Posted by Collin on Tuesday, July 5, 2011 @ 08:00 PM:
Hello,
I have been thinking about adding VGs (Vortex Generator) to the bottom of the elevator.
There are times when thermalling solo at low speeds that I think the elevator is stalling. At low speeds the stick is almost full aft. I have added a removable 8.5lb weight that helps. Has anyone played with VGs?
Posted by Jorgen on Wednesday, July 6, 2011 @ 04:46 AM:
Collin,
that's a very good idea. Thermalling the 5b is great performance-wise, but handling-wise there are probably room for improvements. As you proved with your removable weight the underlying problem is that the RF 5b tend to get nose-heavy(=the elevator needs to provide a lot of down-force) when flown solo. VGs might help, but sealing the elevator gap is probably a first step.
When I sealed the gaps on "SE-UDI" I ran out of tape after sealing the ailerons(upper side only) and rudder(both sides) so I never sealed the elevator gaps. I still found a noticeable improvement on low speed performance (thinking mostly of roll-rate) where as you know you often need full aileron + rudder.
I thought the 5b already had a great handling in pitch, so I didn't think it would make much difference to seal the gaps there. Following your reasoning I see there is maybe even more reason to seal the elevator. That can be done on both sides, I would suggest to start with that if you haven't already done it. I would have loved to try it out myself, but that will have to wait for a while yet. Very interesting quest, to improve thermalling performance of the RF 5b. Which is already in my opinion among the absolutely best a motorglider can provide.
I can't help but wonder how much René was involved in the design of it, or was it more or less a Sportavia endeavour?
May the 4's be with you/ Jörgen
P.S. I had to cut slots in the seals around the hinges, where the fabric is not smooth to avoid possible jamming. I suggest if you try VGs to be conservative in the placement and keep them well spaced from the seals. D.S.
[Edit by Jorgen on Wednesday, July 6, 2011 @ 04:51 AM]
Posted by jb92563 on Wednesday, July 6, 2011 @ 10:25 AM:
I agree with Jorgen, I would gap seal the elevator first, but also like Bob G warned, making the elevator more effective than designed can make it possible to exceed G limits so a word of caution is necessary about that hazard.
I know of some folks with Kolb Aircraft that used VG's on the wing and underside of the elevator.
The results were dramatic as the wing stall speed decreased a fair bit, and in turn necessitated a more effective elevator at the lower stall speed.
The under side surface VG's were placed a couple inches in front of the hinge line and also had the desired effect at slow speed.
High speed was barely effected.
Here is a link to some info I gleaned way back in my Kolb days.
https://docs.google.com/document/pub?id=1uLvdMXGr97Ec1Nef-hLpYDkssRdM1SW1GWvbqmGWLHc
A account of someones experience with VG's
http://lists.matronics.com/viewtopic.php?p=24896&sid=7144e4755d45e7ee4b5369065024db93
The plastic corner protector strip material that was used for the VG's on the Kolb elevator.
They were mounted with a 3M quality double sided tape. I still have tons of it.
A Kolb wing. Apparently the little VG's do the job quite nicely.
And some more experimenting,
http://www.bcchapel.org/pages/0003/Vortex%20Generators.html
[Edit by jb92563 on Wednesday, July 6, 2011 @ 10:32 AM]
--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org
Posted by Jorgen on Wednesday, July 6, 2011 @ 06:18 PM:
Thanks Ray,
great links, sorry couldn't open your gleaned info. So a row of plastic corner VGs on the underside of the elevator 8-12 cm from the leading edge should do the trick? I didn't get why that guy's paired underside elevator VGs weren't parallell.
May the 4's be with you/ Jörgen
Posted by jb92563 on Thursday, July 7, 2011 @ 10:00 AM:
I have reset the first link for public access so you can get to it now without a sign in.
https://docs.google.com/document/pub?id=1uLvdMXGr97Ec1Nef-hLpYDkssRdM1SW1GWvbqmGWLHc
--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org
