How do acrobatic Planes do loops, etc.?

[LongRoadBob]

I've been kind of curious while learning for PPL what makes an acrobatic aircraft be able to do loops, etc.

I'm just wondering. Assuming maybe wings design, that it can take more g force, but when a plane does a loop, does it pass through a stall, and then sort of go over to inverted flight?
Is it the thrust (like a helicopter) of the propeller, size of the motor that gives enough thrust?

Just what is going on aerodynamically in some of these amazing maneuvers?

 

[Cooter]

Aerodynamics is for the straight and level flyers. When it comes to aerobatics, it’s more of a Zen type of thing. You become one with your plane, and eventually learn to will the plane over the top. Having a leg mounted cassette tape piping tunes into your headset helps.

 

[Clark1961]

There are a few regular posters who practice aerobatics so they can give details.

The aircraft are designed for higher g-loads, at least 6 g and some are higher. For comparison our normal category spam cans are 3.8 g designs.

The condition inspections and repairs on show aircraft can be ‘interesting’ to say the least. I rented hangar space from an air show circuit guy. He flew a 400 hp Sukhoi. It got regular sheet metal maintenance. The tumbling stuff (accelerated stalls) those guys do is sorta hard on the equipment.

 

[RyanB]

It’s mostly due to the aerodynamics of the aircraft. Most of the aerobatic specific airplanes utilize symmetrical airfoils and have the wings mounted to the fuselage at a 0deg angle of incidence. These types of aircraft are also designed to handle higher g-loads than the standard 172, PA-28 etc.

As far as going through a stall while performing a loop, the aircraft does not stall or alteast it shouldn’t if it’s done correctly. Enough speed is carried through the maneuver to allow the loop to occur all in one motion, so no stall occurs.

In the Super Decathlon, the stick should be full aft as you’re coming through the top of the loop, otherwise you may get slow during the entry and stall before you reach the top. I’m not the best at explaining this subject, as I’ve only done Acro a few times. Lots of fun nonetheless!

 

[Capt. Geoffrey Thorpe]

You can loop a straight up Cessna 150 if you know what you are doing.

Start with a bit of speed to help you get around and keep the mighty O-200 firewalled until you come down the back side.

No worries. What could go wrong?

 

[jstro]

I fly a Super Decathlon. To do a loop, all you need is an airframe with suitable safety margin to handle the g-loads (and of course certified for such!). In a glider all your energy for the loop comes from the kinetic energy at the start of the maneuver. With an airplane you've got an engine and thrust, but even then some airplanes you'll need to put into a shallow dive to build up enough speed. With the Super D I'll be full throttle and put the nose down to achieve about 140 mph before pulling into the loop. Then a pull of about 3.5 g or so will make for a nice loop. You adjust the amount of elevator in the loop to make it as circular as you can. More powerful planes like an Extra 300 will easily do a loop from level flight. If you go into the loop without sufficient energy, you might end up out of energy before reaching the top and then your nose will drop and then you can pull through to upright flight. That won't be a very round loop!

 

[whifferdill]

In the Super Decathlon, the stick should be full aft as you’re coming through the top of the loop, otherwise you may get slow during the entry and stall before you reach the top.

Not quite...never in the course of any kind flying do you AVOID a stall by pulling the stick full aft. You should definitely not be using much aft stick on top of a loop. The objective is to float over the top in a fairly zero G state, or whatever it takes to keep fuel flowing to your carb if you have one. Zero G means neutral elevator, not aft elevator. Aft stick will produce, not avoid a stall over the top. But stalling on top of a loop is a big non-event. And it takes more than 3.5G in a Super D to do a really nice round loop as anyone who's ever gotten coaching from the ground knows. I've never seen anyone come close to doing a really nice round loop in any airplane who hasn't gotten a lot of help from the ground. It takes between 4-4.5G and waaaay more time spent floating over the top than folks want to do initially. For messing around acro, it doesn't matter - it's whatever G pull gets you up and over and makes you happy.

 

[Checkout_my_Six]

It has it's ups....and downs.

btw....the wing has no idea where the earth is....only the relative airflow.

 

[RyanB]

Not quite...never in the course of any kind flying do you AVOID a stall by pulling the stick full aft. You should definitely not be using full aft stick doing loops.

Not exactly what I was meaning, but I see what you’re saying. What I meant was that if you pull aft stick too quick you’re going to stall before you make it to the top and you won’t have any left. Last time I did Acro in the Super-D, we would have just enough aft stick left over at the top to get it to fall through the loop.

 

[N3368K]

Energy management makes it happen. The more powerful the airplane, the easier it is, to a degree. I've seen some beautiful acro in gliders which are truly graceful. I've seen some unlimited type which can execute gyrations which make you think it impossible. I do it for fun and know my loops aren't exactly round. And my rolls don't always end up back dead-on heading. But I have fun.

 

[denverpilot]

I've been kind of curious while learning for PPL what makes an acrobatic aircraft be able to do loops, etc.

Technically all aircraft are three-dimensional... if you didn't put more than the certified stresses on the airframe, they can all do basic "aerobatics"... FAA doesn't look too kindly on it in things that aren't at least certified to the Utility Category for certain maneuvers and of course, higher for other stuff, but the airplanes don't really care. For the reasons behind why some can do it better than others, that's about the loads presented by centrifugal and centripetal forces.

Think "steep turn". Gravity didn't go up, but you're putting 2Gs of load on the airframe in a 60 degree banked steep turn. That's a force added to gravity, but it's not gravity. Get set up in a level 2G turn and then pull real hard, and it'll be more than 2Gs to climb from it... you get the idea.

I'm just wondering. Assuming maybe wings design, that it can take more g force, but when a plane does a loop, does it pass through a stall, and then sort of go over to inverted flight?
Is it the thrust (like a helicopter) of the propeller, size of the motor that gives enough thrust?

Wing design, wing attach points, physical structure strength, bigger engines, yes... all of that. Bigger flight control surfaces, some aircraft have "spades" attached to the ailerons to help with stick forces... etc etc etc...

Some "aerobatic" airplanes are better at it than others, too. Everything is a trade-off.

And no, no real reason to stall to do a loop, just very little/no "lift" in the downward direction (toward earth) at the top.

Just what is going on aerodynamically in some of these amazing maneuvers?

Technically the aerodynamics isn't different from any other time... maybe during inverted flight since the wing is kinda doing its thing back-assward, but not much true aerodynamic difference. For you sitting in the seat, you're probably not used to being hung from your toes upside down, so that'll FEEL quite odd, but the airplane doesn't really care, aerodynamically.

It DOES care for things like oil sumps and pumps and all the usual mechanical stuff that normally occurs upright... many "aerobatic" aircraft have inverted-oil systems for the engine, for example... some don't and have limits on how long you can be without our old pal gravity in the usual downward/toward the landing gear direction.

You COULD barrel roll a Skyhawk AND keep it well within the load limits of the aircraft, if you knew what you were doing... but it's very ill-advised (and illegal) because it's easy to screw it up and overstress the structure of the airframe. Make sense? It's not really the rules or the certification that makes an airplane "aerobatic", they really make the airplane "much more suitable for aerobatic flight", truly.

 

[James331]

Keeping it around 1G with enough sky real estate you can loop just about anything.

Just watch the G loading

Now here's aerobatics done right in a non aerobatic plane

 

[Cooter]

never in the course of any kind flying do you AVOID a stall by pulling the stick full aft.

This has had me thinking.......aaaaannnd I decided that I’m going to have to go ahead and disagree with this one.

I think.

If you mean stall simply as exceeding critical AoA, then maybe. But if stall can mean controllability, then no. Some aircraft have stabs that are able to continue to move the nose beyond the critical AoA. So if you’re nose high over the the top, full aft can get the nose to track back below the horizon and avoid having the airspeed degrade to the point where controllability is lost.

So basically, there are times when full aft over the top can preserve controllability though the airfoil may actually still stall.

 

[murphey]

Carefully. Very carefully.

But seriously, check out the IAC website for lots of great info.

https://www.iac.org/

 

[coloradobluesky]

Entry speeds for various maneuvers are important. They even write them down on the panel on some of the Citabrias. But its nothing to teach yourself. Get instruction. Lots of ways to screw up. And the consequences are really serious if you screw up badly.

 

[iamtheari]

never in the course of any kind flying do you AVOID a stall by pulling the stick full aft.

“All general statements are false.” If you are inverted, you wouldn’t necessarily pull full back stick to avoid a stall, but it would probably work if you didn’t just yank it from forward to full back in a tenth of a second.

All maneuvers come down to energy management. Stalls, basic turns, chandelles, hammerheads, etc. The normal loop requires the right energy going into it and the right amount of back pressure to keep it round (at the top, gravity helps you, so you don’t need as much back pressure), but it is positive G relative to the airplane all the way through.

 

[whifferdill]

If you mean stall simply as exceeding critical AoA, then maybe. But if stall can mean controllability, then no. Some aircraft have stabs that are able to continue to move the nose beyond the critical AoA. So if you’re nose high over the the top, full aft can get the nose to track back below the horizon and avoid having the airspeed degrade to the point where controllability is lost.

So basically, there are times when full aft over the top can preserve controllability though the airfoil may actually still stall.

Not following how pulling the stick full aft preserves "controllability". Are we still talking about loops? If you're getting too slow and nose high before reaching the top of a loop, if you just hold the stick neutral, the airplane will just fall through a parabolic arc back down. Don't know how that's not controllable or why the rush to get the nose down by stalling the airplane. Use the elevator to keep the nose pitching around how you want, but taking it to the point of stalling the airplane doesn't accomplish anything.

Now that I think I about, there is one time I'll use full aft (or forward) stick to aid in "controllability" - during tail slides to make sure the airplane doesn't flop the wrong way that I want. But that's unrelated to causing or avoiding a stall.

 

[whifferdill]

“All general statements are false.” If you are inverted, you wouldn’t necessarily pull full back stick to avoid a stall, but it would probably work if you didn’t just yank it from forward to full back in a tenth of a second.

I'm still confused how an airplane can be on track to stall (thus requiring stall avoidance) if the stick is never close to full aft. Just because you're pointed uphill and slowing down doesn't mean you're about to stall...you're just an arrow following a parabolic arc.

 

[Cooter]

Not following how pulling the stick full aft preserves "controllability". Are we still talking about loops? If you're getting too slow and nose high before reaching the top of a loop, if you just hold the stick neutral, the airplane will just fall through a parabolic arc back down. Don't know how that's not controllable or why the rush to get the nose down by stalling the airplane. Use the elevator to keep the nose pitching around how you want, but taking it to the point of stalling the airplane doesn't accomplish anything.

Now that I think I about, there is one time I'll use full aft (or forward) stick to aid in "controllability" - during tail slides to make sure the airplane doesn't flop the wrong way that I want. But that's unrelated to causing or avoiding a stall.

You’re assuming an airframe that self corrects a nose high i.e, the nose immediately falls. Not all aircraft do that and the nose won’t track down to the horizon without aerodynamic forces acting not on it. Nose high, too slow means flopping around for several iterations until the speed restores normal control input function. Inverted nose high may require a full aft input to avoid getting there.

 

[whifferdill]

You’re assuming an airframe that self corrects a nose high. Not all aircraft do that and the nose won’t track down to the horizon without aerodynamic forces acting not on it. Nose high, too slow means flopping around for several iterations until the speed restores normal control input function. Inverted nose high may require a full aft input to avoid getting there.

Airplanes are totally self correcting and behave just like the arrow pointed uphill unless the silly pilot gets in the way and tries to keep the nose up by continually adding more and more pitch input. I've flown a bunch of acro in a bunch of different airplanes and never flown one that needed a full elevator deflection input to move the nose down if needed. Still don't understand the motivation to thrash the controls around. No aerobatic instructor teaches what you describe I don't know anyone in the acro community who would say something like this ever needed or helpful. Elevator authority goes way down once you've reached full deflection. A good acro pilot knows that max performance is about NOT getting to this point.

 

[denverpilot]

I'm still confused how an airplane can be on track to stall (thus requiring stall avoidance) if the stick is never close to full aft. Just because you're pointed uphill and slowing down doesn't mean you're about to stall...you're just an arrow following a parabolic arc.

You’re assuming an airframe that self corrects a nose high i.e, the nose immediately falls. Not all aircraft do that and the nose won’t track down to the horizon without aerodynamic forces acting not on it. Nose high, too slow means flopping around for several iterations until the speed restores normal control input function. Inverted nose high may require a full aft input to avoid getting there.

Not to mention arrows usually don’t have a spinny thing hooked to a rubber band on the front and no airflow from said spinny thing flowing over their tail feathers.

Any power being produced in a prop driven airplane is going to have an effect on airflow over the empennage controls and to some extent, over the wing itself resulting in a non-ballistic flightpath. Thus why you can stick stall fences on my airplane that will essentially make it “hang on the prop”, really it’s hanging on the center wing section not being fully stalled due to propwash.

 

[Cooter]

Airplanes are totally self correcting and behave just like the arrow pointed uphill unless the silly pilot gets in the way and tries to keep the nose up by continually adding more and more pitch input. I've flown a bunch of acro in a bunch of different airplanes and never flown one that needed a full elevator deflection input to move the nose down if needed. Still don't understand the motivation to thrash the controls around. No aerobatic instructor teaches what you describe I don't know anyone in the acro community who would say something like this ever needed or helpful. Elevator authority goes way down once you've reached full deflection. A good acro pilot knows that max performance is about NOT getting to this point.

No need to get angry. You made an absolute, unqualified statement and I’m pointing out that it isn’t absolutely true. Needful, helpful, good or bad pilot isn’t the point. I’m sure you’re a good acro pilot but your statement extended beyond your experience. I wasn’t trying to start an argument, just trying to clarify a point for general edification. My experience, in aircraft you likely haven’t flown, is that in certain circumstances you have to get the nose down back down or else your going to be flopping around until the relative wind straightens you out. It may not matter in your flying but it does in mine.

Also, to your analogy. Depending on the construction of the arrow, it will swap ends once and point straight back down or it will flop around until the wind is sufficient to determine its orientation. If we’re talking about a short heavy arrow with a light point and small fletching/feathers, it won’t self correct immediately. That’s what I’m talking about. In the latter case, influencing the nose/point will limit the transition to nose down flight.

Again, just trying to be accurate, not argumentative.

 

[whifferdill]

My experience, in aircraft you likely haven’t flown, is that in certain circumstances you have to get the nose down back down or else your going to be flopping around until the relative wind straightens you out. It may not matter in your flying but it does in mine.

LOL, not angry. What's the aircraft type and specific maneuver situation you're referring to?

 

[Cooter]

LOL, not angry. What's the aircraft type and specific maneuver situation you're referring to?

I’m taking about going ballistic, or rather trying not to.



I also did some acro training in Citabrias and Decathlons but not a lot. They don’t really handle the same as a 65,000lb piece of metal.

 

[iamtheari]

I'm still confused how an airplane can be on track to stall (thus requiring stall avoidance) if the stick is never close to full aft. Just because you're pointed uphill and slowing down doesn't mean you're about to stall...you're just an arrow following a parabolic arc.

I think the source of your confusion is that you are mostly talking about loops, but in the post I was replying to and quoted, you said "never in the course of any kind [of] flying," which is broader than loops. My counter-example was inverted flight (meaning negative-G), not the inverted portion of a loop (which is positive-G). I probably could have been less ambiguous in my wording.

 

[whifferdill]

View attachment 60288

I’m taking about going ballistic, or rather trying not to.



I also did some acro training in Citabrias and Decathlons but not a lot. They don’t really handle the same as a 65,000lb piece of metal.

I cry foul! LOL I’m a little biased toward piston driven GA acro planes.

 

[whifferdill]

I think the source of your confusion is that you are mostly talking about loops, but in the post I was replying to and quoted, you said "never in the course of any kind [of] flying," which is broader than loops. My counter-example was inverted flight (meaning negative-G), not the inverted portion of a loop (which is positive-G). I probably could have been less ambiguous in my wording.

I made the mistake of framing my comments consistent with general GA flight training and aerobatic principles in piston-driven airplanes. Should not have said ALL flying. An Airbus may also call for full elevator deflection at times, I don't know.

That being said, how is negative G any different from positive G maneuvering, and what situation do you feel would call for a full aft stick movement under negative G in order to AVOID stalling? What type of maneuvering would lead to an actual stall if you did nothing but hold the elevator neutral?

 

[iamtheari]

That being said, how is negative G any different from positive G maneuvering, and what situation do you feel would call for a full aft stick movement under negative G in order to AVOID stalling? What type of maneuvering would lead to an actual stall if you did nothing but hold the elevator neutral?

Here's what I actually said:

If you are inverted, you wouldn’t necessarily pull full back stick to avoid a stall, but it would probably work if you didn’t just yank it from forward to full back in a tenth of a second.

I meant the smiley face as an indication that I was not being entirely serious. Perhaps I misused the emoticon and that also contributed to the confusion. But you keep adding qualifiers. Now you're saying that the elevator was held neutral in inverted flight, rather than being pushed forward as one would do to enter a stall.

 

[whifferdill]

Here's what I actually said:

I meant the smiley face as an indication that I was not being entirely serious. Perhaps I misused the emoticon and that also contributed to the confusion. But you keep adding qualifiers. Now you're saying that the elevator was held neutral in inverted flight, rather than being pushed forward as one would do to enter a stall.

I'm not adding qualifiers or moving the target. The original comment that stirred all this up was my response to a post that mentioned needing full aft stick on top of a loop to avoid getting too slow and stalling. I think poster who wrote that used the wrong choice of words, and didn't really quite intend to say that, but I responded as written saying that you do not generally need to use full aft stick to AVOID stalling. I originally said neutral elevator will cause a parabolic trajectory (meant piston aircraft) and no need for stick thrashing which is true....hence my continued mention of neutral elevator. I do plenty of negative G flight and inverted spins and know how to avoid stalling under negative G, just have never had a reason to pull full aft from a negative G situation in any piston driven aerobatic airplane and can't imagine a benefit to doing that. I knew you weren't serious but you continued as if your comment had merit....on my original point about stall avoidance. I think this thread has become a misconstrued waste of server space.

 

[jstro]

Not exactly what I was meaning, but I see what you’re saying. What I meant was that if you pull aft stick too quick you’re going to stall before you make it to the top and you won’t have any left. Last time I did Acro in the Super-D, we would have just enough aft stick left over at the top to get it to fall through the loop.

I think if you took your hands off the stick at that point (inverted at the top of the loop) and waited a second or two the nose would fall and you'd be on the downside of that loop. The reason why is that the airplane (any airplane) in normal level flight is trimmed to provide 1 g of lift in the "down" direction -- "down" defined relative to the aircraft. Having the aircraft trimmed that way means it can maintain level UPRIGHT flight at some specific speed. Now put that airplane upside down and it's still trimmed to provide 1 g of lift in the "down" direction -- but now "down" is actually up. So there shouldn't be really any lift to hold the airplane up at the top of the loop (of course depending on elevator position). For example, to do an Immelman -- maintain inverted flight and half roll at the top of that loop -- you have to quickly feed in a LOT of down elevator at the top of that loop because you're going slow and all the airplane wants to do is drop the nose at that point.

 

[Maciej]

It's fun, give it a shot...

 

[pigpenracing]

It's fun, give it a shot...

Would be better in a biplane

 

[Ronbonjovi]

Now here's aerobatics done right in a non aerobatic plane

What a boss... Hey watch me fill up my glass of tea while I barrel roll this baby . Never seen that before, thanks for the share.

I have been itching to fly outside the norm lately. Obviously I won't be doing anything other than FAA approved maneuvers in our C152 but will be looking at some kind of acro training down the road. Hopefully someone has an acro plane tucked away in a hanger at our airport that I just haven't seen yet.

 

[LongRoadBob]

As often happens, some excellent information here, and right in line with what I was hoping to glean from my questions.
Thanks guys!

 

[Hippike]

LongRoadBob, if you can, go take some acro training while working towards your PPL. I think you will find it very beneficial (and extremely FUN
During one of my solos, while practicing stalls, I almost went into a spin in a C172. I don't know how I got out of it but afterward I got scared s*less and headed back to the airport and I would not fly again until I got some hours in an acro plane with a professional. We practiced the hell out of spins and spin recoveries. (at times doing 3-4 full turns before coming out of the spin) and it helped me tremendously to experience the spin in a safe environment and to learn what I need to do to control the plane in such a situation. Now I am not afraid of inadvertently spinning a Cessna (not that I want to).

 

[unsafervguy]

I made the mistake of framing my comments consistent with general GA flight training and aerobatic principles in piston-driven airplanes. Should not have said ALL flying. An Airbus may also call for full elevator deflection at times, I don't know.

That being said, how is negative G any different from positive G maneuvering, and what situation do you feel would call for a full aft stick movement under negative G in order to AVOID stalling? What type of maneuvering would lead to an actual stall if you did nothing but hold the elevator neutral?

you will never know. in an airbus you are not asking the airplane to deflect the surface when you move the side stick, you are asking it to change the g load on the aircraft. how it moves the surface is up to the computer. the computer may actually deflect the surface fully in the opposite direction, if you are trying to do something that it does not want to do. Ie pull the stick all the way back and it will eventually command down elevator to decrease AOA on its own. its an interesting system.

bob

 

[Doug F]

No worries. What could go wrong?

I had a co-worker some years ago who was a pilot. He went to an airshow and loved the way the Blues were doing aileron rolls. Next time he was up in his plane (probably a 172 or similar) he cranked the controls to the left to roll. He kind of forgot that he had way more lift/weight and a lot less roll/sec than that Blue Angel. He made it inverted and the plane's nose headed to the ground! He was lucky that he has sufficient altitude to just pull through inverted but that was the last time he tried that little trick!

 

[Velocity173]

Aft cyclic, reduce collective over the top, increase collective at the bottom. Easy.