aileron/trim issues

iowaflyer · #1 09-15-2009, 08:32 PM

I am the proud owner of a new-to-me RV4. I'm having a few squawks adjusted by my local A&P. The right aileron doesn't match up with the wingtip or flap--the left is perfect. The right side hangs 3/4 inch low with the stick centered. Also, the plane requires a fair amount of L hand aileron trim to fly level. I'd like to provide my mechanic some advice as I don't think he has much familiarity with RVs. Where should I start with this? How do I fix the aileron issue?

D-Dubya · #2 09-15-2009, 09:12 PM

I'm more familiar with 6's & 7's, but I think the rigging for the 4 is similar. At least I'm assuming it is. First off, 3/4" is a lot to be off. I'd remove the covers/panels at the bellcrank and the stick and make sure that everything is undamaged, tight and secure. Then the pushrod from the stick to the bellcrank as well as the bellcrank to the aileron pushrod can be adjusted as necessary. It should be pretty basic stuff for an A&P.

Your trim issue may improve after everything is properly rigged, but it may take a test flight to be sure.

L.Adamson · #3 09-15-2009, 09:24 PM

Once the aileron is adjusted as suggested in the first reply, you may still have a heavy wing. You can search this website for the "heavy wing" cures. In my case, it was just a slight flattening of the aileron's trailing edge for about 14" with 6" hand seamers. This trailing edge actually had a slightly thicker radius than the right aileron. I've seen an RV4 that had opposite bent trim tabs attached to each aileron...........but I think the heavy wing flattening cure would have worked.

L.Adamson --- RV6A

rv4ator · #4 09-15-2009, 09:32 PM

I went through similar issues on my -4 & -7A. After trying all the recommendations about lining up the ailerons with the wing chord etc., what finally worked for me was to adjust both ailerons so that the bottom of both ailerons were flush with the the bottom of the wings. That took care of 95% of any roll issues. You can fine tune the rest by squeezing the "light" wing, but go slow because a very small amount makes a difference. Both my -4 & -7A fly straight & level hands off with no trim input, but the ailerons do not line up with the flaps or wing tips. I thinks this if fairly common for homebuilt RV's.

Kevin Horton · #5 09-16-2009, 04:37 AM

Carefully read the Wing Heavy Analysis doc on Van's web site.

Hum · #6 09-16-2009, 02:20 PM

Just done 8 hours on a new RV7 7 EI VII - lovely aircraft, but until this afternoon I have been puzzled about why it feels so 'wobbly' in roll - esp compared to my own aircraft, also a '7.
The aircraft feels like it has no lateral stability, sort of like an extra, but
not as nice... Not easy to describe. Also, the ailerons do not seem to 'stiffen
up' at higher speeds like I believe they should. Did a sort of 'stick free
static stability test on ailerons' (tap and let go) - it went rock and roll
almost divergent... esp at low fuel. Initially they seemed to have a 'neutral zone' where little happened with a small deflection and there was almost no resistance to deflection. We drooped the ailerons a little which made a small
improvement, but still not enough. We measured everything, examined bellcranks, throws etc. All looked OK. We Put a spring in (mine has one for the manual trim) which improved it a bit, but
still not enough to be happy. Then I noticed that the aileron leading edges
appear to be slightly 'drooped' giving too much 'Frieze in the breeze' at
neutral aileron (about 1/8" all along the leading edge). The ailerons have a
distinct cambered bottom surface from the spar forward. Those on my own '7 have absolutely flat bottom surfaces. I am convinced this is
what is causing the funny 'wobbles'. The ailerons came as part of a QB kit; I guess they are not unique.
Anyone else come across this?

Hum · #7 09-18-2009, 01:51 PM

Today we swapped the ailerons with another pair that had (almost) flat bottom edges. The aircraft now handles perfectly, the difference was astounding... like Night and day..

Hope these were a 1-off set of QB's

swisseagle · #8 09-19-2009, 02:37 PM

Hello Hum?

I remember the same problems when I was building my ailerons ... the bottom was not flat.

I find out, that on the position where the small ribs (on each end of the aileron) where, the bottom foreward of the spar is bent a bit up (3/32") and after 10" to the center the nose is comming down by the same amount if not even a bit more ... I was thinking to rebuild them, but lets first finish the plane.

If I have to rebuild them, then I would install minimum 2 additional noseribs, so that the form of the aileron is more consistant over the hole lenght.

I woud be happy if you can check the profile differences on your bad ailerons at the center and at the ends and report here.

Thanks alot, regards,

Dominik
RV7A

Hum · #9 09-20-2009, 04:32 AM

Hi Dominik,

You are right, the tips of both ailerons were not as bad, the worst 'droop' was in the middle. I agree, it might be a good idea to put a couple of more ribs in the leading edges if you were doing it again.

The ailerons we had a problem with were 'quick build' ailerons so we did not build them. When mounted on the wing, the leading edges of both ailerons were visible from the front with both ailerons in the neutral position (you could see the pop rivets securing the mass balance tube at the leading edge). This was because of the large 'droop' in the under surface of the leading edge of the aileron.

This is obviously a critical area and needs to be carefully built to achieve as flat a bottom surface as possible.

Regards

Grery Hum

Mel · #10 09-20-2009, 07:14 AM

Quote:

Originally Posted by D-Dubya

I'm more familiar with 6's & 7's, but I think the rigging for the 4 is similar. At least I'm assuming it is. First off, 3/4" is a lot to be off. I'd remove the covers/panels at the bellcrank and the stick and make sure that everything is undamaged, tight and secure. Then the pushrod from the stick to the bellcrank as well as the bellcrank to the aileron pushrod can be adjusted as necessary.

The neutral positioning of the aileron bellcrank in the RV-4 and even more so on the -6 is pretty critical. If not positioned properly, you can reach a point of "over-center" where it can lock into place. Make sure you check this for full travel both ways before closing the inspection panel.