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Old Feb 07, 2013, 02:06 PM
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PC-6

Here are a few photo's of my DH-84 Dragon built from Roger Farleys plans. It is 1/6th scale, electric powered by a couple of AXI 28xx with two 5000Mah 4C paks.It is a great flyer and has no bad tendencies, I can't tell you any of the spec's electrically, I just know it has plenty of power and flys well! The Dragon has such a different wing planform than any of the other three aircraft in the family, no tip stalling here! Couldn't find any pic's of the Rapide, that was in 1986.
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Old Feb 07, 2013, 02:10 PM
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PC-6

As luck would have it the guy I sold the Rapide to years ago sent me this photo, I had built this back in 1986. As it turns out we both reside in Minneapolis and I have built numerous models for him so things worked out well!
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Old Feb 07, 2013, 06:12 PM
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destrat

Very nice job on the 84. Its a great size. I wish I built the 89 about that big. Next time, wether its a 84, 89, 90 or another variation it will be more in that size range. What engines did you use in the 89, and how was the performance?
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Old Feb 07, 2013, 07:42 PM
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When I sold it to this freind of mine I hadn't maidened the plane yet as we moved from Portland to Minneapolis at the time. My buddy wanted it worse than me so I sold it to him and part of the deal was that I got to help in the maiden flight. Back in '86 he put a pair of OS .61 two-strokes in her, more than enough power. We maidened it at a scale fly-in, it tracked straight and lifted off at around 1/2 throttle. Those high aspect ratio wings really made her fly like a sailplane with a reasonably flat glide, no tendency to tip stall, it did have washout built in so that helped matters. He kept it for years never flying it much. He sold or traded it and lo and behold it showed up in my local hobby shop hanging from the ceiling this past fall, so it still is intact and resides here in Minnesota somewhere.

I would think a good pair of .61 4 strokes would be a nice power choice.

Good luck....

Dan
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Old Feb 08, 2013, 04:58 AM
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Quote:
Originally Posted by destrat View Post
PC-6

I would think a good pair of .61 4 strokes would be a nice power choice.

Good luck....

Dan
The nerve of the man!
Recommending gas engines on a dedicated electric forum!
Isn't that a dollar in the swear box?

What would a pair of those motors cost anyway? About $500?
And still have the risk of an engine cutting on climb-out?

Compared to a couple of electrics which can be had for well under $30 plus ESCs at the same again... that's $180 tops - leaving $320 for batteries...
That's an awful lot of spare sets - you could fly all morning!

(There, that should have restored the ethos a little! )
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Old Feb 08, 2013, 01:42 PM
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eye4wings:

I agree, that's why I went to electric also, but PC-6 wanted to know.

Dan
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Old Feb 08, 2013, 02:46 PM
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Hey, I forgive you Dan!... if you'll forgive my lousy Maths... 4 x 30 = 120 NOT 180 !
so that's $380 for batteries.

Robin
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Old Feb 08, 2013, 03:01 PM
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eye4wings:

To tell you the truth, I didn't even notice the math. After working all night I'm usually pretty brain dead in the morning. Hey, what is life anyway if we can't have a little fun bantering back and forth?

Dan
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Old Feb 08, 2013, 09:28 PM
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I feel the need to exonerate myself. I only asked the engine size so I could get a Idea of the power used so I can convert the requirements to electric. I wouldn't dream of powering it with glow, let alone posting it on this thread!
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Old Feb 09, 2013, 03:50 AM
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Well, I've had a good chuckle in this exchange!
Hope you guys have too...

As one who never did reckon up the power in watts that a glow or gas motor was supposed to put out and who never used one that big anyway, the comparison was far too nebulous to be useful to me.

I think the danger I would have run into would have been assuming that the gas engine was 'really big' and I would therefore have to put a couple of 'really big' electric motors in the model... and land up spending a lot more money than I needed and getting an unnecessarily high wing loading as a result.

When I converted to electric (all those years ago) I just learned the new system (as much as I needed of it anyway) and worked out required wattage of motors from the expected weight of the model and resisted the temptation to add too much 'just in case'.
So I found it simpler to reckon up model weight (say 8 pounds) and multiply by the rule of thumb 60W/lb for scale flying and add a small margin (about 25%) for safety... after all we don't want to burn out our motors de we? At first I was quite amazed at how small the motors were that gave the required power - and delighted at how cheap and efficient - but now I just think how grossly inefficient the old glow and gas motors must have been all the time!
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Old Feb 09, 2013, 02:10 PM
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Well, It has been fun and myself I am a convert to electric too. I'm on my 4th model as electric the first three of them being twins! This is where IMHO that electrics really shine, the chances of an engine out at a crirical moment is slim to none, with a scale twin everything has to be in your favor for success.

The Rapide only used the IC engines in its day and I guess I should have clarified myself that I would highly reccomended electric motors for it. I like the general rule of thumb that "eye4wings" uses, pretty simple, think I'll keep that in my bag of tricks.

Dan
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Old Feb 09, 2013, 04:11 PM
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How did you work out your motor sizes before then Dan?
Try a few and pick one?...
Seat of the pants?...
That looks about right?...
None of the above...

Robin
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Old Feb 09, 2013, 08:41 PM
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Since we're on the topic of electric motors for the Rapide, my friend and I are making plans to build a couple of the Schweizter plans DH89s. Any suggestions on the motor sizes would be greatly appreciated.
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Old Feb 10, 2013, 03:52 AM
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It's a bit tricky without knowing the design and builder so as to get a guess at eventual AUW in the ball park yel914.

That is the first step in the way I work out what I need to put in the nacelles.

If the plans you mention are like (or even the same as) the Jerry Bates plans the design is in the old style for glow or gas engines and can be what seems like very heavy to me - or at the other end of the scale if it's more like Ivan P's designs then the AUW comes out a lot less... in the 50-60% range. It makes a big difference in power needed.

Do you have a bit more info please... or a link to somewhere we can view the plans?

Do you know these plans Dan?
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Old Feb 10, 2013, 11:27 AM
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eye4wings:

The plans that Jerry Bates sells are the old Sweitzer plans that he now must have the rights to, and you are right in that it does build a bit towards the heavy side but it was designed around IC engines. I like the lightness that you designed into the DH90 and after I glassed that fuselage it seems plenty strong with very little weight gain. My word I remember the prototype Rapide used oak for spars and the nacelles were all 1/8th plywood, but he does have glass cowls! The fuse started out as a 1/32nd plywood box from the wing TE forward and stick framed to the back. I think a guy could lighten things up a bit by redesigning certain areas but one would have to plop down your money and order the prints to do that.

As far as picking out what size of electric motors to use I have duplicated what the builder originally used except in your case Robin where I went with e-flite 46's. Probably more power than what is needed, but one can always pull back on the "go lever" and get longer flight times.
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