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Old Dec 07, 2008, 08:48 PM
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Everett Wa.
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Fun Build II Guillow's Cherokee, 20 inch plan build

Gentlemen I’m entering the Fun Build 2 contest with a plan built Guillow’s 20 inch Piper Cherokee. These plans are found in the Guillow’s kit #307. As the rules state plans only this forces me to change the cowl design. The original kit suffers from the bane of most Guillow’s kit that is the awful plastic cowl. I have redesigned the cowl to be an integral part of the fuselage and made of balsa wood. I hope to work out a full flying stabilizer. I will have an operational rudder with steerable nose wheel. I also hope to have ailerons. The landing gear will be my now standard torsion bar style with high anchor. Other than the shape of the cowl (I hope I make it more scale) the outline of the little Cherokee will be close to that of what is drawn on the Guillow’s plan sheet.

I have hand cut the fuselage formers to be about 1/3 the weight of what is shown on the plans. I have also redrawn the airfoils to have a large Philips entry. I have also taken out some of the chamber from the front of the airfoil. While there may be some debate as to the virtue of the stock airfoil for free flight it offers no benefit for the R/C pilot. Also as I’m hand cutting all the parts I have decided to try to laminate all four keels from 2 each 1/16 square strips. This will add a lot of strength while saving me the time to cut the side keels from sheet. I have also eliminated the deep keel slot from the fuselage formers. As the Cherokee’s fuselage is almost as wide as it is tall, half the formers grain is going the wrong direction. To solve this I have glued some 1/16 square supports to the top and bottom of the formers These supports not only support the grain of the former but also act as keys to align the other half of the former as one builds the other half of the fuselage (in the air, off the board).
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Last edited by Konrad; Dec 08, 2008 at 08:06 AM.
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Old Dec 07, 2008, 10:51 PM
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Everett Wa.
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Fuselage is starting to look like a canoe! The second stringer from the bottom keel is doubled between B2 and B4 as this will become the side of the hatch opening. This doubler tapers to nothing outside of B2 and B4 so as not to kink the main stringer. You can also see a side stringer doubler in front of B2 to support this stringer, as it tries to bend into the cowl. As the formers are rather weak until all the "H parts are added, I had to add a temporary building aid to keep the top and bottom apart while I bend the stringers. I hope you can see the 1/16 cross pieces on some of the formers top and bottom. This keep the formers from being crushed as the wood grain in the former is going the wrong direction. This is a problem with most Guillow kits and is made worse with the narrow cross section I choose to use.

I have made the cowl a little wider than stock and with a much more triangular shape up front. The nose block will be made from 7 layers of 1/16 balsa. Top of the nose is open until I add the motor firewall and nose gear hard points. Most of the cowl sides will be inlayed with 1/16 (now 1/8) balsa to give strength and shape to the nose.

Konrad
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Last edited by Konrad; Dec 14, 2008 at 02:36 PM. Reason: Add: art work
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Old Dec 08, 2008, 01:50 AM
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Santa Clara, CA
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I tried cuting new keels for the cub (miserable). The laminated keel is a cool idea and it seems like it can solve so many problems....this will no doubt lead me to trying to build something (larger in WS) and far beyond my current capability.

That Fuse is simply Beautiful.

I can't wait to see this one come together!

Brent
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Old Dec 08, 2008, 08:41 AM
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Everett Wa.
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Brent,
Thank you for the kind words.

“...this will no doubt lead me to trying to build something (larger in WS) and far beyond my current capability.”

Will this still be a “stick and tissue gummy band conversion”? The 30 inch stuff is great. I also like the Dumas/ Pat Tritle stuff.

As I like general aviation stuff I have looked at some kits and can recommend that you to stay away from the Guillow’s Cessna Skyhawk and Dumas Bonanza as these kits have too much plastic in the green house for my liking. The Guillow’s Cessna Skyhawk depends on this plastic to hold the wings on (no thanks)!

On the laminated keels make sure you sand lightly and only sand in one direction. NO BACK AND FORTH action as this will snap the keels! I can’t say that my laminated keels are lighter than the stock, sheet cut, keels even though they are 1/2 the size. This is because I made them from 10lbs/foot3 wood and there is a lot of glue joint.

Konrad
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Old Dec 08, 2008, 09:37 AM
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Hey Konrad,

I agree with what brent said and I'll also say that you've out done yourself in the pursuit of Lightness.

I might just have to enter this contest after all.

After the sportster is finished that is.

looking forward to more pics.

Henry
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Old Dec 08, 2008, 04:03 PM
It flew once before...
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Northwood , New Hampshire
Joined Jul 2004
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Konrad ,

Great to see you enter in the fun Looking forward to your build . You guys always amaze me with these small models .

-John
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Old Dec 13, 2008, 08:37 PM
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Everett Wa.
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I'm sorry I misspoke when I said earlier that I would use 1/16 balsa for the cowl inlay work. What I am using is 1/8 contest grade balsa. Contest grade is balsa that weighs about 4 to 6 lbs per cubic foot. This is half the weight of most “good balsa” I build most of my ships from 8 lbs to 10 lbs wood. This means that for the same area of wood my 1/8 contest grade balsa part weighs about the same as my normal 1/16 sheet part.
The added dimension of the 1/8-sheeted inlayed part allows for more shaping with the sanding block. This is a real benefit as there are a lot of contour changes in the front of this Cherokee cowl. In one of the photos you can see the final shape on the right and the raw blocks on the left. It would have been almost impossible to bend the 1/16 sheet to make the shape needed. But with 1/8 contest grade inlays I was able to do this and still be about 3/4 the weight that it would have been had I used 1/16 8 lbs sheet inlays. I hope you can see that some of the curves were so severe that I needed to cut some of the inlays on the bias (grain going diagonally).

I did not like the way the front of the fuselage was blending into the wing mounting box. This is why I moved the bottom stringer up 3 mm from where it is shown on the Guillow's plan on the first Guillow former. With some gusset work later on this should look OK.

All the best,
Konrad
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Last edited by Konrad; Dec 14, 2008 at 07:24 PM. Reason: add: art work
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Old Dec 14, 2008, 10:43 AM
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Hey Konrad,

She's looking good. What are you going to do about the spar since it looks like the plane will have a two piece wing?

Henry
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Last edited by HanksGB; Dec 15, 2008 at 09:29 AM.
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Old Dec 14, 2008, 10:50 PM
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Everett Wa.
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Hank,
While the plane may be a one-piece ship the wings are two-piece with the standard Guillows butt joints. As these are fully cantilevered wings (no struts) this causes a problem. I’m thinking of using 1 or 2 spruce carry through spars. These spars may be 1/8 x 1/4 and go to the end of the landing gear blocks. I’m still thinking about this issue and have to say the design is not finalized.

As you know a cantilevered design is a sin against the structural gods. The aesthetic gods and aerodynamic gods like them but heaven help you when you go against the structural gods.

Still thinking, or would that be praying for a solution.
Konrad
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Old Dec 16, 2008, 03:42 PM
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Everett Wa.
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I have to admit I like the faceted look of well-placed stringer. But the starved horse look of the formers sticking through can destroy the nice look. As the covering can only span straight across the stringers any curve to the fuselage cross-section needs to be controlled by the placement of stringers not the former itself. To test to see if there are enough stringers and that they are properly placed I do a credit card test. This test is accomplished by placing a credit card across two adjacent stringers. Then moving the credit card along the stringers. If you can feel any disruption (bump) to the smooth movement of the credit card this means that whatever it is causing the bump will show through when you cover the ship. To solve this one usually scallops the formers between the stringers.
Now if the credit card actually stops or sticks this means that there may not be enough stringers to define the cross section of the model (former). Should this happen I add extra stingers where needed to help define the shape.
Some times there is no option but to leave the former as it was cut. When this happens such as around windshields and hatches I use a gusset between the stringers to help transition the covering from the stringers to the former.
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Last edited by Konrad; Dec 16, 2008 at 10:00 PM.
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Old Dec 16, 2008, 06:40 PM
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Great work, Konrad. You're a man obsessed (in a good way!).

--Doug
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Old Dec 16, 2008, 09:29 PM
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Hey Konrad,

She's looking better all the time. Thanks for the credit card tip sounds like a good thing to me.

I also like your spar Idea. Will you be using washout or a progressive airfoil?

Henry
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Old Dec 19, 2008, 09:55 AM
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Cornwall, UK
Joined Jan 2008
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I have just this second had one of these arrive at the door, a good'ol ebay bargain.

Looking forward to giving it ago, I am hoping to use Konrads fine work as some good pointers to r/c conversion as I have not attempted something like this befor.

Will now be watching this thread with much interest

Cheers

Guy.
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Old Dec 19, 2008, 10:30 AM
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This is random and sorta only half on topic but there is just something about the flat bottom of that fuse that gets me going....

The possibilites are numerous....I can even imagine a twin (maybe a Seneca II)
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Last edited by vp46; Dec 22, 2008 at 11:07 AM.
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Old Dec 20, 2008, 07:30 AM
Slow 'n Steady...Grease 'r In
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Maine
Joined Oct 2008
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Good to see you building again Konrad!

KP
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