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Old Oct 24, 2001, 10:38 AM
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United States, NY, Spencerport
Joined Oct 2001
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Herr Pitts Special rubber-to-electric conversion

I'm basing my conversion on the November 1999 article in MAN on the Dumas Bearcat conversion.

I've got the major structures built, separated the rudder and elevators, fitted the bottom wing with larger barn-door ailerons in a not-quite-scale location.

Covering will be red Solarfilm.

Power system is a Titanic Airlines 4:1 gearbox with a speed 280 on 7-8 cells with a yet-to-be determined speed control. (recommendations?)

Radio will be a Hitec Feather with three HS-50 servos for full control.

Problems include how to hinge the surfaces, how to mount the gearbox on the rather thick balsa nose block/cowl. (recommendations?)
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Old Oct 24, 2001, 01:55 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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A couple of guesses- although I think some folks have built the airplane-

I might go down to the 3:1 gear drive- a 7 inch prop is probably big enough and the 4:1 may use a prop with torque effects. Not sure on that score-Also will have a somewhat higher pitch speed.

Batteries- try an 8 cell 300 mAH NiMH pack. Castle Creations Pixie 7 should work fine.

Covering- the new oracover lite, Litespan, or maybe solarfilm lite will work better. Solarfilm will add too much weight. I like the Oracover lite so far.

Sam Brauer
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Old Oct 24, 2001, 01:58 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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PS I like some of the new mylar tapes sold by Scotch for hinging- a single strip along the top works fine.

Mounting a gearbox- one trick is to just use a pair of dowels as a stretcher and glue or rubber band the motor to it.
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Old Oct 24, 2001, 10:12 PM
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Spring Valley. MN
Joined Jun 2000
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I would consider going to a speed 300 for the higher k/v, I ran the nubers threw motocalc and the 280 at 4/1 would need probably a 10" prop to make any power the 300 on the other hand looked very good on a 7x6 on either 7 or 8 cells. The 280 should fly it but I think the perfomance would be much better on the 300.
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Old Oct 24, 2001, 11:05 PM
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Spring Valley. MN
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keep us posted on your progress as I was thinking about this conversion myself
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Old Oct 25, 2001, 07:21 AM
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Antioch,CA,USA
Joined Dec 1999
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Mkirsch1, Welcome to the Ezone! Like Buzz said, I think you'll like the performance better on an SP300. Another motor I highly recommend is the 280BB. It's right in line with the power of the 300, but it has ball bearings and replacable brushes. It is a few $ more, but I think it's worth every penny.
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Old Oct 25, 2001, 08:53 AM
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I discovered the P-Calc page, and the numbers are pretty anemic. Best I could do was 8.9 oz of thrust on 8 cells and a 10x6 prop at 4:1. Gyroscopic precession should be dandy...

Too bad I already ordered the motor and gearbox from East Coast Model Center up in Canada.
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Old Oct 25, 2001, 09:21 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Let's back up.

Unless you are planning on doing extreme modifications to the structure, you should be looking at a flying weight of 8-10 ounces-if you can keep the weight down. Doesn't the rubber version weigh about 2-3 ounces?

Ignore the programs- they don't seem to give such hot results in this weight regime. A 280BB or Speed 300 geared motor will probably pull the airplane apart- it's not built for those stresses- plus- those motors are heavier. Your original idea of using Tom Hunt's article is fine- and his Bearcat had pretty sprightly performance on a 3:1 geared 280. I'm not so sure that the 4:1 motor is such a terrible idea either- just make sure that your prop pitch speed is up to snuff- you probably need between 20 and 25 mph pitch speed. (Maybe an 8 x 6 prop?) I'd start with an 8 cell 300 mAH NiMH pack. Get yourself a scale and start weighing stuff- building a rubber powered conversion needs a different skill set than a more conventional and larger glow or electric ship. If you really want to start over- the nice motor is the M-100/TR-389- on an 8 cell 720 NiMH pack, it pulls my 14-15 oz. Curtiss Robin around with grace- but its not overpowered. Would work fine in a 10 oz. Pitts. It's lighter than the Speed 280 as well- or the cheaper and lighter alternative is the MG-1- essentially the same power on one less cell (which makes it lighter than the M-100)- but shorter motor longevity.

Sam
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Old Oct 25, 2001, 03:36 PM
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Quote:
Originally posted by Megowcoupe
Unless you are planning on doing extreme modifications to the structure, you should be looking at a flying weight of 8-10 ounces-if you can keep the weight down. Doesn't the rubber version weigh about 2-3 ounces?

Ignore the programs- they don't seem to give such hot results in this weight regime. A 280BB or Speed 300 geared motor will probably pull the airplane apart- it's not built for those stresses- plus- those motors are heavier. Your original idea of using Tom Hunt's article is fine- and his Bearcat had pretty sprightly performance on a 3:1 geared 280. I'm not so sure that the 4:1 motor is such a terrible idea either- just make sure that your prop pitch speed is up to snuff- you probably need between 20 and 25 mph pitch speed. (Maybe an 8 x 6 prop?) I'd start with an 8 cell 300 mAH NiMH pack.
Sam
Getting rough estimates of the airframe on my electronic fish scale, I figure the covered weight of the airframe, including modifications for servo mounting, pushrods, and control surfaces, should be around 3oz. Figure another 4-5 for the power system, and another 2-3 for the radio, and we're looking at an all-up weight between 9 and 11 oz.

Frankly, I think the plane will fly well on the powerplant I have with a 9x6 APC thin electric or slow flyer prop.
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Old Oct 25, 2001, 05:54 PM
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I have this kit too and will be converting it when I get a round tuit. It could be built as Sam suggests, with the goal of making it an ultralight slowflyer, but I'm gonna make mine a quick micro aerobat in the tradition of the Pitts image.

It is similar enough in size and construction to my 24" span Guillow's SE5A that I'll probably use a similar power system. It will likely be a 280BB or speed300 geared 3.6:1 to 4:1 with 7 or 8 720AAA NiMH cells and a 7x6 to 8x6 prop. All up weight will be 10-11 oz. including full-house controls. It should be quite a bit faster than my SE5A which has loads of draggy scale details and full flying wires.
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Old Oct 25, 2001, 10:08 PM
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Hey, thanks for all the great suggestions. My intention was to have a micro scale Pitts worthy of its full-scale counterpart too.

Pcalc says a Speed 300 with 4.5:1 gearbox and a 7x6 prop should give it a near 1:1 thrust/weight ratio at the targeted all-up weight. Ordered the requisite parts from Hobby Lobby tonight. Two minutes at full throttle on 150mAH batteries, three on 250mAH, and the whole power system still comes in under 5oz!
Weight. Power. Endurance. Pick any two
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Old Oct 25, 2001, 10:59 PM
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Spring Valley. MN
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Quote:
Originally posted by Gerald
I have this kit too and will be converting it when I get a round tuit. It could be built as Sam suggests, with the goal of making it an ultralight slowflyer, but I'm gonna make mine a quick micro aerobat in the tradition of the Pitts image.

It is similar enough in size and construction to my 24" span Guillow's SE5A that I'll probably use a similar power system. It will likely be a 280BB or speed300 geared 3.6:1 to 4:1 with 7 or 8 720AAA NiMH cells and a 7x6 to 8x6 prop. All up weight will be 10-11 oz. including full-house controls. It should be quite a bit faster than my SE5A which has loads of draggy scale details and full flying wires.
Gerald

You and I are thinking along the same lines I just cant see making a Pitts a slow fly powder puff.

BTW I picked up a Sterling Extra 300 24" WS have not figured the area yet but I am looking for a power plant that will do better than 1to1.

I was just playing with P-calc and its numbers are much more optimistic than motocalc, Which one should I believe????
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