anileshrai

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[TD="class: alt2"]Hi Guys,

I have made a Piper Cub J3 1/4 scale with DLE 20 mounted on it. During my maiden flight plane was taxing well, ailerons, elevator and rudder were all levelled.
As soon as plane took off, plane took a hard left turn and rolled left.

Any expert guidance what needs to be checked. I have already balanced the plane with correct cg.

Thanks & Regards,
Anilesh
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4*60

My Feedback: (41)

Possibly you took off too soon. Common problem. You need to do a takeoff roll and make sure no up elevator. Let it get up to speed brfore lifting off. At low speed the ailerons have no real effect and you cannot stop this if too slow.

sensei

You did not state that the nose pitched up and then rolled to the left, so check your wing for any twist issues.

Bob

anileshrai

Thanks 4*60 and Bob, yes nose was pitched up and then it performed a cartwheel on the left as soon as it took off the ground. Kindly advise how to check the thrust line or any modifications to be done, is there any possibility that my thrust line is offset, if required i can post pictures of the engine mount.

flyinwalenda

My Feedback: (5)

Sounds like a typical Cub lifting a little too early. You always need to be ready on the rudder to keep it straight. Cubs are not trainers like most think !

anileshrai

Thanks brian, is there any need to give any right thrust or should i again try with longer run at full throttle?

flyinwalenda

My Feedback: (5)

I'm no expert but I do know you can't "horse" a Cub into the air and you don't "drag race" it down the runway either. Nice and easy taxi and rollout until the tail wheel lifts then gradually increase power and it should lift off on it's own provided the control surfaces where adjusted neutral . You should be on the rudder to keep it straight while on the ground and as it lifts off be ready to add some right rudder if needed. Then increase power and fly it out. If the plane was built correctly you should go with the stock settings and alignment. Once in the air and trimmed see now it flies and takes-off,

jester_s1

That sounds like a tip stall. As others are saying, it would be caused by letting the plane get lifted off the ground before raising the tail and gaining enough airspeed to fly. It's easier to make that mistake if your landing gear is too far forward since that makes it harder for the tail to come up.

4*60

My Feedback: (41)

I would try again with a longer ground roll and more speed before liftoff.

biam

well said! Cubs need to be handled like fine women, nice and easy. Gently coaxed in to the air, and then thoroughly enjoyed while slowly flying around at a scale speed! Try this approach and have fun!

airzona

More ground speed, right rudder, add elevator once tail comes up, shallow takeoff climb.

bikerbc

As the other have said this is a problem common to Cubs caused by lifting off too early ..You need to let it build up more speed and let it lift itself off . Its not a bad idea to let somebody who is familiar with Cubs take it up for you the first time and get it trimmed out because they can be a real handful until you get used to them . They Are not a trainer although they will teach you a lot about flying . When taking off remember to use your rudder .

mazzea117

I have a 1/4 scale cub, you need to ADD slight down elevator to keep from lifting off ground too soon! This will bring tail wheel off ground sooner and decrease angle of attack, just ease into throttle to full. Just watch plane, keep level, build up AIR SPEED on the ground, then just pull back on elevator, SLIGHTLY, and watch a beautiful scale-like take-off. Just remember, the cub will ALWAYS want to take off too soon, Your the pilot, not the other way around! Good luck, and enjoy
































j

JPMacG

My Feedback: (2)

Exactly. Down elevator to bring the tail up to a horizontal position and hold it there while you gain speed. Then, slight up elevator to lift it off the ground and be ready to correct with rudder when it breaks ground.

John_M_

Definitely make sure your tailwheel is set true and straight... so when you push the plane along the ground with the radio on, and NO engine running, it should rolls straight ahead, and doesn't have the tendency to roll to the right or left (not even the slightest amount)... I know it may sound odd, but having the the tailwheel set correctly will allow you to slowly advance the throttle as the plane picks up airspeed... then once the airspeed reaches the point the tail lifts up, there's enough air flow over the vertical fin and rudder to help keep the plane pointing into the wind... then all you'll need to do is make small corrections on the rudder as needed.

The biggest mistake I've seen is to slam the throttle stick to full on takeoff, and then there's sooo much torque roll, the plane dives to the left; then you over control trying to correct with the rudder... you're too busy fighting the rudder, you forget about the elevator, the plane jumps into the air too soon, and you end up with a stall / snap roll into the ground.

Also abort the takeoff if the plane gets squirrel on the ground... once it gets squirrel like that, all you're going to do is make it worse by over correcting... I'd rather abort the takeoff, and run off the side of the runway into the weeds, than to pick up the pieces from a stall / snap roll on take off.

John M,

anileshrai

Hi Guys,

Thanks for your help and suggestion.

I need some more help, I have installed DLE 20 gas engine in my 1/4 J3 Cub. I have break in the engine by flying without cowl turning Xoar 16x8 prop at 7600 rpm. Engine is giving great performance.I have now installed the cowl on this plane and have observed engine's rpm is dipping to 6800 RPM as I am new gassers please help me to rectify this problem. Is it due to over heating or may be my cowl is not letting air to pass in.

Expert advices are most welcome.

Anilesh

PiperDriver

My Feedback: (152)

Done the same thing with my Sig 1/4 clipped wing. Not enough airspeed on takeoff. Jerked it off and rolled into the ground. Airframe weight has more effect on this slower airplane than you might think. In process of rebuilding mine after the last mishap like this.

flyinwalenda

My Feedback: (5)

Overheating would/could be the cause. A cowl will cause overheating if there is not enough air flowing through and around the head. Remember the exit hole(s) in the rear of the cowl should be around 1.5 times the size of the inlet hole(s). You also may need to install baffles to direct the air over the head. Without seeing the installed cowl it's difficult to determine.

Also if there is a spinner attached it could be blocking a good amount of the inlet air.

RCPAUL

My Feedback: (1)

Laterally balancing any airplane is a good thing to do.

John_M_

If your cowl has the plastic dummy engines and air scoops on the sides, cut large openings where the plastic scoops and dummy engine faces the propeller... then open a large opening at the bottom of the cowl to allow the air to exit... on my 1/4 sig cub, I had the simulated air filter housing cut open as well to allow more airflow into the cowl.

I'm in the process now of adding an os ft-160 twin and will be adding the air scoops over each cylinder (like the real thing) and then cut a fairly large opening at the bottom of the cowl.

With the DLE 20 gas engine, since the majority of the engine is inside the cowl, you'll want to make sure you direct a good flow of air from the openings you cut in the cowl, and direct the airflow over the cooling fins on the DLE 20... you can use some 1/8 ply glued inside the cowl to direct the air flow onto the DLE 20 cylinder head... when the plane is flying in the air; the air will be force inside the cowl, so you don't want the air pressure to build up inside the cowl; you want the air to move as freely as possible through the openings in the front and out the bottom, so just make sure you have a big enough exit hole at the bottom of the cowl to allow the air to exit... do this while keeping the strength and integrate of the cowl intact (re-enforce as needed).

John M,

John_M_

Here's some images of what someone else has done with their DLE-20.... doesn't look too bad at all... doesn't take much to keep things cool

.http://www.rcgroups.com/forums/showp...7&postcount=15



John M,

anileshrai

Hi Guys,

Please find the pictures of my cowl and please do suggest what can be done for better cooling as engine rpm is decreasing as soon as i put on the cowl may be its heating up.

I have already cut a big slot in firewall for better opening and have even given spacers in mount.

Should i go for vent hole mod or should i cut more cowl. How can baffle this cowl. Any Idea?

Waiting for your earlier response.

Thanks & Regards,
Anilesh

flyinwalenda

My Feedback: (5)

In my opinion the opening is not large enough in the front of the cowl. I would make two cuts on each side of the rectangular opening down to the small hole at the bottom making a diamond shape opening. If it still gets hot you could make that opening a bit larger . You can also glue some small flat pieces of plywood or plastic inside to make a baffle to direct the air down toward the cylinder.

FlyerInOKC

My Feedback: (6)

If anything you could have the bottom opening started too far forward allowing the air to exit before going over the engine fins. Air is like water it follows the path of least resistance. If it hits the engine and has a place to go it will exit rather than go around the engine. I would close the front of the opening and add a baffle to force the air to go thru the cooling fins. This is done by adding a piece cut close to the engine leaving a small gap around the cooling fins for the air go thru. You want to force the air to travel over the engine's cooling fins before it can escape carrying the engine heat with it.

anileshrai

Thanks for your response.

I would really appreciate if you can post some pictures showing your cowl.

Kind Regards,
Anilesh