Trim Adjustment Screw - B12-406

[Hank Jarrett]

Re: Trim Adjustment Screw - B12-406

Yea, it is going to be a problem, but depending on where you live and how long between recovers it may not be worth worrying about. You have already seen what happens with regular steel screws. They are way less noble than aluminum and because of their alloy are even less noble than structural steel (said plainly, they RUST, usually locking in place). Back when we covered planes with Cotton, the plane would require recover before the screws got so bad they couldn't be removed. With the synthetics we use now covering lasts DECADES and the screws rust in place. One good solution is to put the screws in wet with primer to reduce the corrosion. The problem will be less for the next generation because we have a LOT more respect for our planes than the last 50 years. Most of us take better care of them than the typical "ramp rat" Taylorcraft of the past. The stainless will cause the metal you are screwing into to rust instead of the screw, but the screw heads may sheer off if they are "stuck". At least with a SS screw the drill bit will tend to follow the softer screw instead of the base metal. In 20 years just get some left hand drill bits to remove the stuck screws.

Hank

Or do what I did and rib stitch. ;-)

So hank what do you think about this; I am recovering the Champ and they use #4 PK screws 1/4" long to attach the fabric to the aluminum ribs in the wing and also for the attachment to the steel ribs in the tail feathers instead of wire or rib stitching, the original steel screws were badly corroded and hard to remove when I uncovered it so I am planning on using stainless screws for the recover, no high torque and they are "sealed" in with glue and the fabric fill and enamel top coat.

Is it going to be a problem?

Dave

[Guest]

Re: Trim Adjustment Screw - B12-406

Thanks Hank,

You got me thinking. Perhaps making the screw the anode is the best course of action.

They were a pain to get out but maybe less so than repairing or re-drilling ribs if the screw holes get damaged.

That makes cad plated steel screws attractive.

I am seriously thinking of using cad plated on the wings instead of stainless. The tail is already done and with stainless.

Thanks, Dave.

[Hank Jarrett]

Re: Trim Adjustment Screw - B12-406

The SS in the tail "should" cause the corrosion to happen on the steel tail tubes, not the screws. The screw will still get locked in by the Iron Oxide, but a LH drill should follow the softer SS screw and either back the stump out or drill it out.

Hank

[anotherstevest]

Re: Trim Adjustment Screw - B12-406

Tim said: "Steve, actually there is a lube point in the elevator". At least on my elevator the lube hole only enables lubing of the surface between the brass and the fixed bushing (used as a bearing) but does not enable any lubing of the leadscrew part of the mechanism. That part has to live with whatever was on it at assembly time until it's disassembled.

Steve.

[Ragwing nut]

Re: Trim Adjustment Screw - B12-406

I think I recall that the "B" tail is the same as the L2.

If that is correct then some of the folks here that have the L2 drawing CD should have an actual factory drawing of that part.

So who has that CD that is willing to look? Steve I suspect that you are more likely to find a CD owner willing to look for a drawing than a jack screw owner that is willing to give to you to destroy.

Dave

The DC-65 uses BC12d elevator with jack screw, the L2 uses a slide mechanism with 2 cables

[Ragwing nut]

Re: Trim Adjustment Screw - B12-406

I think Tim is right. Brass has lower friction and galling and in very corrosion resistant. The strength is lower but the gear teeth have a HUGE profile to take the loads. I doubt the strength difference between brass types will mater much.

Hank

Its probably made from oil lite bronze, not brass.

[astjp2]

Re: Trim Adjustment Screw - B12-406

No, bronze is sintered which gives bronze its texture, and its not sintered,. Tim

[Hank Jarrett]

Re: Trim Adjustment Screw - B12-406

Brass is actually a specific kind of Bronze. Almost any copper alloy can be called "Bronze", including brass. When Bronze was invented Metallurgy was not a science yet.

Hank

[Guest]

Re: Trim Adjustment Screw - B12-406

Yea, it is going to be a problem, but depending on where you live and how long between recovers it may not be worth worrying about. You have already seen what happens with regular steel screws. They are way less noble than aluminum and because of their alloy are even less noble than structural steel (said plainly, they RUST, usually locking in place). Back when we covered planes with Cotton, the plane would require recover before the screws got so bad they couldn't be removed. With the synthetics we use now covering lasts DECADES and the screws rust in place. One good solution is to put the screws in wet with primer to reduce the corrosion. The problem will be less for the next generation because we have a LOT more respect for our planes than the last 50 years. Most of us take better care of them than the typical "ramp rat" Taylorcraft of the past. The stainless will cause the metal you are screwing into to rust instead of the screw, but the screw heads may sheer off if they are "stuck". At least with a SS screw the drill bit will tend to follow the softer screw instead of the base metal. In 20 years just get some left hand drill bits to remove the stuck screws.

Hank

Or do what I did and rib stitch. ;-)

Hank,

FYI. I checked with a couple Aeronca gurus, they say they have been using SS screws for a long time for fabric hold down and not seeing any issues. So its not a problem worth worrying about as you mentioned.

Thanks, Dave.