Where to measure plumb

[pnh2atl]

I’ve leveled the fuselage at the wheels. When I put the level on the vertical stabilizer it is .9 degrees off. I’d like to check the angle of incidence and make sure the horizontal stabilizer is level and perpendicular to the vertical stabilizer. I’m sure I could pull the vertical stab plumb with the flying wires. Thoughts? Thanks

[triumphantduke]

when you say you leveled the fuselage at the wheels, are you saying you leveled both front-to-back and left-to-right? sanity check, since the way you have the level on the vert stab would mean you'd need to have 'zeroed' the fuselage at a control point.

normal disclaimer: I am not Mr. Barrows, or a 1+ completed Bearhawk builder.

[pnh2atl]

I used shims under a main gear tire to get it wings level essentially. I used the tube that runs between the forward main gear attach points to measure level. My theory is that the vertical would be plum if the horizontal was level.

[triumphantduke]

ah okay, I'm getting about 89.3 - 89.5, seems to drift further towards the top. but that is with flying wires and it sems very sensitive to the position of the tail wheel. for my build it seems close enough to worry about it later during final assembly if it warrants any worrying at al (based on the sensitivity to the tailwheel position, which would differ in-flight)

[alaskabearhawk]

I’m not sure if this is an apples to apples comparison to the 4-place. Look at your plans. There is a datum line for the fuselage and on the 4-place it’s the lower longeron between Sta B and Sta C. This point is the only reference line you should be using for anything on the fuselage. The plans will also tell you if the tail post is at a 90 degree angle to the datum line. The concern I have is that you are looking for a horizontal stab with zero incidence. On the 4-place there is a negative incidence. So I would check the 5-place plans for that value.

As far as the tail post goes, I would just make sure that it is straight. Welding can change some dimensions. If it’s straight, I wouldn’t worry about it. Also, space permitting, try to broaden the base longitudinally of your digital level with a larger level (i.e. straightedge) underneath. The wider the base, the more representative the values given by your square level will be.

[pnh2atl]

The 5 also has a datum line. I’ve got the pitch level using that. The -2 degree incidence for the 5. The wider base is a great idea. I’ll press on and try to get everything as close as possible. I just don’t have a baseline for what’s acceptable. This is my first whack at building a kit.

[rodsmith]

I wouldn't worry about the .9 deg tilt to the vertical stabilizer. Could be the error is in the way the tube between the landing gear was welded in. People obsess about getting everything within .1 deg and 1/16th" to fly right. Doesn't need to be that perfect to fly right. Couldn't measure to tenths of a degree before digital levels. I don't think Bob ever specified a specific tube to use for measuring lateral axis level. I knew a guy that was scratch building a kit fox. I visited his project and he proudly told me his fuselage was correct to 1/32". He had used a MIG welder to weld it up and the welds were a disaster. I just left without saying anything.

[jaredyates]

My favorite levelling reference for important things is a water level on the wing attach bolts. For less important things, a 4' level across the front door sills gets it pretty close.