numeruous STC's and Flight Characteristic's

[CuBob]

I am flying a super cub with numerous STC's , Vortex generators, tundra tires (31") belly pod, and constant speed prop. I want to do a full stall series in the aircraft including accelerated stalls from a 45-60 degree bank and am concerned about the stall characteristic's . On a full power departure stall I run out of right rudder just before the break. Have checked the rudder and it 30 degrees per type certification. Has anyone with the same mod's spun their aircraft. What happens with a cross control stall.

Thanks

 

[behindpropellers]

I am flying a super cub with numerous STC's , Vortex generators, tundra tires (31") belly pod, and constant speed prop. I want to do a full stall series in the aircraft including accelerated stalls from a 45-60 degree bank and am concerned about the stall characteristic's . On a full power departure stall I run out of right rudder just before the break. Have checked the rudder and it 30 degrees per type certification. Has anyone with the same mod's spun their aircraft. What happens with a cross control stall.

Thanks

I can think of quite a few planes with that config....except for the prop. Mine will be configured that way shortly, the only thing I worry about is having the CG too far aft. A good understanding of the power curve will let you fly your machine to its full potential.

Sounds like a nice bird, does this mean your name should be havacub?

 

[bob turner]

I have had incredible difficulties getting a VG-equipped Cub to spin. Sure you want to take it that far?

Multiple airframe STCs are not proven compatible. The FAA in their infinite wisdom allows the installer to ensure compatibility. So long as only one mod deals with the wing, I think you are pretty safe.

The spin for a Micro-VG cub seems to be power on, about 45 deg nose up, then just before the stall full rudder. No guarantees on that, please.

 

[KingCub]

I'm not sure we ever want to take our highly modified cubs "that far" just for the fun of it, but there is a practical side to the question as originally posed in this forum.

For example, I'm getting ready to take the practical portion of the commercial ticket, and the practical test standards require both a power on and a power off stall at an angle of bank "not to exceed 20deg, +-10deg while in turning flight." (FAA-H-8083-3, AC61-67)

With big tires, a belly pod, and VG's, has anyone had any experience that would suggest this maneuver to be unsafe?

 

[articfox]

yee, haw

Hi, here is my two cents, for what it is worth, hope it helps. I have stalled spun, cubs and 12's with and without the vg's and the wheels and the pods. Here is the critical thing. The VG's are there to help keep the airflow attached during critical angles of attack. That is why it is harder to spin the aircraft. Most of the pipers will hardly spin to the right unless they are aft loaded. Don't fear it though. It takes a whip, hammerhead stall to get it to want to go right. The problem is that the stall and spin to the right if it is aft loaded will usually result in all the crap in the belly or the cargo being lifted and scattered about. So, strap it down. Put your buddy in the back and about 50 lbs in the tail. Then it will spin a little better to the right. Going to the left is a little easier and does not require so much aft loading. The tires don't really have an effect unless you have the super 35 inch. tires. They usually just slow down the roll rate. You really have to do alot of spins before you notice that. Same with the pod. It sounds different but no problem. Floats will have a lateral dynamic thing that gives you a little wobble about the second time around. Other than that. Spin that baby. Remember though, and this is a good one. That all those high lift, super perfomance mods that you put on your cub work. Keeping you in the air. Sometime when you want to land. The guys that I have run through my cub course know one thing. If it starts porpising on take off with or without the vg's you are going too slow and need to give the airfoil a knot or two before you hurk it off the ground.

Hope this helps
Artic

 

[Steve Pierce]

Bob, What airframe mods to you find that are not compatible? Do you think the compatibility should be made by the FAA instead of the installer?

 

[mvivion]

Remember, folks that Super Cubs are only approved for intentional spins in original type certificated configuration, and at all up weights of less than 1500 pounds--as in the Utility category.

VG's are intended to delay the stall, to allow the airplane to achieve a higher AOA prior to stalling. In my experience, with aggressive stalls, the VG equipped airplanes may roll over on you at a particularly aggressive break, but they also recover very quickly with appropriate control inputs.

I'd be VERY careful spinning airplanes AFT of the approved CG for spins. Definitely test pilot work, and they wear parachutes....

MTV

 

[behindpropellers]

I'm not sure we ever want to take our highly modified cubs "that far" just for the fun of it, but there is a practical side to the question as originally posed in this forum.

For example, I'm getting ready to take the practical portion of the commercial ticket, and the practical test standards require both a power on and a power off stall at an angle of bank "not to exceed 20deg, +-10deg while in turning flight." (FAA-H-8083-3, AC61-67)

With big tires, a belly pod, and VG's, has anyone had any experience that would suggest this maneuver to be unsafe?

Tim-
Are you taking your commercial ride in your cub?

I need to do my commercial at some point here in the future so I can get a CFI.

Tim

 

[aktango58]

With big tires, a belly pod, and VG's, has anyone had any experience that would suggest this maneuver to be unsafe?

Read Flip Flop's "you all be careful out there..."

It is called the Moose stall. With inadequate altitude it is deadly.

If more folks went to SAFE altitudes and practiced these stalls, in all of their normal flight conditions, (read loaded for hunting), we would have fewer to report on come the season

 

[bob turner]

Steve - two different STCs on the same wing can be problematic. Only example I know of is the Sportsman for the big Cessnas - when you add VGs to that, you become a test pilot. The wing chord has increased, but you are putting the VGs where?

 

[CuBob]

Thanks for all the replies. It sounds as if a spin has to be a very intentional maneuver with the VG's. Now it is time to go and give it a try. If you never hear from me again you know it did not work. LOL

 

[mvivion]

wanacub,

A spin is certainly possible in a VG equipped Cub. That said, in working with students in trying to induce a "Moose Stall", have almost never been able to get one to tip over.

When it has happened, however, it's instantaneous, violent and fairly quickly recoverable, assuming you've got a few hundred or so feet to recover.

THAT is not a spin, however....it's an INCIPIENT spin, or aggravated stall if you prefer.

Don't get that thing stable in a spin, as in more than one turn, if you value your hide, would be my suggestion.

MTV

 

[RedEye]

No VG,s on my cub so..........the one time (one time only) that I put it in a stall/spin where the wing came over the top instantly and began the spin it was very "catch you off guard" quick, even when I knew it was coming. I put the stick to neutral and let it turn about 3 and a half times before adding opposite rudder and leveling off. What I got concerned with most was the fact that the rotation seemed to be getting tighter n tighter each time. Could it get to a point where you cant correct it?? Don't want to find out. Anyone else been there ?? The other thing that amazed me is how fast it comes over the top when it breaks !! Incredible !

 

[mvivion]

David,

Most airplanes stablize in a spin at around four turns. Beyond that, the spin generally doesn't accelerate further, UNLESS the pilot applies inappropriate control inputs.

The Cub, when operated in the Utility category, is a very gentle and predictable spinning airplane.

Any airplane entering a spin offers a very "different" attitude, as you noted.

Rich Stowell has a great book out now, called "Stall Spin Awareness" (http://www.richstowell.com/) that offers great perspective on stalls, spins, associated research and history. The book also describes in detail some of the really ugly unrecoverable spin events that NASA got into in normally very gentle spinning airplanes by just changing a few minor things. That chapter is a real eye opener on modifications of airplanes.

Again, one turn and most airplanes should recover just fine. Beyond two turns, if it isn't certificated in that configuration, you are a test pilot, and I'd be wearing a good parachute, have a quick release door, and be very experienced in spin aerodynamics.

Get a copy of the book. The chapter on NASA spin testing of light GA airplanes is worth the price of the book.

MTV

 

[Mark Cav]

The Super Cubs 1&2 videos explain this really good if anyone has them.

 

[bob turner]

What MTV says. The book is a good read. The Cubs will tighten up, but there is little value in letting them do that unless you just like to be dizzy. Recover within the first turn. Aero contests rarely include more than 3/4 turn, and you are graded on entry and recovery, not mindless rotation.

 

[skywagon8a]

Remember that in a normal/utility category certified single engine airplane, that it had to demonstrate spin recovery after completing one full turn in order to be certificated. Recovery had to be complete prior to the completion of the second turn. This was done in all sorts of flap and power configurations. If you decide to spin more than one turn prior to recovery YOU ARE THE TEST PILOT!

 

[AntiCub]

I'm going to second the above advice. If you've got aerodynamic mods don't try spinning unless the STC states that spins are still advisable. Otherwise you don't know how it's going to behave. Wear the parachute! If you do more than one rotation its considered an aerobatic maneuver anyway.

Phil

 

[skywagon8a]

There are many aerodynamic and gross weight change STCs available for Cubs. All of them are required to perform to the same regulatory requirements. It is likely that each of them were certified on stock (as they came from Piper) airplanes. If there was more than one modification installed, during the flight test, then they all would be listed on the STC papers and would be required for each installation. Or, there would be specific instructions for the various combinations. Each STCd modification is tested on its own merits not necessarily in combination with other mods. The combinations may, in fact, not be able to pass the flight test regimen. The average IA is not a flight test pilot and is unlikely to have the proper documentation to put his/her certificate on the dotted line.

There is a statement on all STCs which says "This approval should not be extended to other aircraft of these models on which other previously approved modifications are incorporated, unless it is determined by the installer that the modification will introduce no adverse effect on the airworthiness of such aircraft."

I agree with Steve Pierce that we do not want to invite more FAA interaction. However, the installer needs to be very careful on where his signature goes. And, the pilot flying the airplane needs to be aware that perhaps the IA who placed his signature on his airplane may not have been as diligent as he should have been.

If any of you have attended the FAA's annual IA meetings and listened to the FAA legal people make their presentation you will understand where I am coming from.

I am not trying to muddy the waters. I like the mods as much as the next guy. JUST BE CAREFUL OUT THERE!

 

[aviationinfo]

Could someone pls explain how the Moose Stall works? Is it a cross-controlled stall, or merely a stall that occurs during a steep bank?

I have taken my '12 with a guy in the rear seat, extended full flaps, and tried deliberately uncoordinated stalls. As in, full rudder one way and aileron the other. It still won't drop a wing. (Obviously this was done at altitude). I wanted to see how badly the airplane could be mishandled before it would bite. My conclusion is that it's one of the most stable airplanes out there, and I have to think the '18 is the same. This is what confuses me about "moose stalls." Isn't this what supposedly got Shaun Lunt? And his plane had VGs.

Thx

 

[Longwinglover]

I have taken my '12 with a guy in the rear seat, extended full flaps, and tried deliberately uncoordinated stalls. As in, full rudder one way and aileron the other. It still won't drop a wing. (Obviously this was done at altitude).
Thx

Well, there's your problem! Moose stalls happen at low altitude and unexpectedly, not up high and intentionally. 8) :lol:

Here'e a link: http://www.supercub.org/phpbb2/viewtopic.php?t=1202&highlight=moose+stall

John Scott

 

[mvivion]

That link was not very helpful in explaining the phenomenon frequently referred to as a "moose stall", in my opinion.

Take a look at the folks who most commonly participate in "moose stalls"...(forgive me for using only the term "moose", it's just simple)....the typical participant is NOT a low time, inexperienced pilot. In fact, every one of the several friends of mine who have been involved in these things have been VERY experienced, VERY competent pilots.

THAT is scary, folks, or at least it should be. The reason it should scare us is that many of us have probably been right at the door of a "moose stall", knocking away, and never knew it, cause we didn't go over that edge, and depart controlled flight.

This, I believe, is one of the really BAD parts of this whole phenomenon--the fact that it most frequently happens to experienced people, and apparently without warning, and recovery is nearly unheard of.

I was circling a radio collared wolf once and as I was circling the wolf, and descending, the airplane began an uncommanded roll to the OUTSIDE of the turn. This was not a steep bank I was in, and the air was ABSOLUTELY flat calm. I was just circling in a comfortable ~~40 degree bank turn. The airplane, apparently of it's own volition, started a roll to the outside. I put in a bit more aileron INTO the turn, to counteract the roll out of the turn--I wasn't done looking at the wolf yet.

The airplane continued the uncommanded roll toward wings level, even though I had a good bit of aileron INTO the turn.

Being more than a little confused at that point, and not being in any terrain, I simply flew to wings level, accelerated, and came back around to look at the wolf.

For several years, I wondered about that experience. The weather was absolutely PERFECT--cool, totally calm, as in not a breath of breeze, etc. Great weather.

Then I talked to a friend who'd been in a stall/spin accident in a Super Cub. This fellow has a LOT of experience in Super Cubs, and a LOT of experience in low level work, doing wildlife work, and back when it was more common and legal, aerial hunting. He described his accident sequence, and my blood ran cold. What he described was precisely the same scenario I'd experience, only in his case, as the airplane tried to roll to wings level, and he added more aileron, he was in a steep walled canyon, and COULDN'T roll to wings level. The airplane departed controlled flight, rolled over the top, and he hit the canyon wall inverted.

Both he and his gunner (they were trying to drive a wolf down canyon) were seriously injured, but survived, largely because the canyon wall decelerated their fall "slowly" and "gently". Both had broken backs, but survived.

His assessment of that accident was that he encountered his own wake vortex, in an assymetric manner. He described the weather as cold, absolutely flat calm, as in not a breath of breeze, and cold. He's convinced that he flew into his own wake assymetrically, and that created an uncommanded rolling moment. His trying to tighten up the control inputs eventually caused an assymetrical stall, which immediately transitioned into a spin till he hit rock.

I am absolutely convinced that this was precisely what I encountered, but since I was in relatively level ground, I could simply fly away. I firmly believe that I was merely a heartbeat away from eternity.

And, I'll bet there are others out there who have danced up to that edge, peeked over it, but managed, through pure luck or great airmanship to come back from the edge.

Pure dumb luck in my case.

I think this is why this phenomena is so hard to replicate....ALL the specifics have to be in place.

I also DO NOT believe that you have to be THAT far out of coordination for it to happen. Note that many airplanes will spin happily with only the ball half out of the cage in your slip/skid indicator.

This, folks, is a killer of Cub pilots. PLEASE do not assume that your experience or skill will keep you away from the door of this accident waiting to happen.

I've watched the videos describing this maneuver, and I do not believe they've done this maneuver justice, nor do I believe they've adequately explained it.

This is a very specific set of circumstances, and the nuances are really subtle.

But it's a killer.

The problem with this particular exercise is that it is nearly impossible to replicate in normal training. I've tried several hundred times to simulate this event, and without dramatic and ugly control inputs, I've almost never been able to demonstrate it. Again, VERY experienced pilots are NOT going to be inputting dramatic and ugly control inputs, folks.

I have gotten our Top Cub to depart once now in training flights. It was a complete surprise, and the airplane violently went over on it's back. That is out of several hundred attempts. THAT is the problem. If we could reliably demonstrate the phenomenon, as is suggested in those videos, it would be easy to avoid. Just don't do THAT. But it's a much more difficult to duplicate deal than they suggest. And, it's a killer.

And, no, Shaun Lunt's accident was NOT a "moose stall".

MTV

 

[Jerry Burr]

Moose / VG

I would have to agree with most of what MTV says. I don't really think that it is a spin thing. Reasons. I was required by the Fed to do 6 turn spins each direction with fore and aft loading while doing the initial Micro VG testing. I have at least 5 mods on my wings. There was never a problem. I have made videos of my wing tops and stabilizer bottoms while in spins and both wings are flying all of the time. With the exception of the break. Both stabilizers and elevators are also flying with full up elevator in the spin. While the closest I have come to tip-over has been in Super Cub wing tip vortices's. My escape has been to dive 50 or 60 feet under the offending cub to get free. That is- towards the center of the cub and not towards the wingtips. I have a light wing vortex and can tight circle in my own vortex with no problem. My point is that a heavily loaded Super Cub ( both by weight and bank angle ) would create a much larger vortex than one would imagine.
Why don't some of you enterprising types go to altitude and load up your Cub in your own vortex and let us know the results. My tuft testing has shown less vortices's with droop type tips than with stock tips. Let's hear from both types.
I don't think what what we are used to as a stall has anything to do with it. Jerry Burr

 

[aviationinfo]

This is all very interesting, I must apologize for thread creep.

I have noticed that people who are caught by the phenomenon tend to be experienced. I assumed that just meant they knew their planes well enough at slow speed to feel comfortable at that edge of the envelope in a steepish bank. I can see that perhaps if you get in your own wake and you're already at or near stall, the wing could load up further and go the rest of the way.

In the experiment with my '12 I was hoping to find out if the little flaps would blank the elevator as well (they don't). I thought that the results showed that I'd have to really screw up to have a problem, after this discussion I see perhaps I was wrong.

Also, I know the wing incidence and washout are different on the '18 vs the '12. I wonder if that has an effect.

So, MTV, what did happen to Shaun? I haven't seen the accident report. This could be a real learning opportunity.

Andrew

 

[aktango58]

Mike,

you have brought up a point/theory that I have not considered.

I have been in the same scenario a couple of times in the canyons looking at fish, and the bird rolling the wrong way. I always thought it was my on vortex also, but never correlated it with the moose stall. I am worried that I bent the pedals one particular day.

Frankly, I chalk up my saving to inexperience and lack of confidence. I refused to allow the airspeeds to go below 50 mph in the canyons, and I would level off and do tear drop turns back over the hole because I am not good enough to spin around in a tight circle at the tree top level and not have a problem as some point.

I looked Thursday, I have 800 hours in this cub! I still worry it will get away.

I will try the vortex idea soon at slower speeds and let you know.

 

[AntiCub]

Aviationinfo, your experiment with cross controlling was a slip. A slip is very stable and extremely spin resistant. In fact most aircraft can't be stalled in a hard slip.

Spins occur when roll and yaw are in the same direction, this is called skidding and is the opposite of slipping. In a coordinated turn you use just enough inside rudder to cancel all yaw. In a skid you use too much rudder and the ball is to the outside. If you're skidding too much and stall, you can enter a spin toward the inside. If you've never had spin training you'll be amazed at how fast it happens. A snap roll is just a horizontal spin after all. The classic moose turn stall is when a pilot is focusing on the ground and starts using the rudder to tighten the turn and ends up skidding. Caught myself doing this many times. We as pilots seem to have an aversion to banking very far when slow so our reflexes take over and lean on the rudder instead of the ailerons. All it takes then is to get too slow and stall and it's game over. I don't know if it's something inherent to a cubs handling, or just that they get used for low slow observation a lot, but they seem to be more prone to this. I watched a Cub last fall doing touch and goes and I swear his base to final turns were flat! No bank at all, skidding the heck out of the plane. I cringed each time he came by expecting to see a crash.

If you're doing a slow speed turn and the plane makes an uncommanded roll to the outside, that a classic stall from a perfectly coordinated turn. Trying to counter with aileron only makes it worse since it deepens the stall on the outside wing and leads to a tip stall, which is similar to spin but not as sudden and easier to recover from. leave the ailerons neutral, use rudder to keep the wings level, just like in any stall, drop the nose apply power and fly right out of it. Of course if you're already at tree top level any stall is going to be unrecoverable.

If you guys don't believe this pick up Rich Stowell's book on Spins, it's all in there. Better yet, take his course.

Phil

 

[mvivion]

Jerry,

Thanks for the feedback on your tufted experiments. I have, somewhere around 200 times now, attempted the wake vortex encounter theory with a Top Cub. It is equipped with brand X VG's, from the factory.

In all those trials, and ONE of the problems is that we can't see our wake turbulence, so it's hard to visualize where it lies...but in any case, I've gotten it to tip over once really hard, and once kind of enthusiastically. My student when it really went over, was impressed. I was in back so couldn't see the slip/skid ball, but it didn't feel like much out of coordination, the sky was wonderfully calm, and it was like the hand of God came down and smote us... .

The control inputs at that point are NOT that gross. The airplane isn't massively skidded. And, this is the other problem with this thing: It doesn't require us to fly the airplane really sloppily.

This airplane, at the weights we're flying it ranges from 1800 pounds up to about 2000 pounds, which is likely close to the operational weights of a lot of Cub drivers, and as you say, these wings make a pretty enthusiastic wing vortex.

I've taken off right behind another SC, and experimented with the vortices off the lead airplane, and they are pretty powerful, particularly with half flaps and ~60 MPH. Guess what configuration we most often look at stuff on the ground from?

I think what would really be needed, and it would be great if someone would experiment with, would be to tuft a Cub wing, and install smoke generators (small ones at least) at the wingtips. Then go fly the airplane into its own wake. With the smoke, you could visualize the wake, and the tufting and video could record what was actually going on across the wings.

George, you have described the "secret" that most high time pilots who look at stuff on the ground a lot use: Don't circle unless it's absolutely necessary, and then keep it to a minimum. Circling in a canyon is just a bad idea.

Ironically, what seems to be the most dangerous scenario is that which appears to be the most benign, as in cool, totally calm air, which is required to avoid breaking up or weakening the vortices. Any turbulence will break up these relatively weak vortices quickly.

This is all theoretical, and purely based on talking to a lot of experienced pilots, and flying a lot of low level observation flights.

I'd really like to see some actual experimentation to try to document this phenomena.

The REAL problem is duplication. If I could demonstrate this phenomena on any given flight, we could fix the problem fairly easily with training. Duplicating this phenomena almost seems as elusive as winning the lottery, though. Perhaps with a tufted and smoke equipped airplane, it would be possible to duplicate, and better understand the aerodynamics.

Folks, whatever this thing is is real. It has killed a LOT of very accomplished aviators. It appears to be impossible to detect, aerodynamically, right up till it turns loose.

I wonder how many times in my career that I've crawled right up to that edge, peeked over it, and retreated from it, not necessarily because of good airmanship, but rather due to pure luck.

I teach students to look at things on the ground using racetrack patterns, figure eights, 270 degree turns, or??? Anything but circling in tight circles over whatever you're looking at. Even that's not a panacea, but I think it greatly reduces the odds.

Any other experiences out there?

MTV

 

[bob turner]

This has turned in to an excellent discussion. I had never tried to stall out of a full rudder slip until Jim C suggested it. At least in the J3, it doesn't seem to want to stall with full back stick. I suppose a rapid pull aft might be a different story. I do not even consider snap maneuvers in a Cub.

As to inboard rudder in a turn, that seems to be a common student mistake - one I need to stress more.

MTV's idea of actual flight testing is good. Constant parameters are extremely difficult to get, and none of us has instrumentation sufficient to normalize the data. Still, the idea of smoke streams is great.

We don't have many Meese in SoCal, so the stall is less of a problem here - but it would be a nice thing to thoroughly understand.

 

[aviationinfo]

MTV, what about Shaun Lunt?

 

[Dick Williams]

numerous stcs

In answer to Mike's question about other experience out there: This also happened to me, circling a coyote during a predator control hunt in a stock wing cub. Cold and calm, hilly. The coyote was in a ravine and as we circled above him, on maybe the 4th time around, the cub wanted to turn right (into a hill). Immediately abandoning the coyote, nose down slightly for airspeed and full power, I was able to regain control before hitting the hill. It got my attention! I assumed I had flown into my own wake turbulence, also. I completely agree with Mike's comments about this.

I've also wondered about the Husky tail blank/stall that the Border Patrol experienced a few times about 10 years ago. Anybody got more info on that?

Dick