Leveling the Cadet

[Bill Poynter]

Has anyone ever seen a Cadet that still had the mark on the bottom of the fuselage for leveling?  I'm wondering about the best way to locate that spot and place a new mark there.  I guess the factory could have leveled the plane by other means and then found the location for the mark with a plumb-bob.  I think that the PQ's used the forward face of the spar for leveling.   

[Paul Rule]

I have looked a lot but have not seen "THE MARK"!

A few of us have come up with alternate methods of leveling (usually easier).  Next person that has a reason to level your airplane try all 3 and report back!

1)  The door sill should be 2 degrees nose down when the airplane is level.  2 Degrees is equal to a 5/8" block at the end of an 18" straight edge.  Masking-tape a small block of wood 5/8" thick 18" from the end of your level.  Set the level on the door sill (block FWD) and that should read level.

2)  Place a block of wood on the top of the spar inside the cabin to raise the level above the steel tubing and that should be level too.

3) (Added 2/2)   On a review of the LAR-90 TC sheet, it states that the LAR-90 is basicly the same as the PQ-8 which we know to be basicly the same as the LCA / LFA except for the gear.  The Leveling means for the LAR-90 is to remove the wing-fuselage fairing and place a level (vertically) aginst the front face of the spar.  This is effectively the same as #2 above.

[Brett Lovett]

I'd like to know exactly where this mark is supposed to be.  Left or right longeron and where on the longeron?   It looks like no easy task to hang a plumb line from the upper rear engine mount attaching bolt with the fuel tank in place.

[Bill Poynter]

I've always thought that the plumb-line was supposed to be hung from the bolt head on the outside of the fuselage.  That would make it possible to align it with a mark on the bottom of the lower longeron.  That would only require removal of the aluminum panel on the bottom of the fuselage to reveal the mark.  If you look at the type certificate data sheet for the PQ-8/Lark 95, you'll see that the PQ-8 uses the plumb line method and the Lark 95 uses a level placed on the forward face of the main spar.  I believe this difference may be due to the fairing covering the bolt heads on the Lark 95.  If anyone has a Cadet with the mark still visible, it would be great to get a photo of it.

[Brett Lovett]

Bill,

That brings up a good question.  What really is the "lower longeron" that is being referred to?  My assumption has been that the upper engine attaches to the upper longeron, and the lower engine mount attaches to the lower longeron.  However I see in Burke Bell's fuselage drawing that he has the longeron that attaches to the lower engine mount bracket as "cabin longeron".  He labels the longeron that extends from just aft of the main wing spar to the tail of the aircraft along the bottom edge as the "lower longeron", but it does not appear to extend forward of the main spar and therefore not in a location where a mark on it could be plumb with any of the upper engine mount attach bolts with the aircraft leveled.

[Bill Poynter]

Brett,

It looks like you are right about the longeron to which the lower engine mount attaches to being referred to as the lower longeron.  Evidently the factory painted marks on the outside of the fuselage, aft of the lower engine mount bolts.  Here's a link to a scanned page from the PQ-8 Erection and Maintenance Handbook.  I've highlighted the line that refers to the marks.   I doubt that the accuracy of the bolt placement is good enough to say that placing a mark a certain distance aft of the rear lower bolt would work across the fleet of Cadets.  I suspect that the factory leveled the plane, hung the plumb line and placed the mark on each aircraft individually.

http://www.culvercadet.com/Documents/PQ-8%20leveling%20instructions.pdf   

[Brett Lovett]

I doubt that the accuracy of the bolt placement is good enough to say that placing a mark a certain distance aft of the rear lower bolt would work across the fleet of Cadets.

Bill,

That reminded me that for the Jamieson J-1 (Culver LARB or Army PQ-8A), type certificate 2-584 states "Plumb bob line from upper rear engine mount attaching bolt to reference mark 5-11/16 in. aft of lower rear engine mount attaching bolt." for the leveling means.

Considering that all the Culver L models share the same fuselage would the 5-11/16 in. dimension be appropriate for all of them?  It still doesn't tell which side of the fuselage the reference mark was on (both perhaps?)  I'd like to see how the Culver factory made the reference mark(s).

[Paul Rule]

Brett & Bill,

Post corrected 4/2012... after more thimking!

As a check to your posts above; (and brushing off my trig functions calculator) I looked at Bill's LCA engine mount drawing to see that the firewall is dimensioned to have a 20 degree slant.   Also, the vertical distance between the firewall mount bolts is 15.00".  That would be from center of upper longeron  to center of lower , since the steel brackets inside are the same (2 LH and 2 RH).  The 15.00" vertical and the 15.963" hypotenuse give a base of 5.460" or 5 15/32".

The difference between 11/16" (Bret's post above) and 15/32" is 0.119" or about 1" vertical error at the elevator. 

A 1 inch change at the elevator is about 0.38 degrees..... basicly very good !!

Attached is a drawing that should provide a clear picture.