kargo

Hey Gang, Question;

Aerodynamics 101 Why does the large dihederal on the Senior decrease the effectiveness of the ailerons?

I've read some threads about using a OS 70 4 stroke on the Senior. We are planning ours with floats. Anyone have this setup? Pro's Cons?

phread59

OK I've got a SR with ailerons. I built the kit and when I had the wing about done decided to add barn door ailerons. You're right the ailerons are not very effective. The radical amount of dihedral fights the ailerons. They are mutually exclusive. Some dihedral is good. But the SR was designed as a 3 channel plane. And they added a lot of dihedral to make it stable and self righting. I basicly use the ailerons to level it out, usually on approach for a landing. I do have a computer radio and added aileron to rudder coupling. It did help some. If you want ailerons on a SR cut the dihedral in half at least. I did 3 rib bays for my barn doors. I would use at least 4. they go almost to the spar deep. I would also plan on 2 servos. Making a linkage for those big ailerons was a pain. 2 servo's would have been better. It is a sweet flying plane.

As for power a 70 would be way too much. I have a Saito 50 in mine. It is just perfect. I have some negative wing incidence and a ton of weight in the nose to get it to penetrate wind better. Take off rolls are only 50 feet or so on grass. I have a Master Airscrew 12-6 Classic on it. Combination is perfect. 10% Byrons with a little extra oil added. You will love your SR, I sertainly do.

Mark Shuman

bps

My Feedback: (3)

I have the Senior modified with barn door ailerons, tail dragger and Saito .82 four stroke. Remove most of the dihedrel, I built mine with 3/4" and it flies great. I use rudder and ailerons to co-ordinate the turns. Larger slower models just respond much better using rudder and ailerons to make smoother turns. If you own a computer radio you could mix this in or just train yourself to use rudder and ailerons as in the old days before computer radios.

sgillmore

My Feedback: (50)

I can't speak to the aileron effectiveness vs. the dihedral in the kit, but I can tell you the ailerons work very well on the ARF version. You might consider using it as a guide. If you're interested, I can take some measurements and or pictures if you don't have access one of the ARFs.

I also have an O.S. .70 4-Stroke on mine, mounted horizontally with a slimline pitts muffler and turning an APC 13x6 prop. Everyone has their own opinions on power-to-weight, but I think the .70 is a perfect match for the senior. Mine comes out of the water very easily with properly set up floats.

buzzard bait

Hi Kargo, here's what I think is happening: When you give aileron input, there is a little sliding tendency. In other words, you bank the plane, and part of the effect is to slide toward the low wing. On many sport planes this is not very noticeable, but it is there, and often you have to hold a touch of opposite aileron through a turn once it is initiated or else the turn keeps tightening.

So now picture this sliding motion in a turn to the left. Dihedral will cause the left wing to meet the air at a higher angle of attack because the air is really approaching the wing from the left. I don't know how to explain it better than that, but if you picture the situation I think you will see it.

At the same time, the right wing has effectively a lower angle of attack. So the dihedral tends to roll the plane back in the opposite direction. A little of this tendency is fine - it helps keep the turn from tightening. But if there is too much dihedral, it will "fight" the turn.

This can be corrected with rudder. In a turn to the left, left rudder will cause a yaw to the left. That increases the angle of attack on the right wing, instead of the left wing, which rolls the plane in the direction of the turn.

So a plane with a lot of dihedral will require rudder with the turn. In fact, it will turn very well without any aileron at all. But if you use the ailerons to turn, you will need to add rudder to the turn too. The turns will probably be better with aileron and rudder than with rudder alone. But rudder alone is much better than aileron alone for a plane that has a lot of dihedral.

Hope this makes some sense.

Jim

Rodney

Sr. Telemaster? Sr. Kadet? Sr. what? If it is a plane with a high wing like either of the first two, lots of dihedral fight any aileron input by trying to roll the airplane back out of the commanded turn. The dihedral also creates a roll command when a yaw command is given via rudder.

kargo

Thanks for the reply's gang! I think I see how the dihederal is fighting the ailerons, and how it works. I will definetly not use the stock senior dihederal, and will probably copy the ARF versions dihederal. Thanks for the offer for some info, Sgillmore. I think I'll email Sig for the amount of dihederal on the ARF Beautiful airplane, I think I'll use the slimline muffler on a OS70 as well. Did you make a build log by chance? Seeing or hearing what you did to fit the engine and muffler in would be helpful. Kit isn't even out of the box yet, but hopefully we'll work on it soon.

Thanks!

sgillmore

My Feedback: (50)

Thanks. Sorry, I didn't make a build log, but I do have some pictures from the assembly process that I can email you. I'd post them, but I'm not sure ARF assembly pictures belong in a kit-building thread! The only thing special I remember was that I had to use the metal O.S. engine mount to get it mounted close enough to the firewall.

O.S. Motor Mount FS-61/FS-70
[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCB67&P=ML[/link]

If you'd like copies of the assembly pictures, just shoot me an email.

kargo

Thanks again for the replys gang. I emailed Sig on the matter. It sounds as though they get questions about adding ailerons to this kit a lot. Their responce is in the attached picture.