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Avistar with OS 46FX climbs by itself.

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Avistar with OS 46FX climbs by itself.

Old 09-11-2009, 09:59 AM
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mxaexm
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Default Avistar with OS 46FX climbs by itself.


I have Avistar with .46Fx that fliew great. The only problem that I have is that when I add power it climbs by itself. I know that its not nose heavy and its well balanced. Today I will say if I will be able to trim it.

My question is how do I add some down thrust?

Thanks.
Old 09-11-2009, 10:05 AM
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Default RE: Avistar with OS 46FX climbs by itself.

Washers on the top bolts to the engine mount, or the back bolts of the engine where it mounts to the engine mount.
Old 09-11-2009, 10:07 AM
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Default RE: Avistar with OS 46FX climbs by itself.



You shouldn't have to shim the motor to add downthrust. You should be able to correct the climb by trimming out the plane using the trims on the radio as well as the clevis on the elevator. Simply adjust it so that the plane will fly level.

Ken

Old 09-11-2009, 10:08 AM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.

I think washers behind the engine mount will be easier and faster to install. Will fly it today and double check it but most likely I will need to add some.

Thanks for your help.
Old 09-11-2009, 10:09 AM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: RCKen



You shouldn't have to shim the motor to add downthrust. You should be able to correct the climb by trimming out the plane using the trims on the radio as well as the clevis on the elevator. Simply adjust it so that the plane will fly level.

Ken


I will fly today and see if I will be able to trim it with my radio...is not then I might adjust my elevator...if that won't help...I will add some washers.

thanks RCKen.
Old 09-11-2009, 10:15 AM
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Default RE: Avistar with OS 46FX climbs by itself.

Make you adjustments with the trim on the radio. If you there isn't enough trim on the radio then use the clevis to adjust the throw for the elevator, and then try to use the trim on the radio again. Then, once you have the plane trimmed out mechanically adjust the elevator to set in the trim. You want to adjust the elevator so that the trim tab will be pretty much centered while flying.

Ken
Old 09-11-2009, 10:15 AM
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Default RE: Avistar with OS 46FX climbs by itself.

Remeber, it is a trainer and once you have it flying level at about 1/3 throttle it is suppose to climb when you add more power. That is one of the features that make a trainer a trainer. You can dial out some of this characteristic by changing the engine thrust angle or add a shim to the rear edge of the wing to change its angle.
Be carefull though, if you over do it that will make it harder to get the plane off the ground.
Old 09-11-2009, 11:23 AM
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Default RE: Avistar with OS 46FX climbs by itself.

This is one of the few times I have to disagree with Ken. As with anynon-symmetrical wing, the faster you go, the more you will climb.

Adding down thrust to the engine will help pull the nose down as you go faster.
Old 09-11-2009, 12:03 PM
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Default RE: Avistar with OS 46FX climbs by itself.

mxaexm,

This article (three parts) may help you trimming your trainer properly:

http://www.masportaviator.com/ah.asp?CatID=8&ID=141

Did you buid the thing?
Is it possible for the downthrust to be incorrectly set?
Same regarding wing and stab angles of incidence?
Old 09-11-2009, 01:26 PM
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Default RE: Avistar with OS 46FX climbs by itself.

I have 3 Avistars, one has a Magnum .46 XLS, the others have .40 La's ,and all of them do climb a little as throttle is increased. But none of them climb to the point that I can't trim it back to level flight with the slide adjustments on my radio. I would definitely check your throws and make clevis adjustments before I put shims on the motor.
Old 09-11-2009, 01:41 PM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: hugger-4641

I have 3 Avistars, one has a Magnum .46 XLS, the others have .40 La's ,and all of them do climb a little as throttle is increased. But none of them climb to the point that I can't trim it back to level flight with the slide adjustments on my radio. I would definitely check your throws and make clevis adjustments before I put shims on the motor.
Thats the plan for today, I will fly it and see if I can just use my trim tabs (as far as the throws go, they were adjusted per manual so they should be fine.)
Thanks,

MM
Old 09-11-2009, 02:25 PM
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Default RE: Avistar with OS 46FX climbs by itself.

My old Tower Trainer 40 MkII ARF had a .46 FX on it and was a bit overpowered. The first time that I went to fly it, the plane shot right up off of the runway! I had to put a decent amount of downthrust into the engine mount as previously described, and that fixed the problem nicely. A washer or two behind the top of the engine mount works wonders.
Old 09-11-2009, 02:53 PM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: bigedmustafa

My old Tower Trainer 40 MkII ARF had a .46 FX on it and was a bit overpowered. The first time that I went to fly it, the plane shot right up off of the runway! I had to put a decent amount of downthrust into the engine mount as previously described, and that fixed the problem nicely. A washer or two behind the top of the engine mount works wonders.

I know that .46 is a little bit too much for the Avistar but I really like this setup...I usually fly it 1/2 throttle anyway however when I add full power...it climbs like crazy......I will fly it today and make the adjustments tomorrow.

Thanks guys.
Old 09-11-2009, 06:15 PM
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Steve Steinbring
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Default RE: Avistar with OS 46FX climbs by itself.

When flying a high lift wing you can expect more lift as additional power is applied. This results in the airplane wanting to climb if it is not trimmed down. Nothing special here other than understanding some basic aerodynamics
Old 09-11-2009, 08:14 PM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: Steve Steinbring

When flying a high lift wing you can expect more lift as additional power is applied. This results in the airplane wanting to climb if it is not trimmed down. Nothing special here other than understanding some basic aerodynamics

The initial question and subject of this post was not "why" but rather "how" I can correct it...

Trust me, with my background in aviation my understanding of some "basic" aerodynamics is well beyond average

Thanks for your input though!
Old 09-11-2009, 08:31 PM
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: mxaexm

...I know that .46 is a little bit too much for the Avistar but I really like this setup...I usually fly it 1/2 throttle anyway however when I add full power...it climbs like crazy......I will fly it today and make the adjustments tomorrow.

Thanks guys.

What is happening is you have the plane trimmed out to fly at one airspeed, which in your case is about 1/2 throttle. As you add power you increase the speed, but to the plane it wants to stay at the airspeed to which it was trimmed out. To find that airspeed, which is now slower than it is being flown, it wants to climb to slow down. If you decrease power from the trimmed airspeed the plane will want to still maintain that trimmed airspeed, so it'll dive to try to speed back up to it. This is basic aerodynamics and applies to full scale aircraft as well as models.

To properly set-up and trim out a plane, I was taught you fly the plane and use the trim's on the radio to get it flying straight and level. When you land you look at the control surfaces to see how much deflection they have in what direction. Then you want to center the radio trims and, using adjustments by turning the clevis for each control surface, mechanically put the surfaces back to the position they where at when the plane landed. For example, if the elevator was 1/8" up after you landed, then you want to turn the clevis so the elevator is 1/8" up with the transmitter trim now centered.

How is your balance? Since you are running a heavier engine than the plane was initially designed for, is it properly balanced? Nose heavy planes will carry some up-elevator trim and give the same response to what you're experiencing.

As far as shimming the engine mount - try mechanically adjusting the plane first, and expect it will climb when you give it power. If its excessive, then you'll have to look at other factors involved in flight trimming similar to what patter flyers do, but that's a topic for another day. Get it set up properly first.

Hogflyer
Old 09-11-2009, 08:50 PM
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mxaexm
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Default RE: Avistar with OS 46FX climbs by itself.


I just flew it today and it seems that will full trim in down position (trim tab all the way up) it flew the way I like it...so I will have to adjust my elevator and everything should be fine....

Thank you for your explanation and help!


ORIGINAL: hogflyer


ORIGINAL: mxaexm

...I know that .46 is a little bit too much for the Avistar but I really like this setup...I usually fly it 1/2 throttle anyway however when I add full power...it climbs like crazy......I will fly it today and make the adjustments tomorrow.

Thanks guys.

What is happening is you have the plane trimmed out to fly at one airspeed, which in your case is about 1/2 throttle. As you add power you increase the speed, but to the plane it wants to stay at the airspeed to which it was trimmed out. To find that airspeed, which is now slower than it is being flown, it wants to climb to slow down. If you decrease power from the trimmed airspeed the plane will want to still maintain that trimmed airspeed, so it'll dive to try to speed back up to it. This is basic aerodynamics and applies to full scale aircraft as well as models.

To properly set-up and trim out a plane, I was taught you fly the plane and use the trim's on the radio to get it flying straight and level. When you land you look at the control surfaces to see how much deflection they have in what direction. Then you want to center the radio trims and, using adjustments by turning the clevis for each control surface, mechanically put the surfaces back to the position they where at when the plane landed. For example, if the elevator was 1/8'' up after you landed, then you want to turn the clevis so the elevator is 1/8'' up with the transmitter trim now centered.

How is your balance? Since you are running a heavier engine than the plane was initially designed for, is it properly balanced? Nose heavy planes will carry some up-elevator trim and give the same response to what you're experiencing.

As far as shimming the engine mount - try mechanically adjusting the plane first, and expect it will climb when you give it power. If its excessive, then you'll have to look at other factors involved in flight trimming similar to what patter flyers do, but that's a topic for another day. Get it set up properly first.

Hogflyer
Old 09-11-2009, 11:57 PM
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Default RE: Avistar with OS 46FX climbs by itself.

I didn't see anyone mention that the ailerons may not have been centered correctly and could need to be adjusted down a little??
Engine thrust angle usually shows up as a ballooning effect when you chop the throttle.
Old 09-12-2009, 07:29 AM
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Steve Steinbring
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: mxaexm


I have Avistar with .46Fx that fliew great. The only problem that I have is that when I add power it climbs by itself. I know that its not nose heavy and its well balanced. Today I will say if I will be able to trim it.

My question is how do I add some down thrust?

Thanks.


quote:

ORIGINAL: Steve Steinbring

When flying a high lift wing you can expect more lift as additional power is applied. This results in the airplane wanting to climb if it is not trimmed down. Nothing special here other than understanding some basic aerodynamics




The initial question and subject of this post was not "why" but rather "how" I can correct it...

Trust me, with my background in aviation my understanding of some "basic" aerodynamics is well beyond average

Thanks for your input though!
I apologize for being a bit testy about your question.

Unfortunately too many folks come to this hobby with no idea whatever as to how an airplane flies much less knowing how to identify the control surfaces of the machine they intend to fly. All they want to do is fly the airplane without the smallest effort in studying the principles of flight. Very frustrating at times for most instructors because of the instant gratification factors.

Most models today are over powered for the most part. With that said model trainer type aircraft fly better at more reasonable speeds or around half throttle because the higher lift airfoil is not really designed to be flown at higher speeds. I usually recommend to trim the airplane for level flight around half throttle using the extra power for doing maneuvers.


Good flying!



Old 09-12-2009, 10:11 AM
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: mxaexm


I just flew it today and it seems that will full trim in down position (trim tab all the way up) it flew the way I like it...so I will have to adjust my elevator and everything should be fine....

Thank you for your explanation and help!

Before adjusting for that, test the capacity of the elevator to flare during a dead stick situation.

As you know, for proper and balanced elevator action, it should be in line with the tail with no input control.
Old 09-12-2009, 10:48 AM
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Default RE: Avistar with OS 46FX climbs by itself.

You may notice that with added and/or excessive down-thrust on a trainer with flat airfoil that when you slow down and try to land you balloon and have trouble getting it to settle. They're designed to climb with added throttle. If you need speed it's time to progress to a semi or full symmetrical wing.
Old 09-12-2009, 11:25 AM
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: lnewqban

This article (three parts) may help you trimming your trainer properly:

http://www.masportaviator.com/ah.asp?CatID=8&ID=141
Excellent article by Dean Pappas that takes your thru the many steps to correct the quirks of an airplane. He walks us thru setup, flight observation, correction, flight observation, correction and so on - all with the intent of bringing the best out of your plane.

My Avistar (asymetrical wing profile) flew great at all throttle positions with an Evolution .52 NX. My LT-40 with same engine darn near loops at full throttle. The Avistar is not your basic flat bottom trainer. The only flight quirk of the Avistar was that on landing the elevator needed to be "tickled" or quickly but gently fluttered to get it to flare. Too bad it did not survive my poor soldering of the aileron control rod clevis (of course with a student on the buddy box). RIP

Old 09-12-2009, 11:39 AM
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Default RE: Avistar with OS 46FX climbs by itself.

ORIGINAL: Charlie P.

You may notice that with added and/or excessive down-thrust on a trainer with flat airfoil that when you slow down and try to land you balloon and have trouble getting it to settle. They're designed to climb with added throttle. If you need speed it's time to progress to a semi or full symmetrical wing.
Avistar is a semi-symmetrical wing, take the dihedral out of the wing and move the Cg aft and it becomes a pretty capable sport plane.



The only flight quirk of the Avistar was that on landing the elevator needed to be "tickled" or quickly but gently fluttered to get it to flare. Too bad it did not survive my poor soldering of the aileron control rod clevis (of course with a student on the buddy box). RIP SeamusG
Where did you set your Cg? I don't have this problem with mine, but on all my Avistars the Cg is a little aft of the reccomended starting point, my flares are smooth and gentle as long as my approach is not too shallow.
Old 09-12-2009, 11:54 AM
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Default RE: Avistar with OS 46FX climbs by itself.

Thanks for the wing profile correction. Don't know where the CG is because it died.
Old 09-12-2009, 12:23 PM
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Default RE: Avistar with OS 46FX climbs by itself.


ORIGINAL: hugger-4641

ORIGINAL: Charlie P.

You may notice that with added and/or excessive down-thrust on a trainer with flat airfoil that when you slow down and try to land you balloon and have trouble getting it to settle. They're designed to climb with added throttle. If you need speed it's time to progress to a semi or full symmetrical wing.
Avistar is a semi-symmetrical wing, take the dihedral out of the wing and move the Cg aft and it becomes a pretty capable sport plane.



The only flight quirk of the Avistar was that on landing the elevator needed to be ''tickled'' or quickly but gently fluttered to get it to flare. Too bad it did not survive my poor soldering of the aileron control rod clevis (of course with a student on the buddy box). RIP SeamusG
Where did you set your Cg? I don't have this problem with mine, but on all my Avistars the Cg is a little aft of the reccomended starting point, my flares are smooth and gentle as long as my approach is not too shallow.

My CG is wherever the manual says it should be. AS far as the landings goes...it lands awesome!

I really like this airplane a lot and its much better than my Hangar 9 Easy Fly 40 that I crashed while buddy boxing one of my friends....

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