PDA

View Full Version : Discussion Torsionloads at bagged wing and RDS, al servo's in centrepanel


Berrie
Oct 16, 2006, 02:07 PM
After a diskussion at an modelflightclub evening I became confused about the torsionstrength of the wingjoiners of my vacuumbagged wing.
The wing is a 3.3mtr wing for an electric “F3J” plane.

Span: 33,4 dm
Tail area: 6,9 dm^2
Wing area: 70,39 dm^2
Tailboom: 9,38 dm
Aspect ratio: 15,85
wing meanchord: 2,11 dm
TVR: 0,436 (TVR = tail area/wing area * tail arm / wing chord)
Flyingweight approx: 2550,00Gr
Wingload: 36,24
Profile: HQ/W2,5-8,5

This is plane is for thermal juration flying (and for building fun) so there are now very heavy loads to calculate as for dynamic soaring an winchlaunches. Only a 100mtr dive must be survived and some wisthle crossing from left airspace to the right airspace.


For now I have the outher wingpanels ready. They consist of blue foam and have a carbonspar with a round carbon wing joiner. Behind the aileron hingeline there is now secundary spar. The wingpanel rooth is from 10mm thick medium soft balsa, in witch the torsion dowels will come. The core is covered with one layer 50gram glas and 80 gram glas, all under 45°! Close to the panelrooth there is one layer of 80 gram extra glas, under 90°, to reinforce this part.

I would like to drive the ailerons and flaps as misterHarley has with his Genius and mister Drela with his Supra. Witch means that the servo’s all will find a place in the centrewing panel. That means that the core near one of the torsiondowels will be removed to give space to the aileronservo. I’ve tried to make a picture to make my self clear:
http://www.rcgroups.com/forums/showatt.php?attachmentid=1025883&stc=1
The centrewingpanel will be covered with one layer 50gram glas, 93 grams carbon under 45° and the same 90° 80grams glas reinforcing over the 10mm thick medium soft balsa panelrooth. The dowel consists of an 8/6mm glastube with 6mm carbn rod ( a bit heavy, but easy for me to get..) They will be glued into the wingpanels for 20mm. For location see picture.
http://www.rcgroups.com/forums/showatt.php?attachmentid=1025884&stc=1
My question: will this be strong enough to surive torsionloads?!?!? The carbondowels will be strong enough. I have my doubts about the wingcore/glasskin and balsa panelrooth (altough the glastube has a large “pressurearea” and the rooth is 10mm thick..)

rdwoebke
Oct 16, 2006, 02:32 PM
My question: will this be strong enough to surive torsionloads?!?!? The carbondowels will be strong enough. I have my doubts about the wingcore/glasskin and balsa panelrooth (altough the glastube has a large “pressurearea” and the rooth is 10mm thick..)

I sure hope so. I'm building a sort of Aegea wing using the same kind of method.

Ryan

Berrie
Oct 16, 2006, 03:32 PM
I sure hope so.
Ryan

haha!! Let's cross fingers, together. ;) :D

rdwoebke
Oct 16, 2006, 03:53 PM
How is your wing section hinged? Is that top hinged? I'm trying to figure out what that kind of roundish cut out is by the hinge line.

BTW, your wing looks very nice.

Ryan

greyhound flyer
Oct 16, 2006, 05:34 PM
The Genie (3.7m) uses RDS in 4 servos in a 1.54m center section that connects to 1.1m tips.

http://genie.rchomepage.com/FILE%2006,%20ROTARY%20DRIVER%20SYSTEM.pdf

The RDS is quite capable in the big Genie that I built, and Harley says they zoom just fine with RDS. His recommended drive shaft material is 3/32" stainless steel welding rod...

--Byron.

Berrie
Oct 18, 2006, 11:17 AM
http://www.rcgroups.com/forums/showatt.php?attachmentid=1028255&stc=1 http://www.rcgroups.com/forums/showatt.php?attachmentid=1028256&stc=1 http://www.rcgroups.com/forums/showatt.php?attachmentid=1028254&stc=1

thanks for the compliment.
The wingsection is tophinged. The roundish cut is space for the gapcovering, (for nice "aerodyrotica") I have not yet finished that. See pics.


@Greyhound, thanks for your answer. But the problem I feel is not about the RDS itself, but the structure from balsaroothrib, torsiondowels from wing connection and the hole the RDS aileron servo made so close to one of the wing(torsion)joiners in the foam. Maybe I can't make my self clear enough in englisch...

KevinSheen
Oct 18, 2006, 12:59 PM
Your wing construction looks similar to Harley Michaelis' GENIE. If the spar in your wing carries much of the load, then I wouldn't be very concerned with regard to the servo hole being close to the tip of the center panel. Another similar design is Dr. Drela's Supra and his Aegea. Both of those planes have a center section that has a substantial spar as well as RDS servo's for the tip sections near the tip of the center.

Now your only worry is - is your spar as substantial as the above 3 planes?

greyhound flyer
Oct 18, 2006, 01:42 PM
I don't think you have anything to worry about.

I've attached a couple of pictures from the Genie build thread that may answer some questions.

You can also view the thread starting on page 11 where cutting the servo wells, etc., is covered:

http://www.rcgroups.com/forums/showthread.php?t=219550&page=11&pp=15&highlight=Genie

rdwoebke
Oct 18, 2006, 01:48 PM
Kevin,

The spar carries the bending loads. Berrie did not mention any concern about the bending loads, he mentioned concern about the twist (torsion) loads.

On my wing, I sort of tested this by hand to see how much the center section twists. It does not twist very much at all, so I think (or hope) it is OK.

I'm still installing my servos although my wing is pretty much structurally complete. I probably need to do just a bit more work on the LE but otherwise it is ready to fly.

Ryan

Berrie
Oct 21, 2006, 03:43 AM
Thanks for the answers. You all took my sorrow's away!

This model has an electropropulsion, about 350-400W. Enough to get thermal start altitudes. So there are no zoomloads on the wing. The spar is a very strong carbonspar. Lots of carbonroving, foaminside, carbontube to hold it al together.

The models Genius and Supra have inspired me to do my own thing.. :rolleyes:

I have found a picture in the Supra building tread, that gives me a good feeling:
http://static.rcgroups.com/forums/attachments/9/2/7/1/a1011485-52-DSC00400_edited-1.jpg

Berrie
Dec 19, 2006, 03:49 PM
Time has fly by..... After finishing the inner wing panel it wasn't to much work to finish the wingjoiners and torsiondowels. Testing the wing, manual, at torsionloads gives a bath result. The balsaroothrib's where made of TO SOFT BALSA. Stubid me. :(

I had to mill the balsaribs out and replace them for stronger rootribs. After replacing 4 ribs and placing the torsiondowels the torsiontestresults where :D

So the lesson YOU can learn from me is: Dont use to soft balsa, at the rootribs, in your hunt for lower flyingweight... (of course I'm the only one that makes this kind of mistakes...........)