Dave Smith/Tom Martin 1/4 Scale Hall Cherokee Build

[ingrahal]

There is one thing I forgot to mention. The formers G, H and Q are set at 2 deg from vertical to set the wing incidence. I used a protractor to set the angle.

[Dave Smith]

Art, I assume you know about the cherokee "blogspot"? All known Cherokees are here. Pretty sure you can find something you like for a color scheme!

​http://cherokeesailplanes.blogspot.c...roll-call.html

DS

[TonyN]

I will probably make something up since I am going with Solartex natural for the recovering, probably mostly green with open sections left the natural color.

[ingrahal]

Dave, yes I have been on the Cherokee II blog site. In fact Tony's comments reminded of Dean Gradwell's N72DG which after looking at it again really appeals to me.

Tony, Thanks. Your input helped me decide to model N72DG. I like the idea of unpainted covering for it's translucence and weight savings. On the SGS 1-26B I did the solortex and Nelson's Hobby paint added 1.5 lbs to the airframe. The paint was probably 0.5 lbs of that. Ok, well now that that is settled I will get back to building.

[ingrahal]

Update:

Back when I bought the kit for this plane I had just finished building a vacuum forming machine. Knowing I would need a canopy and anxious to try out the machine I carved a plug out of balsa and finished it with urethane. After wasting a bunch PEG sheet plastic and not one good usable canopy I realized that it was much harder than I thought. I got busy with other things and gave the machine a rest. Then later I had a need for a windshield for a 1/4 scale Decathlon. So after some research and a little trial and error I got a successful pull. That was documented in a build thread on the Decathlon on the old forum. So today, with that knowledge and the plug I had carved earlier, I was able to pull a good canopy for the Cherokee.

I first made a pull of 0.010" styrene. Leaving the styrene on the plug, I then applied carnauba wax and buffed it out. Then pulled the 0.030" PEG over the styrene for the canopy. The styrene acts as a filler to hide imperfections.




That's all I did today. I wanted to do something fun, which the vacuum machine is once you start getting good pulls from it.

[ARUP]

Art... I could use one of those canopies for my Cherokee and a box of 45ACP when you are done using them for weight! I really like Dean G's translucent color scheme. I bet it would really show up well at altitude, glowing in the sunlight, just like my 'antique' birds! Let me know what kind of $$$ you need for the canopy if you pull an extra or two. My vacuum former isn't big enough. Cheers, Michael

[ingrahal]

Hey Michael, glad you stopped by. PM me your address and I'll send you a canopy. You can buy me a beer at Huntsville this year. Oh and you don't get to complain about the quality.

[ingrahal]

Ok well right after I got the canopy made Dave Smith pointed out the modifications that N72DG has to the fuselage and canopy. I hadn't even noticed it but the canopy is elongated and the rear canopy was added. This is very fortunate for me because the mods need to be done now at this stage of construction. He also provided me a link to download his collection of photos on N72DG. THANKS DAVE !!!

[ingrahal]

Question for Dave Smith, is the wing center section built flat on the plan or in place on the fuselage?

[Dave Smith]

In place on the fuselage. Once you slot the ribs in place they will be aligned and ready for false leading edge, which will hold things steady. If you look at the builds on RCGroups, especially the very first Cherokee build thread, you'll see a few pictures that will help out. Post #15 onwards.

http://www.rcgroups.com/forums/showthread.php?t=286681&highlight=cherokee

DS

[ingrahal]

Thanks Dave!!! I have looked those photos over several times it just wasn't clear if the basic framing was done on the plan and then moved to the fuselage at some point or what.

Update:
I have started on the wing center section with the modifications for the DG version in mind. Of course I'll have to redo my canopy when it's all said and done. I spent a fair amount of time removing the wing ribs from their laser cut sheets. The laser did not cut clean through on most of them and they had to be cut free with a hobby knife. Why am I worried about wing ribs you ask? Well I wanted to drill the holes for the servo wires which extend out through rib R12. I like to stack the ribs and drill all the holes at once. Once the ribs were prepared I started framing up the center section.

I first applied a light coat of M77 adhesive and let it dry good. You just want a temporary bond. I aligned the ribs by the spar notches so the servo wire hole would be parallel to the spar.


I used a 1/2" forstner bit at 5K rpm to drill the hole.


Next is the hole for the alignment pin. This time I aligned the ribs with the wing rod sleeve so the holes will be parallel to the wing rod. I transferred the position of former I to the ribs which include the R1A, R1 and R2 ribs.


Then drilled a 5/32" hole for the alignment pin sleeve.

[ingrahal]

Update post 26 continued:

Next is the slot for the brace. This is only in the two center ribs. I drilled and then filed to fit the 1/8" X 1/2" plywood brace.


After removing the construction tabs from the ribs I started by clamping the outer ribs square to former H. I then cut the lower spar cap and then the sub-leading edge and rear brace based on the length of the spar cap.


I then glued in the brace and sub-leading edge. Now everything is straight and square.


That's all for now.

[stihac]

That's cool. Moving along nicely. thanks for posting the updates.


Petr

[ingrahal]

Thanks Petr and you're welcome. I enjoy doing these build logs.

Update: I continued work on the center section. First gluing the bottom spar cap in place and then sheeting the bottom of the shoulders. I decided to use a tongue and socket for wing retention.

Sheeting the bottom of the shoulders.




My son makes parts for Falcon Jet and gets scrap pieces of Divinycell foam. I've been trying it in various applications. It has some nice properties but is expensive. Here I'm using it for the retention blocks.


The screw will come up through the bottom. I counter bored the holes so the screw heads will be hidden.


Continued on next post.

[ingrahal]

Continued from previous post.

Pressing the T nuts in the tongues with the drill press.


Here the tongues are screwed in place. Of course they will be glued into the wings once the wings can be mounted to the fuselage.


That's it for now. Next will be the spar/wing rod sleeve, the alignment pin sleeve, trailing edge carbon fiber strip (on order) and the top sheeting.