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Sep 27, 2011, 11:22 PM
Troy Bowman
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Build Log

Yet another Guillow's Cessna 170 Conversion


I remember dreaming as a kid to get those rubber-band Guillow kits to fly RC, but at the time RC was really big and heavy. (Radios had barely finally become proportional back in the 80s.)

I flew my UMX Beast to shreds (tape everywhere holding it together, a real mess), so I picked up a new one (of the last of them for $99) and cannibalized the guts of the old one. Next was to find a kit I wanted to use the guts in. I found a Cessna 170 kit at the local hobby shop, and bought some extra balsa, too. My gut feeling told me that the 180 outrunner should be able to easily handle a 24" wingspan high wing scale flyer.

I am in no way a build expert compared to many of you, as I've seen many of you do wonderfully beautiful builds. I've read through several of the other Guillow conversions on this site and it has been very enlightening. Thanks to everyone for posting their experiences and ideas. I'm definitely going to use some ideas you've posted, like Matt D.'s ideas for wing removal, and Konrad's idea for getting rid of the starved-horse look.

Anyway, I've been working on the fuse and wing. I'll try to post some pictures. Please be patient if I don't get it right, this is one of my first posts on this site.
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Sep 28, 2011, 12:10 AM
Troy Bowman
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Other modifications to the wing:

I didn't want the starved horse look on the wing either, so I skipped the frontmost stringer entirely and sheeted the leading edge with 1/32 balsa (this provides more strength too) to the middle stringer.

To get rid of the starved horse look on the aft portion of the wing, I cut the stringer notches deeper and put the stringer deep into the formers. I covered the stringer with a tiny piece of scrap stringer and sanded it to shape. No blocky airfoil on this baby!

For the ailerons, I bought some trailing edge balsa stock that appeared to be the right size for the wing to become an aileron. I used that stock in judging how deep to cut the formers, and I used the kit's harder balsa on the trailing edge where the aileron will hinge. I plan to drill some holes in the aileron stock to reduce their weight, they each weigh 1.5g (0.05oz). I dunno, maybe if I need more tail weight (after all that weight I've added to the nose, ugh), I might just keep them whole.

To join the wing together without the fuselage involved, I let the leading, trailing, and center spar continue out off the end of the wing plan. I didn't put the two formers next to each other like the plan suggests. Instead, I put the next former an inch away, just as the other formers are. After spending some time in measuring and cutting the spar and leading/trailing edges, making sure that the leading edge for both wings was perfectly straight with the top stringers touching with a minimal (1/2") dihedral, I built a balsa ply to act as the leading edge to fit the saddle, and used it to also add strength in joining the two wing halves together at the same dihedral. After measuring the wing for alignment, I formed some small front airfoil the spars to hug the front part of the saddle and hold it in alignment. They go from the balsa ply to the leading edge and are strengthened by the sheeting.

Anyway, what a blast! I blew away over 9 hours on this wing alone today, and I still have to figure out how I'll mount the servos.
Sep 28, 2011, 07:40 AM
Registerd Beaver
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Nice work Troy, I hope it flies as good as it looks

Phil
Sep 29, 2011, 01:49 AM
Registered User
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I have never worried about the starved horse look, I always make sure to make the grain of the covering (Litespan is what I usually use) run the short way across so it has less chance of sagging.

This is especilly important when covering the wings, if you do it the wrong way you can have some real sags develop between the ribs.

Just my 2 cents worth.......

BTW, build is going great.

Dan
Oct 09, 2011, 10:06 PM
Troy Bowman
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Thread OP
Quote:
Originally Posted by Dan Parson
I have never worried about the starved horse look, I always make sure to make the grain of the covering (Litespan is what I usually use) run the short way across so it has less chance of sagging.

This is especilly important when covering the wings, if you do it the wrong way you can have some real sags develop between the ribs.
You make a good point about the grain, but I don't plan to use tissue. I'm using Parklite, and it doesn't seem to have a grain. At least I can't tell if there is one.

Either way, these Guillow kits are notorious for starved horse look. I'm sure other kits are better designed so that bulkheads don't poke through on the fuselage, and so that stringers don't add a checkerboard look to the top of the wing. I've finished covering the wing and I'll post pictures in a bit. It doesn't look like a Guillow wing at all.
Oct 09, 2011, 10:48 PM
Troy Bowman
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Servo Extension


Like heck I'm going to pay $6 for this tiny wire. So I began my quest to find a wire. Ethernet wire is way too thick and heavy. I eventually found some old 80-conductor udma cable (everything is sata nowadays anyway), and I found that it is very comparable in being stranded and its weight! The $6 extension cost is 0.59g, according to the website, but 6" of this udma cable is 0.4g! I'm sure the connectors factor into the extra weight, but hey.

I got some neodymium magnets from indigo instruments... They're cheap and powerful. I used 7.5x7.5x1mm. Interestingly, one side seems to hold a lot more than the other side. Both should be quite powerful enough to hold the back of the wing on.
Oct 09, 2011, 11:03 PM
Troy Bowman
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Tail feathers


Here are some pictures of the tail surfaces.

I modified the rudder to have more strength in the bottom since it's going to be holding a tailwheel, and added a little carbon rod to hold the elevators together. Other than that, they're basically the same-old conversion stuff, splitting where they should split with some extra balsa...

I weighted before and after covering as I was curious to see how much more the covering weighs. Apparently a lot more than I thought!
Oct 09, 2011, 11:11 PM
Troy Bowman
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Engine and Cowl


Here are some pictures of the engine and cowling.

I used indgo instruments neodymium magnets, 5x5x1mm to stick the cowl on.

I'm using an adapter for the prop I found at shapeways by shapeways user ICU.
Oct 09, 2011, 11:23 PM
Troy Bowman
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Covering, Linkages, Windshield


I've finished covering, and here's a picture or three. The wing doesn't look much like a guillows wing, does it?

I used 0.050" carbon fiber rods as pushrods as they're light and really hard. I threaded them on to 0.025" piano wire.

I've started tonight on glueing the windshield on. I did NOT like the kit's way of having a balsa support running down the center, so I fashioned my own cut of the plastic and made my own wrap-around. I think it looks way better, but time will tell if it will hold up and if the canopy glue will keep it glued.
Oct 10, 2011, 01:42 AM
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wizard of odd's Avatar
A very neat buid indeed- well done. Do you know what the AUW is yet?

Hope it flies well!

Odd
Oct 10, 2011, 09:11 PM
Troy Bowman
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Quote:
Originally Posted by wizard of odd
A very neat buid indeed- well done. Do you know what the AUW is yet?

Hope it flies well!

Odd
I'm waiting for the canopy glue to dry to get a final weight, which I'll post later (canopy glue trapped between canopy and covering takes quite a while). I also need to paint the cowl first, which will add more weight. When I weighed it before the canopy and pushrods, it was about 102g (3.6oz), 112g (3.95oz) with battery. It'll probably be a bit more when I'm done. Yup, this isn't the lightest ship, but on the other hand, I used mostly stock guillow kit wood, as well as adding extra structure on the nose, battery hatch, landing gear mount, and removable wing. Either way, I expect it to fly well at about 112g. To think the covering added about 25% to 30% of the 100g, and the radio equipment and motor is another 20g, the balsa structure is at about 50g...
Oct 11, 2011, 09:23 PM
Troy Bowman
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Finals


Here are some final photos before I go destroy it in the maiden flight Sorry, a couple of them are blurry, my camera wouldn't focus on the right thing.

The weight was a little more than I had hoped, but then again, I didn't really try to keep it light. I was more concerned with getting it built! Ha. I'm sure it'll still fly with all that wing area.

I've just got to wait for a really calm day, and off I go!
Oct 11, 2011, 09:39 PM
Troy Bowman
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Cog


The center of gravity is dead-on with the 180mah battery all the way to the front. Thank goodness I don't have to add extra weight anywhere to balance. I was thinking it'd be nose heavy before I covered it, but after I covered it, the empennage ended up getting a little too heavy, so I can't really run the 120mah battery without adding weight. I could put a spinner on, like this one. The spinner adds the necessary nose weight to fly with a 120 mah battery, putting the weight at 114.5g, saving 3 grams. It looks a tad too big though.
Oct 12, 2011, 04:31 AM
Suspended Account
I should have bought one of those ARFs for the parts. The little bl board is almost as expensive, any you get 2 servos and a bl motor with the plane.

The little Cox and FlyZone spinners can work well. They have a screw mounted backing plate, and can be hacked a bit for your specific app. Moving the needed noseweight to the spinner and reducing batt size is definitely the right idea, to get as light as possible. I think you'll be more than fine at your weight. Their little Cessna 150 is not a bad flyer at 6.5oz. The little Guillows spinners work well if you can trim them straight, and CA glue to the prop. Not exactly a serviceable setup however, unless you drill an acdcess hole in the center. I had one mounted perfectly on the C150, and of course managed to lose it also. I think it got knocked off while landing in the tall weeds, and I didn't notice it until after leaving the spot. You'd think something red would stick out like a sore thumb, but it managed to hide.
Bill
Oct 12, 2011, 02:56 PM
It's a Great Day to Fly
LenBFP's Avatar
Nice work, your pictures are very nice too.

Len


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