RE: J3 cub, crash on take off nearly every time.
 

This looks like the one. (click on the link)
[link]http://www.carlgoldbergproducts.com/airplanes/gbga1064.html[/link]

RE: J3 cub, crash on take off nearly every time.
 

I really don't understand all the talk about cubs being hard to takeoff. everyone here so far has said that their cubs will fly at a very reduced throttle setting. That is everyone from the 66" with an O-200 up front to the 108" with the .91 and all the .40s.

I have flown many many cubs, I love them never had any real problems taking off or landing. Maybe because I understand WHY planes ground loop. It is P factor. P factor is a problem at HIGH power setting and LOW airspeed. you know like on take off. I also know that a cub will fly on a very little power. 'clip the wing it floats too much' sound familiar?? if it floats like that then an .049 would keep it in the air a very long time, Longer than you might believe. so any way use your .40 and advance the throttle slowly to about an eighth, let it roll, when the tail comes up then and only then begin to apply more throttle. while gently easing it off the ground. climb out at a power setting that will ensure you dont stall it, but the takeoff roll is done very gently.

The cub snap is a very real thing, but flying in to a head wind you can land at a little more than a walking pace. The snap takes some persistence on the part of the pilot. you really have to slow it way down, then say 'gee its awfully slow, maybe I should slow down' It doesn't just happen it takes pilot input. Every cub I have ever flown has flown at least as slow as any trainer, and slower than some, difference is that a trainer has a gentle stall and a cub has a death spiral.

Take your cubs up high and stall them, notice how slow they get before the stall, then just keep it a safe margin above that speed and viola you, like me will swear that a cub is as gentle and docile as any other plane in the air.

And did I read in this thread that someone seriously compared a cub to a pattern ship??
Oh wait that was Capt. O-200. Hmm wonder if that explains anything at all

RE: J3 cub, crash on take off nearly every time.
 

they ARE hard to take off when you're not used to them, i can get almost any plane off the ground with a ground loop on the first try, the cub took a little getting used to. if you arent expecting it, it can be hard and costly. its always better to warn someone that might not have experience with it, than say its easy. i agree once you learn it, it is very easy. i think the main issue with the death spiral is that the cub gives you TOO much confidence in its slow flight ability. it can slow down soooo much and it still fly fine, but as soon as it crosses that threshold it goes into the spiral and catches you completely off guard.

RE: J3 cub, crash on take off nearly every time.
 

yeah my cub gives no major signs, once it crosses the low speed sweet spot down it comes!

RE: J3 cub, crash on take off nearly every time.
 

After reading all this stuff, I'm thinking about a Seagull Decathlon. I'll have to contend with slow throttle up and keeping it on the groun 'till it flies regiman, but I doubt it'll be any more difficult than a Cub. And then there's that nasty Cub snap that can come out of no where if it slows down too much, as described by other posters here. I could be wrong. I won't know 'till I've tried one for myself.

NorfolkSouthern

RE: J3 cub, crash on take off nearly every time.
 

Hi superflea
I like the analysis you offered. Thanks. I have always wondered why the J3-Cub reacted so much more different than other models. For you and others interested in this subject I would like to offer something that I discovered on the three J3-Cubs I have had.
I learned to fly R/C in 1972 in PA. One old timer in the club loved the Sig J3-Cub, which was a kit, 71” wing span (WS) and usually had about a .45 engine. I saw him crash, usually on landing, maybe a dozen times, totaling 3-4 planes. There were a few other Sig J3-Cubs in the club and all seemed to eventually crash on landing; I stayed away from them since they seemed more than I could handle.
In 1980 I lost my Sig Cougar due to a failed solder connection and decided to get a Sig Cub. An old timer in my new club in NC did not fly anymore but loved to build the Sig 71” WS J3-Cub. He sold them at cost. I soon was crashing that Sig Cub. I don’t recall any useful advice and we did not have RCUniverse then. I kept rebuilding it and landing it slow and crashing. It had a violent snap roll. I was determined to conquer it but it conquered me. I gave up.
About a year later I decided to build my own Sig J3-Cub. While building the wing I noticed that the wing had almost no structural integrity. It was limp as a wet noodle. The wing struts is what held it together, but MOST important, determined the washout/wash in of the wing. I had my answer now.
My theory is that after repeated landings of the Sig J3-Cub, the top of the “weak” cabin and the light wing structure would crush a little, which would allow the struts to change the washout/wash in of the wing tips. Unless I have got this backward, it is desirable to have washout (the leading edge {LE} lower than the trailing edge {TE}) at the wing ends. The struts were forcing the wing tips into wash in and the plane was a disaster waiting to happen since the wingtips would stall first and there would be NO WARNING. All of my other planes would warn me of a pending stall by rocking the wings.
On the Sig J3-Cub I was building I made the strut wing attachments adjustable and I checked the wing tip wash in EVERY time I assembled the plane for flight. Not one time did I ever have an uncommanded snap roll on the Sig J3-Cub that I built.
I have noticed that now there are many much better J3-Cubs on the market than the Sig Cub I described. Most have a cantilever wing and at least some of the wing struts are not functional. I believe that my theory may still apply if uncommanded snap rolls are involved. Presently I fly a 71” WS J3-Cub I designed and built from Coroplast, using the Sig layout drawings I had as a guide. My wing is fully cantilevered, my struts are adjustable, and I have never had an uncommanded snap roll with it on landing. I completely forgot everything I had learned about taking off a J3-Cub and as a result had 3-4 snap rolls on takeoff. Plywood models would have been totaled. My CoroCub, as I named it, sustained little damage. I keep an eye on the washout and adjust the flying struts as needed.

RE: J3 cub, crash on take off nearly every time.
 

OK. I guess I have this way of over simplifying thing s and under stating other things to a degree that my point gets lost. What I was trying to say is that the Cub is no more difficult than any other tail dragger out there. BUT that comment relies on people flying their other tail draggers correctly, which many don't. They learn some bad tail draggin habits with a four star or P51 then try to carry those over to the cub, or worse yet transition from a trike to the CONVENTIONAL gear of the cub. The nose gear was brought about for two main reason;

1) visibility.
This doesn't much matter to us modelers we are not sitting inside.

2) the tendency for ham fisted students (real life) to ground loop causing damage and injury.

So the trike was brought about, it eliminated the possibility of ground looping for the most part. But instead of teaching students how to fly it dumbed down the curriculum to fit them. But all that really did was push the ground loop problem up higher performance A/C for military pilots and to post solo pilots in the civilian world, yes I know that they need a check ride but after the little bit of instruction and a short ride they all alone and ground loops happen all the time in GA. If you look closely, here in the RC world you have the same things happening. One of the no brainer traits of a "good" trainer is tricycle gear. Fine. But what happens when that guy wants a shiny new P 51 or cub??? Well I'll tell you. They try to fly it like a trike on take off and it don't work. pilot error.

Part of the reason A cub doesn't like to be flown that way is because it one of the most over powered models out there.
The Goldberg anniversary cub .40 has a 76 inch wing and weighs over seven pounds, it calls for a .40 to .61
The Tiger II has a 56 inch wing weighs in at a hefty 4.5 pounds and calls for a .35 to .45. This according to Tower.
The cub is big and its heavy, Its natural for people to think .60 but the cub doesn't need it. And despite what Capt. O-200 has to say about it A bigger engine will make the Cub harder to launch. Much more torque, and the bigger prop will cause a much bigger problem with P-factor, both things CAUSE ground looping.
Learn to fly the cub with a smaller engine, or at least one that is in the middle of the recommended range then move up if you desire. But ALWAYS remember that it will fly at half throttle, that includes takeoff. Advance throttle to no more than half, work that rudder, and when she is ready to fly you will know. Let it just sort of drift up off the ground and then start feeding in more power. Take off at half climb out at full. P factor is the worst at high power, low airspeed. in other words when the prop is significantly out running the plane. Think of a clutch slipping in your car, what do you do?? do you floor it or do you ease off of it? the cub is the same way advance throttle a little wait till plane catches up then advance the rest, always slowly and smoothly. You will learn what it will tolerate.

Landing. I really don't what else to say about this. If you don't know how slow the plane will fly and continue to stall it then you will continue to have problems. it does not enter the spin with out warning. The warning is slow air speed. You should be able to look at it and figure that it is getting slow and add power. One of the basic things to check on the first very few flights is the stall. How severe, how sudden, and pay attention this is going to be on the test out at the field, HOW SLOW.

The cub will fly slow so it is easy to take off. it is probably over powered so let it break free of the ground then power up.
The cub will fly slow BUT it has a wicked nasty stall so stay the hell out of it. How will you know when your getting there?? well try watching it. If it looks slow then it is slow.
And yes I know that stalls can happen with extreme AoA and no I'm not going there.

RE: J3 cub, crash on take off nearly every time.
 

Hi superflea
How are you able to know the airspeed so accurately? From our vantage as R/C pilots, our view gives only an estimate of ground speed; how the plane is reacting is a hint of airspeed. I try to touch down at the same distance relative to my position each time in order to cut down the variables. However, I still occasionally miss my target. I don't have landing problems any more with my J3-Cub.
I guess you are not familiar with the wash-out/wash-in problem I described since you did not comment on it. Maybe my description will help others since it completely eliminated my landing snap-roll problem.

RE: J3 cub, crash on take off nearly every time.
 

I am familiar with the the problems of wash out/in but I was, and am assuming a properly built, trimmed, and balanced plane. obviously if any of those three things are way off then bad mojo happens.

You don't need to accurately know the speed of the model. It does have an absolute stall speed that is totally independent of weather wind and altitude. it will stall at X airspeed. you don't need to know what that speed is cause as you pointed out you have no way of knowing exactly how fast its going. BUT slowing down till it snaps then saying 'i didn't know that would happen' is plain nutty. again take it up 2 or 3 "mistakes high" and stall it. pay attention to how slow it LOOKED. do that a few times then you will better be able to judge when its going too slow on landing. BTW this isn't strictly speaking a cub thing, a person should have an idea of when all his planes will depart controlled flight.
I once had a quickee 500 type plane with razor thin wings and an old royal .46 on it that thing was insanely fast, our flying site had about a quarter mile on all sides of the flight line available for flying and it would cover that 1/2 mile from end to end in around 10 sec. lotta fun but if you banked at anything below 3/4 throttle it would snap. landing below roughly 70 mph was out of the question. My above advice is valid in that case too learn what the full flight envelope is and stay in it or you crash

RE: J3 cub, crash on take off nearly every time.
 

Hi superflea
I think I understand now. You seem to be able to tell by just looking (that is all we have) how close to the flight envelope the plane is regardless of the heading, distance, altitude, wind direction, etc. I'm not that good. I do my best to estimate those things, knowing the humane limits, such as depth perception of 17 feet, and I frequently get it wrong. As a result I build my planes with very strong landing gear.

RE: J3 cub, crash on take off nearly every time.
 

Well i didnt really think i was a prodigy but I guess I must be.
I just sorta figured that after after running a few test flights, just in the spirit of getting to know the plane that some of these things would become apparent. I guess not.
I am a little confused why any one would be just simply flying that close to the edge of a stall so far away from the pilot as to be unsure of how fast its going. But still the prodigy in me tells me that if one had done some basic testing/familiarization flights then one would know that maintaining altitude while flying downwind (the prodigy weatherman in me says I would know which way the wind is blowing before take off) at idle for any length of time might be bad news.
Any way i'm either Mozart with a transmitter or its 18 yrs of experience coupled with a dose of common sense.
It is pilot error EVERY SINGLE TIME A PLANE STALLS period. it is the pilots job and responsibility to know when that will happen. It is unacceptable to say
It was far away, the wind was blowing and i didnt know how high it was and so its not my fault.
But I am begging to figure out what the problem was ;)

RE: J3 cub, crash on take off nearly every time.
 

I currently own two Cubs, one a Goldberg Anniversary with a Saito 50 and the other a World Models with a Saito twin 100. The Goldberg displays no tip stall tendencies but the World Models requires caution. The front end is nearing completion of a rebuild following a stall when lazily putting around.

The fueslage of both are about the same size but the wingspan of the World models is about 8 inches longer than the Goldberg, though the Goldberg is not short enough to be considered a clipped wing version. The primary difference between the two models and the reason the Goldberg will simply drop a nose instead of tip stalling is the Goldberg was kit built and evidently by a good builder who carefully built in washout.

I bought the Goldberg used and in fairly clean condition at a swap meet from the original builder who said he damaged the plane on its first outing in a very strong cross wind and simply laid it up for several years and finally did the repairs including a new cowl to dispose of it.

I don't know if the washout is detailed for the Goldberg build or if it was a builder option... either way, it makes the Cub a much better flyer.

btw... Both Cubs have inset ailerons but because the World Models Cub has a longer wing the ailerons are more outboard on it and a friend who used to own a full size Cub suggested trimming the ailerons up a bit to simulate washout as many full scale owners often did. I will definitely try that with an up trim mix at lower throttle settings. I can't imagine it having the same effect as wing washout but it is worth a try.

I do have an Ultra Stick Lite that has a quad wing setup with flaps and ailerons and when crow mode is entered where flaps go down and ailerons go up... it is impossible to tip stall and the plane will fly at walking speed.

Last... a Cub wing should be examined carefully for any warps... any trailing edge down warp out near the tip can be critical. An experienced builder can see this quite easily by eyeballing the wing. A more novice builder might want to examine this with an incidence guage by first establishing the root of the wing zero and then moving the meter near the wing tip. Any trailing edge droop at the wing tip can quickly spell Wicked Cub and the need to reach for the heat gun to twist it out. Remove the struts, twist the wing to make wrinkles and heat out the wrinkles. Readjust the struts.

RE: J3 cub, crash on take off nearly every time.
 

hehe i have to say something i have a J3 cub from them worst manual i ever seen lol the cub is build but will not track in a line for nothing the amount of thrust on the motor keeps it heading to the right does not matter what trim you use or adjustment hate to thoss it in the air just to see it fly maybe my last thing to try

RE: J3 cub, crash on take off nearly every time.
 

Interesting Cub thread. I'm learning to fly RC and just bought the Nitro Models 120 J3. Should get it tomorrow. Now I'm wondering if I can master it. An experienced member in our club bought one also. I will get him to help me. I have experience with full scale cubs. Have owned all of them except the J2 at one time or other. They are all rigged with washout to make the stall less abrupt. The E2, J2 and early 40HP J3 had to have the aileron gap sealed with tape or they would fly poorly. I wonder if these things can be applied to the model. The full scale cubs are easy to fly but are hard to fly real well. Of course people learning in a Cherokee or Cessna have a hard time learning to fly them. Larry

RE: J3 cub, crash on take off nearly every time.
 

larrysl,
I hope your rc experiance is a good one. I will be interested to see what others have to say about you starting with a 120 size however. I have always figured it best to start with a 40 - 50 size although the bigger the plane the less impact wind has on it (before I get corrected, I did not say the wind does not have an impact, just not as much as a smaller plane).

I know a guy that flys "full scale" planes but can not fly rc what so ever. He has tried several times and all have been failures. He simply needs to be in the cockpit in order to fly. He says it's hard to make the transition from using real controls to hand held radio controls.

Don't let this scare you, he is just one person that is that way. You may be just fine.

RE: J3 cub, crash on take off nearly every time.
 

Jpann, My wife will kill me if I wreck it. I have a 120 size Flybaby almost ready to go. Will play with that before the cub. Also have a 84" Quaker. Last fall I got to the point where I could take it off and land it pretty well. But it is throttle, rudder and elevator only. With the rudder on the right stick. So I will have to relearn flying with ailerons. I spent a lot of time learning with an electric Wing Dragon without ailerons. Got an aileron wing for it and will spend some time flying it. You are right Flying full scale airplanes doesn't help much with RC. It took me awhile to start getting it. Larry

RE: J3 cub, crash on take off nearly every time.
 

don't know what a wing dragon is, but if it is an inexpensive trainer i would definitely spend a lot of time with it before moving to the fly baby or cub! i would suggest an advanced trainer with a glow engine to start with instead of jumping straight to either of the other two planes you own! good luck man!

RE: J3 cub, crash on take off nearly every time.
 

larrysl,
I know what you mean about the wife thing!!! Just some advise, you can do whatever you want with it. I would consider moving the rudder to the left stick if you can. I started with the rudder on the right as you have and found it difficult to fly with that configuration once I started using ailerons (I think there may be a discussion about this somewhere on this board). Once you start using ailerons you will not use the rudder as much (if at all), to "turn" the plane while in the air. You will mainly use rudder on takeoff and that will be tricky if you do decide to move the rudder to the left like I have stated. The reason being that you will almost involuntarily try to steer the plane (while on the groound) with the right stick wich will be the ailerons and it will not respond.

RE: J3 cub, crash on take off nearly every time.
 

Jpann, Thanks, I am moving the rudder to the left stick. I will be flying the Wing Dragon now with ailorons. The snow is getting gone and it's warming up. Thought about flying it today but it's a little too breezy. As far as the cub and flybaby, there are a couple of real good RC pilots at our club, I will get their help. Larry

RE: J3 cub, crash on take off nearly every time.
 

Just wanted to chime in on the Cub stall stuff. I'm not sure why folks get so hung up on stall speed, except that that's the way flight schools tend to (misleadingly) correlate the stall. It really has less to do with speed and more to do with angle of attack (as far as just the physics are concerned, it has NOTHING to do with speed). And that is something you have direct control over, via the elevator. It's a little easier in full-scale planes because you have physical feedback (stick pressure, mostly), but it works in models too. You can be DESCENDING at 2 knots and not stalling, just don't yank the elevator back.

As to how this relates to a Cub, well, once you get it, you don't have to try to gauge speed quite so much. If you keep having to ease back the elevator and the plane is still barely maintaining altitude, or dropping, then look out. I find myself using this a lot more than speed estimations on landing, especially when the plane is almost coming straight at me. If the plane seems to be wanting to drop on approach even as I ease back the stick, then I usually let off pressure a little bit as I add power (or, in dead-stick situations, just ease off more and try to extend the glide as much as you can....better to land softly in the weeds than to snap-roll over the runway).

Once ya get in-tune with that pitch control, it really gives you a lot more control over the stalling/snapping situation, regardless of airspeed.

RE: J3 cub, crash on take off nearly every time.
 

I'm glad dabigboy said it before I had to... Stalls have nothing to do with speed, it is all angle of attack. A stall can happen at any speed short of sub-sonic. It's not as noticable on R/C aircraft because their thrust-to-weight ratios are so high that simply slamming full throttle will remedy a stall almost immediately (by changing the angle of attack, not increasing speed).

RE: J3 cub, crash on take off nearly every time.
 

My DPM Super Cub takes off easily with no threat of departure stall whatsoever. Not so with my late GP 60 "clipped wing" Cub. That thing had a relatively high wing loading and I had to let it run down the runway a good ways before I dared apply up elevator. Otherwise, it'd snap and roll over on me. I learned my lesson after two repair jobs. I used a Saito 130TD in the GP Cub, which gave it plenty of power. Still, you had to fly the thing "on the wing" because shear power wasn't enough to prevent nasty stall behavior. My Super Cub, on the other hand, has an OS 160 twin and never seems to give the slightest indication of impending stall except when I force it into one. Needless to say, I like flying it a lot better.;)

RE: J3 cub, crash on take off nearly every time.
 

my hangar 9 cub flies perfect with a saito 60 twin four stroker,i wondered about being underpowered but it works great..i think many people overpower their planes...fly it with the wings..not the prop!

RE: J3 cub, crash on take off nearly every time.
 

I used to have a 108" cub with an OS 120 gemini, was a real pleasure to fly. take off's could be hairy in a good wind over 10kn but as has been said before, catch it early and no problems. I very rarely used full throttle, just slowly eased the throttle open as she rolled and was often flying at under 1/2 throttle. up in the air it was usually about 1/4 throttle or less. One of the things I loved to do in windy condition was either just hanging the cub in the air going nowhere or even going backwards. Downwind runs always needed more throttle, but thats par for any plane to one degree or another flying slow. While not the easiest of planes to fly, it isnt hard if you keep an eye on it, and amazing how much fun it is pushing the envelope flying slow. I regret selling that plane, but I have a 144"ws cub under construction now which will have an OS320 Pegasus for power. those multi cylinder 4 strokes sound simply awesome and suit the cub perfectly.
As for the cub not being a trainer I couldnt think of a better plane to learn on. It will teach you all sorts of skills that most new trainers wont that will stand you in good stead for later models, like the P51, some pattern ships, etc. Just my 2 bits worth
cheers Johnno

RE: J3 cub, crash on take off nearly every time.
 

Hummm, could you explain what you're referring to? When you're flying with the wind, your groundspeed will be higher, so you'd want to throttle back if you're trying to keep the plane from getting away quickly.

Definitely. I still recommend a conventional trainer for initial RC training, simply because the total newbie needs just to figure out the basics of keeping the plane properly oriented and working the controls (without worrying about the plane wanting to ground-loop on takeoff or snap roll in flight), but once that hill is climbed, something like a Cub is an excellent idea. I learned how to "control" an RC model with my trainer and Tiger, but the Cub taught me how to "fly".

RE: J3 cub, crash on take off nearly every time.
 

ok, what I am refering to is when slow flying downwind the wind is actually robbing the wing of airflow from the front, and therfore in effect stalling the wing. you dont notice it so much if at all flying sport planes doing a high rate of knots, but poking around slowly can give you problems in a hurry, especially you're low too

RE: J3 cub, crash on take off nearly every time.
 

Naww, the airplane couldn't care less what direction the wind is blowing or how fast it's going. The only time this comes into play is when transitioning to/from the ground, or trying to keep the plane oriented to a ground object (like when we try to keep our models within a certain distance from us). If you maintain the same throttle setting, your plane will have exactly the same airspeed going upwind as it does downwind. Flying objects have no concept of "upwind" or "downwind" or "crosswind" or any kind of wind other than relative wind.

The problem occurs when you try to maintain the same GROUND TRACK flying downwind as when you're flying upwind/calm conditions, and is also where you may get the impression that flying with the wind, slowly, can give you problems. For instance, say you're on the downwind leg of your landing pattern and are about to turn base. Since the plane is in an air mass that is moving relative to the ground (and you), you will need to start your base turn earlier than usual to end up at the same distance on the base leg. If you don't consider this, you will start your turn at the usual point in the pattern and get blown further away from the field.......or (more likely), you will involuntarily make a steeper-than-normal turn and pull back more on the elevator to keep the plane from drifting out. And this is where the danger lies and your wing loading goes up. This is harder for us RC'ers than for flying full-scale, because at least in a full-scale you have a better view of bank angle and also can refer to your instruments to maintain a more consistent airspeed....so even if you make your turn too late, you can discipline yourself to keep the airspeed up, stick/yoke pressure down, and stick with approximately the same bank angle that you typically use. For RC, all we really have to go on is what we can tell of bank angle, and amount of back-stick. The latter, actually, is a pretty good gauge of how close you are to stalling, assuming you have a fair amount of stick-time with the aircraft in question (and haven't dialed in a bunch of trim).

Try it some time. Force yourself to fly the plane the same way in a strong downwind leg as you typically do in calm conditions. Same throttle setting, bank angle, back-pressure, etc. Your descent gradient will be shallower, and the plane will drift with the wind, but it won't handle any differently, and you won't run into any stalling issues (assuming there are no gusts/wind shear).

RE: J3 cub, crash on take off nearly every time.
 

if you are flying 30mph plus you are right, but if you fly like I used to fly my cub at around 15 to 20, and you are flying in in similar wind speeds it makes a big difference. at same settings as you say I wouldnt have had a cub left, simply because the controls did not have enough airflow to work and it would just stall. As slow as I liked to fly the cub it did make difference with my cub

RE: J3 cub, crash on take off nearly every time.
 

No, wind speed makes no difference whatsoever as far as the plane is concerned. If your Cub was getting slow enough to stall it's because you were slowing it down involuntarily in order to keep it at a familiar speed relative to you: groundspeed. Now, there is a danger in flying slowly in GUSTY conditions, and that is that as gust intensity increases, so must airspeed, for safety. An example would be flying stable at 20kts and suddenly getting nailed with a 5kt gust in the direction the plane is flying: airspeed drops to 15kts and then rises back to 20 as the plane seeks its original (stable) 20kt condition where all forces are balanced.

It definitely looks misleading from the ground, when your plane is hauling booty downwind and yet you have very little elevator control and are near a stall. But it's because you are deliberately throttling back and pulling the elevator back to make the plane look "normal" from the ground. The thing with RC models is we have no speed reference other than groundspeed, so we must consciously consider what the wind is doing and factor that in. Consider this example: a plane is flying normally in a stationary mass of air. Now imagine the ground is zooming by beneath it at 20kts. How does that affect the plane? It doesn't.

RE: J3 cub, crash on take off nearly every time.
 

Where can I buy can of cub yellow in a spray can?
K.O.

RE: J3 cub, crash on take off nearly every time.
 

then explain to me why i can fly a plane into the wind at 0 ground speed, basically keeping it in one spot and even climb, but when i turn downwind i drastically lose altitude and it wont climb at all unless i throttle up. not to mention my cub met its doom by flying slowly into the wind and then turning downwind and not throttling up enough and my plane basically fell out of the sky.

RE: J3 cub, crash on take off nearly every time.
 

Finally got it together to test your last line where you statements regarding moving air mass etc.
conditions were 15kn S/E breeze that was fairly constant, we had a good windspeed monitor and a radar speed detector and crew to work it all and take notes. Air plane was another embers 144" cub running a saito 300 twin
Our airfield lies on the coast, no hills etc for miles around us
The throttle was touched at all once airborne

We did a few runs cross wind to try to get a reference speed to work with and found at our chosen setting we had a groundspeed of 32 mph.
we then proceeded to fly 15 circuits directly with the wind and then directly into the wind
average winspeed 18mph
Groundspeed differences flying into the wind were an average of 8 1/2 mph slower
groundspeed differences flying with the wind were an average of 7 1/4 mph faster
each leg was recorded for both wind speed and ground speed and the variations over all the runs was minimal within 5%

But it confirms my thoughts that our aircraft are NOT locked in a cell of moving air mass, and tail wind will rob you of airflow velocity over your wings and control surfaces if flying slow like I enjoyed doing.

RE: J3 cub, crash on take off nearly every time.
 

I have the old Hangar 9 Cub 40 with the 80" wing. I've had it now for at least 12 years. I built it using the advertised Saito 56 with a 12/6 prop.

When I first took it to our club field I had one of the pro's put it up as I always do with a new build. He said it was fine so I tried it. It seemed a bit squirrely to me and I didn't like it. I was flying tail draggers at the time but this wasn't right, not my cup of tea. I took it home and hung it up until this past summer.

This year I got back into heavy flying, war birds, sport planes, etc.. I saw a Cub flying at our field and thought how nice it looked and how well it flew. When I got home I spent the next week preparing mine for another try. I found the balance slightly tail heavy and made it a touch nose heavy. I also found the wing incidence +2 degrees but, a reference on RCU forums said this won't be a problem.

I took her to the field, fired her up, and off she went. This was a nice warm day and maybe 10 mph gusts coming right down the tube. No speed demon but it left the ground without a problem. A nice smooth realistic take off. As I'm gaining altitude I'm banking right and I'm about 50 ft. over a stand of trees. All of a sudden the plane wants to roll over and I'm going wild trying to level out. It's as if my ailerons aren't functioning. One of the best 3D pilots in our club was with me and grabs the radio. He levels it out as if nothing happened. I'm a wreck and have him bring it in without incident.

I ask him what happened, is the plane under powered? He says, " No, it's flying scale. You ran into thermals at the tree line and you have to learn to fly with rudder."

That one piece of advice has changed everything and opened a whole new flying experience for me. I now enjoy a good wind when flying my Cub. I'm not burning up the sky but it's a new challenge and it's become one of my enjoyable, relaxing aircraft.

And all this time I thought rudder was for ground handling, knife edges, and hammer heads! Flying fast is easy, flying scale is flying.

Just my $.02 of rambling.:D

RE: J3 cub, crash on take off nearly every time.
 

Glad you now enjoy your cub phatbob, I got that advice before I maidened my old cub and it made a huge difference, I was told to fly it like my fave glider (3ch electric) and I had a ball with it. Only times I really used aileons on the cub was on landing approach. I loved to fly her low and slow just puttering around and playing with the breeze [8D]

RE: J3 cub, crash on take off nearly every time.
 

Ummmmmm........you're not disagreeing with me here. You can "hover" in a wind because the plane is moving forward within that air mass. However, the air mass in this case is moving the opposite direction in relation to the ground. Consider my example of the plane moving in a mass of air, and the ground suddenly zipping by at the same speed as the plane. Say the plane is doing 20 knots true airspeed, heading east, then imagine the ground beneath it suddenly starts moving 20 knots east as well. Logically, the "speed" of the ground has no effect at all to the plane, but an observer on the ground would perceive no motion (plane is hovering). As to why your Cub crashed, you answered that question yourself: "not throttling up enough". Any time you bank, wing loading must go up if you are to maintain altitude. If you're in a slow-flight configuration (which you almost certainly were at the time, unless you had a mighty strong wind), then you were already somewhat close to stalling. To get the lift you needed for the turn, you needed to maintain airspeed while still initiating the turn...this would require dropping the nose, or adding power. All this is exacerbated by the fact that the ground observer/RC pilot is more likely to make a steeper turn when turning with the wind, because we're used to the plane making a certain turn radius and we will involuntarily try to keep the same radius (will require a more extreme turn when turning with the wind).

qldviking....wow, kudos to you for actually taking this to the field and trying it out for yourself. Your observations sound like what I'd expect, how do you think they contradict what I said before? Let's look at your results for a minute. First, keep in mind that your groundspeed while in a front-quartering crosswind (which is what happens when you are trying to maintain a straight ground track, as I assume you were for radar-measuring purposes) is going to be LOWER than your true airspeed, because you are essentially in a "partial headwind". This is basic vector math, and thus does not change with aircraft type (so a Learjet at 180 knots TAS in a 10*, 20 knot crosswind will have the same groundspeed as a Bonanza under the same conditions at 180 knots TAS).

Now, your speed difference upwind vs downwind is 7.25 vs 8.5....a difference of 1.25 MPH, which actually is just under 7% of the wind speed - well within the likely variations in wind speed during your tests. So the actual ground speed difference upwind vs downwind is 15.75 MPH. Consider the margin of 5% of wind speed, which is 0.9 MPH, on a run both upwind and downwind, for possible 1.8 MPH change, and we are very close to our known wind speed, 18 MPH. For an unofficial test, your numbers are actually very consistent. This completely supports the concept that the plane was moving within an ~18 MPH air mass the entire time. As a ground observer, you saw this difference and recorded it.

If you could somehow fly the plane at a heading exactly 90* from the wind course (would require a compass in the plane and knowledge of the exact wind course), you as a ground observer would see the plane moving "sideways" at 18 MPH. Something else to think about: when you are flying in a steady crosswind, does the plane continually try to weathervane into the wind, or does it maintain the same crab angle?

RE: J3 cub, crash on take off nearly every time.
 

ok take my figures as relative to actual airflow over the wings, upwind they are increased and downwind decreased, that affects handling bigtime and noticeably too. cross I am always on the rudder and crabs too, as is expected. This is just the start of our experuimentation with our models, We are currently looking into getting sert up with telemetry to fit the cub to give a variety of data including airspeed, gps groundspeed, altitude and attitude variations etc there are set uops that do some for gliders, and we are trying to adapt gps and airspeed to the set up, saving it all on a mp3 so we can d/l to a laptop and see what we shall see what and how. Our electronics whizz is having a ball trying to sort it out in a small package that works, looking forw to getting the setup and trying it out

RE: J3 cub, crash on take off nearly every time.
 

No, movements that you measure from the ground do not have any intrinsic ties to actual airflow over the wings. If they were, you would not be able to "hover" in a headwind.

Are you saying that if you did not hold in any rudder, the plane would never stop rotating until it was heading into the wind? I'm not talking about using rudder to hold the plane in a slip in order to maintain a ground track, forget the ground in this case. Think of when your plane is flying straight over the field at altitude, when you're not trying to hold an approach......it might be going straight down the runway, but what do you see when you look up? The plane is pointed into the wind slightly.

Tell ya what, I can't really say anything that I haven't already, and I don't want this turning into a flame war, so I'm done for now. Have you done much organized study on aerodynamics (college aerodynamics course, flight school, etc)? You might want to pick up a book on the subject if you haven't already (Jeppesen's "Private Pilot Training Syllabus" is a good place to start if you just go straight to the chapters dealing with flight), plus the background knowledge will prove useful in interpreting your upcoming flight tests. This isn't a cut-down to you, I think you will find some of the published info out there to be genuinely useful.

Sounds fun, keep us posted. This may be of interest to you:
[link=http://baron.flightgear.org/~curt/UAS/Rascal110_1/Instrumentation/]Curtis Olson's wired Rascal[/link]

RE: J3 cub, crash on take off nearly every time.
 

hi,

http://search.rcuniverse.com/search....one+conversion

Do NOT use the steel wing hold-down screws included in the kit
 

Was just browsing the threads regarding the Goldberg Cub crashes. Just a word of friendly advice: Do NOT use the #6 x 1-1/4" metal wing hold-down screws included in the kit. Use 1/4" NYLON BOLTS instead. I witnessed two Goldberg Cubs destroy themselves by ground looping on takeoffs. The crashes literally destroyed the cabin structures. In both instances the Cub's wings were fastened with the kit-included steel screws, so the cabin structures absorbed the total impact because the metal screws did not break. As an alternative, I suggest using 1/4" NYLON bolts instead. Nylon bolts are terrific for wing hold-downs because they will typically snap on impact thereby minimizing structural damage. I know -- I've done it. Touched down with wing tips on landing which caused the airplanes to flip. Always pleasantly surprised that the nylon bolts absorbed most of the impacts by snapping in half rather than passing the stress to the surrounding structure. The cabin structure of the Goldberg Cub is notoriously weak. Using nylon bolts to attach the wing may not prevent crash damage but, I believe, it will help minimize it. Virtually everyone our club uses nylon bolts for their wing hold-downs. Just thought I'd just pass this along. Thanks.