H9 33% Pawnee Tug Conversion

[MarnochS]

Hidden tow release,

I copied Rick Shelby's tow release using a Sailplane release mechanism. Not terribly more involved installation - upper assy is removable for servicing
I can confirm that it is strong enough to release a fully ballasted Antares from a "vertical" (descending) torque roll position.

All the pieces required


Upper tow release mechanism with servo installed


Lower attachment assy


A view of the assy from the underside of the fuselage

[Xroadie]

I got the Top Model release installed in the Pawnee, it took less than an hour to cut the pieces and epoxy them in. Now I just need to mount a servo and a pushrod. I got a little scared when Jim mention the "off center" hole in his release, as I had already installed mine (it is removable BTW). Luckily my holes line up, but I did notice that the pushrod supplied was 7/64" and the hole in the release is 1/8"....that seams like a lot of "slop" to me! I am also not sure what kind of metal the supplied pushrod from Top Model is? Has anyone used that rod or has everyone upgraded to a hard steel 1/8" rod? I am going to use a different rod for multiple reasons...... one is it is not long enough to reach where I plan to mount the release servo.

Here's a couple pics.

[JimD]

Pete,

The units that came with the Porters had a pushrod that was larger diameter than 4-40 pushrod and it matched the hole in the release. The most recent unit I got from Esprit had a smaller pushrod, as you describe, but the aluminum part had the same size hole as the Porter units. I kind of wondered about the sloppy fit, but used the unit in my most recent Decathlon with no issue. The unit that came with the Bidule has the heavier rod, but the hole diameter is smaller toward the top half. Seems like hole was drilled part way from the bottom with a larger diameter bit and then from the top with a smaller bit. Actually, a piece of 4-40 rod works perfect, but the included rod will not fit up through the upper hole.

[Stew]

A good source of 3/32 and 1/8" rod is welding rod. 3/32 will easily accept 2-56 threads and 1/8 will accept 4-40 threads. A long time ago, I bought a kit called Rod-Chuck I believe. It is simply a set of dies to hand thread the welding rod. Very simple. They start with a size bigger thread but of the same pitch, so for 2-56, you first thread the rods with a 3-56 die and then rethread with a 2-56, similarly for 4-40 threads on the 1/8 rod, you first run a 5-40 die and then a 4-40 die. There is to much material to be removed to go straight to the smaller dies. None the less, in the end you end up with very strong rods of a diameter we can easily drill holes for, and when you use the weld rod for control rods, they all end up the exact custom length for super clean installs. The down side is that most people don't want to take the time to cut and thread welding rod, but I have found no better solution to getting really strong control custom control rods.

Here is the link to RodChuck.

http://www.rodchuck.com/

[Xroadie]

I like that welding rod idea Stew! Maybe next time. I had a piece of 1/8" music wire that I cut to length. The original release's rod and clevis were threaded for 3mm, so I decided to reuse the clevis and locking nut that came with it. I had a 3mm stainless socket head cap screw that was left over from mounting the release to the bulkhead, so I used an 1/8" bit to drill out a pocket in the head of the cap screw, then silver soldered the cap screw on the end of the pushrod. It works great! Tow release done

Pete

[stevekremer]

What tail wheel do you all recommend. The old posts said that the stock tail wheel system is JUNK. So, what is a good one? Thanks.

Steve K

[lenb]

Hi Steve,
White Rose Engineering makes nice units. Not cheap, but very high quality. http://www.whiteroseeng.com/products/
For 1/2 that price you can get an Ohio Superstar http://www.ohio-superstar.com/

[stevekremer]

Finally getting busy on the Pawnee. I have the wings and struts basically finished. Got the release installed in the fuse and am planning reinforcement of the landing gear area. Reading all the posts without pictures is difficult. I am thinking that boxing in the two landing gear beams and beefing up the shock mount area will be sufficient. I read some post about adding a bulkhead, not sure where this was intended to go.
Attached are photos of release and gear mounts (indicated with the green tape) I plan to box in with ply and tri stock. Any other comments or pictures would be great. Especially pictures of canister area.

Thanks

Steve K

[stevekremer]

Got the Plywood cut and realized I cant box in the rear langing gear mount. That is where the wing bolt goes. I think I will put a ply piece on the bottom of the fuse as reinforcement.

Steve K

[lenb]

The release looks good!!!
You can add a little more support on the sidewall if you feel its needed, then use a little longer bolt.

[Xroadie]

Got the Plywood cut and realized I cant box in the rear langing gear mount. That is where the wing bolt goes. I think I will put a ply piece on the bottom of the fuse as reinforcement.

Steve K

Steve, I don't think adding ply to the bottom of the fuse will solve the issue. I added a "doubler", in front of and behind the "box" that the shocks mount in. Yes...you have to knock out the blind nuts front and back to do this....but you will want to upsize the bolts anyway which means going with larger blind nuts...so it's not an issue. I upgraded to a 10/32 bolt with a long shank....so the shocks aren't riding on threads. Having the long shank also means you'll have to drill the threads out of the front blind nuts, so that the new bolts will pass through and thread into the rear blind nuts. The front blind nuts essentially become a bearing. I will try to post a pic of what I did later. I did basically the same thing Len did.

Peter

[stevekremer]

Thanks Peter. I got the shock box supported as you did. I am trying to come up with a way to support the landing gear pivot bearing blocks I will get a picture when I get it glued in. Thanks.

Steve K

[lenb]

You probably dont want to see this,

But this is what happens when you roll into the little rut that runs along the bottom edge of the crossing runway in Cumberland back in 2012
The repair was excellent, although I would use thinner plywood next time. I did cut big lightning holes in the plate after it was installed and before it was covered to help reduce any weight I could. This plane is sensitive to extra weight. If you keep it light, it will AUTO LAND. ( no kidding )

[Steve P]

I was just cleaning up and deleting files on the computer and this one should live on here. Photo is the canister bay modification done by Len to my 33% Pawnee.

[stevekremer]

Thanks Steve - This will be helpful.

Steve K