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Old Oct 02, 2012, 01:41 AM
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China, Guangdong, Shenzhen
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Guillows 172 Skyhawk

I have decided to build this kit as a high wing aileron trainer for myself. It looks like a simple kit, as far as Guillows kits go, and I am impressed with the results others have gotten on this kit. I am also going to use this build to learn the ins and outs of Doculam covering. I haven't used heat set coverings yet. Originally I was going to go the silkspan route since I experimented with that in my youth, but I am curious about Doculam.

I plan to use this motor, since I have a spare. I bought three of these when I built my PBY, incase I had trouble getting a good matching set.

http://www.headsuprc.com/servlet/the...h-16%29/Detail

It looks like the prop data published would give me several possible options for this plane. I hope to be able to use a 2 cell lipo to keep weight down. Choosing motors is still confusing for me I must admit, but this one looks like it could work. There are some really ugly propellors in the 7 in. range that look like they would have good thrust specs for a model this size. I figure this will come in at 10-12 ounces with a battery installed, hopefully less.
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Old Oct 02, 2012, 01:50 AM
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A few more pics

A few more shots of where the plane is at currently. I am putting some 1/32 cap strips on the fuselage stringers. My skill with the Doculam is not so good, maybe these will help. I will sand them down as thin as possible before putting on the covering. I only have access to 3 mil Doculam, so this covering is not as lite as I would like. The joys of Alaska, take what you can get. I am considering ordering a roll of the 1.5 mil stuff, maybe it will stretch better for me.
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Old Oct 03, 2012, 07:33 AM
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Just a few more pictures of the build as I go. I am not having much luck with doculam on the fuselage, so I removed it and will try something else.

I built a balsa structure for the wing to bolt to with some nylon bolts, and this will also hold the cabin plastic in place and provide a mount for the aileron servo. This wing mount attaches to the fuselage at four points with screws, and has wire hoops to take the stress off the balsa. The window plastic is basically sandwiched between this and the wing. I will probably put a couple small screws on the plastic into the fuselage as well.

The motor mounts is roughed in with some 1 inch aluminum threaded stand-offs. I am planning on some down, and starboard thrust on the motor. I will use shims to get the thrust angles ajusted.

I am planning to mount the battery up against the firewall behind the dash and above the servos. I can get away with this I think if I use a 2s lipo.

Anyway it is where I am at so far, nothing trick, real basic build.
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Old Oct 03, 2012, 08:29 AM
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I'd call that nose gear "trick"... Very nice! Regarding the Doculam.... I've used the 1.5 mil on a 60" 7lb Stearman, and it works fine. Using it on a small model is more difficult. The stringers on the fuselage are very flexible, and it was difficult to attain a wrinkle free surface. Patience pays off. The Doculam requires high heat and longer exposure to achieve maximum shrinkage. I found that once more of the fuselage is covered, it becomes more rigid, and the covering becomes easier. If the first sections are wrinkled, don;t be discouraged, keep going. You can always cut out wrinkled sections later, and recover.
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Old Oct 03, 2012, 10:54 AM
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I would use one of the very light iron-on coverings that do not require painting on this small of a subject. Try to avoid any unnecessary weight aft of the wing and locate RC and power stuff so that you don't need to add nose ballast. Use very light power and RC gear for scale-like flying. End of standard sermon, Guillows 1.1
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Old Oct 03, 2012, 11:46 PM
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Phillip, thanks for compliments on the nose gear. It came together kinda accidentally with no pre-planning. Rather than write off Doculam because of this build, I will do as you suggest and save it for a larger project, then try again.

E- Chall. perhaps lite span? I don't know all the trade names, but I think the local hobby store has some iron coverings, I will look into it. I can also always go to sillk-span also. My main goal is to get a plane in the air that I built myself. I see everyone always preach the need to build light on these Guillows, and to that end I ordered some contest grade balsa to incorporate in my build when extra wood is needed. The kit came with very good quality wood for half the formers, and the hard heavy stuff for half the formers, very aggravating. On the wings I split up the light ribs and heavy ribs side to side to try and keep balance.

Sermons are always welcomed by me, lest I forget what I am trying to learn from the other build threads in here!
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Old Oct 04, 2012, 09:50 PM
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Hi conrad, quick question, you mentioned putting 1/32 cap strips on the stringers, what are cap strips? I looked closely at the photos and I can't tell what they are or what they do.

Other than that, your build looks fantastic. I really like the idea of the balsa support for canopy and wings. I know everyone says the plastic is quite sturdy and it seems strong in the box but I like the idea of some reinforcement. I opened my kit two months ago and it hasn't progressed since : thumbs up for the front sprung strut too
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Old Oct 04, 2012, 11:16 PM
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bellyup,

Maybe I am not using proper terminology when I say cap strip. It is an 1/8th inch wide strip of 1/32 balsa glued down on top of the stringer, so the covering rests on a wider area. I am new to building RC and have noticed many of the good builders do this to get a smoother covering. I also scalloped between the stringers with some sandpaper for the same reason, to get smoother lines. I burglarize every good idea I come across in the build threads! Hard part for me is remembering all the good ideas!

Today I did some weights on the various pieces so far, and I must say not only do I not trust the plastic cabin piece to be the wingmount by itself without help, it is also quite heavy. Since I have built a removebale structure to mount the wing to, I think I will trim as much uneeded plastic from this cabin piece now as well. I angled the supports in the wingmount I built, so they should be hidden behind the clear plastic door frames pretty much.

I copy what others do if it looks good, but always try to do some original stuff as well. I am also rethinking my motor setup. Something I know very little about. I think what I have would work, but I am not so sure it is the best setup.

conrad
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Old Oct 05, 2012, 10:45 PM
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Ah yes, I see now. Thanks for that. I've thought of doing similar in the past, or instead of mounting stringers in the cut outs, I'd put wider but thinner stringers directly over the cutouts. Still unsure, because I want to sheet mine with balsa.

For the canopy I bought some plaster to make moulds so I could make a master to build up a balsa/celluloid hybrid canopy. Still not sure which way I'll go there but apart from the points you make about the canopy, I'm also worried about the sun warping the plastic. In summer the UV is very high hear and we still go fly on the hot days, albeit with the sun on the way down.

Regarding motors, I plan on something similar, direct brushless, but others I've seen have geared setups, though much lighter ships than what mine will end up. You've probably seen all the vids and other examples but there were two I found a while back that flew great, nice and slow with gearboxes and no doubt very light builds. I'd post links but just can't find them now.
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Old Oct 06, 2012, 02:42 PM
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bellyup,

I bought a very used, and beat up small parkzone yellowcub foamie the other day from a guy. It has a geared motor set-up with a firewall mount that has down and outboard thrust designed in. It will fit this plane, but it has a 8x4 prop, which would be difficult to manage, unless I put taller tires on my plane. This geared set-up can be bought in hobby stores, motor with mount and gears, for about $25 I think, as a replacement unit. Not sure how the performance would be with a 7 inch prop. Just something I am thinking about. The foamie this engine come off of has a similar wingspan as this Cessna, but it is heavier, and uses a 8.4 volt NI MH battery, 600mah. I do not know if it will survive on a small 3s lipo or not. It is a 24mm motor I think, I suppose I could try swapping the motor also.

I think if you were planning to plank sheet, you could lay the side strips right on the formers, except that they would be very delicate to work with while sheeting with no stringer under them for rigid support. I did end up planking the fuselage on mine yesterday, but I used 1/64 th sheeting, which is pretty fragile, I have never used it before. Extremely light.

I think any modifications canopy wise are worth persuing. This is a pretty little plane, and seems to be an easy builder. I will try and post some more pictures of where my build is at later today.
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Old Oct 06, 2012, 05:20 PM
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Small geared brush type motors have been used for a long time on small rubber kit conversions. I have used them and have been disappointed with slipping pinion gears and stripped plastic spur gears spoiling a flying session. The plastic gearbox frames often break in a "hard landing" You need a gear puller to replace tiny brass pinion gears onto motor shafts and some finess to avoid ruining the motor. For these reasons I much prefer small brushless outrunners, even though they sometimes are hard to fit an a scale model cowl. Small outrunners are now available with low enough KV numbers to spin large enough props on 2 or 3 cell lipo packs. Sorry I can't recommend a specific motor or supplier for the C-172, but take a look at what BP hobbies and Heads Up RC have to offer


Flash! This looks like a likely motor with 7" prop and 2-cell lipo:
http://www.headsuprc.com/servlet/the...0-Sport/Detail
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Old Oct 11, 2012, 03:40 PM
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E-Challenged, my build will come out close to 11-12 ounce, so I am thinking maybe a slightly larger motor,
http://www.headsuprc.com/servlet/the...50-Plus/Detail.

I like that site because of the published prop data with the motors. I will scrap the idea of the geared setup. Like you say it is hard to beat a simple outrunner, and the one I am trying, is probably a bit on the large size, but it fits under the cowl just fine.

I got the 1/64th sheeting on, very fragile stuff to work with! I put two coats of clear epoxy over it then sanded the epoxy down as far as I dared. The fuselage with LG and servos is about 5 3/4 OZ.

Conrad
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Old Oct 11, 2012, 08:35 PM
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Quote:
Originally Posted by conrad907 View Post
E-Challenged, my build will come out close to 11-12 ounce, so I am thinking maybe a slightly larger motor,
http://www.headsuprc.com/servlet/the...50-Plus/Detail.

I like that site because of the published prop data with the motors. I will scrap the idea of the geared setup. Like you say it is hard to beat a simple outrunner, and the one I am trying, is probably a bit on the large size, but it fits under the cowl just fine.

I got the 1/64th sheeting on, very fragile stuff to work with! I put two coats of clear epoxy over it then sanded the epoxy down as far as I dared. The fuselage with LG and servos is about 5 3/4 OZ.

Conrad
Wow I bet 1/64 sheeting is tender to deal with, it is balsa right? You figure to make 12 oz or so auw even coating with epoxy, thats interesting. Sure will be watching to see how you turn out. BTW I used that same motor on a 36 in Guillows Champ a few months ago and it was plenty of motor even at 14 oz.

Bill
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Old Oct 12, 2012, 10:53 AM
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Bill,

I enjoyed your Champ maiden thread very much. And as I posted, I will also film my maiden, and let the experts on here troubleshoot things for me. I learned alot on your thread by reading what others had to say.

The 1/64th balsa is so thin it sort of floats like a feather. Very tricky to work with. The epoxy is actually needed to put a stiff skin on it I found. It is an experiment. I am just trying new things, new approaches. Also, the epoxy needs to be sanded down as much as possible without going into the woodgrain. This works well on 1/32 sheeting, but scary on this thin stuff. A very light paint coat is all that is needed then because it sits on the surface with good coverage and no soaking in.

I built a new horizontal stabilizer with bent wood perimeter frame and light balsa crosspieces, covered it in Doculam. The rudder is Doculam covered, and I may try solite or litespan type covering on the wing. I am experimenting with different things on this build that I have never tried before. Still trying to find my style of building I guess.

If I can get away with a 2s lipo, maybe 900-1000 mah size, after adding in the weight of the battery, I will be everybit of 13 -13.5 oz. I am sure. not exactly a lite build for this kit. I do not know what the term auw means, but if that means flying weight with battery and everything, then I will definitely be over 12 oz.. I am encouraged you think this motor will work, it was laying around and I hoped it would work in this build even if it is a bit more motor than I really need.
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Old Oct 16, 2012, 07:55 AM
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Nice work! – nose wheel gear looks great – look forward to the finished result
Best
Charles
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