RC Gliders, Sailplanes and Slope Soaring Discuss rc gliders,rc sailplanes and slope soaring in this forum. Thermaling techniques, airfoils, tips, etc

Glider trim and balance issue

Reply

Old 08-14-2018, 04:48 AM
  #1  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Glider trim and balance issue

I need help with trimming or balancing my electric glider. It is built up covered in monokote. The problem is the thing wants to climb even with the power off. It requires full down trim and then still climbs with power off. I don't mind it climbing like a rocket with the power on but want it trimmed out when gliding. Here is what I have done:
I exactly followed the instructions for setting the CG. The first flight required full down trim and holding the elevator down. Second flight: With the transmitter trim full down, I added 1/4 oz lead in the nose with negligible results. Third flight I then added another 1/4 oz lead (now total of 1/2 oz) in nose. The plane still climbs when gliding. This is not a drastic climb like a tail heavy situation but it is enough that I often have to hold in down elevator plus full trim to fly level.
I am seeking any assistance.
Thanks!
John

Last edited by JGalt; 08-14-2018 at 04:50 AM.
JGalt is offline  
Reply With Quote
Old 08-15-2018, 10:00 AM
  #2  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Sacramento, CA
Posts: 6,512
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Have you measured your stab and wing incidences? My first hunch is that you have too much positive incidence in the wing. Usually climbing while under power is a common trait with a powered sailplane but is influenced by incidence, airfoil and CG. One of my powered sailplanes took a mix to add down elevator with throttle. Once power is off elevator goes back to neutral.
speedracerntrixie is online now  
Reply With Quote
Old 08-15-2018, 08:31 PM
  #3  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by speedracerntrixie View Post
Have you measured your stab and wing incidences? My first hunch is that you have too much positive incidence in the wing. Usually climbing while under power is a common trait with a powered sailplane but is influenced by incidence, airfoil and CG. One of my powered sailplanes took a mix to add down elevator with throttle. Once power is off elevator goes back to neutral.
Thank you for your response. I didn’t measure incidence...guess I can look up how to do that. One thing I did do in that respect is try a very thin balsa shim between the wing saddle and trailing edge of the wing. It raised the back of the wing up very slightly. The flight characteristics were better with much less climb in the power off, glide mode. But I could hear a strange buzz sound when under power....almost flutter like...so I cut power and immediately landed. Again, thanks for your help.
John
JGalt is offline  
Reply With Quote
Old 08-18-2018, 05:26 AM
  #4  
Appowner
 
Join Date: Nov 2017
Posts: 815
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by JGalt View Post

Thank you for your response. I didn’t measure incidence...guess I can look up how to do that. One thing I did do in that respect is try a very thin balsa shim between the wing saddle and trailing edge of the wing. It raised the back of the wing up very slightly. The flight characteristics were better with much less climb in the power off, glide mode. But I could hear a strange buzz sound when under power....almost flutter like...so I cut power and immediately landed. Again, thanks for your help.
John
Since the shim under the TE improved things, you definitely have an incidence issue. Do you have a handle on the various incidences and what they do? Wing, Stab and Thrust are the main ones.

Another way to "adjust" things would be to put down thrust in the motor. Simply add a couple of washers to the top mounting screws to shim that down. The idea being to raise the rear of the motor in relation to the front. However you have to do it in your particular application. Last you can put a shim under the LE of the stab. Depending how bad things are, I'd probably adjust all three. Start with the motor down thrust and work towards the tail.

A simple search for "incidence meter rc" will bring up a variety of tools for checking things. There's even a way to do it with a smart phone.
Appowner is online now  
Reply With Quote
Old 08-18-2018, 05:26 PM
  #5  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default


Originally Posted by Appowner View Post
Since the shim under the TE improved things, you definitely have an incidence issue. Do you have a handle on the various incidences and what they do? Wing, Stab and Thrust are the main ones.

Another way to "adjust" things would be to put down thrust in the motor. Simply add a couple of washers to the top mounting screws to shim that down. The idea being to raise the rear of the motor in relation to the front. However you have to do it in your particular application. Last you can put a shim under the LE of the stab. Depending how bad things are, I'd probably adjust all three. Start with the motor down thrust and work towards the tail.

A simple search for "incidence meter rc" will bring up a variety of tools for checking things. There's even a way to do it with a smart phone.
Thanks for the response Appowner. I examined the plane closely from the side and it looks like the leading edge of the
horizontal stabilizer is angled down. The attached image sort of shows it. The climbing under power is not a problem but the severe climbing when gliding (no power) is a problem. All of the down trim plus holding the elevator stick down is bleeding off precious flight energy. The image shows the elevator trim in neutral position. Perhaps breaking the glue bond and putting a shim under the leading edge of the horizontal stabilizer might work. Many thanks to you and the other's for helping.

Last edited by JGalt; 08-18-2018 at 05:36 PM.
JGalt is offline  
Reply With Quote
Old 08-18-2018, 07:58 PM
  #6  
aeajr
My Feedback: (2)
 
aeajr's Avatar
 
Join Date: Jan 2003
Location: Long Island, NY
Posts: 8,567
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Talking

Originally Posted by JGalt View Post
I need help with trimming or balancing my electric glider. It is built up covered in monokote. The problem is the thing wants to climb even with the power off. It requires full down trim and then still climbs with power off. I don't mind it climbing like a rocket with the power on but want it trimmed out when gliding. Here is what I have done:
I exactly followed the instructions for setting the CG. The first flight required full down trim and holding the elevator down. Second flight: With the transmitter trim full down, I added 1/4 oz lead in the nose with negligible results. Third flight I then added another 1/4 oz lead (now total of 1/2 oz) in nose. The plane still climbs when gliding. This is not a drastic climb like a tail heavy situation but it is enough that I often have to hold in down elevator plus full trim to fly level.
I am seeking any assistance.
Thanks!
John
My first impulse is that you are nose heavy. Many instruction sets and plans tend to lean toward being a little nose heavy as it is a safer position than tail heavy.

The effect is that, if you are nose heavy, you end up trimming in more up trim to support the heavy nose. When you pick up speed the glider wants to climb due to that up trim. Under power it really wants to lift that nose and might even want to loop.

Another way to read this is that the glider tends to porpoise. Get it in a smooth glide and release the stick. The glider will slow down, then stall. As it dives it will pick up speed and climb, then stall and drop the nose. it will do this over and over.

Try taking weight out of the nose, about 1/4 ounce at a time. Then test flight. If it is still climbing, take out some more weight.

As you do this you will end up putting in down trim, which is good as you are taking out the excessive up trim caused by the glider being nose heavy.

Another way to test for this is the dive test. If the glider is perfectly balanced and perfectly trimmed then if you put it into a dive then release the stick the glider should stay in the dive or pull out slowly. You might even have to pull it out of the dive to keep it from hitting the ground. Be sure to do this very high. Get the glider flying straight and smooth and into the wind. Best done on a quiet wind day.

Now gently put it into about a 30 degree dive and gently release the elevator stick. If it pulls out quickly you have a lot of up trim. Chances are you are nose heavy.

If it wants to tuck, to go deeper into the dive you are likely tail heavy and have down trim in to support that heavy tail.

If it holds the dive or pulls out slowly on its own, you are good.

BTW, this can also be caused by too much incidence in the horizontal stab. But if you have a fully flying stab then that is not the problem.
aeajr is offline  
Reply With Quote
Old 08-18-2018, 08:01 PM
  #7  
aeajr
My Feedback: (2)
 
aeajr's Avatar
 
Join Date: Jan 2003
Location: Long Island, NY
Posts: 8,567
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

The only way to really measure the incidence of the h-stab to the wing is with an incidence meter. You can't eyeball it.
https://www.towerhobbies.com/cgi-bin...?&I=LXET66&P=7

But I would try the balance process first. It is usually the balance, especially if this is an ARF or RTF.

I have to put a quarter on the tail of my Radian to get it properly balanced.
aeajr is offline  
Reply With Quote
Old 08-18-2018, 09:23 PM
  #8  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by aeajr View Post
The only way to really measure the incidence of the h-stab to the wing is with an incidence meter. You can't eyeball it.
https://www.towerhobbies.com/cgi-bin...?&I=LXET66&P=7

But I would try the balance process first. It is usually the balance, especially if this is an ARF or RTF.

I have to put a quarter on the tail of my Radian to get it properly balanced.
Thanks aeajr, I appreciate the feedback. Yes, it is an ARF plane. I thought the ‘tail feathers’ looked odd with the horizontal stabilizer slanted down like it is but perhaps that is the way it supposed to be. The difference between what you described and my situation is the plane climbs like crazy with full down trim and in the glide mode. With the trim set in the neutral position, no power (just glide mode) the plane climbs to a stall. Apply power and the plane would loop unless full down trim is dialed in and also holding some down elevator. I‘ll get an incidence meter when they are back in stock. Thanks!
JGalt is offline  
Reply With Quote
Old 08-19-2018, 01:28 AM
  #9  
UStik
 
Join Date: Oct 2006
Location: Augsburg, GERMANY
Posts: 976
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

It really looks like the stab is distorted. I'm writing because I had this problem with my little ARF aerobat; I even crashed it recently and only then understood what the problem was.

The stab was distorted like on your model, the LE tips bent down on both sides, so I had to add lead to the front. That didn't really help, though, so I straightened the stab halves fairly well with a covering iron. That helped the balance but made the model unstable in pitch. A small elevator throw up let the model go straight down.


The elevator was distorted as well and I hadn't (couldn't) correct that. The chamfer was a bit above the stab's rear spar (picture), which got pushed down a bit by up elevator so the stab acted like down elevator. I tell that just to show that the unthinkable is possible; not that I mean your model has exactly the same problem.

But if I were you I would not only check the stab's incidences at root and tip. (Just compare them with a small level and correct with an iron if need be.) I'd also take the elevator off, make it straight if it isn't, and re-hinge it with new hinge tape both at top and bottom. The elevator's chamfer and the stab's rear spar should not overlap anymore.

Besides, measuring wing and stab incidences, as you intend, seems advisable since the stab's negative incidence seems to be rather big. In any case, checking the balance is most important because you can balance even for a big decalage (if there's no control reversal like on my model).
UStik is offline  
Reply With Quote
Old 08-19-2018, 02:36 AM
  #10  
aeajr
My Feedback: (2)
 
aeajr's Avatar
 
Join Date: Jan 2003
Location: Long Island, NY
Posts: 8,567
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by JGalt View Post

Thanks aeajr, I appreciate the feedback. Yes, it is an ARF plane. I thought the ‘tail feathers’ looked odd with the horizontal stabilizer slanted down like it is but perhaps that is the way it supposed to be. The difference between what you described and my situation is the plane climbs like crazy with full down trim and in the glide mode. With the trim set in the neutral position, no power (just glide mode) the plane climbs to a stall. Apply power and the plane would loop unless full down trim is dialed in and also holding some down elevator. I‘ll get an incidence meter when they are back in stock. Thanks!

Do the balance procedure I suggested. 90% probability that is the issue.
aeajr is offline  
Reply With Quote
Old 08-19-2018, 02:34 PM
  #11  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Many thanks to all who responded with expertise! I am learning the world of gliding and electric power.
John
JGalt is offline  
Reply With Quote
Old 08-30-2018, 02:40 PM
  #12  
H201B
 
Join Date: May 2018
Posts: 4
Default

I have a Vista also. From your photo it looks to me like the factory made an error in cutting the stabilizer platform on your particular glider. The incidence of your stab should be parallel with the bottom of the rudder on this model. You will need to carefully remove the stab, trying to minimize damage even if it results in collateral damage to the saddle area since the next step will be to rebuild the saddle to reset the stab at the correct angle. If you have forgotten how the stab goes on, check your Vista manual.
H201B is offline  
Reply With Quote
Old 08-30-2018, 03:11 PM
  #13  
H201B
 
Join Date: May 2018
Posts: 4
Default

It occurs to me that rebuilding the stab saddle on this glider might be more work than it's worth. You could alternately shim the wing T.E. until the model glides properly at the correct CG. You will likely have to adjust the down thrust to get an acceptable climb rate. The Vista under power climbs like a rocket so you have some latitude there. My Vista flew fine out of the box.
H201B is offline  
Reply With Quote
Old 08-31-2018, 12:23 AM
  #14  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by H201B View Post
It occurs to me that rebuilding the stab saddle on this glider might be more work than it's worth. You could alternately shim the wing T.E. until the model glides properly at the correct CG. You will likely have to adjust the down thrust to get an acceptable climb rate. The Vista under power climbs like a rocket so you have some latitude there. My Vista flew fine out of the box.
Thanks H2O1B. Yep, I think that is the problem too. I tried everything...verified the CG, dive test and the only thing that seemed to work is a TE shim. But, I could hear flutter with the shim so I quickly landed. Might have been because the shim was a ‘field expedient’ thing rather than glued. This plane had some quality control issues from the manufacturer. Three pushrod tubes were glued in the fuselage rather than two. I had quite a time removing the extra tube that flopped around back there. Also the rudder pushrod exit was misaligned. The pushrod was severely binding. This is my first glider and I sure wish I had noticed the stab was misaligned. Thanks for your posts.
John
JGalt is offline  
Reply With Quote
Old 08-31-2018, 10:38 AM
  #15  
H201B
 
Join Date: May 2018
Posts: 4
Default

The issue with the pushrod guides occurred in my Vista also and I had to experiment with each pushrod to determine the correct tube for each. I still had to add 2 mild bends beyond the exit to allow the rudder pushrod to work freely. The 3rd tube is likely for the antenna of those who still use 72 Mhz radios.
If you chose to shim the wing, see that the wing rests solidly in the saddle.
H201B is offline  
Reply With Quote
Old 09-16-2018, 06:59 PM
  #16  
JGalt
Thread Starter
 
Join Date: May 2016
Location: Galt's Gulch
Posts: 36
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Originally Posted by H201B View Post
I have a Vista also. From your photo it looks to me like the factory made an error in cutting the stabilizer platform on your particular glider. The incidence of your stab should be parallel with the bottom of the rudder on this model. You will need to carefully remove the stab, trying to minimize damage even if it results in collateral damage to the saddle area since the next step will be to rebuild the saddle to reset the stab at the correct angle. If you have forgotten how the stab goes on, check your Vista manual.
I wanted to get back with an update. The problem turned out to a factory defect with the stabilizer platform being misaligned. As a result, I added all sorts of weight in the nose to compensate so the excellent advice to do a dive test proved the plane was indeed, nose heavy. But your keen eye led me to closely examine the alignment and that clearly was the root of the problem. I ‘bit the bullet’ and performed major surgery to resolve the misalignment. Painful for sure but it was worth the effort. The plane is trimmed and simply amazing. It soars beyond my expectations. 1/2 throttle jets it to altitude. I joined some birds thermaling and actually had to fly out of the thermal to keep from losing the plane. Thanks again to everyone who offered advice. I never knew how much fun gliders can be.
john
JGalt is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service