SonexBuilders.net

All -

So its time to finally put my project on her gear, but I ran into a problem today that has befuddled/concerned me for 4 hours and counting. I'm firing off an email to Sonex Tech Support but would also love to hear what all of you have to say about this!

I successfully got the engine-mount aligned and drilled to the fuselage last week. To get the mount pins to line up per spec, I flipped the fuselage upside-down, measured and marked everything, and then drilled it to the attachment plates/angles. Once that was done, I wound up with the lower-left engine mount attachment being about .041" higher (relative to the lower longeron corner) than the lower-right engine mount attachment. This seemed like a pretty minor difference, and the pins lined up properly so I thought that all was going to be fine. I proceeded to drill the upper main landing-gear attachments (ah, what a fun job that is), and got them in nicely. The gear legs started out the same length and both sit just flush with the upper end of the tubes that they mount in - so I figured they were almost exactly the same distance below the fuselage and everything was still A-OK.

Today I stuck the lower axles & sockets onto the gear legs, slipped the alignment collars over the axles, and taped up some spacers and an alignment bar (i.e. a sturdy wooden stick with angle-aluminum reinforcing it) across both axles. BTW I've read about the wooden U-channel alignment method, but I figured that it would be easier to use the factory method since the fuselage was upside down already. In any case, I got things set up and it looked good - until I started taking detailed measurements... I found that the right side axle was about 3/4" lower than the left axle, when measuring the distance from the center-point of the axle to the lower longeron! And even at its minimum height (i.e. with the legs bottomed out in the sockets), the right side gear is at least 17.25" below the lower longeron (about 1/2" longer than the plans call for) :shock: I also found that there was a 1/2" difference between the axles in the fore/aft dimension! I triple-checked to make sure the whole setup wasn't skewed off to one side (i.e. not tracking down the centerline of the fuselage); but I couldn't find any evidence of this. After monkeying with a few different setups, I confirmed all of these measurements in multiple ways. I then went back and experimented with pulling the left side axle socket out from the end of the gear leg (to lengthen the overall leg). I eventually moved the left axle/socket 7/8" down the gear leg, which resulted in all of the left & right side measurements agreeing except for the fact that the left axle is now 3/4" further away from centerline than the right axle...

So I have multiple concerns here:

1. I'm trying to figure out how the geometry got so goofy in the first place. Is it possible my (factory-supplied) engine mount warped while being welded together, and my gear leg tubes are not at the same relative angle?
2. Leaving 7/8" of empty/unsupported space in the left axle socket seems like a really big gap. Should I fill it with something? Or cut down the right gear leg 7/8" instead? Or at least cut down a bit of the right gear leg so that the space in the left socket won't be so big? (Of course, I'm not sure if my bandsaw will cut titanium, and I'm also worried about ruining the leg)
3. Will the fact that the "centerpoint" between the two gear legs is 0.75" off the centerline of the aircraft cause noticeable problems? Obviously the spacing means the left gear leg will take more weight during ground ops (compounded by the fact that I'll be sitting on the left side flying it solo a fair bit), but are there any other foreseeable problems with this setup (despite having the wheels aligned to the centerline of the aircraft)?

Photos showing my setup: https://www.flickr.com/photos/noel_wade/albums/72157679752596096

Has anyone else had this much of a mismatch in gear leg length/alignment when they initially bottomed out their gear legs in the lower sockets? Any thoughts or suggestions of things I've been overlooking?

Thanks a bunch,

--Noel
Sonex #1339

How about drawing a centre line on the firewall and tape a stright edge to it so you can measure either side to the axles??. I wouldn't leave a 7/8" gap in one of the axles, i would rather cut one of the legs.
For what its worth when I put my gear legs in, I knew they were both the same length, so I just marked where they had to go and drilled the holes, then put the wheels on. It is entirely possible that if I had put the fuse upside down and checked as you have I could have found the same problem as you. Putting a spirit level across the longeron was always good in the garage so I guess I never checked any further.

Corby202 wrote:How about drawing a centre line on the firewall and tape a stright edge to it so you can measure either side to the axles??

Hi Phil,

Thanks for the info. As for drawing a centerline, I've already done that with the edge of some blue tape. You can see it on the bottom of the fuselage in this photo, here, along with the squares & straightedges I was using to take measurements with:
https://www.flickr.com/photos/noel_wade ... 752596096/

Would love to hear from others if they have thoughts or ideas!

--Noel
Sonex #1339

Noel,
If it was me, I would trim the long leg and live with the .75" difference side to side. Although would that not change as the leg got shorter? You could put a shim behind one wheel to eke them closer in measurement.

Good luck!

Picasso must have designed our motor mounts. My mount is apparently a test to see just how a-symmetrical you can build one, and still have it work (maybe).

The gear legs come out of our mount about 5 degrees different from each other. The center of the mount (at least, what one would expect to be the center) is offset by about 1/4in to the left. Measuring corner to corner at the motor attaching pins gives a disparity of 3/16in.....................................................sorry....a B25 just flew over. The upper left pin is 1/4in lower that the right. The two bottom pins are, amazingly, even and equidistant.

The statement uttered at the workshop we attended rings true: "We aren't building watches"

We're thinking about changing the name of our airplane to "Horse Shoes and Hand Grenades".

Have you considered putting a 4" tire on one side, and a 5" on the other?

Tongue planted firmly in cheek here at Area 51%.

Area 51% wrote:Picasso must have designed our motor mounts. My mount is apparently a test to see just how a-symmetrical you can build one, and still have it work (maybe)

Thanks for the laughs, sympathy, and notes! I think you're on to something... Especially since you noted the pin misalignment on your engine mount and I'd found mine were every so slightly off-square as well.

So I ran out to my workshop without turning on the heat (brr!) and make some quick (due to lack of heat) protractor measurements. It seems that the left gear leg is 3-4 degrees more "upright" (in the longitudinal direction, relative to the lower longerons), and 1 degree more upright (in the lateral direction, relative to the lower firewall crosstie).

I'll re-measure them again after the shop warms up, and see what Sonex Support has to say, but I'm definitely leaning towards cutting down the right gear leg (hopefully my bandsaw can hack it) and I'll live with the centerpoint of the gear being 0.75" off of the centerline of the aircraft.

I'm not looking to build a watch, but I still want to be able to use my tires for more than 1 season... ;-)

--Noel
Sonex #1339

My mount is also off with the left gear being at a more vertical angle than the right side. I left mine and haven't had any kind of handling issues with it on the ground.

I do however notice the wear pattern is more in the middle of the right tire than the left and will likely need to change the right before the left. That being said I will still get well over 100 hrs on that tire, which isn't terrible seeing as they are cheap tires.

NWade wrote:I'll re-measure them again after the shop warms up, and see what Sonex Support has to say, but I'm definitely leaning towards cutting down the right gear leg (hopefully my bandsaw can hack it) and I'll live with the centerpoint of the gear being 0.75" off of the centerline of the aircraft.

An alternative to cutting a gear leg might be to reposition that gear leg in the motor mount to compensate and drill a new bolt hole.

Also, I'd expect the ~5 degree misalignment to be visible on the engine mount. Is one of the sockets obviously less parallel with the firewall than the other?

No way am I going to measure mine any further. Nothing good can come of that.

Don't feel too bad. I had mine drilled and sitting on the gear for a year during the build before I realized I had the toe in and toe out angles reversed. I found the 2x4 method to actually work alot better than the way the plans call out how to set the angle.

Keith
#554