I recently acquired a SIG CAP231EX that belonged to a friend. He was an accomplished IMAC flyer, and had done a lot of experimenting with upthrust and side thrust for torque roll purposes. Presently it has 1.5 deg upthrust, and nearly 4 deg right thrust with a Saito 180 and 17x8 APC.

For routine flying, what would be a "normal" starting point for this plane? I could not find it in the instruction manual and I'm not sure I trust the firewall angle.

Thanks

Lee

Lee

I have a SIG 231EX W/an OS 1.60. I cant tell you the angle of the firewall (mine was 2nd hand also) but I can tell you I have added .80" shims for more right thrust and 0.0" downward. Seams to fly pretty good.

Otter,

To make sure I understand you correctly, you added 0.080" (a bit more than 1/16" thick) spacers at the firewall, under the motor mounts on the left side to increase the right thrust. And you left the down/up thrust alone, with whatever angle the firewall is set at.

Do I have it right?

Yup...

Much thanks, Otter. This will help when I put everything back together.

Much thanks, Otter. This will help when I put everything back together.

One of my flying buddies and I were comparing our Caps. His is the Sig, Mine is the H9. He told me it came with 0 (zero) right thrust. He called Sig and they had the nerve to tell him the plane didn't need right thrust ????????. He is an old pattern flyer and has ended up with around 2.5 degrees right thrust for IMAC style flying.

The plane flies very well and came in lighter than my H9 lead sled.

Jim,

Funny you should mention that. Actually, I just got an email back from SIG that said that said the firewall (and engine) should be at zero down and zero right thrust.

My friend has flown his SIG CAP at the factory firewall setting for 2-3 years now with an RCS 1.4 and really loves it. No idea if his is actually at zero or not, but he doesn't fly precision aerobatics (me neither) so he might not notice it.

Don't know if this plane really needs some right thrust or not, however, I calculated that with the .080" shim that Otter added, it computes to around 2 degrees of right thrust. That seems like a relatively "normal" amount of right thrust that many planes seem to have as a starting point.

My SIG CAP was used when purchased. It came equipped with a ST 2000 and no shims under the mounts. It flew fine (except it was gutless). I up-graded to an OS 1.60 and found plenty of Left torque pull on take off and during vertical flight. Also pitched during throttle chop. I added .080" shim under the left mount...files A-OK. Might trade it out for a Moki though

I have a new sig that I have about 25 flights on and I have NO thrust right or down...it is not needed.
I to called Sig on this as there is nothing in the manual and just wanted to double check, Mike from Sig told me they flew the Cap 231 with no Right thrust or Down thrust with the Irvin 150 and felt there was no need to add so they didn't and neither have I with a Moki 135...she flies GREAT!
I did not have to add weight with the Moki after I put the cowl on and I am right at 30% balance on it 4.5 " back, I have my elevator throws about 3/4 " she is a little pitch sensitive with any more than that but with 3D rates WOW! she sure is GREAT!

BEST PLANE I HAVE EVER OWNED.

Cheers, Robin

I just bought a 2nd-hand SIG Cap231 EX...

I added nothing to the firewall to adjust thrust angle...

O.S. 1.60 w/ a wooden 16x10 prop...

Trimmed out nicely flies very well... UNTIL...

I go straight verticle... the plane will BADLY pitch to the left... almost like I'm holding 1/2 stick left rudder...

So I assume I NEED a couple degrees right thrust...

Am I reading the plane's response right?

My plane is a little tail heavy and wants to climb when increasing the throttle. I have to trim in some down elevator. If i shim out the motor do i shim the top or bottom. If i shim out the top is that called down thrust because it will cause the nose to push down or am i backwards and its called up thrust because it pushes air up? Anyway what do i do if i do not want the plane to climb when increasing the throttle.

You need downthrust...

Placing washer in the top 2 holes will pitch the thrust angle of the engine down (in relation to the planes thrust line)...

Most often planes that "balloon" when increasing throttle need downthrust... however, wing and horz. stab incidence can cause it too... most planes has equal incidence in the wing and stab, but not always...

Say the hstab is slightly negative in pitch (i.e. it slants UP a bit and acts like down elevator) You can trim it out at lower speeds but at higher speeds the effect is exponential and the trim isn't enough to prevent the nosing up of the plane...

Again it is more likely the thrust angle of the engine... Most design's wings provide lift that will "pick up" the nose of the plane instead of lifting the whole plane... a bit of downthrust couteracts the "over-lift"...

Kindof like 2 guys pulling a sign up with 2 ropes on each end over pullies... If one guy is pulling with more force his end will rise before the other, but get the forces equal and the sign will rise level... Make any sense?

I just did a search on RCU and found this thread. I too think that my Sig Cap 231ex needs some right thrust. One problem though......I'm using a Moki 1.8 w/ a radial mount......Any ideas on how I could add right thrust to this airplane? Isn't the whole purpose of a radial mount to have contact on all sides?

I've previously used an Irvine 1.2 on this airplane with the regular 2 piece mount.....the width of the Irvine is different than the width of the Moki....so I have to drill new holes. Only prob. is that the spacing is only slightly different....so it's like making my old holes bigger. With that said, switching the kind of mount is probably out of the picture.

Thanks,

Patrick