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Old Jul 16, 2012, 12:04 PM
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Cartoon A-7 prop driven

I know you guys are accustomed to pointy, fast and scale. Ever thought about blunt ,short, and fat with slow landing speeds? This may not be the perfect fit for this thread topic since the prop is a "puller " but at least you don't have to worry about stitches.
I feel I need to spread the word about this model category. You may have seen the fatty planes and the cartoon profile models but the ones I've been designing lately are a bit different.
My definition of "Cartoon scale" is simply models that are caricatures of a scale plane but not skewed enough to make them hard to fly. I've seen and built two of the planes called "Fatty planes" and it was not what I was looking for in a model. Same goes for the profile models.
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Old Jul 16, 2012, 12:10 PM
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Another problem with the fatty planes is the foam shaping required to make it look like a scale model. If you have to tell somebody what the plane is supposed to be it's not close enough to call it scale.
I have developed plastic parts that cover the compound curved portions of the models to ease assembly and simplify construction to the point that if you can bond flat foam sheets together you can build any of the models below.
ME-109
http://www.rcgroups.com/forums/showt...5&goto=newpost

mustang / Miss America
http://www.rcgroups.com/forums/showt...4&goto=newpost

Mig and saber
http://www.rcgroups.com/forums/showt...2&goto=newpost

P-40
http://www.rcgroups.com/forums/showthread.php?t=1525775

spitfire
http://www.rcgroups.com/forums/showthread.php?t=1525775
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Old Jul 16, 2012, 12:12 PM
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This addition to the collection is the A-7
This model has the ability to be powered with a propeller or as an EDF.
(The kit will make either version) Parkflyerplastics
The design makes use of the popfly wing; one of the most forgiving airfoils I have ever used.
so I'll start the construction there.
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Old Jul 16, 2012, 12:14 PM
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development

I have built four of these models, two of each type. As the thread moves on I'll let you in on the assembly mistakes and why I changed the steps.
The first version was the prop driven model. It crashed after a few flights but not before it taught me the importance of getting the fin straight. Again . . .the fin must be straight.
I installed a rudder servo to try and fix it and it worked very well. The extreme yaw the model had went away. However if you put a rudder input in during flight it was too effective, even with only 3/16 travel. if you like flying knife edge go for it.
The model died on the return trip from a fun fly in a friends trailer. A large model that we thought was tied down fell on it. On the up side I was able to confirm the patterns.
The first EDF version is still around. I did have an elevator servo failure though , stripped gear from the same trailer accident. the problem was that the servo was buried between the duct and the wing.
The servo has been moved and the patterns was tested on this version as well.

I'll give you guys a little while to subscribe then off we go.
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Old Jul 16, 2012, 12:46 PM
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subscribed!
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Old Jul 16, 2012, 01:50 PM
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Joe
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Old Jul 16, 2012, 03:57 PM
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Now in TN!
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I rarely describe models as "cute" but these really cute little models. And the workmanship looks to be exactly as I would expect from you Keith. Carry on!

J
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Old Jul 16, 2012, 05:23 PM
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I'm in, subscribed! What size EDF are you going with?

Ksqm
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Old Jul 16, 2012, 08:39 PM
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55mm
I figure if I have several looking for a job others do to.
My units are several years old so I figure that if it fly's this good on old stuff you guys will do better.

(there is a thread running on that version in the EDF foamies section)
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Old Jul 17, 2012, 02:59 PM
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This is how it works best for me.
I'll throw down some build thread and wait a day for questions and comments.
After I'm done with the build I'll add updates and any improvements .
feel free to do the same.

Cartoon A 7 prop driven (3 min 10 sec)
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Old Jul 17, 2012, 02:59 PM
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Wing

Quick note:
If you are building your wing from the popfly wing kit, your new root rib number is R3, this will give you enough sheeting material to make the wing tip. discard ribs R-1 and R-2.
1
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Old Jul 17, 2012, 03:01 PM
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I started construction by cutting the bottom sheeting and marking the rib locations at the trailing edge. I marked the location on the control surfaces to make it easy to mark for us. The ribs are cut from the patterns and bonded to the leading edge with polyurethane glue and allowed to dry completely over the plans to ensure rib alignment.

Before the ribs were attached to the sheeting I had to shape the leading edge to make the sheet to rib contact easy. I used a 2 inch tube to bend the sheeting by trapping it against angle stock . The sheeting edge is placed in the angle stock where the tube makes contact and held there by holding the tube against it. The tool and sheeting is held against the edge of the work surface and rolled; keeping the tube against the table for support. One half rotation with a 3 inch tube was all I needed.
Or you can shim the forward edge with a tube and use weights to hold it down.
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Old Jul 17, 2012, 03:02 PM
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I applied polyurethane glue to the ribs and the bottom of the leading edge along the front. The assembly was placed on the sheeting using the marks for alignment. Weights were placed on each rib at the trailing edge then a weighted stick spanned the ribs to apply clamp pressure to the middle. Foam wedges can be used to hold the sheeting against the leading edge but I used a tube. The wing tip frame is tapered at its trailing edge. it is then bonded to the leading edge and trailing edge tip only.
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Old Jul 17, 2012, 03:03 PM
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To prepare to bond the top sheeting in place I had to shape the foam sheeting again with the same method as before with a 3 inch tube and almost a full rotation. A little curve is all you need.
I block sanded a slight taper in the trailing edge sheeting and on the leading edge spar. I applied glue to the ribs, trailing edge and leading edge and put the weights in place working from the back to the front then gave it a day to dry completely.
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Old Jul 17, 2012, 03:04 PM
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now the only real problem you will have is the plans only show the right wing.
Printing the left would be a waste since you only really use it for about 15 min to lay out the panel.
Some people hose down the paper with hairspray and just flip the page over.
All you really need is the wing rib location at the trailing edge. The slot in the forward spar will point it in the right direction and R-1 will set the angle in relation to the wing panel.
don't worry about being off a little, it's a very forgiving wing as you can see here.
Popfly2 Night Flyer (2 min 34 sec)


questions?
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