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Super Decathlon Ground Looping On Takeoff

Old 06-07-2011, 08:01 AM
  #1  
invertedthoughts
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Default Super Decathlon Ground Looping On Takeoff

Went to fly my Ultrafly Super Decathlon (only around a 35" wingspan and of course short-coupled fuse as well) and the thing was ground looping to the right every time I got it right near liftoff speed.


Very frustrating to say the least as it wasn't weather-vaining. The only thing that my friend and I saw was that the landing gear mount where it mounts the fuselage was a little loose and was allowing the entire gear unit to wiggle forward and back about a 1/4" total and also the right wheel was splayed out a couple of degrees as well.


Would those things cause pretty violent ground loops at take off speed? It taxis nice and straight until all of a sudden it just jerks to the right.


Any input would be 'preciated!
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Old 06-07-2011, 12:23 PM
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CHELLIE
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Originally Posted by invertedthoughts View Post
Went to fly my Ultrafly Super Decathlon (only around a 35" wingspan and of course short-coupled fuse as well) and the thing was ground looping to the right every time I got it right near liftoff speed.


Very frustrating to say the least as it wasn't weather-vaining. The only thing that my friend and I saw was that the landing gear mount where it mounts the fuselage was a little loose and was allowing the entire gear unit to wiggle forward and back about a 1/4" total and also the right wheel was splayed out a couple of degrees as well.


Would those things cause pretty violent ground loops at take off speed? It taxis nice and straight until all of a sudden it just jerks to the right.


Any input would be 'preciated!
http://www.rcgroups.com/forums/showthread.php?t=604400


some info from RCG

Ready for the first flight.
I don't do ROG take-offs very often, so I chose to hand-launch. It was easy, uneventful. The Decathlon climbed and required little trimming. I kept it in the pattern to make sure everything was in order, and quickly enjoyed her performance.
When I decided to try an ROG, I hadn't even thought about the need to apply rudder to control prop torque. So that first attempt ended with a quick runway exit and a small cartwheel. On the next flight, the roll out was not pretty, but I did get it off the ground. It was a reminder that I need much more tail wheel practice. Applying throttle SLOWLY and being ready to add rudder before even starting out greatly improved the process.
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Old 06-07-2011, 12:27 PM
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also check your CG, being to nose heavy will cause that too, lateral balance the plane too, with a string at the cg point and a string epoxied to the fuse cg spot, lift the plane up with the string and see if the wing is level, if not add weight to the high wing to make it level
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Old 06-07-2011, 12:29 PM
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if all else fails, move your front landing gear more forward. and put a bigger tail wheel on it to reduce the angle of attack on the wing, i think its trying to take off prematurely, when flying a tail dragger , you need to add down to get the tail wheel up and ground roll with the rudder, then give the plane up, to take off, but most people don't do that, just my 2 cents worth.
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Old 06-07-2011, 12:54 PM
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notice the take offs on both planes in the video

[media]http://www.youtube.com/watch?v=gGOoki3panc&NR=1[/media]
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Old 06-07-2011, 01:15 PM
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Also.. your loose landing gear and 'splayed out' wheel are very likely to be componding the problem. Fix the gear and get the wheels properly aligned. Opinion varies on if 'toe-in' or 'toe-out' works best on tail-dragers but certainly having one wheel obviously out of alignment is not going to be helpful. Also try to remove any 'wobble' from the wheels themselves.

It's always better with tail draggers to roll on the throttle gently and get some airflow over the control surfaces before giving it too much gas. If the plane has ample power then you can almost certainly lift off on part throttle and only go to WOT (if necassary) after lift off, which may help keep things straight.

Make sure you are taking off exactly into wind.

Steve
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Old 06-07-2011, 05:54 PM
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invertedthoughts
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Thanks Chellie and Jetplaneflyer! That video you posted Chellie really shows the technique you were describing regarding getting the tail wheel off the ground first while building up speed on the ground. I think that was my problem because I was doing the EXACT OPPOSITE unfortunately! I was giving it UP elevator as I was throttling up so in essence I was balancing on the tail wheel before right at the liftoff point and that didn't work too well.

On my longer coupled tail draggers that mistake was masked I guess as that is how I have taken them off with no issue, but certainly not the right way as I can see now. Landing gear is all lined up and straight. Will check lateral balance as well but I think that is pretty spot on as of now.

It has to be that I was putting in up elevator on roll out!!!
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Old 06-12-2011, 10:15 PM
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Moving the landing gear forward typically makes a ground looping problem worse instead of better. Moving the gear forward puts the wheels even further in front of the CG of the model, which increases the force/moment of the groundloop.

Reducing the ground angle of attack can help some, though.

Always worth setting up the model so that the main gear is well rigged, with identical toe in, camber and alignment on each wheel., with no play in the tailwheel.
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Old 06-12-2011, 11:52 PM
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Default Gyro

Short coupled aircraft and tail draggers - and all aircraft for that matter - are much easier to bring up to speed with the addition of a very expensive ($15) rudder gyro. Set it for high rate (not heading hold or AVCS) and after lift off toggle if to low rate so it's basically inoperative.

It's pretty impressive to gradually roll out 200' strait as an arrow and then ROG directly into vertical climb. I do that with my shoestring and it always warrants comment.

If you've got a fast aircraft you definitely need to toggle the rate lower after lift off or you'll be in a high speed maneuver and suddenly waggle like a fish on crack.

On the other hand, turn it back on and both inside and outside loops track extremely well with yaw gyro on, and if your nose drops on banked turns it will hold it up.

DISCLAIMER: Some pilots think gyros are cheating. Tell that to full scale fly by wire (F-22, F-35) pilots or heli pilots. Just like channel mixing, expo, dual rates, gyros have there place - and if they make the hobby more fun, exciting, or interesting, that's the place for me.
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Old 06-14-2011, 01:12 AM
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Good example is the old Fokker DR1 tripe, Make that a bad example Sitting at high angle puts the landing gear far forward of the CG, narrow landing gear, Sitting at a high angle blankets the rudder from airflow and a small rudder, and no taiwheelsteering..!! First thing on one of those is to throttle up gently and get the tail up. Probably been through half a dozen over the last 50 rc yrs. Here's my latest indoor jobby. EPP fuse and $foam wings. He looks like a happy pilot. He just doesn't know what's comin.!
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Old 06-14-2011, 01:34 AM
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Slow addition of power also helps on almost any plane that has a roll tendency on takeoff. Slowly feed the power to it. Not super slow, but don't stab the power and yank it airborne.
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Old 06-14-2011, 03:55 AM
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Originally Posted by dkrhardy View Post
Slow addition of power also helps on almost any plane that has a roll tendency on takeoff. Slowly feed the power to it. Not super slow, but don't stab the power and yank it airborne.
like taxing quickly to the end of the runway. allows you to add rudder as the torque increases and airflow swirls around the fuse.
this is the same as a full scale.

this is also why pitts s2 are such hated takeoff planes.
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Old 06-14-2011, 04:05 AM
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I agree with most of whats been said so far - fix the slop in the gear and wheels first before you do anything else.

With squirrely tail draggers, Ive always had the best results from using moderate tow-IN on the main wheels while keeping them back close to the CG and a gradual - but not toooo slow - application of power.

I cant imagine how tow-out would help at all. Just from the geometry Id think it would only make things worse. Thats also been my experience in the field.

If your looping right before lift off - are you giving it an extra stab of power just before lift off?
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Old 06-14-2011, 05:37 AM
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Originally Posted by Larry3215 View Post
.... Ive always had the best results from using moderate tow-IN on the main wheels while keeping them back close to the CG and a gradual - but not toooo slow - application of power.....
FWIW: The EAA teaches toe-out to reduce ground looping. See pages 3+.
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Old 06-14-2011, 06:29 AM
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I've taken her out to the field on 3 occasions since dialing in the landing gear and still haven't been able to try it out yet. Anything over 5mph wind I won't fly this plane, it's still too nice and I don't want to mess it simply for being impatient in regard to the flying conditions.


As far as a sudden burst of power right before take-off I don't think I'm doing it. I think it was the landing gear being sloppy and I was holding in right rudder the whole take off in an attempt to counter act the torque steer.


Lessons learning.............
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Old 06-14-2011, 07:50 AM
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Originally Posted by gyrocptr View Post
FWIW: The EAA teaches toe-out to reduce ground looping. See pages 3+.
Which is why i said in my original post in this thread
Opinion varies on if 'toe-in' or 'toe-out' works best on tail-dragers but certainly having one wheel obviously out of alignment is not going to be helpful
The toe-in / toe-out debate can get quite emotive. The thing that is difficult to understand is that folk on both sides of the debale swear they have tried both options and proved their preference to be the clear 'winner'. The guy writing the article in EAA is an example of one who claims to have tested both 'in' and 'out' in both model and full size planes and found toe-out to tame a ground looking plane, and for toe-in to be dangerous. Yet there are many others who will vigorously argue the opposite

Go figure......

Steve
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Old 06-14-2011, 07:58 AM
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I Had a Laser 200 with a K&B 60 in it, about 25 years ago that did that on take off, i almost saved it by giving it down elevator when it was inverted, but the speed was to slow, It took me a long time to figure out why that happened, some of the fliers said it was an inherited part of that type of aircraft, years later did i learn that it was Me not getting the tail up and getting more speed on Take off, yes it was a tail dragger, I hate Tail Draggers, Funny thing is that all of my planes are Tail Draggers LOL

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Old 06-14-2011, 08:01 AM
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I have found that for me, that a little toe in helps my planes to track straighter on Taxing, I dont know if it helps with ground loops, but it helps me to taxi better
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Old 06-14-2011, 08:10 AM
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Originally Posted by gyrocptr
FWIW: The EAA teaches toe-out to reduce ground looping. See pages 3+.
Which is why i said in my original post in this thread
Opinion varies on if 'toe-in' or 'toe-out' works best on tail-dragers but certainly having one wheel obviously out of alignment is not going to be helpful
The toe-in / toe-out debate can get quite emotive. The thing that is difficult to understand is that folk on both sides of the debale swear they have tried both options and proved their preference to be the clear 'winner'. The guy writing the article in EAA is an example of one who claims to have tested both 'in' and 'out' in both model and full size planes and found toe-out to tame a ground looking plane, and for toe-in to be dangerous. Yet there are many others who will vigorously argue the opposite

Go figure......

Steve
LOL

Im in the 'opposite' camp as far as models go - Im an 'innie'

Ive no experience on full scale but have "tamed" models by adding toe in.

I suspect the reasons for the controversy might be because there is more going on with ground looping than just toe in/out.

From the little Ive read on it, over all model geometry, all up weight, mass distribution, height of the CG above the contact point, distance the CG is behind the contact point, type of gear legs and how they flex or move, not to mention right thrust, prop size and pitch, AOA at rest and probably several more.
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Old 06-14-2011, 08:18 AM
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Sorry double post

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Old 06-14-2011, 08:20 AM
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Originally Posted by CHELLIE View Post
I Had a Laser 200 with a K&B 60 in it, about 25 years ago that did that on take off, i almost saved it by giving it down elevator when it was inverted,
Chellie,

Did what on take off?.. if it ground looped then i cant see how you could have left the ground, inverted or not

Ground looping is when the plane (on the ground) rotates horizontally around it's wheels (yaws) so severely that it end up pointing in the opposite direction to which it's travelling.. So unless you took off in reverse i don't think it was a ground loop (a reverse take off really would be something to see)

Check this video at 1 min 20 seconds: [media]http://www.youtube.com/watch?v=MAWa9uxtZj4[/media]

Steve
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Old 06-14-2011, 08:26 AM
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Originally Posted by JetPlaneFlyer View Post
Which is why i said in my original post in this thread

The toe-in / toe-out debate can get quite emotive.

Steve
Just split the difference, do one wheel in and the other out.
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Old 06-14-2011, 08:26 AM
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Originally Posted by JetPlaneFlyer View Post
Chellie,

Did what on take off?.. if it ground looped then i cant see how you could have left the ground, inverted or not

Ground looping is when the plane (on the ground) rotates horizontally around it's wheels (yaws) so severely that it end up pointing in the opposite direction to which it's travelling.. So unless you took off in reverse i don't think it was a ground loop (a reverse take off really would be something to see)

Steve
Ok got it it rolled over, that to me was my idea of a ground loop Skidding of the runway and turning around, Thats How I fly all the time

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Old 06-14-2011, 08:45 AM
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I love this video

[media]http://www.youtube.com/watch?v=q5trygRQaV0&feature=related[/media]
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Old 06-15-2011, 06:35 AM
  #25  
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SUCCESS! Locking in the landing gear at perfectly square to the fuse as well as a little toe in with a dose of more careful rudder control and we had 3 take offs with her this evening. The first one was sloppy and ugly, the last two progressively got better.


Pilot error on this one all the way, including the crappy setting up of the landing gear which allowed them to loosen up with only a couple of landings. Lessons learned!


Thanks again everyone!
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