I've got a question regarding my great planes at6. With too much elavator it'll try to roll over to its side, unable to even complete a loop. I've lessened the elavator and it's fine, but i was wondering what this problem is called and what needs to be done to correct it.. I thought it was called control surface stall but my searches aren't coming up with anything. I fly realflight G3 and this question comes up again because i notice all the warbirds are suseptable to this.. Any info would be appreciated.. thanks

brandon

It sounds like your aircraft is snap rolling with an abrupt full elevator application. If that is the case, the wing is stalling, not the control surface. The model may also be unbalanced laterally, &/or have a slight warp in a wing.

T-6s are particularly subject to stalls due to elevator... it's a function of movement and c.g.
It's better to move the c.g. forward, and maintain some slight excess elevator to control the landing flare.. but also remember the plane will snap with too much elevator.

The other name for this phenomenon is an accelerated stall. With too much elevator you are raising the wings' anlge of attack so fast that the airflow separates from the upper surface. And as the other poste mentioned you may have a warp or other mis alignment because it goes the same way each time. I had a friend with a HOB FW-190 beautiful airplane, would do a perfect 1-1/2 snap to the up right at the top of every full elevator loop.

i appreciate all the great information. I guess there are just limitations to certain designs. The plane fly's fine reduced elavotor. The first time i took it out and tried to do a loop, it really scared me.lol thanks again.

brandon

Elevators do stall with excess control. Say you are doing a loop, and have too much throw available. You try to tighten the loop by giving more elevator. This works fine until the elevator stalls, then the loop opens up as you loose lift on the elevator. I did some experimenting with a control line airplane and this is what I found. This was a case where the wing wasn't stalled.

Jim

brit brat has got it!!!!! try adding some flap ,or airleron mix.. down as you add elevator. fools the aoa RD

This sounds like a simple case of too much elevator travel, which stalls the wing. When setting up a new model, I take it safely high, and apply full up elevator at full throttle. If the model completes less than one full loop before going badly off line and yawing all over the place, I reduce the elevator travel. If it continues to loop, while holding its line pretty well, I increase the travel, until I get close to a full loop before the model goes crazy. I have seen too many fine models written off by excess elevator travel, which can result in a snap roll into the ground when the flyer applies full up elevator in a dive pullout. This does not apply, of course, to models that are set up for so-called 3D flying, that needs excessive elevator travel, but it is best, I think, to use high rates for 3D, and set up the low rate elevator throw for a non-stalling turn.

A big AMEN for Rotaryphile's comment. I almost had that happen to me. With modern proprotional controls we tend to overlook the maximum control limits. I was flying a T-34 and having a ball experimenting with stuff and found myself pointing down with a need for up elevator. I yanked up and snapped big time. Luckily I had enough altitude and composure to relax the elevator command and pull out (barely). The moral behind this embarassing confession is that you need to do some careful testing to find out the limits of elevator throw.

With the T-34 I went back to altitude leaving the control throw in high deflection and did the following. I started a large loop with just a bit of aft stick. Slowly pull back the stick which will tighten the loop - do this very gradually keeping track of the stick position. You will find a position where the airplane will snap out of the loop every time. Note this and land and set that elevator deflection (well just a smigdegon less than that) as the low rate elevator setting. Test fly and see if that setting on low will allow the airplane to loop every time or pull out of a dive with no snapping. Leave the high rates setting for maximum throw for doing on purpose snap maneuvers.

We didn't see this kind of effect in the old days too much because the maneuvers we flew were big smooth ones and everybody set up their airplanes with just enough elevator to do them. That was true also of scale ships. There were very rare instances of snapping and plopping into the dirt on landing but not all that often.

Today we tend to think of lots of snapping maneuvers, tight maneuvers, etc even on scale ships and so we get into the area of too much elevator throw. I actually had this happen on a Sig Little Rascal. CG too far aft and too much elevator travel (I don't read directions - too much testosterone). I did a little hand launch and pulled a lot of up elevator about 4 feet off the ground. What followed was 3 snaps with random recovery that never got higher that 5 feet or lower than 1 foot. Finally I stopped messing with the stick and whow, it flew away just right! I then took my own advise and did the loop and snap/elevator tests.

A high wingloaded plane will snap out easier too. A bandaide is to raise the ailerons about 1/8 of an in.. Acts like washout. Be interesting to do the loop test like you do,Ben, Then do the up aileron thing to see how much of an improvement.

Here is another goofy law of aerodynamics to ponder---
If wing loading is low enough - the deflection of the elevator will never be excessive---
before you yell "impossible!"
fly a really GOOD 3D Shock Flyer type model - with any good one -- you can do a full bore vertical dive -chop power -yank elevator to 50 degrees (easy to do) and the model will simply snap to horizontal flight and settle .
I grew up on models which sometimes rolled upon application of elevator - including control line stuff which was really wierd.
The more I play with these really low inertia electrics - the more I see where flight problems really originate.
- we are all used to designs which are fairly heavy and/or low on power
.This is a logical intrepretation of the flight envelope of the majority of full scale designs from the past.
No one is to blame -
It is simply a fact that from the first flight - any meaningful advance was based on better power to weight and lower weight to size.

When a control surface actually stalls, it becomes ineffective. Because the pitching tendency of most conventional aircraft is nose-down, the stabilzer/elevator is used to produce a downforce on the tail. If the elevator stalled during a positive 'G' maneuver, then the model would pitch out. As was stated above, a loop's radius would increase, or the model might even quit looping and pitch the opposite way, outside.

Full-size aircraft have used a variety of devices on the horizontal stabilizer/elevator to help them. The Boeing 727 has vortex generators on the underside of the stabilizer to help keep flow attached when it's at high pitch in relation to its relative wind. This makes sure it won't stall during times when high control surface deflections are needed, such as during maximum performance low-speed flight and landing.

Bax I think the problem isn't one of the stabilizer/elevator stalling out, it is more the wing is pushed to a high enough angle of attack to stall but it still has a large velocity (dynamic pressure) which combine to cause the viscious snap roll, the cases that I have seen the snap is up with roll. If the wing lift goes away then the down loaded tail (especially with the up elevator commanded) certainly increases the nose up pitch.

Even a modern pattern ship which flys level with a up load on the tail will have the down load in the case where the airplane approaches the high speed snap. At low speeds and level flight the tail load is up and when the wing stalls the nose just drops due to that up load.

Dick it certainly is interesting. The low linear and angular inertias certainly have a major impact. For the maneuver you mention there is a good chance the airplane rotates fast enough that the wing never approaches the stall angle of attack even though it has the huge elevator deflection. Low Reynolds number and light weight along with some flow diverting thrust effects get together and make an interesting result, and it is a heck of a lot of fun to play with. You know better than most that the big monsters are a treat but there is something really relaxing about flying a little foamy just a few feet off the ground and doing outside loops.

We just built two more indoor setups - now down to amost exactly 6 ozs auw
I am supposed to get a LENS motor today and bro Rojecki is bringing a handful of stuf inc a Lilscreamer Saturday for an afternoon of crash n burn.
the new models are Mini 3Dx and Knuffel
the Knuffel ist eine German design-
Have you ever pondered this :
What would our full scale aircraft look like --if somehow ---there were available engines of 4 times the power (same size/ weight ) and airframes 1/4th the weight at same size strength --- 50 years ago?
have a Scotch - sit back and let me know what you think could have happened to basic design.

You mean the Wright Bros couldn't hover??

The fuselages would look the same because people need to sit in it and the fuselage drag problems would be the same. Wings would be smaller but would have the same aspect ratio, sweep angles and other things because drag would still need to be minimized. The motors (assume propellor driven) would be smaller and less weight for the same power and still smaller for the lighter weight of airframe. Since aerodynamics are still the same you would end up with a light airplane that goes just about the same top speeds as now. The fuel flow would be a fair amount lower because of lower weight but since there is only so much energy per ounce of fuel to work with as you hit the high drags at high subsonic Mach numbers it might be close to the same.

Aerobatic machines would have the biggest benefit however there is still benefit to lighten as much possible and to use only as much motor as you need.

It is certainly an interesting queston.

I thot-- there would be more private aircraft - slow speed, safe puddle jumpers .
The stuff sold to most private pilots still has wretched low speed performance -in my book.
I always hoped for a good plane whch flew from say 15 mph to 100 mph.
maybe such a plane would have caused thousands of air to air crashes - (based on the stupidity of surface vehicle operators) but the idea of such a design for personal use, always seemed ideal to me.

Good point, along the lines of the Sport Pilot license type of airplane but lighter. It would depend if they kept the wing area and made a real floater or if they kept the wing loading and just made the wings smaller. We all dream of something that would fly slow, fast, go anywhere and park in the garage. The trouble is that most people shouldn't be flying a 3D craft!

.
Isn't what you describe something like this?

Except really pointy in the front!

About 20 years back -a designer in Ogden Utah made a plane he called the Weedhopper - I visited with him looked over the manufacturing facility -discussed his goals ,which were for a faster Weedhopper (?!).
The story ends tragically in Ca., with his demise in a new design --which stalled in at low speed .
I have always been puzzled by the desire , always for faster ,very small personal craft.
My idea was for a small extremely light design which would fly from say a walking speed to -whatever speed -
anyway, a plane which in an emergency, could be simply reduced to walking speed then allowed to hit whatever terrain existed.
At my tender age ,I have far too many friends who died in light aircraft -and the reason was always . moment of judgement lapse --in a non forgiving enviroment..
Never a airframe failure -except for a takeoff flameout on a Dyke Delta - a horror of a design.
The reason I mused on the idea of much lighter and more power , was to try to imagine just how good a small air machine could have been, if these "super" materials and engines had ever existed.
I really doubt the machine would look like anything we now fly.
Maybe a backpack engine wih a folding wing -like those panels used on sattelite solar collecters.
These tiny model electric contraptions we play with, seemingly contradict many fixed ideas of controlled heavier than air machines .
They rekindle my thoughts along these "what if" lines.
Makes for great dreams----

Indeed - having a plane light enough such that a motor off "determalizing" approach to emergency landing would be nice.

The little monsters don't contradict any ideas of the aerodynamic world when you include the Reynolds number effects. Things that fly range from a little flying bug a fraction of an inch long to a mega monster size airplane. To make things easy we slice up the range of Reynold's numbers into big and medium and do a lot of studying there because that is were the money is to be made. There is no money in the study of the real small Rn so not much gets done and little study is performed so knowing how some real small things fly is hard to describe. But in reality there is a smooth variation from very low to very high. Understanding that variation is necessary to analyze anything that flys including our beloved foamys.

The "hard to describe",is the catch in this .
I got paid lots of money , to fully describe what really caused accidents.
I learned quickly that "if you can't describe it in plain ,everyday conversational speech--- you really don't fully understand it ".
Pretty harsh - but true.
Technical jargon and graphs do NOT play well in court.
Neither does "If you can't convince em - confuse em".
Last week we went to an indoor flyin- some of the old farts (my age) had beautiful film covered craft - tiny motors - magnetic actuator "servos" etc..
Their craft followed the design criteria common on indoor rubber and microfilm setups.
Weights ranged from a very few grams to 2 ounces for the really big stuff.
Absolutely fascinating at how different the approach is, between these and the electric aerobatic foamies.
They used heavily washed wingtips , super stable CG positions which self stabilized etc..
Our stuff simply would dart around or fly at any attitude - due to extremly high power to weight.
The obvious difference was in wing loadings - tho my bipe has a loading of 3.8 oz per sq ft-at 400 squares - it was an absolute tank -compared to the large film covered models.
How do you do a wind tunnel test on a model which flys at grams per acre loading?
A hard sneeze would wreck these models.
Obviously, the old tried and proven rules of wing configuration (inc washout) work at these numbers- but then - so do the flat foam plates -
Looks like I get to do some more comparison srudying --

" How do you do a wind tunnel test on a model which flys at grams per acre loading?
A hard sneeze would wreck these models. "
.
Make the wing shape from titanium... wingloading has no meaning in a tunnel.
And then get a buncha us old farts yapping away at each other to provide the wind....
One of the locals (old fart, continual *****er) complained to me about the Cub he was trying to fly...
11 inch chord, c.g. at 4-1/4"...or in engineering terms, 38%... and he said it was "tail heavy"...
Goodness who woulda thunk it?
Talks up as if he knows it all, but in practice....

In another lifetime(1960s) I experienced true elevator stall but it was caused by external influence on the aircraft. Part of the requirements for a fullscale commercial glider pilot ticket was a certain number of winch or auto tows.
We used 1100 ft of .120 single strand wire hooked to an automobile for the towing apparatus. When the maximum altitude was reached, the stick could be pulled back against the stop and the elevator would stall letting the nose down slightly below the horizon. When the stall occured the wing would be at very slight positive angle to the horizon. This was caused by the fact we used the nose release as the towing attachment as the old S-222 serial number 07 had no cg hitch.
Over the years I flew and instructed in a number of different aircraft type including some with stick shakers but the old 222 glider was the only situation where I experienced true stalling of the elevator and not the wing.

Titanium foil-
I think I might have a roll of it somewhere----
maybe quilted tho--