Checking for a level fuselage

LettersFromFlyoverCountry · #1 06-13-2010, 03:16 PM

When you're mating wings, and you want to check that the fuselage is level fore and aft, where'sthe best place to do that, at least on an airplane where the top skins are already on.

I used to set a level on the longeron after of F-705, but that's inaccessible now. what about the floor beneath the seats?

For side to side level, I use the center spar, because putting it across the longerons could be inaccurate because one could actually be slightly higher than the other.

Mel · #2 06-13-2010, 04:04 PM

The cockpit side rails are the "leveling" point for the 2 seat RVs.

And you are correct in using the main spar carry-thru for side-to-side level.

LettersFromFlyoverCountry · #3 06-13-2010, 04:27 PM

It's interesting how this is a bit more difficult with the gear on and engine hung. On sawhorses, you get some more options for keeping it all level.

My fore-aft measured on the rails differs by .3 degrees.

Of course, all of this is made possible by the great edge distance mistake. Because I have one hole in the rear fork already drilled, it's going to be really close this time, too.

Such fun.

BillSchlatterer · #4 06-13-2010, 05:17 PM

Does fore and aft level really matter when mating the wings if the relative difference between the fuse and the wings is the same.

Meaning that if you lay a couple of pieces of angle accross the cockpit and then put a digital level on it,... and it indicates .6 degrees (example) and you set the wings to .6 degrees as well, you have 0 difference which is what the plans really call for with the 3 inch block and level set up?

Leveling the fuse and then going for 0 degrees on the wings with the block seems to be essentially the same thing?

Just curious since that eliminates having to put the plane on blocks to get the fuse level for mating the wings? If you mate the wings before gear and engine, getting the fuse to 0 is easy but if you mate later after it's on the gear, it is more of an issue. Just seems that it matters not as long as the final difference between the longerons and wing/block/level is 0.

Bill S
7a almost there

Mel · #5 06-13-2010, 06:19 PM

Quote:

Originally Posted by Bob Collins

My fore-aft measured on the rails differs by .3 degrees.

Use the average.

Mel · #6 06-13-2010, 06:21 PM

Quote:

Originally Posted by BillSchlatterer

Does fore and aft level really matter when mating the wings if the relative difference between the fuse and the wings is the same.

Meaning that if you lay a couple of pieces of angle accross the cockpit and then put a digital level on it,... and it indicates .6 degrees (example) and you set the wings to .6 degrees as well, you have 0 difference which is what the plans really call for with the 3 inch block and level set up?

Leveling the fuse and then going for 0 degrees on the wings with the block seems to be essentially the same thing?

Just curious since that eliminates having to put the plane on blocks to get the fuse level for mating the wings? If you mate the wings before gear and engine, getting the fuse to 0 is easy but if you mate later after it's on the gear, it is more of an issue. Just seems that it matters not as long as the final difference between the longerons and wing/block/level is 0.
Bill S
7a almost there

It's just a reference.

LettersFromFlyoverCountry · #7 06-13-2010, 07:17 PM

Quote:

Originally Posted by BillSchlatterer

Leveling the fuse and then going for 0 degrees on the wings with the block seems to be essentially the same thing?

Unless I'm misunderstanding something, it's probably even simpler than you describe. Since the left wing was drilled for incidence back when it was on sawhorses, I figure I'll just take a reading on that wing, and make the right wing the same thing.

But now that I'm thinking of it, what would be the in-flight characterisitic of a set of wings that are off by, say, 1 degree?

Mel · #8 06-13-2010, 07:34 PM

Quote:

Originally Posted by Bob Collins

But now that I'm thinking of it, what would be the in-flight characterisitic of a set of wings that are off by, say, 1 degree?

It's much more important that both wings be the same.
If both wings are off by 1 degree, you will have slightly more drag as the wing will not properly match the horizontal stabilizer and thrust line.

Bruce · #9 06-14-2010, 07:27 PM

Bob ,

On my 7A I used 2x6's under the mains and let air out of
the nose wheel and the fore aft level was perfect.
Then the side to side put shims under the low side and
I measured on the spar for the side to side.
Pretty easy to level if you do it this way.

Also you can use NASCAR air pressure if you want
from side to side to level it out instead of the shims.

Isn't this experimental stuff great.

LettersFromFlyoverCountry · #10 06-14-2010, 08:38 PM

What is NASCAR air pressure?

I spent about 2 1/2 hours on this tonight before calling it an evening. Having locked in the left wing a few years ago, my options are a little limited, and I just can't get the fore-aft reading on the left side skirt to match the right. (Explanation here). So I just don't trust what the level is telling me on the right side.

Because of my already-drilled rear spar hole in the rear fork (it's all related to the edge distance screw up a few years ago), I drew on the rear spar where the area of it that is within the 5/8" of the edge and it's going to be really close again (I'm waiting for a 5/16" to 1/8" bushing from McMasterCarr before I do anything serious).

No forward sweep, triangulation is perfect, but I can't get the right wing closer than within .1 degree of the left .

I'm getting close enough to the end of this project that I'm ready to pay someone to finish it.