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Author Topic: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General  (Read 8109 times)
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Konrad
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« on: August 10, 2012, 05:40:23 PM »

As this site has a dedicated form for the building (conversion) of stick and tissue models to R/C I thought it might be best to have a thread about the general requirements. This thread is intended to cover general modifications of rubber band kits for the electric R/C conversion, such as those made by Dumas, Herr and Guillow. These procedures can be applied to just about any keel and former type build. I’ll be showing how I do these conversion using mostly Guillow and Comet kits.

While it is important to eliminate weight it is nowhere near as critical as it was for a good rubber band free flight model. As a general rule I like to remove weight from behind the center of gravity. Much of the weight I removed is often added back in the way of stronger wings, landing gear, cowl and motor mounts.

I like to keep this philosophical point in my mind as I do the conversions. Any weight you save from the tail will result in 3 times that weight being saved from the need of nose weight. So for one gram saved from the tail will save you the need to add 3 grams of nose weight. This one gram savings from the tail will save a total of 4 grams from the overall weight of the aircraft. This is key to getting many of the short nosed scale ships to fly well. Try to build and set up your model to be nose heavy. It only takes about ¼ as much ballast to correct a nose heavy ship as it does a tail heavy ship.

The only real hard and fast rule is that it is critical to have a properly balance ship. This is much more important than a light ship. I like to add structure where needed to my models rather than ballast. This is why I make the nose and gear strong. But I will add ballast to bring the center of gravity where it needs to be!

All the best,
Konrad
« Last Edit: August 10, 2012, 07:10:58 PM by Konrad » Logged

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« Reply #1 on: August 10, 2012, 05:43:31 PM »

With the introduction out of the way lets see how it is done. In an effort to add strength and lighten the structure I like to make laminated outlines of most wing tips and curved tails. The first thing I do is draw an outline of the curved part 1/8 smaller than the finished size. I then use this sketch to make a foam form on which I will laminate 4 strips of 1/32 x 1/4 balsa. (See photos 1) I soak the strips in hot water prior to forming. I dry these hoops in a microwave oven in 15-second intervals followed by a 2 minute cool down. It takes about 20 minutes for the hoops to dry.

The hoops (outline parts) are made up of several laminations of thin balsa wood. For this size, 18” to 30 inch or so wing span, aircraft I like to cut my laminations from 1/32 sheet balsa. As I want the finished parts to be 1/8 (0.125) thick I cut my laminating strips a little bigger (0.200 wide) to allow for the miss-alignment of the lamination. This 1/16+ (0.075) oversize will allow me to sand the top and bottom of the hoop to the final thickness of 1/8. In this case the hoops are also 1/8 wide (1/32 balsa x 4 strips).
I soak the strips in boiling hot water for a minute or two. I then lather (slobber and make a mess) the strips with Titebond glue (made by Franklin international). This is a yellow sandable (PVA wood glue). I use the “original” formula. (See photos 2 & 3)
I then stack this lamination together and wipe off any excess glue and water with a paper towel. I then form these strips around the form holding the strips to the form with scotch tape. (Note I protect the mold with scotch tape applied to the thin forming surface of the mold as a mold release because Titebond glue will not stick to scotch tape.) (See photo 4) I use as little tape as I can to hold the laminate on the form, as water does not evaporate well through the scotch tape. I force dry this mess in a radar range as noted earlier.

You will note that I use a lot of gussets in the high stressed areas. These gussets have the wood grain going across the glue joint. After all the glue has dried I radiused the gussets to give a pleasing look and remove the stress riser a sudden change in cross section makes. All forms, hoops and built up stabilizer with elevator ( See photo 5 & 6, Guillow Series 300 Cub shown)
Note the use of many corner gussets, Also note that the gussets are radiused. Please note that the lower rear fin gusset (by thumb) is large to allow for elevator movement. This is needed to allow for clearance of the elevator joiner
(See photo 6, Guillow Series 300 Cub shown)
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Konrad
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« Reply #2 on: August 10, 2012, 05:46:15 PM »

Post of Photo 6

All the best,
Konrad


Just some rambling notes:
Some people try to make hoops by pushing pins into the plan along the outline of the part. I often find that as you try to form the balsa wood it kinks on the pins. This can cause a weak spot in the lamination. I always use a form to laminate the balsa around. I don’t soak my wood in ammonia, as this seems to make a curdled mess of the Titebond glue. I use Titebond glue for all my laminating glue joints and most of my other structure as CA makes heavy and brittle glue joint. Don’t try to use soap or other release agent on the forms as these will interfere with the bonding of the internal structure later on. The residue doesn’t allow for a good glue joint on the inside of the hoops,

Sorry for the flash. I build on glass as it makes a great surface to datum off of, it is flat, but it does wreak havoc on my photography.

All the best,
Konrad
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« Reply #3 on: August 10, 2012, 05:52:22 PM »

I like to thin the vertical and side keels to 1/2 their original thickness aft of the wing. I also thin the width of the aft formers to about 1/3 the original width by enlarging the center hole of the former.  (See photo 7 Note there is no need for the side keel bulges in the formers aft of the wing, my error. (Series 300 Cub shown)

As most of the landing stress is torsional not vertical my landing gear is made of small plywood mounts with a high torsion arm anchor. On ships that have wing struts I carry the strut through the wing so as the attach to both the upper and lower spars. For the fuselage mounting of the wing struts I use a 0.015 carry through wire to bind the wing struts together (left and right). (See photo 8 & 9 I hope you can see that the wing struts are connected with a thin 0.015" wire through the fuselage on the white Guillow Champion is from Hank GBZ)


All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #4 on: August 10, 2012, 06:09:48 PM »

On Guillow's aircraft that are less than 30 inches I remove any spars that are bigger than 1/16 square.

As most of my wings have ailerons the need to have some spars to hang the aileron on makes this large spar redundantI also replace this removed spar material with 1/16 square bass wood stingers (spars) that add up to approximately 3/4 the cross section of the spar I removed. (See photos 10, 11 & 12) I also cut down the wing trailing edge to approximately 1/3 the width shown on the plans. Last I remove half the wing ribs. (See photo 13, Guillow 300 series Cub shown)

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
« Last Edit: August 10, 2012, 06:34:04 PM by Konrad » Logged

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« Reply #5 on: August 10, 2012, 06:39:08 PM »

As noted earlier, for strength I often will add gussets with the grain of the gusset going across the joint.

Almost all of my gusset work to support the butt joints is done with balsa inlays, the grain should span the joint. I rarely do a lap joint for gussets, as this will often result in a change in some critical dimension.

I find that I can add gussets to just about all part types joints. Proper gusseting adds a lot of strength and rigidity with little weight gain. (See photo 14 Guillow Series 300 Cub shown)

You may also have seen that I add gussets (scalloped fillers) between some of the stringers. These are often made from 1/32 balsa and do not Have the grain spanning a joint in any direction. These scalloped fillers are more of an aesthetic feature trying to allow the covering to match a former of other defined edge. (See photo 15 Guillow Series 300 Champion 85 lower hatch)

All the best,
Konrad
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Konrad
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« Reply #6 on: August 10, 2012, 06:43:48 PM »

I'm always trying to figure out how the structure will effect the final look of the ship. I do like the faceted look of a stringered structure (Full size aircraft often show this. Even aluminum sheeted ones, as this is caused by the rivets attaching the skins to the stringers) What I don't like is the formers sticking through the covering giving the starved horse 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. (See photo 16)

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. Sand well to remove any bumps. To control the starved horse look of formers sticking through the covering , I scallop the formers between the stringers (See photo 17) (Also see photo 19 in next post).I do this by wrapping sand paper around a cylinder to use as a curved sanding block. (See photo 18)

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #7 on: August 10, 2012, 06:49:32 PM »

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). (See photo 19 & 20) Guillow kits are notorious for poorly or misplaced stringer. Should this happen I add extra stingers where needed to help define the shape. (See photo 21)
Sometimes 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 1/32 (or contest grade 1/16) filler gussets between the stringers to help transition the covering from the stringers to the former. (See photo 22 & 23 Guillow Cherokee)

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Konrad
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« Reply #8 on: August 10, 2012, 07:47:03 PM »

Some more random notes.
The photos may not show is but I like to carry the rear vertical fin spar all the way down the fuselage on models that allow this. The Champ, Cub and Cessnas  allow this. The Cherokee 140 does not.
I also like to make the spars that form the tail feather hinge lines from basswood.

Unfortunately, I tend to cart wheel a lot during my landing attempts. As such I spar my wing with 1/16 basswood for most of my sub 30" conversions.

I still like to use the covering itself as the hinge for most elevators and rudders. ( I don't have to try to slot any spars!)

As for covering I like iron on film. As of this date my favorite is R.A. microlite. In the USA a great source is here http://www.homefly.com/products.asp?id=31

R.A. µlite is half the weight of So-Lite and is much more thermally stable. It doesn't sag near as much as So-Lite.

If you have any general build question please post. I or somebody more knowable will try to help. For more specific question about individual models it might be best to start a dedicated thread.

All the best.
Konrad
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Konrad
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« Reply #9 on: August 14, 2012, 12:25:27 PM »

On ships that have wing struts I carry the strut through the wing so as to attach to both the upper and lower spars.


All the best,
Konrad

This is to expand a little on what was mentioned in reply 03.
I like to give myself a lot of room for adjustments. The classic rib pocket for the receiving of struts doesn’t allow much adjustment nor does it afford much glue area. I like to tie my struts to spars. I do this by placing some filler (shear web) between the spars. I glue the struts to this web. I hope you can see that the strut if free to find its place after the wing is  aligned on the assembly fixture. I do add some filler where the strut passes through the wing to attach the covering.

The white wing is a Guillow Series 300 Champion. The yellow photo is of a Comet 25" Aeronca "K" in a wing alignment fixture. Please note the film fillet on the vertical fin (more on this later).

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #10 on: August 14, 2012, 07:50:51 PM »

One of the largest problems with many of these rubber band scale models is that the wings are effectively 2 piece. That is there is nothing that directly keys the right and left wing at the same incidence relative to each other. 

I have found it necessary to build a fixture much like the one shown. The two inner platforms are on the same plane (geometric term). This defines the angle of incidence to the fuselage. The outer two platforms are also on the same plane relative to each other but they are higher of the building datum (glass) as defined by the needed dihedral.

In the photos you will see some shims. These are used to align the fuse (vertical fin vertical, and to define the washout at the wing tips. Once this is all set I glue the struts in place. I don’t like to rely on the cover to hold trim setting (washout is a trim setting). I do use water based glues should flight testing show that there is a need for adjustment.

Now try not to do what I have done in the last photo! I have made a monkey trap. That is the lower strut anchor point puts the struts inside the fixture. I will have to destroy the inner platforms to free my model from the fixture.

(Model is a Comet Aeronca 'K' 25" seaplane but with wheels)
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #11 on: August 14, 2012, 08:57:19 PM »

Low wing models often use two-piece wings. Most low winged models are also true cantilevered designs (No external supporting struts or wires). It can be a problem coming up with a strong center section that doesn’t weigh a lot.

I can’t say as I have found an elegant solution. I’m showing a solid 1.5 mm 5 ply carry through spar. This spar will key to each wing. I also use it as a support for the landing gear. This spar and some spreader stock on the fuselage formers (wing's de facto center section) near the trailing and leading edges should handle any flight load and most landing loads.
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Konrad
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« Reply #12 on: August 14, 2012, 09:01:14 PM »

(continuation of photos)

(Photos are of the Guillow Piper 140 Cherokee, Series 300 kit)

All the best,
Konrad
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sparkle
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« Reply #13 on: August 15, 2012, 03:40:50 AM »

 Grin Greetings konrad. This info is important to people who have thought of converting this way. i'm glad you have found a use for a credit card!
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Konrad
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« Reply #14 on: August 15, 2012, 09:28:47 AM »

Grin Greetings konrad. This info is important to people who have thought of converting this way. I'm glad you have found a use for a credit card!
Thank you.
If you know of better ways to convert these models to R/C please post. I would love to learn better ways to solve general build problems. What I show is how I do it and isn't by any means the best way to do it.

With credit cards well, I always try to find the good aspects in all things.  Wink

All the best,
Konrad
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« Reply #15 on: August 21, 2012, 05:37:16 AM »

YEah I'll chuck me hat in for yarn,
I've built a Guillow's 500 Series Hellcat- converted to 4channel RC using Nine Eagles gear from their Yak54 model.
16" wingspan and a touch under 2 Oz. flies ok - the big issue was the lack of aileron authority, short flight time, 1:1 glide ratio (Perhaps a bit heavy?)
Built from the kit materials supplied, it was a fairly succesful experiment. Basically it worked "AS IS" out of the Guillows box with as much of Nine Eagles parts as I could glean.

http://www.youtube.com/watch?v=UQfK5wvAWto

Afterwards - I built a "Sonex" from HPA plans - actually I built the Onex, single seat version. this was a little more planned as a build.
The plan shows 1/16 everywhere at 13" - I enlarged mine to 16" wingspan and went with 3/32 everywhere - fairly light wood.
AS yet unflown I'm hoping this model will perform better than the Hellcat.
4 x 1.5g Linear servos, AP02 Motor, 3amp esc, FlyDream receiver, 150mAh 1s Lipo... FlyDream is great!!! 4 channel 1gram receiver!!!
Pics for the forum!!
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #16 on: August 21, 2012, 05:38:56 AM »

I thinks it best put this way - Have a go!
Tom.
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« Reply #17 on: August 22, 2012, 11:18:21 PM »

Control authority is a subject that should be discussed.
Per the lift equation control power (lift) goes up by the square of the speed. Now as these mini R/C aircraft are becoming lighter and lighter they can fly slower. This means that as the ship gets slower to have the same response the control surfaces need to get larger (or move more). You may have noticed that some of the better micro and mini R/C have oversized ailerons.  There are also some other aerodynamic reason for making the control surface wider (chord wise). A low aspect ratio (short fat) control surface on these smaller models often work better than long skinny control surface. Also setting up the ailerons with the upward aileron moving more than the downward aileron often pays huge dividends concerning aileron response (authority). All of my aileron equipped models with wing spans under 30" have oversized (larger than scale) ailerons.

Weight has little to do with glide slope. That is more a function of drag. Yes, weight and speed do effect drag.

All the best,
Konrad
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« Reply #18 on: August 25, 2012, 10:21:41 AM »

Staying on the subject of control power, I like sealed hinge lines. Sealed hinge lines result in more control authority. This is because the high pressure air does not bleed through the hinge line disturbing the pressure differential between the top and bottom of the surface.

Proper hinging can result in tight fitting control surfaces. Drawing one shows some of the ways and concerns with hinging. The second picture shows a pined, at the ends of the control surface, hinge.

In the third picture I show that even with a tight fitting control surface there is still a gap. You can see this by the seeing the green cutting board through the hinge line on the top wing. The bottom wing has the hinge gap sealed with a bit of covering. One can use scotch tape or the film covering as a seal. I like to use film covering as the seal (it is easier to push into the 'V' gap). Insert the seal and trim to fit. Make sure that the seal does not limit the control movement. (Photos are of a Guillow "Champ 85" series 300 kit)

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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« Reply #19 on: August 27, 2012, 02:05:23 AM »

Good stuff Konrad,

  I'll add some pics of what I do with the Dumas stuff i.e. the Gee Bee and the Peashooter tomorrow when I have time to do a proper post.  Still it's nice to see pics of the Champ being toted about as a "what to do" example. 

Hank

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« Reply #20 on: August 28, 2012, 10:27:00 AM »

Thanks Hank,
Anything you can add to the general conversation would be welcomed.


The Vertical Fin Fillet.

With the advent of modern coverings I think it is a shame not to model a cloth vertical fin filet if the full size ship had one. This fillet is not that difficult to do (it is not a beginners project) if you know how to stretch and shrink iron on coverings.

What is needed is a place to attach the covering above the stabilizer and a dorsal fin radius between the fuselage spine and vertical fin.  This might require a bit of planning like moving the stab mount down or allowing a stringer to go over the stabilizer.

There are a few tricks I have learned to do this fillet. One of the most important detail is that everything must be smooth. The second is to wrap the covering over the spin and upper longeron so that there is some film adhesive that won't get re-heated when the over lapping piece is ironed on. On the actual fin I often seal these flaps with a layer of CA glue. This is because there is a lot of pulling and sliding going on here when the opposite piece of the fin covering is added.

This film fillet goes a long way towards not making your model look like a glorified Ugly Stick! It should also give you a lot of scale points, without a lot of weight, if the original aircraft had a vertical fillet.

(Photos are of a Comet 25" Aeronca K and 24" Guillow Cub and Champ)

All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
« Last Edit: August 28, 2012, 10:37:48 AM by Konrad » Logged

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Hank G B Z
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« Reply #21 on: August 28, 2012, 08:34:47 PM »

Ok Gang here's a bit from my info.  

  I've worked with Konrad closely on several conversions of both my stuff and his stuff.  The thing that I've found that makes a great FF to R/C conversion is to make it a R/C model.  Positive control over a 1.5 oz model is just as important as a 15lb model.  So choose equipment and hardware wisely.  

  Also wash out is very important.  I have given up on trying to hold wash out in a model with the covering material. I have started building wash out in to the wing as I build the model.  The most common way I do this is by raising the wing tip up on a flat bottom air foil.  This makes the last two ribs or so more semi-symetrical and give built in wash out that is much more stable and predictable than trying to use covering.  I did this on my Dumas Gee Bee Z, Fairchild Fc-2 and i'm currently doing it on my Dumas Peashooter.  I'll post some pics up of the different wings to show the wash out.  

  In the case of the Fairchild i just laid the wing tip on top of the spar and let it come around to the trailing edge.  Then I grafted on some material to the ribs to make them blend smoothly to the wing tip.  I then sanded away at the bottom of the rib again until it was smooth and gave me the wash out I was looking for.  

  For the Gee Bee Z I brought the wing tip lamination up to the top of the wing to make the upper spar run all the way to the tip.  Then I did the same grafting and sanding technique as the fairchild.  

  On my Guillows champ I just set the wash out with the struts but that is hard to do with a low wing model that doesn't have struts.  

Hank

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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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Konrad
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« Reply #22 on: August 31, 2012, 10:45:04 AM »

Hank,
Great post about washout. I too can't over emphasize the importance of washout with these small models. Another great point is to make them more like an R/C model. That is lower the decalage (angle of incidence) between the wing and stab on most models. This more so on models that are reported to fly well as free flight models. I also set up my motor thrust lines to have about 2° to 3° down thrust and about 2° of right thrust if for no other reason than to make sure that I don't have any up thrust of left thrust. Embarrassed

I'm coming close to running out of ideas for general discussion about these conversions. Since you have successfully converted a lot more of these than I, do you (or anybody else) have any general ideas about landing gear, firewalls, radio mounting, or control actuation?

All the best,
Konrad
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dosco
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« Reply #23 on: August 31, 2012, 10:53:33 AM »

What do you use for "pushrods?" Pull-pull setup with Kevlar? Piano wire?

I know that Stu Meyers uses Beadalon "wire" and teflon tubes ...



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Konrad
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Measure twice cut once

« Reply #24 on: August 31, 2012, 12:27:15 PM »

Control setup is a constantly evolving subject. I like to use control horns made from .75mm (0.032") plywood.
On pull pull set ups I have used Kevlar. But now like spider wire (from the fishing tackle shop). It is cheaper and doesn't develop the yellow kevlar fuzz.  For push rods I like .75mm carbon rod with 0.38 (0.015) wire ends held on with heat shrink tubing.

I often like to use clear 3 ring binder hole reinforcements where the cables and push rods exit.

For Bowden tube set ups, I like to use CA capillary tubes with 0.36mm coated wire cable. I think that a simple loop with ferrel fitting works good for the ends.

(Photos are of a Dumas P-6E, Guillow Fairchild 24, and Comet Aeronca K)
All the best,
Konrad
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Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
Re: Conversion of Dumas, Comet, Herr and Guillow rubber band kits to R/C - General
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