQ-25, Avenger, XQ-58 are all full jet so no propeller.
So you can see out the front…….?
Radar is in the front
radar in the front, party in the back.
How about two vectoring parties in the back?
Not today foreign intelligence agency
That and loitering
My guess is that they don't have to go as fast as a manned aircraft. If it gets shot down, the only thing that's lost is money.
Cost and efficiency, pusher props are more efficient in flight but require different landing gear and longer runways.
Some smaller version engines displace oil all over.
In the event of an accident there occurs zero risk of a heavy engine making its way through the passenger compartment under own momentum?
Merican that's why
I think the answer is Weight Distribution. In this configuration the engine right at wing level
Classified
Quick Google search says: rear-mounted prop stabilizes the aircraft in pitch and yaw, much as an additional tail, but without control surfaces
I keep seeing posts asking seemingly innocent questions about military technology. MOD doesn’t this seem a little suspicious? Like phishing for classified info?
Seriously do you think those who search for classified infos will find it on Reddit?
They're seemingly innocent because they are. These are very, very basic questions that all but the most decrepit and embarrassing military would quickly and easily figure out for themselves with only a quick round of testing and experimentation, the answers here might advance Sudan's military R&D efforts by like a week tops. I mean, maybe it's fishing for *something* special but it's also plausible that more wars = more people interested in stuff about fighting wars. Occam's razor and all that. If somebody starts asking a bunch of highly detailed questions about the arrangement of the layers of molecular structure of the radar absorbing materials, or the sequences and methodologies used to encrypt the command links and secure them against jamming and hijacking, then I might be a little more alarmed.
If it's manned it's not a drone
Picture two is a Raytheon RQ7B legacy, it is a pusher with a rotary engine! Loud little fucker on the ground but the exhaust points up with no muffler, in the air it sounds like it’s 100 miles away if you can hear it at all! I operated these my last few years in the army! It uses a catapult to launch and lands on any flat and semi hard surface. Definitely a bad ass little platform for what it is
Sensors for the military are heavy, emf resistant cages and as much hardware that can not be knocked out with any kind of energy weapon, usually has old school relays and circuit breakers, it all adds up for sure. Not to mention mission specific payloads.
I would say electronics packaging if I had to guess.
PT6 engine is backwards. Intake in front and exhaust in the back, just in front of the prop. Makes maintenance easy to have rear power section which can easily split off from forward gas gen section.
The robot pilot needs to see over the nose..🙄
Fuel efficiency and loiter time
As Burt Rutan has shown many times it’s very efficient, low engine power settings good wing profile huge endurance
Cheaper to and way easier to work on
Prop wash distorts the camera view which is positioned in the nose or belly. Putting the prop in the back removes prop wash all together. Spoke to some pilots a few weeks ago and had same question.
Better laminar flow, less drag, balance, and higher payload.
Pushing P
Other than for W&B, it gives the optical sensors a clear, unobstructed view of what is ahead and off to each side.
why not? protects the motor when it crashes
More viewing angle for sensors, better thrust angle for the engine, in other words none, it also looks pretty badass probably the number one feature. Also if it's a terrible prop there should be almost no em interference, the military does not care about carbon emissions.
There are many aerodynamic advantages of pusher configuration over tractor. No prop wash over the wings, more compact fuselage with less wetted area and hence less drag and less weight. They are generally more stable because less wash, so they need less control/stabilising surfaces which has a number of benefits such as cross wind performance. The main disadvantages are they are structurally more complex and maybe more difficult to design. Look at the second drones twin boom configuration for example. One of the reasons tractor configuration is common in ww2 monoplane fighters is because these planes were designed to be produced in mass. I think why you see these more interesting configurations with drones are because they are unmanned and because of this fact the designers are more liberal and can take more risk in the design and hence often produce something more innovative.
Bailing out of pusher-config planes without ejection seat is quite dangerous, for obvious reasons. That's less of an issue for UAVs.
Better RCS from the front for sure