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Scratch

Old 03-22-2008, 10:46 AM
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ebeneezer3
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Default Scratch

I bought a Fly RC yesterday mostly because it said "Free Pullout Plan". The rest of the issue was all about ARFs, one set the author back 3K when complete. The plan wasn't exactly free since it has to be enlarged 250%. It designed for electric or Norvel .074. 40 inch span, box fuse and all up weight 20-24 oz. control is 4 channel. A little heavy? Might make a good aileron trainer. Designed to be a very simple first build.

Oh it's named the "Scratch"
Old 03-22-2008, 11:12 AM
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combatpigg
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Default RE: Scratch

A well designed and equipped .074 powered plane shouldn't weigh more than 20 ozs to be airworthy. The extra ozs above that are significant, they will limit what the plane is capable of at that power level.
At 24 ozs it's time to be thinking .10-.15
Old 03-22-2008, 11:42 AM
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Default RE: Scratch

I've got the plan sitting next to my keyboard. I don't usually buy Fly RC (I've never done an ARF) but the plan lured me in. I was wondering about trying to scale it to sure start size with just ailerons and elevator. Maybe a 34 or 35 inch wing. It looks like there are plenty of places to trim a little weight.
Old 03-22-2008, 12:42 PM
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soarrich
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Default RE: Scratch

The best thing about the 1/2A forum is people still build, some even scratch build, it's so refreashing. [sm=wink_smile.gif]
Old 03-22-2008, 01:21 PM
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combatpigg
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Default RE: Scratch

Matt, some designs lend themselves well to scaling down. In some cases you can scale down the whole plane, but leave the wing, fin and stab area a little bit longer/larger depending on what you're looking for. Some designs just don't scale down well because they were bricks to start with.

One thing is for sure, all those doublers, triplers, braces, pieces of liteply, extra ribs, twice heavy spars, etc. sure make good kindling after the plane tries to make a short cut to china.

I think a good rule of thumb for any sport design is that after a crash, if the engine case breaks, but the fuselage survives....then the plane is probably built too heavy.
Old 03-22-2008, 02:00 PM
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soarrich
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Default RE: Scratch


ORIGINAL: combatpigg
I think a good rule of thumb for any sport design is that after a crash, if the engine case breaks, but the fuselage survives....then the plane is probably built too heavy.
That would diffently be a good clue!
Old 03-22-2008, 09:42 PM
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Default RE: Scratch

Hmmm. Yea I see your point CP. You could nearly get by with a .15 and some spruce spars. With that ply doubler it is probably stronger than some of my 1/12 scale combat birds. Why two 1/4 in ribs?
Old 03-24-2008, 12:22 PM
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Default RE: Scratch

I have found the norvel 074 to be able to fly aircraft significantly heavier than 20 oz, and do so with authority. I guess it all depends what you want to do with your airplanes. I consider 24 oz to be a fantastic weight for the 074.

I'm not one to hover or break speed records, but I feel my planes are very "Airworthy"

At the risk of sounding like the former Pres Clinton, "That depents on what your definition of the word 'airworthy' is" (Done in my best Arkasas drawl )

I built and flew the Herr Mustang on an 074 with full sized gear. She flew 300 plus flights at 32 oz with almost trainer like qualities.

A HOB p-47 on the 074 was spirited at 24 oz. I never felt she was hurting for speed.

The airtronics Warlock is very fast!, and highly powered at 20.5 oz on the same engine


Digger
Old 03-24-2008, 03:06 PM
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mtntopgeo
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Default RE: Scratch

Although I may question the term "airworthy" in CP's statement, I tend to go along with his 20 OZ figure for performance. I've gone as high as 30 OZ, (& heard of guys saying that the little engine moves a 40 Oz plane nicely), but 20 OZs seems to be the line for spirited performance & decent verticle. Had/have a Mini Super Sportster with a .074 Norvel, & it is a load of fun. Comes in at 20 OZS, dry. Also might mention that if you need more than a 6x4 prop, you're really not into the H.P. range of that little engine. Seems that most guys like to use a 7x3. .........The .074, with a 6x4 prop, on a plane with a big (about 270 sq.in. area) wing weighing in at 16 OZs is a blast, & can be a floater, stunter, or hot-rodder. I've tried to build that size lighter, (goal of 14 OZs) but seem to hit a barrier at the 16OZ point. Probably something to do with my finished product looking more like a piece of truss-work for a bridge than a model airplane. ......................... George K.

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