Control Lines For all you fly-by-wire fanatics!

Well, That was Exciting! Trim help, por favor.

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Old 10-20-2010, 09:57 PM
  #1
01sporty
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Default Well, That was Exciting! Trim help, por favor.

I picked up a Ringmaster Jr. on eBay a while back and finally got around to trying to see how it flies. It has an O.S. Max .015 with a 7x6 prop, 42' .011 dia. lines and 4 deg. rudder offset. It also has 2/3 oz. of weight in the tail for balance.

Liftoff was smooth and uneventful. I did a couple of laps straight and level and let it lean out and get up to speed. It had really good pull on the lines but I didn't give it much thought at the time. It was way fast. The 42' lines were obviously not enough. I was dizzy by the end of the run.

I eased in some up elevator to see how it reacted. It went up smoothly. Just a bit sensitive but smooth.

Then it was time to go back down.

Down elevator was REALLY sensitive. It dove down with a vengeance and not smooth at ALL. I corrected and it shot back up. And so it went for half a lap trying to get it back to straight and level.

Once level, it didn't seem a problem staying there. Up, nice. Down bad. Really bad. I tried several times. So, I stayed level and examined the attitude. Yaw was significant. No wonder it had such good pull.

Surprisingly, when the motor quit, it glided to an excellent landing. Perfectly well mannered.

My first thought is for longer lines to both slow it down and get rid of some, if not all, of the yaw. I think it can take at least 48' and maybe even 52' lines. Comments? Suggestions?

The crazy up/down thing seems like it must be a balance problem, isn't it????

TIA,
Walt
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Old 10-20-2010, 10:56 PM
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icerinkdad
 
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Default RE: Well, That was Exciting! Trim help, por favor.

How stiff is the pushrod? It could be flexing and giving you very irregular control. If so add a doubler (wooden dowel bound with a bit of thread works) or a guide about half way down the rod to at least minimize flex. The lines are a bit short. If the leadouts are from the kit location the rearmost is probably too far back but not really worth cutting into the plane till you need to. At most they should be about an inch apart and near the high point of the wing.
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Old 10-21-2010, 06:38 AM
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da Rock
 
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Default RE: Well, That was Exciting! Trim help, por favor.

Yup, sounds like it could be pushrod flex.

It probably wouldn't hurt to adjust the elevator throw to be slower. Move the pushrod connection out on the elevator horn. Check for play also.

Where does it balance?
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Old 10-21-2010, 06:57 AM
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Default RE: Well, That was Exciting! Trim help, por favor.

Dittoos to the rod flex and also consider what line spread you are using at the handle, You may want to reduce this a bit also.

John
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Old 10-21-2010, 08:50 AM
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Default RE: Well, That was Exciting! Trim help, por favor.

Maybe the push rod. Elevator throw should not exceed 20 degrees each way and 48- 52 foot lines are  in order.

Check that balance!! Tail heavy makes for a very wild ride!!!!

Good luck,

John
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Old 10-21-2010, 11:54 AM
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Lou Crane
 
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Default RE: Well, That was Exciting! Trim help, por favor.

Walt,

Many great suggestions to work with... Particularly going to 52.5' lines. That WILL slow your RPM very nicely.

A suggestion to overcome galloping? PIO means pilot induced oscillations. Happens when a pilot gets out of phase with his aircraft. If the plane seems to be going nose-up too fast, it would seem pushing in some down is needed. If the plane doesn't respond just right... - takes more time than the pilot would like to ease over from nose-up back to level, say - he's likely to push in MORE down, about the time the plane has started to turn down.

See how that can get away from a guy?

To beat this, make note of how your forearm, wrist and handle point at the plane when it is flying smooth and level. Lock in that memory. If (when) it starts to gallop, it will probably be PIO, so lock your forearm, wrist and handle like for level flight, and 'aim' a little higher than you were flying level. The model should settle down almost immediately, where your arm, etc., are pointing. "Aim" a bit higher, because the ground is harder than your model, don't give it a chance to eat it.
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Old 10-21-2010, 12:11 PM
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01sporty
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Default RE: Well, That was Exciting! Trim help, por favor.

I double checked the push rod and it's plenty ridged. Besides, on down elevator, it's in tension.

The CG was set up per these plans: {akamaiimageforum}/upfiles/490514/Va72108.pdf

Well, the info I needed the most was whether I was tail heavy or light. Thanks for clearing that up for me John. I never seem to be able to sort that out.
Next time out I'll take weight off the tail until it turns cleanly.

Sounds like 52' lines are definitely in the offing. How do I tell if the lines are too long?

Thanks for all the help,
Walt
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Old 10-21-2010, 02:01 PM
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da Rock
 
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Default RE: Well, That was Exciting! Trim help, por favor.


Quote:
ORIGINAL: 01sporty
Sounds like 52' lines are definitely in the offing. How do I tell if the lines are too long?

Line tension and lap times. All subjective (your opinion).
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Old 10-21-2010, 02:26 PM
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Default RE: Well, That was Exciting! Trim help, por favor.


Quote:
ORIGINAL: 01sporty

The CG was set up per these plans: {akamaiimageforum}/upfiles/490514/Va72108.pdf

Well, the info I needed the most was whether I was tail heavy or light. Thanks for clearing that up for me John. I never seem to be able to sort that out.
Next time out I'll take weight off the tail until it turns cleanly.
Walt,

The CG on the plans looks OK BUT it still is good to start nose heavy and then add weight, Too nose heavy will make it slow to respond and it will tend to glide like a rock but it will be controlable.

Iadvise you to take OFF the tail weight and fly it. If that settles it down add back a bit of weight each flight until it flies to suit you.

By the way, those plans are copyrighted by Pat King's company Lock Stock and Barrel. Pat is a friend of mine and I am not sure that he has given permission to post them on the internet for everyone to access.

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Old 10-21-2010, 02:54 PM
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01sporty
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Default RE: Well, That was Exciting! Trim help, por favor.


Quote:
ORIGINAL: da Rock


Quote:
ORIGINAL: 01sporty
Sounds like 52' lines are definitely in the offing. How do I tell if the lines are too long?

Line tension and lap times. All subjective (your opinion).
That's what I assumed but I was hoping there might be a better way.
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Old 10-21-2010, 02:55 PM
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01sporty
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Default RE: Well, That was Exciting! Trim help, por favor.

The image came from this thread: http://www.rcuniverse.com/forum/m_82...tm.htm#9086414
Post #23. It's been there for quite some time.
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Old 10-21-2010, 07:20 PM
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Default RE: Well, That was Exciting! Trim help, por favor.

Smaller airplanes seem to need the CG forward of where it would be on a larger airplane. I would move the CG forward to right behind the leading edge spar. But then I like nose heavy airplanes. Anyway, I would expect an airplane with the plan CG to be tail heavy for me.
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