• The Biplane Forum is a large global active community of biplane builders, owners and pilots. From Pitts to Skybolts, to older barnstormers, all types are welcome. In addition to our active community, our content boasts exhaustive technical information which is often sought after for projects and maintenance. This information has accumulated over the 12+ years the forum has been in existence.

    The Biplane Forum is a private community. Subscriptions are only $49.99/year or $6.99/month to gain access to this great community and unmatched source of information not found anywhere else on the web. We are also a great resource for non biplane users, since many GA aircraft are built the same way (fabric and tube construction).

Beejs Blog Latest

Beej

Creator of this place
Staff member
Administrator
Moderator
Joined
Jan 1, 2006
Messages
6,496
Reaction score
1,438
Location
Austin, TX






<TD vAlign=top>Trim tab in the wrong hole...


Having finish painted the rudder pedals, I decided next to tackle a relatively 'biggie', the empennage and controls. Of course, I am cheating a little since I am utilizing mucho parto's from this salvaged plane I have. Although the amount of 'fixing' things and head scratchingsometimes makes me wonder if building new would be sometimes easier :0|


The rudder cable turnbuckles were removed, polished, lacquered and refitted. The rudder cables were thenfitted, rudder and pedalslocked at neutral, and the turnbuckles tensioned accordingly. At this point I discovered some binding with the cables on a tube as they exit to the rudder horn, so I have to add another pair of fairleads. Amazingly, there were no stops on this old fuselage, except for the elevator stops at the reverser. I have added stops in the torque tube, and stops at the rudder.


Fitting the stabilizer was interesting, since the wires had not been labelled upon removal by the previous owner. I eventually worked out through trial and error where which wire went where, some fitted where they shouldn't, so the key was to find a fit that had optimum adjustment left on the threads, since the manufacturing process of these uniquestreamlined wires means no two wires are of the exactsame length or thread length. Fun :0|


Once the horizontal stab' was set and bolted down. I did notice a few things I didn't like:


1.Lookingdown the stab spar, throughthe tail tothe other stab...I have a taper, like a slight 'sweepback' of the stabs. Although slight, this really annoyed me. I initially thought about upsizing the two front stab connector bolts from 3/16 to 1/4 so I could then move the stabs in at the front, this would bring the stab spar line straight, then I thought I may as well make a new small stab connector tube with the two bushings so i have blank tube endsto drill new holes through. Trouble is, whenI dry-set the required position (linear spar line)with clamps, the travel of the stab was binding at the horn. So, having called in my IA/A&amp;P buddy along with luckily finding an FAA designated inspector who was signing off a plane a few doors away, they advised me that although it obviously doesn't look right if you 'reaalllyyy look' down the spar line, it will not be noticeable whatsoeveronce covered, and since there is no binding when in the existing position, it isn't an issue.


2. The port elevator is lower than the starboard side :0|. This I will fix. Running a line across, the difference is 1/2". Luckily, when the starboard stab isclamped at neutral, the whole of the port elevator is off. This means there's no funky twist anywhere to fix, I just need to either weld a patch plate on the port elevator horn, or make a new horn, set the port elevator to neutral,then match drill through from the starboard horn.


3. The original elevator travel to the stops at the reverser is 29 deg up and 24.8 down, they should be 25 up and down. Down is ok, but I am going to cut off the stop tube at the reverserand weld on another to achieve the 25 degrees.


4. With the elevator at neutral, the rear control stick in the cockpit is not vertical, so I will be changing out one of the control connectortubes for a new oneand adjusting its length to suit.


5. When the rear cockpit stick was vertical, the one in the front cockpit wasn't :0\ it was off 4 degrees, to fix this, I would have had to make a new connector rod going through the torque tube, the easy way out was to simply heat bend the front stick slightly, it looks OK now.
6. The stab angle of incidence was achieved by washers..all 14 of them on each bolt. I will be makinga bushing instead.


I know this sounds like a bunch of crappy work on the original plane, but there are some good signs in the old build, the welding for example, is beautiful. I am scratching my head as to how one can achieve such aneat stack o dimes look, when for example welding something thin to something much thicker..boggles the mind. There are also signs of crappypost work by someone else: In the trim tab pic below, the steel web thing spanning the tubes is definitely a retro fit sometime later. I will be cutting it off.


I found a vernier trim tab mechanism in a box that came with the project, I found only one hole the thing could fit in in the cockpit [see pic above], and came to the conclusion after 3 million hours of playing with itthat it was never on the original plane. There was amysterious T-tube on the vernier deal which didn't seem to have a purpose, so I went browsing through some old Skybolt newsletters looking for ideas for trim, and there it was, a diagram of the samevernier trim tab deal by Mac McKensie! The T-tube was meant to be welded to the side of the seat. Mystery solved.


I also have to modify the elevatorsfor thetrim tabs. Whatever hinge mechanism that was there is no longer there, and the hinge gap is way too big.


I was going to mention my attempts at welding, but I thinkthat deserves another post of its ownlater... :-\





Making sense of the empennage...

trim tab hinge gap...
 

Latest posts

Top