H9 33% Pawnee Tug Conversion

[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

[lenb]

Great Idea, may have to think about that

[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.

[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.

[Asher Carmichael]

Pete,
The snap slide latches work great and help make assembly a "snap." The next best thing you can do to help speed assembly is..... get rid of the struts....

For those not familiar with the snap latches....



Here's a new take on wing retainers. I am repositioning the fuel tank over the wing rod and CG and decided I needed a different retaining system since it would be problematic trying to install the plastic thumb screws supplied in the kit. I fumbled around for awhile and stumbled across these snap latches at McMC. One per side near chord center should be plenty. I used a 10-24 screw to hold the stub and installed a plate with T nut in the root of the wing. The pics and video should explain it.

https://www.youtube.com/watch?v=ZvIbIjWdzyY

[Xroadie]

Thanks for the info gentleman!

Len.....I'll check the strut, threaded rod length and if I can add those clevises with out having to lengthen the rods, then I will suggest to my client that we get a set of four for his Pawnee. I'm all about making model quicker to assemble

On the subject of quick assembly ....I have helped the Horizon guys assemble their Pawnees before and putting in the wing bolts in, was a real pain. I am thinking of trying the "snap slide latches" that Asher and Swiss1 have tried....or using the quick latches that Red Wing RC sells.

I took a look at the hatch doors and I can see what you mean about the glue joints....on this model the wood where the hinges mount are pretty securely attached, but the latches at the top are not, so I will secure those and give all the other glue joints a once over.

So as far as the shock mounts go... it sounds like I will remove the existing blind nuts, add a ply doubler to both the front and rear shock mount plate, to keep the bolts from shearing out, add some triangular stock....or FG cloth, to keep the plates in place and upgrade to a 10/32 bolts for the top shock mounts. I will also replace all the bolts on the LG assembly that have threads riding on the bearing surface.....and from the photo you supplied earlier make sure that the ply doublers do not interfere with the throttle servo arm.

Thanks again!
Pete

[Swiss1]

Len....why did you use the splice collar and threaded piece on the end of the strut, before you added that clevis? I noticed that the clevis is already threaded for 4mm...which is what comes on the end of the strut...did you need added length with the new clevis?

Also...what fails on the cabin doors....so I know what to reinforce?

And.....does the plywood shock mount plate break free or do the bolts that attach the shock to the plate tear out? I assume if the plate breaks free, I will need to reinforce the plate mount. (triangular stock etc.)..if the bolts are tearing out then the answer would be a thicker/stronger plate....right?

Pete

As Len said Pete, double up the shock box mounting plates and increase the bolt size, the very same happened to Snatch's Pawnee at the Summer event in Cumberland. One bolt ripped through the plate and the other was bent to a 90 degree angle!

Jeremy and Ben
SCC AAA TT TN

[lenb]

Pete,
The threads were not long enough on mine, not sure if they were cut to length previously ( I bought it second hand ) You'll have to see.
The cabin doors glue joint on the lower corners fail. Leaves the piece of wood with hinges hanging on the airplane as the door flutters away.
The bolts bend and hole in the wood will rip out.
I put an 1/8 ply piece on the outside of each side of the box and replaced the bolt to a 10-32

LEN

[Xroadie]

Len....why did you use the splice collar and threaded piece on the end of the strut, before you added that clevis? I noticed that the clevis is already threaded for 4mm...which is what comes on the end of the strut...did you need added length with the new clevis?

Also...what fails on the cabin doors....so I know what to reinforce?

And.....does the plywood shock mount plate break free or do the bolts that attach the shock to the plate tear out? I assume if the plate breaks free, I will need to reinforce the plate mount. (triangular stock etc.)..if the bolts are tearing out then the answer would be a thicker/stronger plate....right?

Pete

[lenb]

Pete, they were installed to speed up assembly of the Pawnee.

Len

[Xroadie]

The parts for the struts were from McMaster Carr. I had to use a splice collar and then a threaded piece to attache the clevis.
I believe these were the ones

Those clevis rod ends are slick! But there is no failure problems with the what came with the kit....right?

I like those....it's got me thinking about trying those on the Carbon Cub to speed up assembly!

[lenb]

Pete, The photo above was not supposed to be included in the upload, however its showing how the throttle servo came back and hit the bulkhead resulting in a burned out servo at full throttle.

With a DA 100, an 80 or 100 oz tank is great.

The parts for the struts were from McMaster Carr. I had to use a splice collar and then a threaded piece to attache the clevis.
I believe these were the ones

M4 × 0.7

2448K41

[Xroadie]

....and what am I seeing in this photo?

[Xroadie]

....just saw your second post Len.....where did you get the new strut hardware....something from McMaster Carr?

Pete

[Xroadie]

Thanks for the input Len...I would go with a DA120 if this was for me, but it's what my customer supplied for the model. Most of the models he will be towing will be in the 1/3 scale range.

I was about to say....I got springs for the Carbon Cub and not the Pawnee...when I realized you meant the other Peter G LOL

So...basically beef up the landing gear plywood and bolts, at some point get beefier springs and a tailwheel, and replace the main wheels.

What wheels did you go to and will a 100 oz tank fit?

Also...where are the doors failing...at the hinge or at the latch?

Pete