fairing alignment alternate method

[mark manda]

anybody just I eyeball the arch of the leg fairing with plane on the ground? have someone bend them while you eyeball them from back under the HS.

and the pants, just align them with the longerons not the ground?

thanks, mark

[dan]

If you don't mind your plane being slow & uncoordinated, use the eyeball method.

Do yourself a favor and use the fishing line/string method that Van's outlines for us. It works wonders to get those leg fairings precisely in trail and keep the ball unaffected.

I just helped Mike Holland (fellow Chino Power Squadron member) with his main leg fairing installation on his RV-9A last week. We used the same method that I used on my (fast) RV-7, the same method that Van's describes -- weight off the mains, longerons level, string around a pole at the tail, precisely located plumb & level, adjust trailing edge of the fairing to split the strings. Use "Great Stuff" foam to "lock" the fairings in place...forget about the clamped tab method.

Mike flew again after we did this and he said the ball hadn't moved at all -- feet on the floor, ball centered. Mission accomplished. Now granted, there could be errors cancelling each other out here, but I don't think so!

You gotta take the extra effort and get the plane up, weight off the mains, and go through the motions to get those fairings perfect. 1-2 knots for the entire life of the plane for a few hours of work is a big deal and an easy win imho.

)_( Dan
RV-7 N714D
http://www.rvproject.com

[f1rocket]

Here's some food for thought. One, another method for aligning the leg fairings is to mount your engine mount on a table and level it. Then, just drop plumb bobs on either side of the fairing. It's a piece of cake. Details are on my web site. Of course, if you are finishing up you don't want to unbolt your engine to do it, but if you can plan ahead, this is much easier than the string/plumb bob contraption that Van's calls for.

Two, I think (and fellow Rocket builder Tom Martin has some empherical data to support this) that the effect of fairing misalignment is somewhat over emphasized. While it might have a slight effect and slow you down maybe a knot, but not much more. Also, it doesn't really move the ball much either. Maybe they would if they were strengthened and had ribs in them, but as flexible fiberglass, they really can't push the airplane over much.

I know folks might disagree and I can't quote Tom's numbers, but he purposely flew with them out of alignment. Now, the Rocket fairings have twice the cord length as RV fairings, and he couldn't tell any difference.

It's always better to get them straight, but I suspect minor misalignments have little to no effect on whether your airplane will fly straight or fast.

Now, the vertical stabilizer.........that's a whole another story.

[dan]

Originally Posted by f1rocket

Two, I think (and fellow Rocket builder Tom Martin has some empherical data to support this) that the effect of fairing misalignment is somewhat over emphasized. While it might have a slight effect and slow you down maybe a knot, but not much more. Also, it doesn't really move the ball much either. Maybe they would if they were strengthened and had ribs in them, but as flexible fiberglass, they really can't push the airplane over much.

I have to disagree, from personal experience. Early on, I used Van's method of clamping the "fingers" on the ends of the leg fairings, and they just kept on breaking.

When they'd break in flight (usually during an aileron roll...which puts predictable stress on the fairings), it would send the ball out 1 to 1.5 ball widths. I could not only feel the difference, but I could actually HEAR the difference, and power required at every speed was higher.

Granted, this is an exaggerated effect relative to just a slight misalignment, but the principle is the same.

Maybe the uncoordination effect is reduced on "A" models, with the gear legs closer to the CG? I know on my taildragger the misalignment had a huge effect.

Maybe some people think fairing alignment is overblown. It comes down to attitude, if you ask me. Make it fly straight if you can, right?!?!

)_( Dan
RV-7 N714D
http://www.rvproject.com

[f1rocket]

Originally Posted by dan

Maybe some people think fairing alignment is overblown. It comes down to attitude, if you ask me. Make it fly straight if you can, right?!?!

Well, sure....do it right. However, I don't think it's worth obsessing over. I can understand you breaking attachments if the fairings are misaligned. Maybe your fairings were fluttering ever so slightly after they broke and that's the noise? I know we've had some problems with flutter with the fairing eventually departing the gear leg.

I can't dispute your experience. It just seems that a flexible fairing that is asymetrical would have a tough time pushing the airplane a ball out of straight. Look at how much rudder pressure it takes to do that with a big rudder connected to an 8 foot long lever? I guess it's possible, I'm not an engineer.

My only point is that get it straight if you can, but if it turns out to be 10 degrees off either side of straight, don't sweat it. Bolt it up and go fly.

[Dayton Murdock]

Hi Mark
I did mine on the bench in the comfort of my shop and they turned out great!
1. Level your bench top in both directions, Bolt your engine mount gear leg assy. to the top of your bench with the gear legs in a down attitude.
2. Prepare gear legs and stiffeners per Van?s builder manual
3. Hang a plumb bob over the edge of the gear leg at the upper and lower ends of the stiffener location. I used a drop of super glue to keep them in location. Measure the diameter of the gear leg at the plumb bob line location, (Half of the diameter is the center line of the gear leg at that location.) Attach the stiffener to the rear of gear leg with Bondo between the plumb bob lines. Measure from the plumb bob lines to the center line of the stiffener to locate it vertical. This distance is half of the diameter.
4. Wrap with fiberglass per builder manual
5. Install tires, brakes, brackets, brake lines per builder manual
6. Tape the 1? spacer on the tire. Locate the rear fairing from the bottom up over the inner and the outer brackets. Center it over the tire and clamp it to the brackets. With a long level check the distance from the bottom of tire (the vertical line) to the most aft lower corner of the fairing. My dimension was 8 5/8? from the vertical. When you are satisfied with the location of the fairing drill and cleco to the outer bracket only. Check the dimension from the top of the fairing to the most aft upper corner the fairing. Write this number down you will need it later.
7. Remove wheel and tire assy. Pre drill the inner fairing bracket with a #30 drill for the mounting screws
8. Install wheel nut and outer bracket. Install cotter pin at the correct location for the nut, cleco the fairing on the outer bracket. Clamp the fairing to the inner bracket Check location from the top of the fairing to the most aft upper corner the fairing. Drape a line with a plumb bob on each end over the upper edge of the fairing at about the center line of the axle. Measure the distance from the plumb bob lines to the aft tip of the fairing. Adjust by loosening the clamps on the inner brackets. Adjust distance to be equal. This will align the center line the fairings vertical, or perpendicular to the firewall datum. Drill and cleco to the inner bracket with a angle drill from the inside of the fairing.
9. Install the forward fairing per the builder manual.

[mark manda]

I think i've stressed to him enough that he'll do it Van's way; since I might not be able to be around.
my partner that is.

thanks again for input

[gmcjetpilot]

After you do all the eye balling, string lines and plumb bobs take it flying. Using wind tunnel methods you can determine if it is aerodynamicly straight. If you want to know what wind tunnel methods I am talking about let me know (color die, tufts). G

[RV7ator]

I relied on Fairings-etc.'s upper intersection fairings to align the gear leg fairings. That isn't accurate enough. Besides, they won't prevent a twist along the trailing edge on the way down to the wheel pant. Net result for me was a 3/4 ball displacement from unfaired legs. Current project will establish the gear fairings in trail, the intersection fairings will conform to them, not the other way around.

On my -7, there was enough slop in the preformed upper intersection fairings to twist the trailing edge through 3/16" on either leg fairing. This amount of twist, and twist it is because the TE is immoveable at the pant, can cause 3/4 ball displacement. I got lucky tuning out the initial misalignment. I'd say gear leg fairing alignment is rather critical.

I agree with Dan, forget the tab clamping folderol. The clamps are only a friction restraint - never a good idea on an airplane - and the tabs will break.

John Siebold

[szicree]

I know the effect would be small, but it seems that clamping the engine mount/gear legs to a table would allow the legs to sag slightly and throw things out of whack.

Steve Zicree