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Author Topic: Launch problem.  (Read 402 times)
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Mofroggy
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« on: April 11, 2020, 05:06:45 PM »

New here and I built a Stan Buddenbohm "Scout".  Easy built and he did most of the shaping on the surfaces.
My problem is that on launch like he shows on the plans the glider goes up and a little to the right and transitions and makes a flat quarter turn to the left and keeps on turning left into an ever increasing steepness until it hits the ground.  It usually never makes a complete circle even from 40-50 feet up. I have changed the nose weight all over the place but can't seem to make it circle.  The circle it makes is probably 50 feet wide.
Any suggestions would be appreciated.
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jswain
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« Reply #1 on: April 11, 2020, 07:17:40 PM »

this is what i would do, or may have done in the past but don't remember exactly anymore Smiley

1) start putting more weight - just a *dab* of clay at a time (see #3 below) on the RIGHT wing tip,  reason = to begin to counter act the left turn
2) progressively take off some clay weight from the nose of fuse (you could even take off the nose clay and put it on the right tip),
reason = to make the model more likely to want to stall or slow down rather than head long spiral in.
3) when i say a *dab* i mean about the size of a sewing pin's plastic ball end - just squish it on to top right wing tip. you can weigh and
substitute hammer smashed thin lead later and CA that on.
4) Both 1 and 2 will begin to negate the 'down' and 'left' effects the model is experiencing now.
5) if you can try to fly in taller grass reason = the model can only pile in so many times on hard surface before it cracks or breaks Sad

My suspicion is there is either  built in wing skew or (more likely) the boom is warped ever so slightly to the left, or left wing weighs more than right wing (thus unbalanced)  causing the model to want to spin in.
I have built this model before and the fixed surfaces make it challenging where as Stan's other models have the adjustable
boom.
take care, john s.


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Mofroggy
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« Reply #2 on: April 11, 2020, 10:17:10 PM »

John S.
Thanks for the response.  I will try all of the things you suggest and I appreciate you taking the time to reply.
I started with a dime-store balsa glider to work with my 8-year-old grandson and you know how that went!  I have 135 RC airplanes in my "hanger" but working with clg's is totally different.  It is like playing 3-dimensional chess with all of the variables involved.  Of all the designs I have tried the "Scout" has done the best but anything over 10 seconds is a miracle around here. 
Joe
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Tapio Linkosalo
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« Reply #3 on: April 11, 2020, 11:48:49 PM »

keeps on turning left into an ever increasing steepness until it hits the ground. 

Sounds like a spiral dive, which typically is a result of too little decalage, combined with possibly too much left rudder. So the first thing to try would be to add a small wedge (10 to 20mm long) under the left wing, to add some lift there. If that does not help then the incidence of the wing would need to be added a bit. Also you may have too much left rudder, as you say that the model turns to left already during the climb. The pattern should be such that the climb spiral goes all the way to the right, and only when the climb speed wears off, the model changes to left hand glide. The wedge should help keep the model banked to the right longer.
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-John-
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« Reply #4 on: April 12, 2020, 04:29:02 PM »

Hello Joe, the Scout is a nice flying catapult glider, and seems to have quite a bit of built in forgiveness. We had a group of young people build kits
reciently, and all the models ended up successfull(some needing a little more trim work, and others flying right off the bat).

Firstly, check for warps, then set the CG to what Stan shows on the plan, and check that there's no wing skew as jswain has mentioned. Check for too
much left rudder and maybe add a small amount of up elevator as Tapio L. has suggested to get it to stop diving. Make sure that the outer panels of the
three panel wing are at the same incidence as the central panel(otherwise you'll have an aileron effect causing the glider to want to roll). Flying in tall
grass is a great idea!, and it does appear you are dealing with some kind of spiral instability, or static instability. Make sure the washin wedge is mounted
correctly and not just a tab out there creating drag. Best of luck, and if that one doesn't work out, build another.
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Mofroggy
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« Reply #5 on: April 13, 2020, 11:59:24 PM »

Thank you, Thank you, Thank you!  I was just on the verge of giving up on the whole concept of CLG's but thanks to your suggestions I got the Scout to do what I kind of expected it to do.  My nearly 10 year old grandson and I read what you posted, applied it and went out to a tall grass field and gave it a shot.  First launch was 18.6 seconds and with a few tweaks we were getting 24 seconds. A world record for us!!  I really appreciate your help and thanks for taking time to share your expertise.  He and I have been "quarantined" for 10 days out of caution and 1-2 hours out in the sun did wonders for the both of us.  Thanks a LOT!!
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flydean1
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« Reply #6 on: April 14, 2020, 12:49:02 PM »

Where do you live Mofoggy?
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Mofroggy
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« Reply #7 on: April 14, 2020, 03:50:45 PM »

Jacksonville, in East Texas.
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Mofroggy
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« Reply #8 on: April 16, 2020, 05:25:22 PM »

Scout Dipping.
The Scout is flying in the 20-25 second range now.  I think I could get better times if I could solve one problem.
After transition it starts a wide left turn and then about a quarter of the way through the turn it dips down like it needs to pick up speed and then levels off and finishes the circle and then dips down somewhat less and completes the turn and does this again but less and less each time.  I have tried a lot of things but nothing I am doing seems to fix the problem.  I don't know if it is the tuning of the plane or the way I am launching it.  Any help or suggestions would be greatly appreciated.
Joe
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flydean1
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« Reply #9 on: April 16, 2020, 11:29:55 PM »

Sounds like it's "nibbling" at a stall.  Airspeed slowly dribbles off, not enough to notice.  The nose dips to restore the airspeed, and cycle repeats.

Cure?  possibly a very, very tiny bit of nose down trim, or possibly a very very tiny bit of left rudder.  CG is probably OK.

Others may have a better idea.
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Skymon
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« Reply #10 on: April 17, 2020, 04:18:42 AM »

It's a classic stalling pattern.
The plane is trying to climb, but because it has no power to pull it through the climb, it slows, then dips, picks up speed in the dive and starts the cycle again.
The quickest and easiest way to cure it is to add a tiny bit of nose weight.
Just stick a small blob of blutak on the nose.

Part of trimming is to remove nose weight until this flight pattern pops up, then add it back until it just stops.
You may find if you are right on the balance, that when the plane flies in to the wind it will stall due to the increased wind speed.

Ideally iron out the flight pattern with trim changes, because adding weight is not the best solution.
Maybe thin the tail feathers slightly by a bit of gentle sanding.
Then you are removing weight Smiley

Happy flying

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OZPAF
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« Reply #11 on: April 17, 2020, 05:36:00 AM »

It sounds like your launch and transition are good but as the others have mentioned you have a slight stall. I agree with Skymon in that it is best to resolve this with a small addition of nose weight- however I feel that proper artist modelling clay is better than bluetak as you can add much smaller amounts.

I wouldn't advise changing the settings of the wing/tail as this will affect your climb and transition.

Adding small amounts of nose weight has very little effect on the stability but does cause the model to fly at a lower angle of attack and thus flying faster away from the stall, and thus by patient changes you will eventually end up with a trim just higher than the stalling speed. The model will probably need to be trimmed a little faster to fly in more wind and closer to the stall in the calm.

Another point to keep in mind during the trimming stage is to keep the launches consistent by stretching the rubber the same distance and by keeping your bank angle and launch angles the same.

30 - 40 secs in calm air should be your next goal Smiley

Good luck

Cheers John
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Mofroggy
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« Reply #12 on: April 17, 2020, 10:58:59 AM »

Thanks for all of the suggestions.  I can't imagine flying for 40 seconds but I am going to give it my best shot.
Joe
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