Horizontal Stab Alignment

Veetail88 · #1 03-24-2009, 10:39 PM

Help!

I'm attaching the horizontal stab on my RV-8.

Plans say to align the stabilizer yaw wise, to measure from the tip of the stab to a point on the tail cone on each side, and to position the stab assembly within 1/4" tolerance side to side.

This seemed like a pretty big allowance to me. When I set this dimesion equal on each side the center of the assembly is very much off center to the tail cone. (see attached picture)

When I center the assembly at the attach point, the tips are out exactly 1/4"!

This leads me to believe that this is common and thus the 1/4" allowance, but it just doesn't seem right to me! In fact, it really doesn't seem possible! What dimension is out of whack? Is it possible that the tail cone itself is not true? This is a QB kit, so I don't take credit for that issue!

What is the norm here? I'm holding off drilling the front spar attach points until I'm comfortable that the 1/4" is really ok.

As usual, any help is greatly appreciated!

By veetail88, shot with Canon PowerShot SD850 IS at 2009-03-24

Norman CYYJ · #2 03-24-2009, 11:01 PM

When I have aligned the HS I measure forward towards the cabin up the centre of the fuselage. I figured the further away from the mounting point the more accurate you could get it.

flion · #3 03-25-2009, 08:56 PM

Quote:

Originally Posted by Veetail88

Plans say to align the stabilizer yaw wise, to measure from the tip of the stab to a point on the tail cone on each side, and to position the stab assembly within 1/4" tolerance side to side.

That would be an accurate way to measure assuming that the points you select on either side are accurate. Actually, it will probably be pretty accurate anyway, at least as far as the flying qualities of your aircraft are concerned. Were it me, I'd find a known centerline position and, like Norman, as far forward as practical. Then I'd measure both tips to the exact same point.

clam · #4 03-25-2009, 09:30 PM

on an RV-8 QB. I used the punch mark on the center of the center rivet in the canopy slider rail depression just aft of the rear seat on the turtledeck, and measured to a rivet on the inside corner of the HS where the elevator c-balance aligns. It took many iterations, but I was able to get this dimension to within 1/32" between the left and right. I haven't yet drilled the incidence angle holes through the rear spar but should do that this weekend. I ended up using a long piece of 3/4" angle with markings on it instead of a drooping tape measure.

I agree with the other posts - use a point as far up the fuse as possible

Randy Hooper · #5 03-26-2009, 08:34 AM

Jesse in your photo, the lower angle which mounts to the fuselage looks as though it may interfere with the rubber gap molding.
I ran into this situation after everything was mounted. Rather than backing up and trimming I will have to live with a small gap in this area.

Randy Hooper

APACHE 56 · #6 03-26-2009, 07:26 PM

I note that Jesse has the aft fuse skinned (in photo) and Jeff talks about measuring from the canopy slider. My RV8 QB builders book has me fitting the empenage now that I've finished the floors. Following the emp are the emp controls, fuel/ brake system etc. The aft skin and canopy are way down the road.
Why did you folks do the emp out of Van's sequence?

Thanks

Norman CYYJ · #7 03-26-2009, 08:34 PM

The final bolting on of the HS/VS can be done at any time.

clam · #8 03-26-2009, 08:57 PM

Quote:

Originally Posted by APACHE 56

I note that Jesse has the aft fuse skinned (in photo) and Jeff talks about measuring from the canopy slider. My RV8 QB builders book has me fitting the empenage now that I've finished the floors. Following the emp are the emp controls, fuel/ brake system etc. The aft skin and canopy are way down the road.
Why did you folks do the emp out of Van's sequence?

Thanks

Don,
You may have the newer matched-hole QB fuselage, that I believe leaves this aft top skin off. Mine, and I'm assuming the original poster's, have this skin already riveted on. Access is much easier in your case.

APACHE 56 · #9 03-27-2009, 04:19 AM

Jeff et al,
I see that my -8QB is different in that some parts are already fabricated. Case in point, the throttle quadrant cable anchor. I spent about an hour and a half looking and relooking thru my inventory and Van's parts trying to find the raw stock from which to fabricate said part. Working myself into a major snit I took a break and actually looked into the QB fuse. Lo and behold the part had already been fab'd. I should have known in that this isn't the first time I've run across this problem. I'm hoping that the canopy and frame will turn out to be the same situation....lol.

Veetail88 · #10 03-27-2009, 09:39 AM

Thanks for the help guys!

At the end of the day, I ended up positioning the front spar joint as close as possible to the centerline while not exceeding the 1/4" tolerance in the horizontal stab tips to forward tailcone point dimension. Course that means I'm right up against that max tolerance, but the whole assembly is a better fit this way. Can't imagine it's going to make any difference.

Yep, my QB fuselage came with the top skins attached. Although I just recieved it in December, it was an older QB kit where the fuselage was built up from pre pre-punched parts. Saved a cool grand that way. Van's was trying to unload some old stock. The wings were built up from the pre-punched parts though.

As I have the preview plans and instructions that are of the latest greatest kit makeup as well as the plans and instructions from the older non pre-punched kit, I find myself going back and forth between the sets, and at first, I had the same problem in reverse as an earlier poster of looking for a fabricated part only to discover that I have to fab it myself! I'm over that now and am able to keep it straight. I do use the newer instructions though as much as possible as they are MUCH more comprehesive than the older ones.

Thanks again