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-   -   J3 cub, crash on take off nearly every time. (https://www.rcuniverse.com/forum/crash-rebuild-96/6464055-j3-cub-crash-take-off-nearly-every-time.html)

layback2 02-27-2008 09:17 PM

RE: J3 cub, crash on take off nearly every time.
wow cool to hear i have a smaller cub wing span 50inches and 31 inch fuse that i have problems understanding the )_(_&^%^%^$$##$ manual its in a langlish no one can understand i have it build but the cg and the rons and rudder and elevator is not right the airons say 1.1 up and 1 mm down funny and the rudder says 30 to the right and 36mm to the left what a mess and the elevator say 36mm both ways they cant be right oh the cg is really not that bad 56 to 66 mm how can i set the thows i need to read more and ask for help darn model is a CY model sold by texasrcmodels they cant even help i email them 4 times and got no help at all

JPANN 02-28-2008 03:33 PM

RE: J3 cub, crash on take off nearly every time.
this may take a few mins to reply as I am laughing at this: "i have problems understanding the )_(_&^%^%^$$##$ manual its in a langlish no one can understand". I feel your pain!! Langlish:) I have my rons at about 3/8" both ways keep them even. The rudder has by far the most travel at about 1/2" both ways, keep them even. The elevator is at about 7/16", both ways keep them even.

Others may tell you diff, that is just the way I did it. Every palne may be a little diff. Keep in mind that my cub has a 71" wingspan and is 42" long. Theese are what I think are high rate settings, you should use dual rates (if you have the radio that will do this) and start with the shorter throws.

" means inches.

JPANN 02-28-2008 03:41 PM

RE: J3 cub, crash on take off nearly every time.
The cg you mentioned sound about right too. Mine was 67mm.

jaybird11 02-29-2008 02:23 AM

RE: J3 cub, crash on take off nearly every time.
1 Attachment(s)
Anyone know the name of this Goldberg cub??
It has a 76 inch wing span,I bought it about 9 months ago ,put a Saito 82 in it with smoke and hung it in the hanger,.
Now Im ready to fly it and cant find much info on it. I have never flown a cub and do know to use redder on take off as it rolls on two wheels when taking off.
It is s Goldberg _______ ? thanks and any info on set up thank you too.

jaybird11 02-29-2008 02:24 AM

RE: J3 cub, crash on take off nearly every time.
Sorry about the picture it shows the la 65 it had in it when I bought it.

JPANN 02-29-2008 12:13 PM

RE: J3 cub, crash on take off nearly every time.
This looks like the one. (click on the link)

superflea 03-02-2008 11:13 PM

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

Yaniel 03-03-2008 06:37 PM

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.

fozjared 03-03-2008 11:28 PM

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!

NorfolkSouthern 03-04-2008 02:10 AM

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.


Villa 03-04-2008 10:38 AM

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.

superflea 03-04-2008 12:51 PM

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.

Villa 03-04-2008 03:39 PM

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.

superflea 03-04-2008 04:10 PM

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

Villa 03-04-2008 05:37 PM

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.

superflea 03-04-2008 06:15 PM

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 ;)

AA5BY 03-10-2008 11:21 AM

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.

layback2 03-10-2008 02:13 PM

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

larrysl 03-17-2008 12:07 PM

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

JPANN 03-18-2008 11:28 AM

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

larrysl 03-18-2008 06:16 PM

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

fozjared 03-18-2008 07:27 PM

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!

JPANN 03-19-2008 09:11 AM

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

larrysl 03-19-2008 11:09 AM

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

dabigboy 03-30-2008 11:06 PM

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.

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