Warbirds and Tip Stalls

Ahem, garf, gurgle (various throat clearing sounds) - Figure 8s at one foot?? Havin' a senior moment Ed ;-))

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It isn't any fun if you don't have to replace the covering on the wingtips every fourth or fifth flying session.

Yes, I guess I was having a senior moment, but you get the idea. Really low.

Ed Cregger

I know Ed - Just couldn't resist ;-) *But,* low eights *are* a way of showing the troops you can put her where you want!

On Fri, 16 Mar 2007 04:47:14 -0400, "Ed Cregger" wrote in :

I'm happy to hear that I'm not the only one who found one of the edges of the Fun One's envelope. :o)

Marty

Coordinated turns are necessary, using both rudder and aileron. Aileron-only will result in a slipping turn, which is safe enough but sloppy. Rudder only, or too much rudder, will create a skidding turn, which is dangerous at low speeds and will result in the inside wing stalling first, dropping it into an incipient spin which usually breaks the airplane against the ground. It's not usually the wingtip's problem, though washout or reflexed aileron might help. The whole wing's stall pattern is ahead of the other wing's stall, and so it drops earlier. Need more speed and coordination.

Dan

CM wrote: (top posting fixed)

Depending on the kit you may be able to twist some into the wing and re-shrink the covering, too -- but trailing the ailerons upward is fine.

I think you're confusing tip stalls with something else. A tip stall causes a snap roll (or a part of a snap roll followed by a part of the airplane snapping). Generally, setting the C/G ahead makes the aircraft more likely to stall in a straight-ahead mush as the tail can't force the wing to stall, where moving the C/G back makes the wing more likely to stall of a sudden. I have a "stunt weight" that I stick onto the tail wheel mount of my AT-6 when I want to practice snap rolls. When I'm out of spare aircraft I take it off, to avoid practicing departure stalls followed by aircraft rebuilds.

Consider this...

Choose Warbird. - P-51 will do.... tapered wing, high wing loading..

In a right final turn, low and slow....

When any wing is at a high angle of attack, adverse yaw with aileron action is accentuated, requiring MORE rudder to co-ordinate the turn..

So our pilot now attempts to roll OUT of the turn with LEFT aileron. The left aileron moves UP, streamlining airflow on the LEFT wing (in a "reflex" position), effectively LESSENING drag and adding washout to the LEFT wing.

At this time the RIGHT aileron moves DOWN, ADDING to the drag of the RIGHT (still lower) wing in the right banked turn. The down aileron effectively INCREASES the angle of attack of the right wing, while the adverse yaw slows the wing tip, (adversley yawing RIGHT as LEFT aileron is applied) and it stalls, the RIGHT wing loosing all lift. The aircraft , now having lost ALL lift on the right side, rolls suddenly to the RIGHT, while LEFT aileron is being comanded, with no altitude for recovery.

Only cure is to recognise the situation, and apply a HEALTHY shove of LEFT rudder to counter the adverse yaw, hopefully SPEEDING UP the inside (right) wingtip, moving it AWAY from the potentially "tip stall" possibility..

This is all to common blamed on a radio "hit"..

"It rolled RIGHT, while I gave it "LEFT"....

Nope....

Dave

On Fri, 16 Mar 2007 23:20:00 -0300, Dave wrote in :

Or a somewhat overweight Fun One. OK, it was heavy!

Yep. I broke it two or three times before the light dawned that it wasn't a radio glitch.

Made me a better pilot, sort of, I guess.

Marty

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This is why I adopted the policy of flying the model to the ground using power and not trying to glide in as we learned to do with our trainers.

Keeping the air speed up avoids these situations, but I find that many pilots cannot resist the temptation to throttle back too far and then try to land at a steep angle, but too slow for good control. The latter is fine if no turns are to be made once throttled back, but is a disaster waiting to happen if they throttle back too soon, too high and too slow.

Ed Cregger

On Sat, 17 Mar 2007 05:28:27 -0400, "Ed Cregger" wrote in :

At the other end of the spectrum was Mack, a Canadian pilot, now deceased (RIP) and whose ashes are scattered on our field. He would land his modified Astro-Hog at full throttle, hold it on the grass for a hundred yards, waggling the tail the whole time, then pull up vertical.

I don't remember any other maneuvers that he flew. That one was unique. He died before I gained enough confidence to ask him to teach me how to do that, and I haven't been willing to teach myself.

Wolfgang Langewiesche has a lot to say about landing on the mains in Stick and Rudder, too. Model warbirds aren't the only aircraft that need to be landed hot.

Marty

Speeding up the inside wingtip isn't what does it. The relative increase in tip speed is very small, considering the wingspan versus forward speed. In a descending turn, the inside wing has a higfher angle of attack and is more inclined to stall first, and using rudder to advance that wing reduces the AOA significantly. It's tough to picture in your mind, and we can't see it in the air, so I built an AOA demontrator model using steel rods and a small airplane. The airplanes wings ride on the rods; the rods represent relative wind, and it becomes really obvious what happens to AOA in climbing and descending turns, steep turns, and during sink. One of these days I should publish some pictures on Flickr so others can get the idea. Our students get the idea instantly when they see it. We regularly operate in slow flight during training. One the edge of the stall. We turn at bank angles up to 30=B0 and recover using coordinated aileron and rudder. It doesn't take much. If we want to sping the airplane, we get a skid going just before the stall, and it can take a lot of rudder to stop the wing dropping. The nose has to go down, too.

Dan

Thanks a whole lot for mentioning that stunt, Marty. I'll let you know how many models I wreck (when all this snow melts.....) ;-)

Good flying, desmobob

ROFLOL!

Practice fast low passes first. Then make sure your wheels turn freely, dragging is very bad. Well, I guess if you are on grass it probably does not matter.

Marty, thanks for sharing that one it is good to know I am not alone . I am also known for silliness very similar to that but on a paved runway where the speeds get real fast. On a paved runway the challenge is holding it down until it is time and then when you pull up it is like a rocket reaching for the moon. In fact, someone came looking for me at a giant scale flyin because they saw a plane do that and he knew I had to be there.

Jim

On Sun, 18 Mar 2007 03:39:31 GMT, "Six_O'Clock_High"

*Or* get three hell away from the edge of the envelope! Pop the stick (down elevator reduces AoA), Punch the throttle (full throttle increases airspeed - *unless* you're on the backside of the power curve :-( IOW, get comfortably back inside the envelope - rapidly! If the snap has started and you're rapidly heading toward inverted - go with the snap (with ailerons) and come out happily on the other side - not inverted :-))

Excellent! Ed

You nailed it Dan "... the inside wing has a higher angle of attack..." That's why dihedral works. Nothing to do with wing speed delta!

Speeding up the inside wingtip isn't what does it. The relative increase in tip speed is very small, considering the wingspan versus forward speed. In a descending turn, the inside wing has a higfher angle of attack and is more inclined to stall first, and using rudder to advance that wing reduces the AOA significantly. It's tough to picture in your mind, and we can't see it in the air, so I built an AOA demontrator model using steel rods and a small airplane. The airplanes wings ride on the rods; the rods represent relative wind, and it becomes really obvious what happens to AOA in climbing and descending turns, steep turns, and during sink. One of these days I should publish some pictures on Flickr so others can get the idea. Our students get the idea instantly when they see it. We regularly operate in slow flight during training. One the edge of the stall. We turn at bank angles up to 30° and recover using coordinated aileron and rudder. It doesn't take much. If we want to sping the airplane, we get a skid going just before the stall, and it can take a lot of rudder to stop the wing dropping. The nose has to go down, too.

Dan

On Sun, 18 Mar 2007 09:37:51 -0400, "Ed Forsythe" wrote in :

I didn't get to the edge on purpose.

I kept falling over the edge.

Playing with a simulator yesterday at the hobby shop, I saw that rudder helps tremendously in 3-D recovery.

Lots to learn ... That's what keeps the hobby fun!

Marty