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2M Sailplane repair goof--how bad?

Old 02-14-2013, 12:50 AM
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Beemerider
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Default 2M Sailplane repair goof--how bad?

I have been slowly rebuilding and recovering a 2m sailplane. Among other repairs I had to rebuild and reattach the complete tail after it snapped off after falling from a tree. In the process of installing and hooking up the push rods to the elevator and rudder I discovered the horizontal stabilizer has a 2.1 degree down pitch in relation to horizontal. The sailplane is a 2m Explorer that was made by Thunder Tiger. I don't remember what the original setup was (I assume the tail should be 0 degrees compared to horizontal?)

I hate to think I need to cut the tail off and reset it?
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Old 02-14-2013, 07:08 AM
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Wildflyer
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Fly it and try it. If it's only 2.1 degrees, try it a little (cautiously) and see it it seems all right. If it is weird, try shimming the wing a little. you should be able to determine if you need to redo the stab.

I'm not sure I could measure 2.1 degrees. Keep in mind some sailplanes don't fly with the fuse at the angle we would normally think of.
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Old 02-14-2013, 06:36 PM
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Beemerider
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Thanks Wildflyer--

I'll be careful and give it a try. The tail had snapped off just forward of the stabilizer right where the fuse is the narrowest. Had to use some 1/32nds ply to ensure it's strength. I was just not careful enough. The plane is near complete save for reinstalling the motor and esc. I will report back after it's new maiden flight. Just need some calm winds here in Virginia. The local clubs are hosting a swap meet on Saturday so that's a priority! Might find something I can't live without.

btw--I have a small digital level (about $30) I used when I was in the communications industry. When I would install cellular antennas on a tower for wireless companies i.e. Verizon, AT&T etc, they had to be installed with a very specific and precise amount of down tilt. Anywhere from 0 to 6 degrees usually. After installation we'd have to take a picture of the down tilt reading with the level on the back of the antenna so the customer knew it was installed correctly. I'm retired now so the level finds other application. Hanging pictures for the wife, measuring my mistakes etc!

The pic I just took shows 2 degrees down---2.1 when I first measured. I doubt a tenth makes much difference if any at all.
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Last edited by Beemerider; 02-14-2013 at 06:53 PM. Reason: added pic
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Old 02-15-2013, 05:24 AM
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Wildflyer
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I forgot that I actually have a level like that.
I used to do very high end finish carpentry work, sometimes in $15 million condos.
I am also retired so I should get it out and find other uses for it.
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Old 02-15-2013, 06:21 AM
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kyleservicetech
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Originally Posted by Beemerider View Post
Thanks Wildflyer--

I'll be careful and give it a try. The tail had snapped off just forward of the stabilizer right where the fuse is the narrowest. Had to use some 1/32nds ply to ensure it's strength. I was just not careful enough. The plane is near complete save for reinstalling the motor and esc. I will report back after it's new maiden flight. Just need some calm winds here in Virginia. The local clubs are hosting a swap meet on Saturday so that's a priority! Might find something I can't live without.

btw--I have a small digital level (about $30) I used when I was in the communications industry. When I would install cellular antennas on a tower for wireless companies i.e. Verizon, AT&T etc, they had to be installed with a very specific and precise amount of down tilt. Anywhere from 0 to 6 degrees usually. After installation we'd have to take a picture of the down tilt reading with the level on the back of the antenna so the customer knew it was installed correctly. I'm retired now so the level finds other application. Hanging pictures for the wife, measuring my mistakes etc!

The pic I just took shows 2 degrees down---2.1 when I first measured. I doubt a tenth makes much difference if any at all.
Being a sailplane, it should be able to handle 2 degrees down. You'll have to correct with up elevator, producing a bit of drag though. Would be easier to correct by shimming the wing.

Out of curiosity, did you compare the pitch of the elevator stab against the pitch of the wing? That would be the important measurement.

I've also got one of those digital levels. It really works out well for precise measurements on those model airplanes we fly. Picked it up at a local (Menards) lumber yard for about the price indicated.
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Old 02-15-2013, 09:58 AM
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Originally Posted by Beemerider View Post
I have been slowly rebuilding and recovering a 2m sailplane. Among other repairs I had to rebuild and reattach the complete tail after it snapped off after falling from a tree. In the process of installing and hooking up the push rods to the elevator and rudder I discovered the horizontal stabilizer has a 2.1 degree down pitch in relation to horizontal. The sailplane is a 2m Explorer that was made by Thunder Tiger. I don't remember what the original setup was (I assume the tail should be 0 degrees compared to horizontal?)

I hate to think I need to cut the tail off and reset it?
tape some thin card board on the stabilizer and elevator to protect them, thin card board from a soda case works great, take a hacksaw blade, bend a angle on one end to hold onto it with, you may have to heat the blade red hot to bend it, put some electrical tape on the handle area, and cut the stabilizer only out, reposition it and epoxy it in place. Done
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Old 02-15-2013, 03:31 PM
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When measuring the pitch of the stabilizer I did compare it to the wing and there is a 2 degree difference.
I installed the motor/esc/rx last evening and verified operation of everything. I've a couple of other things I need to do before a test flight. If it flies ok I may leave it alone or I might try shimming the wing first. That would most certainly be the easiest although I like your idea Chellie on the hacksaw blade trick.
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Old 02-21-2013, 04:28 AM
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I think Denny mis-spoke when he said you would have to compensate with some UP elevator.

Actually, its just the opposite. Having the leading edge of the stab DOWN is like giving the model UP elevator. You may need to add a good bit of DOWN trim to compensate.

Most of those older wood sailplanes had between zero and +2 degrees of decallage. Thats the difference between the stab angle and the wings zero lift angle (NOT the same as the bottom of the wing!).

If your measurement of 2 degrees is relative to the bottom of the wing, then you are more likely at 3 to 4 degrees positive decallage.

Thats a lot of built in UP trim to try to over come.
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Old 02-21-2013, 04:58 AM
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Originally Posted by Larry3215 View Post
I think Denny mis-spoke when he said you would have to compensate with some UP elevator.

Actually, its just the opposite. Having the leading edge of the stab DOWN is like giving the model UP elevator. You may need to add a good bit of DOWN trim to compensate.

Most of those older wood sailplanes had between zero and +2 degrees of decallage. Thats the difference between the stab angle and the wings zero lift angle (NOT the same as the bottom of the wing!).

If your measurement of 2 degrees is relative to the bottom of the wing, then you are more likely at 3 to 4 degrees positive decallage.

Thats a lot of built in UP trim to try to over come.


I've got that same exact level, so it was put on my computer table, and one end was lifted to match the photo. And, raising the "trailing edge" of my level about 5/16 of an inch allowed the level to show the same 2 degrees, with the same line graph indication.

Since raising the trailing edge of the horizontal stab would result in the model climbing up, it would take down elevator to correct. And, likely a LOT of it, since the elevator is much smaller in area than the whole horizontal stab.

Maiden flight should be interesting.
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Old 02-21-2013, 01:07 PM
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Beemerider
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Y'all are real encouraging!

Reckon I'd better video it too---just in case it might be it's last......

Next calm day (wind) will be Monday. I will report back!


edit--ok--I went out to my shop and took another look. You got me worried. I'm going to cut the stabilizer and reset it.

Last edited by Beemerider; 02-21-2013 at 04:26 PM.
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Old 02-21-2013, 07:18 PM
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Originally Posted by Beemerider View Post

edit--ok--I went out to my shop and took another look. You got me worried. I'm going to cut the stabilizer and reset it.
Before regluing it, I'd suggest you pick up one of those incidence meters such as this one:
http://www.hobbylinc.com/htm/rob/rob404.htm

I've got the Great Planes Accupoint unit, a very nice and accurate device, but it has been discontinued.
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