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Gear leg fairing alignment

bryanflood

Well Known Member
Hello all,

the string method of gear leg fairing alignment has always bothered me, as it does not seem that accurate, but that is how I installed my gear leg fairings (following instructions).

i wanted to check the alignment with a more accurate method to see if my gear leg fairings were really aligned to the airflow. So I made a laser alignment jig that slips over the fairings and self centers.

https://photos.app.goo.gl/EejMKNbEiLCmRgL66

Then i used a laser level to measure the gauge offset. The technique is to spend time measuring the beams distance from aircraft center line and height above the ground at two points to assure that the beam is aligned properly with the aircraft center line. You can then use the scales on the gauge to measure the angle of rotation in the 45 degree reference plain to the gear leg.

You will need to take the arctan of the off set of the gauge distance and the distance between the guage scales to get the angle. I.E. the scales on the gauge are aligned to the 45 degree beam line and show the offset distance between the front and rear of the gear leg and therefore the angle.

https://photos.app.goo.gl/cqNnzNoH5Ftvr3ie6


Anyway, it looks like the gear legs are within 1 degree of their intended rotation. If I had made this gauge during the build it definitely would have helped get the alignment more accurate. Probably not worth changing anything, but it's nice to know the alignment is close.

Bryan
 
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Good on Ya!

I didn't feel super confident with the strings running fore/aft. To make it worse I even thought I detected a little change in yaw with the pants/leg fairings on...but that could have just been the anticipation.

Without the math it looks like we could use your angle stock method of finding the centerline then level a long straight edge across each and compare to longitudinal axis.

If I were at that stage I would certainly try what you are showing.
 
Gauge method

wawrzynskivp.

Yeah agreed. After actually using the gauge I think there must be an easier way to set it up if I had to do it again. One thing that makes it so hard is that the gear legs taper in thickness and cord from fuse to wheel. A challenge to get everything lined up correctly without the gauge.

The angle of attack of the gear fairing is also on a 45 degree reference plane to the ground, I just couldn't figure out an easier way to do it in my mind. If I used a string or a ruler I kept getting confused as to what datum to compare the angle. I.E. is has angles in 2 planes, the ground plane and the center line plane. I am sure there is an easier way to measure but my brain couldn't figure it out.

Would love to see someone build on this idea as I am sure smarter people can figure out a clever and straightforward solution that makes measuring the gear fairing angles trivial.
 
Indexing gear leg fairings

Some of the available fiberglass upper gear leg intersection fairings are built to index the gear leg fairings. This saves a lot of hassle with strings and plumb bobs.

Steve
 
I'm at this point in the build, and really scratching my head to understand how the string / plumb bob method is supposed to work. One idea I have been thinking about is trying to figure out a way to position/angle a laser level, located exactly aft such that the laser line tracks up the center of the gear leg AND the center of the fairing trailing edge. Haven't sat down to figure out how to do this yet.

The string/stick method seems like how a cave man would do it. I know, I know, thousands and thousands of RVs are flying today that were built using sticks and rocks, but I really wish there was a better way that inspires more confidence.

I kind of "eyeballed" the nose gear wheel fairing, and the more I look at it, the more it seems crooked by ~2 degrees or so. Might end up re-doing. This part of the build is so squirrelly.
 
Seems like 1 degree is just fine in Vans world and it seems reasonable but I have another question. How close to the free stream line in cruise is the proposed alignment really? Has anybody accurately measured an RV in cruise flight before installing their fairings? Id be interested how close to the Vans recommended value the flight condition (Waterline relative to horizon in level flight at cruise (Beta?)) really is for any given model.

Mike (Repeat offender)
 
Rather than be perfectly aligned to the fuselage, I decided to use my leg fairings to correct for a little bit of rigging misalignment. I was happier with this subtle fix rather than install tabs on the rudder or wing.
 
Some of the available fiberglass upper gear leg intersection fairings are built to index the gear leg fairings. This saves a lot of hassle with strings and plumb bobs.

Steve

I’ve used Steve’s method before more than once, and I’m about to again on my new RV6. Works for me.
 
Rather than be perfectly aligned to the fuselage, I decided to use my leg fairings to correct for a little bit of rigging misalignment. I was happier with this subtle fix rather than install tabs on the rudder or wing.

Yep - this trick will work however consider the moment arms in play. The gear leg fairings will need to have more force to correct yaw as they are closer to the center of rotation. A small trim tab on the rudder would present less drag.

Rigging is an interactive process. Fly the plane with the wheel pants and leg fairings off, rig to get the ball in the middle and no heavy wing. After that put the pants and fairings back on and then rig them to get the same result.

This is simple rudder trim tab to fix small errors. It is a good choice for temporary experimentation with or as a permanent fix.

Carl
C72-C02-F3-1220-4003-BC45-28-D0-B6-B09-E61.jpg
 
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