H9 33% Pawnee Tug Conversion

[Stew]

I would rethink having just one snap-latch near the chord midpoint on the Pawnee. The stock wing joiner/spar on the Pawnee is 1/4" thick aluminum plate about 1 3/4" in height oriented vertically at about max thickness. The concern with the single snap-latch will be forward momentum of each wing panel in an abrupt stop, often what I have to call a landing... The external wing struts have no leverage to stop the wing pivoting forward and the joiner/spar is thin enough that it will be bent in an abrupt stop. The stock configuration is 2 1/4x20 nylon screws a few inches in from the leading and trailing edge along the chord. On my Pawnee, they were replaced with steel 1/4x20 bolts with anti-vibration washers. During the "abrupt stop" that I had, knocking the gear off the bottom of the fuselage, they worked well and I am sure are the reason that the spar joiner was not bent during that incident. I'd look at replacing the stock bolt locations with snap-latches.

[Xroadie]

I would rethink having just one snap-latch near the chord midpoint on the Pawnee. The stock wing joiner/spar on the Pawnee is 1/4" thick aluminum plate about 1 3/4" in height oriented vertically at about max thickness. The concern with the single snap-latch will be forward momentum of each wing panel in an abrupt stop, often what I have to call a landing... The external wing struts have no leverage to stop the wing pivoting forward and the joiner/spar is thin enough that it will be bent in an abrupt stop. The stock configuration is 2 1/4x20 nylon screws a few inches in from the leading and trailing edge along the chord. On my Pawnee, they were replaced with steel 1/4x20 bolts with anti-vibration washers. During the "abrupt stop" that I had, knocking the gear off the bottom of the fuselage, they worked well and I am sure are the reason that the spar joiner was not bent during that incident. I'd look at replacing the stock bolt locations with snap-latches.

I was planning on doing two per side.

[lenb]

Great Idea, may have to think about that

[Asher Carmichael]

If you have provisions for two and the airframe warrants it then by all means use them. I'm not familiar with the Pawnee construction but if a fuselage has substantial formers at the LE and TE of the wing then they will help carry the load rather than relying on just the spar and retainers. Think of incident/anti-crush tubes on our sailplanes which typically use one retainer. Having said this, I guess using two on a towplane might be good insurance against vibration causing one to fail. I better keep an eye on mine :-0

[Xroadie]

Okay.....yesterday I started on the Pawnee, not really any "building"...other than giving the cabin doors a once over with some Foam Safe CA, so as to not fog the clear plastic. Mostly what I did was sort out all the hardware. I wanted to use the slide catches that Asher and Swiss1 have used, but realized that 1/4 20 wing bolts are to big for the "stud" that the slide catch grabs on to. I plan to get four of them anyway, because they will work on my Carbon Cub. Instead of the Slide Catch, I am going to use another item that Asher found a while back, the Xion Wing Lock System, that Red Wing RC, here in St. Louis sells. They are designed for 1/4 20 and are a little simpler to mount than the slide catch system. The only draw back is that the "latch" on the Xion system is a separate piece, that is lose and will fall off the stud when the wing is not attached to the fuse. So as to not loose them, I plan to drill a small hole in the end of each latch and slip a safety cable through the latch and secure them to the inside of the fuselage.

Here are the Xion Wing Locks.

[Swiss1]

Okay.....yesterday I started on the Pawnee, not really any "building"...other than giving the cabin doors a once over with some Foam Safe CA, so as to not fog the clear plastic. Mostly what I did was sort out all the hardware. I wanted to use the slide catches that Asher and Swiss1 have used, but realized that 1/4 20 wing bolts are to big for the "stud" that the slide catch grabs on to. I plan to get four of them anyway, because they will work on my Carbon Cub. Instead of the Slide Catch, I am going to use another item that Asher found a while back, the Xion Wing Lock System, that Red Wing RC, here in St. Louis sells. They are designed for 1/4 20 and are a little simpler to mount than the slide catch system. The only draw back is that the "latch" on the Xion system is a separate piece, that is lose and will fall off the stud when the wing is not attached to the fuse. So as to not loose them, I plan to drill a small hole in the end of each latch and slip a safety cable through the latch and secure them to the inside of the fuselage.

Here are the Xion Wing Locks.

Pete, I added the latches to my H9 Cirrus SR22T a few weeks ago, and the stock wing bolts were a larger diameter than the retaining bush, I was able to drill them out to accept the larger bolt, they are not hardened!

Jeremy and Ben
SCCAAA TT TN

[Snatch]

Pete, silver solder the catch to the end of a 1/4x20 threaded stud.... Works great

[Xroadie]

Pete, I added the latches to my H9 Cirrus SR22T a few weeks ago, and the stock wing bolts were a larger diameter than the retaining bush, I was able to drill them out to accept the larger bolt, they are not hardened!

Jeremy and Ben
SCCAAA TT TN

I would need to drill a 1/4" hole and the narrowest part of the retaining bushing is 11/64".
Pete

[AGriffith]

One thing I did on the doors on mine as to take RC 56 canopy glue and go around all the edges of all the windows using one of these http://www.amazon.com/gp/product/B00...ilpage_o04_s00

The quick locks from Red Wing work well especially in the front where a blood sacrifice is required to get the wing bolts tight.

[Xroadie]

I ended up using the Red Wing Xion locks Andrew....I had a set of four that I bought for my KA6, but they weren't long enough, so I tried those. I could have soldered the bushing on a 440 bolt, like Tom said and mounted the McMaster Carr slide catches, but the Xion locks literally take seconds to mount in the fuselage and I already had four I am going to use the slide catches on the Carbon Cub.

I also upgraded the strut end clevis, to the ones that Len suggested...again from McMaster Carr. I got the size threaded for 4mm, a 25mm long 4mm threaded rod and a 4mm coupler nut that I found at a Menards store. The new clevis is only 16mm long...which is much shorter than what comes with the kit, necessitating lengthening the 4mm threaded rod on the end of the strut. I cut down the strut end rod to half the length of the coupler nut and added the 25mm long rod then added the 4mm nut supplied with the kit and the new clevis...I used Red Loctite on all. On the strut mounting plate on the side of the fuselage, I drilled out the hole to 1/8" for the new clevis and because the new clevis has a 1/8 wide jaw and the strut plate is only about 1/16" thick I added phenolic washers, that I had sitting around to the underside of the plate with JB Weld. I did that so the clevis would not rattle on the plate.

Here's a pic


Len in your photo there is a fan shaped ply bulkhead under the turtle deck, the model I'm working on just had a piece of foam there. I thought the ply was buried in the foam and I dug away the foam looking for it. Also who sells tow releases that are designed to mount on the back of a bulkhead like you used? The pilot I am building this model for supplied two releases, one from Iflytallies and one from Espirit....both are designed to mount to the front of a bulkhead.

Pete

[lenb]

The ply bulkhead must have been changed out since mine was made. The tow release came from Ben Diss, I think he has retired and moved on. I had some ordered and never received them.
I'm glad you were able to get the strut fittings worked out. Looks great.

[JimD]

The one from Esprit http://www.espritmodel.com/tow-hook-...eavy-duty.aspx Is the same one that TopModel supplies in the Bidule and previously in the Porter.

Lots of experience with this tow release and never had a problem.

[Xroadie]

The one from Esprit http://www.espritmodel.com/tow-hook-...eavy-duty.aspx Is the same one that TopModel supplies in the Bidule and previously in the Porter.

Lots of experience with this tow release and never had a problem.

Jim! You took the mouth right out of my words...or something like that. Yes the Esprit release is from Top Model....I was just about to post that Funny....if you look at the pics on the link that Jim just posted, you will see three totally different designs of tow releases. Only the one in the top left photo is accurate as far as what you get...the other two designs are made for mounting on the rear of a bulkhead, but what you get is one designed for a front mount. I solved the problem by flipping the tow release over, adding four hard plastic spacers, that I had sitting around that were the perfect height and some longer 3mm bolts. Pic below.
Pete

[JimD]

I did something like what you did in my Decathlon:

[Steve P]

The tow release came from Ben Diss, I think he has retired and moved on.

I think I got the last two - dug them out of an old jar of parts on his garage workbench. ;-)

[JimD]

Okay, this is interesting...the unit that came with my Bidule 170 is like the one you have in that the mounting flange is on the opposite face compared to the one in my Porter. Now that I look at the one I got for the Decathlon (see pictures above) it is not made the same as the older one on my Porter.Also, looking more closely at the one that came with the Bidule, the quality is not very good. The prior ones I got were all nicely machined, but this one is not and the hole for the release rod is off center! Not only that, but the release rod will not even slide up through the hole!

Wow, must have been made by the lowest bidder by the new guy that never ran a machine before. Very disappointing!