jereahidiaboam

Hello everyone,

Well i just want to tell eveyone that i know first hand that this airplane tip stalls like you wouldent beleave.
Please can anyone tell me how to make this airplane fly like it should?


Thanks

GaGeeBees

My Feedback: (23)

What is the wingspan, chord (width of the wing) and the weight ready to fly (minus fuel)?

crasherboy

I am not sure as to the wings. Are they straight to the ends or is there some taper? At any rate ,have you checked the wings for warp-age ? How are they covered,in shrink film,if so you can use some heat on them and twist in some negative washout[trailing edge up] .If you can't do that try a little adjustment on your ailerons. Move each one up a little,maybe a 16th in.[at a time] at the trailing edge. Some planes are built with built-in wash-out,that is the idea to reduce tip stalls. With out seeing the model first hand ,This would be my advice.

da Rock

Balance it better.
Correct any misalignments.
Remove the warps.
Insure the ailerons are properly aligned.
Adjust the elevator throws to better utilize the full TX stick throw.
Setup and adjust dual rates appropriately.
Employ exponential on elevator and aileron.
Fly it faster on approach.
Resist the desire to flare too soon on landing.
Lessen pitch changes on approach and particularly to not pitch the nose up.

da Rock

The picture I found of that model airplane shows a non-tapered, straight wing. They naturally stall from the root. That planform shouldn't be stalling from the tip unless something is screwed up. The list above addresses that.

When a straight wing is straight and it and everything else is true, one wing will still stall before another if you push that wing beyond it's flight envelope and the airplane isn't dead true to the airflow it's encountering. Which is almost always the case in flight, since we seldom fly perfectly straight upwind or downwind. A straight wing, or any planform for that matter, doesn't have to stall at the tip to stall to one side. And almost every stall winds up biased to one side. So don't fixate on the tips. Look at the whole airplane.

Are you float or ski flying the model? They've got to be true as well.

Scar

My Feedback: (3)

You didn't mention what you were doing when you experienced this stall. I'm going to guess you were taking off. Correct? If so, that's probably not a tip stall.

If you'll describe the behaviour, you'll get better responses.

Best wishes,
Dave Olson

rmh

safe bet - it is simply overweight
The fix is almost always the same:
reduce control inputs or slow inputs to prevent fast changes in attitude
you cannot change airfoils (no magic airfoils exist) etc., to help anything - so go to basics and make sure all controls operate very smoothly and at a even predictible rate as you move the sticks. I have worked with model problems such as this for many years - partly because I made and sold kits for 25 yrears
The MAIN causes in problems such as you note
over weight and over controlled.

crasherboy

Re: da Rock's comment that the wing will likely stall to one side,how true. I have many hours in Cesna 150 ,152 180 ,etc. I have done many stalls in them [to feel the response of the aircraft],so you don't do this to close to mother earth! As you enter the stall at first the plane stays level.But as the stall gets more advanced you have to be on the ball with the rudder ,cause if you aren't you will[can] go into a spin . For those of you that maybe have not flown full scale that is how you do a spin[kick the rudder full over just as the craft is about to break over.Same with models,they work the same way. A full power stall in a full scale is a real thrill ,it can get pretty steep before it goes over. But I wont ,because of health problems be getting a medical again to fly full scale. It looks like I will have to settle for ultralighs or models.

jereahidiaboam

Well guys,
to answear some of your questions, this particular airplane is notorious for tip stalls, according to my research.
-no i cant twist the wing for washout
-it was on floats the first time i crashed it
-78in wing span, 12in of chord, and a little on the heavior side 6-9 lbs
-Non tapered straight wing
-This happened way after take off in a sharp turn.
- it has a .60 size engine
- at the time i had a ****ty old basic four channel radio, but i have a 7 channel that can do all the works but havent flown it with it

But basicly everything you guys said all makes sence, all i want to do is make this model fly better. the more help the better.

Thanks for caring

P.S Here is a link to what the airplane looks like.

[link]http://www.richmondrc.com/frameset.htm[/link]

crasherboy

Just looked at the beaver on the link you gave. It looks to me that it should be a stable aircraft,but who knows ,it could have some issues. I have an RCM Funster which is about the same size. It has no tendencies whatever to tip stall ,and in fact with flaps down ,it will stay flying at around 10 mph. It is built like a battle tank to. Of course it does not have floats on it,but it is heavy . I had a 4c60 on it last when someone crashed into it ,I landed it while the other model was completely destroyed. The last I know,they never did find the Rx to it. I have fitted a 70 4c in it ,we will see how that pulls it. Question ,do you have any idea as to the speed when it stalled? In my opinion ,it could do with a little bigger engine with floats on it ,but a 2c 60 should keep it flying,BUT you need to not slow it down to low a speed. I think it were mine,I would put in a little bigger engine and give the ailerons a little ajustment as to my other post. I am wondering how you will come out on this one.

BMatthews

9 lbs may be a hint on the heavy side but not by much or not at all. If it's less than 9 then it's a floater. You're not overweight by any big degree if at all provided you're correct about the weight. Obviously you don't have a scale though. I'd suggest you invest in one. Digial scales that go to 15 to 25 lbs are cheap these days if you shop carefully.

You say it stalled on takeoff during a sharp turn. That tells me that this could well have been a pilot error that is related to using too much aileron while flying too slowly. When you're hanging on the prop with little airspeed the last thing you should be doing is hauling the aileron stick hard over. That drops the inside aileron and greatly increases the angle of attack on that side of the model. WHen you're near the stall like in a hard climbout this can be the last straw and the wing with the downward aileron can easily stall and drop. When flying slow like in a hard climb right at takeoff you need to just ease the stick over a little and wait for it to roll slowly into the turn. No hard pulls allowed.

Once it's fixed again get it up "3 mistakes high" and from a very slow near stall mush power up and climb sharply as though you're in a takeoff mode. Before the model builds up much speed shove the stick over. I'll bet you can easily replicate the "tip stall". Try it again but with less stick. Learn what the model's limits are.

There's no way to "fix" this other than learning to respect the laws of aerodynamics and the limits of this particular model. Glider flyers using aileron sailplanes know this and do not use lots of aileron input when flying slow. It's just part of flying.

Now if you come back and tell us that this is a 16 lb model then the same thing applies. But you just need to be even more careful about how you use the ailerons at slower speeds.

Once you get it up to speed you can yank and bank all you want. The wing at that speed is so far above the stall speed that this aileron related stalling isn't an issue.

Consider too that you'll NEVER see a full sized Beaver or other light plane or any sort of airliner hauling around in a pylon turn right at takeoff. They all know it would be suicide. Even good aerobatic pilots in the full sized stuff know they need to reach a specific critical airspeed following takoff before they shove the stick for whatever the show routine calls for. But in their case that time is pretty darn short.

Scar

My Feedback: (3)

Bruce,

I went back and read his post, and what he said was He was probably responding to my suggestion that the snap had happened at takeoff, and I think he means the snap occurred long after takeoff.

I'm thinking a sharp turn with this thing is going to require a high airspeed. Best to keep the speed up and the wings close to level.

The full-scale Corsair had a tendency to drop the left wing, if I remember correctly, and they would fasten a chunk of angle iron to the right wing, to make it stall out at the same speed. Then the stall would just make the plane drop the nose, instead of rolling to the left. Probably not relevant here, best to just keep the airspeed up until it touches down.

Best wishes,
Dave Olson

BMatthews

Ah, yeah. I saw "takeoff" and "sharp turn" and put 2 + 2 together and came out with split pea soup.

So it could be a couple of things. If the control throws are set up with very generous travels for snappy response and the ailerons are used at the same time a lot of elevator is added and the model is up to a higher weight then it could be tip stalling from just being driven too hard. More of an unwanted snap roll really. But with lots of control travel you'll get that even at higher speeds.

jereahidiaboam

well guys the airplane is back to one peice again and i am near ready for the first flight since she was practicly distroyed. It is now back on just wheel skis and i am going to take everyones advise.
i just wanted to clear up somthing about the tip stalling. this happens at a farely high air speed and does not matter witch way you turn. So what i need now is any suggestions on how to set up my controls this time to maybe give me some chance out there. you guys seem to know your stuff and any little help is appreciated. cause if i crash again thats it for the beaver known a C-FJOM.


Thanks J

da Rock

"witch way you turn"..............

OK, if it's happening in turns, there is another thing to consider. High wing layouts with cambered wings and some dihedral can also have a bad reaction to the ailerons in aileron/elevator turns. Since most turns are not rudder only turns......

Basically, the ailerons on those wings create a fairly unbalanced effect on the airplane. And cause a yaw that is opposed to the direction of the turn. And the yaw is from quite different amounts of lift/drag being created by the two different ailerons.

And since the airplane is yawing, having one wing see a greatly different situation than the other, one of them probaly will stall before the other.

Consider applying a very popular RealLife solution. Differential ailerons. It's actually quite easy and quick to rig right on the airplane.


............. btw, the higher the wing, the more dihedral effect. The greater the dihedral effect, the more apt the design is to experience the negative yaw. The "higher the wing" is really a measure of how far below the CG is and the drag of the parts below the wing. Add skis or floats and you've move both the CG and the airframe drag farther below that wing.

otrcman

Another spinning Beaver? Seems like a common thread on this forum. I haven't seen your airplane first hand, but perhaps can give you some general thoughts.

1. If the airplane starts to roll and descend rapidly, particularly during a hard turn, then it is no doubt stall related. When it rolled out of control, did it roll in the same direction as you were turning or did it go in the oposite direction? In other words, did it "tuck under" or "go over the top"? I can tell more if you will let me know which way it went.

2. Stalling is generally a function of too much wing angle of attack. And rolling during the stall generally indicates sideslip along with the angle of attack.

3. So maybe you had too much angle of attack and had some sideslip all at the same time. Let's talk about what controls can cause this situation. Other folks have already touched on these causes, but I'll try to put their inputs in a logical order:

4. Angle of attack: AOA is caused by pitch control, the elevator. You probably have more elevator control than you need. Some airplanes, such as the famous Ercoupe, have such limited elevator travel that they can't stall at all. That makes them very safe. You will probably be a lot happier if you cut your elevator travel 'way down to limit your angle of attack so your airplane will hardly stall at all.

A word about CG: Your elevators become less effective as you move the CG forward. So in lieu of restricting elevator travel you may want to simply move your CG forward. Or maybe do a bit of both.

5. Sideslip: Sideslip can be caused either by rudder or by ailerons. Da Rock already touched on this subject. Basically, if you use rudder at or near the stalling angle of attack, the airplane will roll in the direction of the rudder used. In other words, left rudder will produce a left roll. But in the case of ailerons, left aileron can produce right yaw. And of course right aileron produces left yaw. So you can aggravate a stall by use of ailerons at the same time as you are using elevator.

What to do about the sideslip? Since you were probably trying to turn by use of ailerons alone, you need to reduce the "yaw due to ailerons", commonly knon as "adverse yaw". You can do this by increasing the up travel of the ailerons and decreasing the down travel, although this fix doesn't seem to fully stop the yaw. The surest fix is to use a bit of rudder input along with the aileron. You said that you now have a fancy transmitter. Does it have aileron-rudder coupling? If so, program it so that left aileron causes the rudder servo to also move slightly left. And right aileron should cause right rudder. Not too much, say five degrees of rudder for 20 degrees of aileron.

6. Another thing that causes sideslip: the floats. I'm not certain whether you were flying with floats, but the floats degrade directional stability. Whenever you use floats you will probably need to add the extra vertical fins that you see on real Beavers. And move the CG forward a bit.

6. Summary of things you can do to make the airplane fly better: Remove the floats and use wheels or skis at first. Move the CG forward. Reduce your elevator travel. Incorporate differential aileron trvel if it's practical to do so. Incorporate rudder mix into your aileron travel. Be less aggressive on use of elevators in flight. Don't try to make steep tight turns.

Dick

GaGeeBees

My Feedback: (23)

"spinning Beaver"? Sounds like something that costs extra at the local strip joint

BMatthews

Try to not use so much elevator in the turns near the ground. Get it up about 3.5 mistakes high and then experiment with steep turns and using more and more bank and elevator until you learn what the model will tolerate. From there if it's got issues then it's time to start looking at options.

Just a thought.... Is this an ARF or a kit? If it's a kit how much care did you take to ensure that the airfoil is properly rounded at the leading edge? Or is it quite sharp? A 12 inch chord airfoil should have a leading edge nose radius that looks like 1/2 inch dowel at least. If it's a lot sharper than that then you may be getting a sharp stall from that.

jereahidiaboam

Well thanks alot OTRCMAN, that is some excelent advice, everything you said is absollutly true. when ever we get out of this -40 below 0 stuff i will let you know how it goes.

Thanks a million to everyone who put there input.

oh and GA GEE BEES just ask your woeman she can tell you.

J