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Old Mar 25, 2012, 01:01 AM
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Question
25" Comet Coast Guard Waco JSW-1

I was truely impressed the YouTube video of a Comet 25" SR-7. So I think I want to take this on as a conversion for R/C but I have a couple of questions:

I've been collecting references to build this plane. I found the Comet plan and pictures of the actual Coast Guard plane. However, they are all B&W. So far, I've been unable to figure out what basic color the plane is. My impression is that it is doped/painted silver overall. However, I've been fooled by B&W photos before. It could be yellow for all I know.

There is also only one view in any photos from above and it's pretty washed out. It would appear that no markings were carried on the upper wing (the plan shows no markings also, but could have been drawn from this photo). Is this correct?

The last question is; I notice that a lot of builders use the P-51 motor/gearbox and not the one from the Champ. Is there a particular reason for this? What is the difference - noise, durability, gearing, motor, availability?
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Old Mar 25, 2012, 07:11 AM
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The black back motor used on the P51 and others is more powerful than the white back motor used on the champ. all 8.5mm motors are interchangeable in the gear boxes.
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Old Mar 25, 2012, 07:35 AM
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The PDF plans say that the entire aircraft is light blue with black lettering.
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Old Mar 25, 2012, 07:47 AM
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More on the USCG Comet Waco

Scot Dobberfuhl on the CometModelAirplanes Yahoo! Group gave me a link to a page on the USCG official history site for USCG aircraft paint schemes. So, given that the pictures seem to be taken around 1937-ish, then

1936 Pre-war Navy scheme:
Fuselage: Silver
Upper wing surfaces: Chrome yellow
Lower wing surfaces: Silver
Vertical Stabilizer: Upper 1/3 blue, lower 2/3 divided into 5 stripes of red
and white
National Insignia: None
Coast Guard Insignia: Emblem with yellow anchors

This is totally consistant with the photos and the Comet plan. On closer
examination, BTW, I realized that the upper wing in one photo I have that shows
it, isn't washed out, it's covered with a canvas cover.

RR
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Old Mar 25, 2012, 08:00 AM
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Blue? Were any USCG aircraft ever blue? I doubt that that could be right. The pictures of V158 and V159 both show the lettering on the bottom on the right lower wing clearly as U S C G which not what the plan says. There is also a USCG badge under the forward window on both sides which is not on the plan.

The plan is realyly well done (like the SR-7) but I have serious doubts about the markings. I think I will opt for the coloring as specified by USCG regulations of the time. As for the lower wing, I can't really make out what's on the under surface of the left wing, but it kind of looks like another set of U S C G letters. Lacking any other pictures, I guess I'll go with that.

I really wish someone would re-kit these Comet models laser cut would be soooo nice. As it is, I'm off to Office Max with Thumb Drive in hand to get some 25" Comet plans printed full size. I'm on a business trip this coming week and will have nothing to do better than tracing parts...
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Last edited by RayRangel; Mar 25, 2012 at 08:12 AM. Reason: grammer and spelling
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Old Mar 25, 2012, 08:10 AM
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Thanks for the info on the motor. The prop on the P-51 is the same as the Champ isn't it? So I guess the difference is the gear ratio which will swing is faster. The Champ takes a bit of a head of steam to loop, when I wear the Champ's motor out, I'll replace it with the P-51 set. Since the Waco is 25" AND a biplane, that's a lot of wing and struts to be hauling around. The P-51 set will be the way to go to overcome the drag. I don't want to over power it though, as it will be light as a feather and have a lot of wing area.
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Old Mar 25, 2012, 10:46 AM
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The gear ratios are the same the difference is the motor winding.
The P-51 motor (or 4-site) would be ideal for the Waco.
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Old Mar 25, 2012, 10:50 AM
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Thanks, I'll use that one.
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Old Mar 25, 2012, 01:00 PM
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Just a guess, but maybe they listed light blue because silver tissue was uncommon or unavailable when the kit was still being sold.

Pete
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Old Mar 25, 2012, 01:55 PM
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That could very well be. I hadn't thought of that, but it sounds reasonable.
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Old Mar 25, 2012, 09:05 PM
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A 25" biplane is probably a little much for a Mustang motor. Either Scale it down to 18" AND build light, or build it little heavier than the plan shows and go 2S brushless with an HXT 5g or 10g
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Old Mar 25, 2012, 10:13 PM
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Based on my experience with the converted Comet SR-7 I would say the P-51 motor will be plenty of power for the 25" biplane. The P-51 motor has tons of power overhead with the Stinson. I fly it at slightly less than half throttle. I think the motor/gear drive will work very nicely in the Coast Guard Waco. Just pay attention to your material selection so you can keep it a light as practical.

Paul Bradley
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Old Mar 26, 2012, 06:31 PM
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Paul Bradley!

To be honest the videos of your SR-7 (one of the prettiest Golden Age airplanes and personal favorite) that go me thinking of converting another one of Comet's 25" line. I have the foamie Aeronca Champ that I'm using to relearn flying--been away since '79--and I love it dearly. It has to be one of the best behaved RTFs there is. Since the Champ is a typical high wing design, I thought I'd build something a little different so I picked the Waco biplane. BTW, I have a Stevens Aeromodel DH 53 Hummingbird in progress.

The Waco has a little more wing area than the SR-7, but should be about the same weight depending, of course, on how many scale "extras" I add. If I keep the struts and LG fairing to a minimum, then I shouldn't be adding too much weight of parasitic drag. Honestly, being a old stick-n-tissue rubbber power indoor scale FF guy, I look at these little electrics as being way over powered. I'm looking for the Waco to have a scale like appearance when it flies. I'm not going to be disappointed if it won't barrel roll or do multiple consecutive loops. I doubt whether the stucture would pull the G's anyway.

I tool around the airfield on 1/4 to 1/2 throttle with the Champ so I figured that the P-51 power pack would be about right for a Waco. I haven't decided, yet, whether to build a tray like your SR-7 or not. DId you actually put the tray to use in other airplanes? The way I look at it is that the motors and gearboxes are cheap, It's the Spektrum 6400 that is expensive. So I've been considering ways to lift out the rxr by unpluging the motor and without disturbing the pushrods. Perhaps a strategically located hatch, a clip of some sort to hold the rxr in a specified spot and simple L bends in servo end of the push rods with a removeable retainer of some sort. All would have to be access and removed with needle nose pliers or some such.

Maybe I'm over engineering this whole thing. When it's all said an done, the fact is that a scratch build plane of this size with the 6400 in it probably costs less than any of the micro RTFs anyway. I probably should just build it, fly it 'till it hits a tree, then rip the guts out an bulid something else.

BTW, I happen to be in LA is week on buisness so I went by Ultimate Hobbies and picked up the rxr and motor. I also picked up the push rod repair kits for a Sukoi and a Champ (they only had one of each). These repair kits contain the carbon fiber push rods, wire ends (pre-bent) and the shrink tubing to connect them. Having those pre-bent wire ends and the shrink tubing is going to save some time and hassle.

What did you use for the push rods on the SR-7?

BTW, I've been considering the wisdom of replacing the balsa wing spars and all surface leading edges with spruce to provide a little more strength--I'm not the best at soft landings or avoiding collisions. Do you think the additional weight would be worth it?
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Old Mar 26, 2012, 10:20 PM
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Ray - I think several of your questions can be answered by reviewing the build threads in this forum for the SR-7 and the beta kit build of the Park Scale Models Monocoupe 90a. Both show how I set up the receiver/pushrod make and break connections using magnets. Both models use the slide out equipment tray. The principal purpose, for me anyway, in using the slide out tray was for easy battery and motor access. Now that I have the experience with the SR-7 and Park Scale Models Monocupe slide out trays, I will probably try that approach for all of my future micro models. It is much easier to implement on radial engine airplanes. Your Comet Waco conversion would be an ideal candidtate.

Pushrods in the SR-7 and the Monocoupe are .025" carbon fiber with .025" piano wire ends. The ends are attached to the carbon fiber pushrods with small diameter shrink tubing and a drop of thin CA.

For a lightly built model you will be suprised how much abuse balsa spars and leading edges can absorb. The key is a light model does not generate the forces of a heavy model when they land hard. I would be inclined to not use the heavier spruce for the spars or leading edges. The weight difference would not be great so if your comfort level is better with spruce or bass wood go for it.

Paul Bradley
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Old Mar 27, 2012, 11:27 AM
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Thanks Paul. I went and read through your build log for the SR-7. I see that the real driver for the tray is the accessibility. The tray also allows for some adjustment to the CG. I think that I will pursue that course with both radials and in-line models. It certainly avoids the having to make hatches or leaving unsightly openings in the bottom of the fuse.
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