Yikes!! - Seat Construction

[Jackal]

First of all a caution to those who have not yet built seats. I built my fuselage exactly to plans (to the best of my knowledge and ability) and although the plans call for pretty much identical front and aft seats, there are considerable differences in geometry in the front and aft seats, and neither of them match the geometry shown in the seating position in the top left quadrant of the page which shows the seats. The angle of recline needs to be considerably different in the front and aft to make it work out and mount in the fuselage. More than one angle will work, but it affects the mounting position (All of this will become clear when you are building/installing them). I used a 10 degree slope angle on the seat back (100 degrees in other words) on the forward seat and 16 degrees (106 degrees) on the aft seat. Also, I suggest keeping the front seat narrow to make room for the pilot's feet on the rudder pedals beside them (per plans) but don't yet see a problem with making the aft seat wider to make it more comfortable and look more substantial. Even the standard FAA Adult at 170 pounds will appreciate the extra width (I used 16 1/2")

In short, make some simple wooden mock ups of the seats before building them out of aluminum - and do it after you control sticks and cables are in to be sure you have clearance.

Now for my problems (An appeal to those who have built seats): I made the seats per plans (except for the geometry changes noted above) using the per plans material (I think it was 2024-T3 by .050 Alclad) The seats folded up beautifully and all the edges and angles came together like Bethoven's symphony - only problem was that after I had them all sheared and broke (or braked) I noticed that ALL of the bends had cracks on the back sides of the radius. Well, now that I had plenty of scrap aluminum to work with (about 105 dollars worth) I adjusted the brake (or break I think) with more "setback" to theoretically form a wider radius - and still had cracks in any case which I broke along the grain and significant cracking coming from the "relief holes" I had drilled (and chamferred - 1/4" holes) where the corners would be. I opened the break up to an "impractical" degree and still had unacceptable results as far as cracking is concerned.

I have access to a press break with a "bull nose" die (or maybe mandrel - I'm not sure what its called) that probably will not crack upon construction, but the "margin" of the material integrity can't be much and I'd expect cracks in a couple hundred hours of flight.

This is my 5th airplane project and I will admit that the weirdest sh..tuff always happens to me, but has anyone else experienced anything like this???

My options are (as I see it):

1 - Try the press brake and hope I don't ruin more aluminum or have to build new seats after 100 flight hours.

2- Use a thicker and softer alloy than called for in the plans.

3- Make "corner channels" (say 3/4" by 3/4" by 90 degrees) out of a heavier and softer (more bendable without cracks) alloy and rivet all the corners together instead of simply bending and use the called for material in the actual "panels" of the seats.

4- Live a cleaner/purer life and only then attempt again to commit aviation.........

Disregard #4 - I think I'm gonna go have a beer and think about carbon fiber seats.

-Jackal

[mmcgrew]

2024 - T3 aluminum is terrible to break form. You need to use a very large radius bend. Against the grain bends will crack most of the time. Best bet is to use 5003 series.

Michael
N838MM

[Jackal]

Michael,

Thanks for your input. On Wicks web site I found 5052 and 3003 series but not 5003. Is that something other than what Wicks lists? Also, I am assuming this is softer since it bends better. Should I increase the thickness from the .050 specified, do you have a recommendation on how much if so?

[mmcgrew]

5052 is fine. Anything in the 5000 (or even the 6000 series) will bend ok. I would not increase the thickness. .050 is ok for the seats.

Michael
N838MM

[Jackal]

OK, great. Thanks again for the info.

[Meadowlark]

As I am rebuilding my Hatz, one of the considerations was replacing the pilots seat. I went to the local speed shop (hotrod and dragsters) and found a fiberglass seat that was a few pounds lighter than the aluminum seat I have. It was as I remember around $80 and would fit perfectly. I didn't buy it as it only saved two pounds and would have required a lot of work to install. I stayed with the seat the Hatz came with.......... but that is an alternative for you.

J/C GTF