Post war trim retrofit.

[jCandlish]

I'm doing a preliminary investigation (parts search!) for retrofitting the trim in my pre-war t-craft.

parts B12-a405, B12-a406, B12-a407 seem simple enough. I'd rather just buy a repairable B12-a402 elevator assembly.

I'd need that and the trim crank stuff up front.

Anybody here done this? The control attachment at the elevators is different. Do I also change the control horns on the right side elevator?

Any suppliers have ready to go parts for this? Anybody know if these parts are available from the Swick-kit guys?

Thanks.

[VictorBravo]

Re: Post war trim retrofit.

You will need to replace the elevator in order to have the cutout and hinge for the trim tab. To replace the elevator, you will need a stabilizer that has the correct number of matching hinge points, which means you will be replacing both the stabilizer and elevator on one side at an absolute minimum. If for some reason your "new" elevator does not line up correctly with the control cable attachment on the other side "old" elevator, you're in for replacing all four pieces. Not exactly a weekend project.

On the other hand, you could just make the external trim tabs work properly and more powerfully. In addition to solving (what I am assuming is the reason for the inquiry) the trim authority problem, you also benefit by keeping an entirely separate emergency pitch control system on the aircraft. If a post-war elevator jams or seizes (rare, admittedly), you would have the trim tabs to fly with and be able to make a less damaging arrival.

A potentially easier solution is to enlarge the existing trim tabs to the point where they actually work. This of course depends on how effective yours are, which problem you're trying to solve (high speed or low speed), and at what speed they "stop working".

[Ragwing nut]

Re: Post war trim retrofit.

Not as simple as it sounds. You canbolt on 2 hinges elevators and stabs, but the tail brace wire attach point is in a different location, uses a different length wire, and can't mix 2 hinge and 3 hinge. What you need to find is a Deluxe elevator and tab. it will bolt on without changing any of the other tailfeathers or wire, and then you would only need the overhead trim. What i don't know how you would deal with is the cable guides unless your airplane is apart for recover and then changing the trim system over would not be a big deal.

[jCandlish]

Re: Post war trim retrofit.

Hi Guys

Its within my capabilty to modify my existing elevator. My question goes more to the finicky little bits.

How is the jack screw in the elevator bushed? I haven't seen that detail. What is the clearance between the elevator control horns to allow for the jack screw pully? I don't know that detail either.

In a rational world I would add a hinge to current trailing edge of my pre-war elevator and actuate a servo-tab with a boden cable. (Like a Bücker). That would be easy.

But I'd like a simple 337 that reads: "installed model b12 type trim".

[jCandlish]

Re: Post war trim retrofit.

I need to read Ragwing's posts more carefully.

I need to find a Delux elevator and trimtab! Or a reasonable facsimile thereof.

But are the control horns the same? On my pre-war airplane there is no room between the control horns for the servo-tab jack-screw pulley.

[Ragwing nut]

Re: Post war trim retrofit.

Distance between the horns is unchanged between prewar and post war. Jack screw sets behind horn and the pulley is the only thing between. Something I have thought about but have never tried is adapting a L-2 trim system. You would have to modify the elevator of course, bolt on exterior pulley sets, and depending on routing, and still use the cables but may require a new handle to allow more tab travel.

[jCandlish]

Re: Post war trim retrofit.

What happened to the L-2 blueprints that used to be at this site?

[jCandlish]

Re: Post war trim retrofit.

Distance between the horns is unchanged between prewar and post war. Jack screw sets behind horn and the pulley is the only thing between. Something I have thought about but have never tried is adapting a L-2 trim system. You would have to modify the elevator of course, bolt on exterior pulley sets, and depending on routing, and still use the cables but may require a new handle to allow more tab travel.

This isn't true for my airplane. There is no room for the jackscrew. I'm not familiar with the L2 system. Could someone post a drawing.

Otherwise, electric trim seems like the simplest retrofit. (heresy I'm sure!)

[Ragwing nut]

Re: Post war trim retrofit.

It still fits nothing dimensionally is different. When you change the left elevator for one with a tab, you would also need to change the right elevator for one with a hole to clear the jack screw.

The L-2 elevator uses a cable operated tab on a slide with external mounted pulleys on the stab and elevator, soory, no pic easily accessible