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Author Topic: Trim for lower level flight  (Read 6181 times)

Offline Dennis Toth

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Trim for lower level flight
« on: December 13, 2010, 09:32:40 AM »
Guys,
I have a pretty well trimmed 46 size ship, it groove nicely and has good tension throughout. One area that I would like to improve is the height of the level flight groove. This ship seems to settle in at 8ft both upright and inverted. I can push it down to 5ft but to do that I need to fly it to that level. I have tried adjusting the handle with more down and this cause it to fly lower upright but requires serious concentration inverted. Is there any trims that could be applied that will lower the natural groove?

Best,           DennisT

Offline Dennis Toth

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Re: Trim for lower level flight
« Reply #1 on: December 13, 2010, 11:41:09 AM »
Phil,
I understand what you are saying, my problem isn't flying inverter nor do I have a fear of flying close to the ground. What I was getting at was this ship hits a groove both upright and inverted at 8ft. If I pull in the down a tweak it will push it down while upright but inverted it then requires over coming the now slight up that the handle setting put in.

I fly with my handle straight up and down, no bias. The ship is balanced at 24% back from the LE of the average cord. The wing is 18% thickness with normal sweep. Tail is around 17% of wing area. It seems to me that if the ship seems to naturally hit the same natural altitude upright and inverted the trim change needs to affect both, that's what I am looking for.

Best,         DennisT
« Last Edit: December 13, 2010, 02:50:19 PM by stuntguy13 »

Offline Steve Fitton

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Re: Trim for lower level flight
« Reply #2 on: December 13, 2010, 11:57:50 AM »
If you figure it out let me know.  My new plane does the exact same thing, wanting to fly level at 6 or 7 feet both upright and inverted.  Its almost like having to force it down against ground effect, but its too high to be that.  My old plane is the polar opposite, you have to hold it up to keep it from drifting below 5 feet both ways.  Its puzzling.
Steve

Offline Randy Powell

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Re: Trim for lower level flight
« Reply #3 on: December 13, 2010, 12:49:56 PM »
What's your alignment like: engine, wing and stab centerline? Any down thrust dialed in? How about stab incidence?
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Offline Bill Little

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Re: Trim for lower level flight
« Reply #4 on: December 13, 2010, 12:55:54 PM »
Good question, and one that needs a better "trimmer" than I am to answer.  But, I don't think a handle adjustment is the way to go.  That forces you to accommodate the handle setting when you are in inverted.  You don't want to have to do that.  Down thrust "might" do the same thing to an otherwise trimmed out plane.  The plane will want to sink up right, but climb inverted with either solution to my understanding.

I am awaiting answers!  I want to learn about the cure. ;D
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Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #5 on: December 13, 2010, 01:14:10 PM »
You may think I am whacked, but IMHO I would add a half ounce nose weight. I have had two planes that when they were trimmed, ( well trimmed to me anyway) would want to fly high in level, One I fixed with handle adjustment. the other when I did that made the level flight assymetrical,  adding a half ounce to the nose worked both upright and inverted. and yes I know this will affect other areas of trim.
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Offline Jim Thomerson

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Re: Trim for lower level flight
« Reply #6 on: December 13, 2010, 02:25:13 PM »
This is very strange.  I adjust the airplane to fly the same height in level flight upright and inverted with the handle. Thinking about it, this ends up with the airplane flying where I wanted it to fly, even though the "where" is different for OTS and modern stunt.  My airplanes tend toward nose heavy anyway.  I'm interested to learn more and will pay more attention to what I am doing as well.

Offline Bill Little

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Re: Trim for lower level flight
« Reply #7 on: December 13, 2010, 02:38:36 PM »
You may think I am whacked, but IMHO I would add a half ounce nose weight. I have had two planes that when they were trimmed, ( well trimmed to me anyway) would want to fly high in level, One I fixed with handle adjustment. the other when I did that made the level flight assymetrical,  adding a half ounce to the nose worked both upright and inverted. and yes I know this will affect other areas of trim.

No Mark,  not "whacked"....... maybe a *little* unbalanced........ ???  LL~ LL~

You might be on to something.  That nose weight would not tend to lead to asymmetrical problems.
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Offline Dennis Toth

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Re: Trim for lower level flight
« Reply #8 on: December 13, 2010, 02:48:47 PM »
Guys,
I think the nose weight is part of the answer but this ship holds it's line when the motor is cut. If it were to tail heavy I would expect it to jump up at motor cut off, if nose heavy it would drop slightly, it does neither. Could be that a little nose weight will help.

Alignment is 0-0-0. No downthrust, small rudder offset (1/8") no stab incidence.

I have been reading some threads on this and also thought back to my trainer ship way back in 1956. That ship had a 3/4oz chunk of lead on the tip, it flew what seemed like 20' off the ground in level flight (lots of air for my uncle to grab the handle when needed). I'm starting to think that this ship might need a very small reduction in the tip weight. The ship doesn't hinge during squares or hard loops so I think it is close. To get down only a few feet might be the difference of 1/8 oz or so. Anyone have this experience?

Best,         DennisT

Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #9 on: December 13, 2010, 02:54:04 PM »
No Mark,  not "whacked"....... maybe a *little* unbalanced........ ???  LL~ LL~

You might be on to something.  That nose weight would not tend to lead to asymmetrical problems.

The clue to me is that if the plane flies the same altitude upright and inverted, then its not likely a handle adjustment, if it flies at different altitudes then I try adjusting the handle first.
My goal is to hold my handle naturally and achieve level 5 foot flight,,

( for what its worth, Randy Powell will pop in here and say that I never fly that low,, you watch,, HB~>
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Offline Bill Little

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Re: Trim for lower level flight
« Reply #10 on: December 13, 2010, 02:58:37 PM »
The clue to me is that if the plane flies the same altitude upright and inverted, then its not likely a handle adjustment, if it flies at different altitudes then I try adjusting the handle first.
My goal is to hold my handle naturally and achieve level 5 foot flight,,

( for what its worth, Randy Powell will pop in here and say that I never fly that low,, you watch,, HB~>

Yeah, Mark, we agree.  It is simply a matter of the model in question doing the same thing upright AND inverted.  A handle adjustment wouldn't cure that, in my experiences......

And I don't think that Dennis' idea of tip weight would cure it, since the wings are not out of "whack".  And he says it's not hinging. ;D
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Offline dale gleason

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Re: Trim for lower level flight
« Reply #11 on: December 13, 2010, 03:15:46 PM »
Somewhere, perhaps the "Scared Kitten" construction article?  Bill Netzeband addressed this problem. I think he flew a few laps with his eyes closed and then looked to see where the plane was tracking, upright and inverted.....then he told what he did to fix it.

I'm not making this up, but I can't recall where I saw it.

"Tonto not quite put finger on".

dg
 

Offline Bill Little

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Re: Trim for lower level flight
« Reply #12 on: December 13, 2010, 04:54:46 PM »
Somewhere, perhaps the "Scared Kitten" construction article?  Bill Netzeband addressed this problem. I think he flew a few laps with his eyes closed and then looked to see where the plane was tracking, upright and inverted.....then he told what he did to fix it.

I'm not making this up, but I can't recall where I saw it.

"Tonto not quite put finger on".

dg

Hi Dale,

If you are speaking of the "eyes closed" deal, I can believe that. 

After watching combat pilots never watching their OWN plane during a match, I can see how one would be able to close their eyes and fly.

I ain't up to trying it though! LL~ LL~
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Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #13 on: December 13, 2010, 05:13:08 PM »
Hey Bill, I will try it for ya,,
with YOUR airplane of course  ;D
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Offline Randy Powell

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Re: Trim for lower level flight
« Reply #14 on: December 13, 2010, 05:44:54 PM »
My point was if something is out of alignment, it can cause a tendency for the plane to "prefer" a certain flight level or attitude.
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Eric Viglione

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Re: Trim for lower level flight
« Reply #15 on: December 13, 2010, 06:17:29 PM »
Sounds like handle to me... I can't picture a plane the size we fly getting into ground effect so high at 8ft...

Since we are all pretty good at mentally compensating for upright level flight, I usually use inverted flight, and horizontal round eights and overheads to tell me whats going on with the handle instead.

When inverted, does it feel like you are fighting to keep the plane out of the ground, (feeding down, which is up inverted) ? Chances are you need to shorten the down line. (try small increments, 1/8" at a time or so)

In your eights, is your outside loop hard to keep from being taller than your inside? Insides tighten up? Again, different symptom, same problem, shorten your down line.

Overheads, same question, same answer.

Do you bobble or overcontrol your insides? same answer...

I'm skewing the examples all to one side here, but it works the other way too obviously.

Any who, those are the kinda things I look for.

Hope it helps,
EricV

Offline Howard Rush

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Re: Trim for lower level flight
« Reply #16 on: December 13, 2010, 06:30:41 PM »
I'm starting to think that this ship might need a very small reduction in the tip weight.

On my airplane, reducing the tip weight cured a tendency to dive when flying inverted.  I don't understand it, but it worked.
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Offline Steve Helmick

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Re: Trim for lower level flight
« Reply #17 on: December 13, 2010, 06:46:12 PM »
"Ted's Rule" is to put the CG at the same percentage of the MAC as the horizontal tail area (i.e., 17% in this case). It might take more than 1/2 oz, but remember that 17%'s a starting point, not an ironclad regulation! You'll be moving the LO's forward the same amount, I hope.  H^^ Steve

« Last Edit: December 13, 2010, 07:57:01 PM by Steve Helmick »
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Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #18 on: December 13, 2010, 07:31:28 PM »
My point was if something is out of alignment, it can cause a tendency for the plane to "prefer" a certain flight level or attitude.
Randy, I dont disagree on that,,
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Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #19 on: December 13, 2010, 07:32:38 PM »
Sounds like handle to me... I can't picture a plane the size we fly getting into ground effect so high at 8ft...

Since we are all pretty good at mentally compensating for upright level flight, I usually use inverted flight, and horizontal round eights and overheads to tell me whats going on with the handle instead.

When inverted, does it feel like you are fighting to keep the plane out of the ground, (feeding down, which is up inverted) ? Chances are you need to shorten the down line. (try small increments, 1/8" at a time or so)

In your eights, is your outside loop hard to keep from being taller than your inside? Insides tighten up? Again, different symptom, same problem, shorten your down line.

Overheads, same question, same answer.

Do you bobble or overcontrol your insides? same answer...

I'm skewing the examples all to one side here, but it works the other way too obviously.

Any who, those are the kinda things I look for.

Hope it helps,
EricV
Eric, in most cases I would agree, but he states it flies the same upright and inverted
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Eric Viglione

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Re: Trim for lower level flight
« Reply #20 on: December 13, 2010, 07:50:50 PM »
Oh, I missed that, and I re-read the thread before I posted too... long threads get me like that sometimes, sorry.

If it does it upright and inverted, well, that's a good trick! All I can envision is some kind of tail heavy condition with a little too much slop in the controls, where the the tail drops against the slop and holds an attitude when your hand is comfortably neutral... and does the same thing in the other direction when inverted, taking up the slop in the controls the other way.

Other than that, it's above my pay grade. Looking forward to hearing what you eventually find to be the cause, if you ever do...

Thanks,
EricV

Offline john e. holliday

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Re: Trim for lower level flight
« Reply #21 on: December 15, 2010, 08:21:14 AM »
In my opinion it is the pilot not the airplane.  If the airplane flies the same upright and inverted it is the pilot.  Especially if it flies the pattern the way you want it to.  No slacking of the lines or dropping wing tips.  For several flights do only two maneuvers, upright and inverted flight only.  Drop that arm until you are at the altitude you want.  Then go  inverted and do the same.  I think someone referred to it as muscle training as well as the mind.  Don't do any loops or other maneuvers until you get yourself trained to the altitude you want to fly.  Once you can take off doing a full lap to get to altitude then maybe throw in a maneuver.  I know  it gets boring, right coach, same as doing laps on the football field.  Try it and see if it don't work. H^^

PS:As was told in a stunt clinic, when practicing and fuel tank is large enough, do three reverse wing overs with two laps between each before continuing the pattern.  But, then you have to remember to only do one in copetition.jeh
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Offline Howard Rush

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Re: Trim for lower level flight
« Reply #22 on: March 20, 2011, 02:37:30 PM »
After watching combat pilots never watching their OWN plane during a match, I can see how one would be able to close their eyes and fly.

I just noticed this item from a few months ago and thought I should post a picture of something I saw at the 2008 world champs.  This lady from Khazakhstan is flying an F2D model so jumpy that I have trouble aiming one while looking at it.  She's not looking at hers, and she's flying it upside-down.
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Offline phil c

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Re: Trim for lower level flight
« Reply #23 on: March 20, 2011, 06:42:06 PM »
You might try holding your handle a foot or so lower and see if that brings it down.  If it does, then I'm with Eric, there is too much slop in the controls and by the time you get it out(with handle movement) the flaps are drooped a degree or so and produce enough lift to bring the plane up.

If you want to see some neat flying, look up the last combat world champs on You Tube.  One flight shows the eventual champion doing pretty respectible reverse wingovers down to no more than ten feet behind his back while looking down at the ground.
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Offline proparc

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Re: Trim for lower level flight
« Reply #24 on: March 20, 2011, 09:23:46 PM »
Based solely on what you saying Stuntguy13, our "Mr. Little" got it right. Thats handle baby!!
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Offline Wynn Robins

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Re: Trim for lower level flight
« Reply #25 on: March 20, 2011, 09:54:25 PM »
Based solely on what you saying Stuntguy13, our "Mr. Little" got it right. Thats handle baby!!

cant possibly be handle - if it does it upright and inverted - it is something else - I had the same issue with one of my vectors - never figured out what it was - just compensated when flying - which is the cheat way! 

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Offline Larry Renger

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Re: Trim for lower level flight
« Reply #26 on: March 20, 2011, 11:41:52 PM »
Gee whiz guys, there are several things that can interact, and you are all trying to focus in on a single fix!  Just to enumerate the variables, all of which may be out of whack at once (and I am probably missing something crucial here):

Stab incidence
Elevator/Flap ratio
Elevator/flap angles (may not be neutral, or perhaps should not be neutral!)
Center of gravity
Line spacing
Handle setting
Bellcrank rotation when flaps and elevator are neutral, including the geometry of the control horns
Pilot fear of ground

I have had models that fly great at 8 feet and hunt at 6.  I think that is due to the slightly greater lift and thus drag at the higher altitude providing more dampening.  Wider handle spacing and more noseweight will provide extra dampening of oscillations.  And I would rather have the model dip slightly when the engine quits compared to having to fight both upright and inverted altitude.

Interesting thread!  H^^
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Offline Neville Legg

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Re: Trim for lower level flight
« Reply #27 on: March 21, 2011, 02:34:58 AM »
I do recall seeing a photo of Bob Palmer flying horizontal eights with his T'bird, while looking in the opposite direction! ;D

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Offline john e. holliday

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Re: Trim for lower level flight
« Reply #28 on: March 21, 2011, 10:09:10 AM »
It was documented years ago while on a tour with another noted flyer of RC, that Bob flew a complete pattern blind folded.   Bob at the time stated it is all in the timing and trim of the plane.  Very great gentleman and so happy that I got to meet him. 
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Offline jim gilmore

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Re: Trim for lower level flight
« Reply #29 on: March 21, 2011, 10:35:33 AM »
Complete pattern with A cl or rc model?  I could see cl line pull can let you feel plane position but rc has no feedback,

Offline Bill Little

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Re: Trim for lower level flight
« Reply #30 on: March 21, 2011, 11:01:57 AM »
Complete pattern with A cl or rc model?  I could see cl line pull can let you feel plane position but rc has no feedback,

Hi Jim,

Mr. Palmer flew a C/L pattern, of course. ;D  He was "on tour", sponsored by the State Department, IIRC, to South America, Australia, and possibly South Africa (can't remember exactly where they went) and was traveling with a R/C flier (well known at the time, name escapes me now! LOL!!).  It was a "good will" tour, so to speak, and highlighted flying model airplanes.  Something that would never be done these days! LOL!!

That Mr. Palmer had to have a special glove to use on his flying hand after losing part of the hand in an industrial accident, and the fact that he could still fly as well as he did, is more than amazing.

Big Bear
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Offline Kim Mortimore

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Re: Trim for lower level flight
« Reply #31 on: March 21, 2011, 12:48:32 PM »

Hey Stuntguy13 (DennisT),

This is a 3-month old topic that got picked up and continued.  Have you solved the problem in the interim?  We are curious what you came up with.  The only time I had this problem was when using a very narrow handle spacing with the lines just slightly out of adjustment.   
Kim Mortimore
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Offline Neville Legg

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Re: Trim for lower level flight
« Reply #32 on: March 21, 2011, 12:58:48 PM »
They came to England, I think it was '58? and I think the R/c flyer was Bob Dunham? As the Doc says it's all documented in an Aero Modeller magazine of the time. Did all of the Thunderbird Mk's have lead outs mounted above each other at the wingtip? I assume they'd be on the CG?


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Offline jim ivey

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Re: Trim for lower level flight
« Reply #33 on: March 21, 2011, 01:33:48 PM »
Sounds like a serious case of what Bob used to call "terraphobia".  "fear of airplane hittin th ground". *I wonder if he is looking down chuckling at me remebering that*?  Darn it Bill ya beat me to it. What bill said, "adjust your hand not th plane".  have someone, a friend of course. Hold the plane in a level posistion firrmly, like it was in flight. Then hold your hand in a comfortable posistion. Put pulling pressure on it about like you feel when the airplane is in flight. Then adjust your handle to keep your elevator to level. Have the guy flip the plane over to inverted position and repete. Have him check to see if elevator is in the same level possition, it should still be level with your hand in a natural posistion. Dont forget the approximate pull pressure. Sounds to me like your a novice flier, don't worry you'll get over it. If ya got a junker. try what floyds brother-inlawand I used to do. if your on grass try cutting th grass with th prop.  you'll hear the engine change and see the grass fly if your sucessful,the plane wont if you get to close :'(  . also get some balloons, tie them on three foot app. 1/4" dia wooden sticks. Place them around the circle and try to break the baloons try to keep the plane at the same hieght between baloons.( I almost typed baboons  LL~ )  it use to be called "baloon bust."   This  may help with your ground fear. Watch, even most of the experts, bounce the "coffin corner on  reverse wingovers. y1  jim

Offline Ted Fancher

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Re: Trim for lower level flight
« Reply #34 on: March 22, 2011, 01:28:48 PM »
Dennis,

How much does it weigh?

Why did you find it necessary to push the CG back to 24% of the average chord?  Sluggish response?

Ted

Offline W.D. Roland

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Re: Trim for lower level flight
« Reply #35 on: March 22, 2011, 01:49:17 PM »
Sounds like the Pilot is to tall.
8ft-5ft=3ft.
3ft is about the length of human legs. Sounds like a good place to cut. :!
Good thing it doesn't try to fly at 10-12ft LL~
The moral of this is quit while your a head n~

Or is the airplane wing loading to low? I have bricks for sale...


Did have an airplane years ago that had ground effect problems when landing. would drop down to about 12 inches high and refuse to go on down. Actually needed down to land before stall. The airplane was set up with a reward CG.

Several of mine seem to settle at 8 to 10 ft.
A few like it shoulder high with a couple that seem to like 2-3ft.

So my best idea is ???

(try 1/4-1/2 oz nose weight?)

When you figure it out please post!

Thanks
David
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Offline Steve Helmick

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Re: Trim for lower level flight
« Reply #36 on: March 23, 2011, 07:46:49 PM »
I predict it will take more than 1/2 oz noseweight to fix this problem. I'm too shy to suggest over an ounce, but I do think that's likely.

Waiting for Ted to ask if the hingelines are sealed....  ;D Steve
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Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #37 on: March 23, 2011, 09:22:53 PM »
On the Gee Bee it took just under a 1/2 ounce to move the plane down about 18 inches . It felt balanced in flight, good turn response, nice power off glide, it just flew to high inverted and upright both.
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Offline Steve Helmick

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Re: Trim for lower level flight
« Reply #38 on: March 23, 2011, 09:50:04 PM »
"The ship is balanced at 24% back from the LE of the average cord. The wing is 18% thickness with normal sweep. Tail is around 17% of wing area."

Mark, your Gee-Bee was probably bench-trimmed closer to correct, knowing you. I don't know Dennis T., but I do know you! I'm guessing how much nose weight it'll take, but if the CG needs to move forward even 5% (Ted's rule suggests 7%), that will take some doin'. 

I've put at least 2 oz. on the nose of "KISS!"...and maybe over 3 oz. Yet, it was very flyable when I first flew it, and Mike had flown it for most of a season and won 1st in several contests with it! The first time I flew it, I knew it was tailheavy, not because it did anything badly, but because it would only glide a quarter lap. I flew it for a season or two, before I added the last ounce of nose weight (to make up for what Mike had stashed under the engine, and I had not reinstalled). It's not perfect (too heavy!), but it goes pretty much where I think I want it to go! Opinions vary, apparently...    LL~ Steve

"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Mark Scarborough

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Re: Trim for lower level flight
« Reply #39 on: March 23, 2011, 10:22:42 PM »


 but it goes pretty much where I think I want it to go! Opinions vary, apparently...    LL~ Steve


LOL, boy are you leaving yourself open on this one,, but being the nice guy I am, I think I will leave it alone,, for now anyway,,

Granted according to Teds rule, yes,, it needs to move a bunch, so I will concede that to you. Though as I recall, my twisters balanced at some point closer to 24% ,and the tails were around 20% I THINK, but thats been awhile ago, and MANY many airplanes ago, lol
For years the rat race had me going around in circles, Now I do it for fun!
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Offline Bill Little

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Re: Trim for lower level flight
« Reply #40 on: March 24, 2011, 12:29:47 PM »
I will finally admit to being totally dumb in this discussion.  I have just never experienced a model that wanted to groove at a higher flight attitude, both upright AND inverted.  Even after adding some "Down Elevator" to the equation, the model flies at the height I set it at.  Just the original blind hog, I guess...... extremely lucky......... ??  Too dumb to know the difference??

Anyway, I wold be curious to find out what the fix was, also.

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Offline Ted Fancher

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Re: Trim for lower level flight
« Reply #41 on: March 25, 2011, 10:26:58 AM »
I predict it will take more than 1/2 oz noseweight to fix this problem. I'm too shy to suggest over an ounce, but I do think that's likely.

Waiting for Ted to ask if the hingelines are sealed....  ;D Steve

Are the hingelines sealed, Dennis?

Ted Fancher

Offline Ted Fancher

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Re: Trim for lower level flight
« Reply #42 on: March 25, 2011, 10:31:40 AM »
Are the hingelines sealed, Dennis?

Ted Fancher

Just teasing, Dennis?

Like Steve, I don't know you so please don't take offense at this question.  How would you describe your current flying ability?  That will help us assess your descriptions of the effects of what we suggest.

Again, no offense intended.

Ted


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