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Old Apr 18, 2005, 06:46 PM
Balsadust Everywhere!!!!
Concepcion, Chile
Joined Jan 2005
106 Posts
Yippee!
Greatplanes RV-4: Great parkflyer!!!

Hello there!

I just built a Greatplanes RV-4, this is my first electric plane after more than ten years on glow.

I'm using a Sagami 280BB, 5:1 BB MPJet gear and APC10x4.7SF. With a 9.6V 650mah Nimh it has 10 minutes of part-throttle power and it spins the APC at 4750RPM.

The pane flyes slowly very well at 1/4-1/3 throttle and at full power it has a nice steady climb. However, I can't get a decent loop or stall turn from level flight.

The airframe is very stable and precise, rolls well, has a good rudder and glides smoothly. Because of this, I think with a "little" more power it would perform solid scale-like aerobatics. (that is loops, point rolls, cuban8, split-s, immelmans, stall turns, etc for you "3D-only" flyers out there!) If I get good feedback on the power systems forum I'll get a MPJet 28/7-35D outrunner.

The picture is at a site "just discovered" less than a mile from where I live. Our club has a nice tarmac strip, short grass but lots of wind!!!!

It took me 1-1/2 months from box to air.

The build is good, nice fit of the pieces but there are some details not mentioned on the manual, for example: the rear elevator joiner needs some room to fit well.

I used two servos on the wing, much more precise than the stock linkage. I also used dubro mini ez-link on the four servos.

I used less dihedral than recommended, something like 2/3 of it.

Wood is so-so, some sheets were ligth, some heavy. I haven't weighted it but it feels very light, can't imagine how light it'd be with premium wood and lipos!!! The gear is very soft, I'll try some stronger rubber bands or hard mounting it.

I covered it with Coverite microlite, very good material, even easier to use than monokote. 3M Blenderm tape hinge, and ply horns. I used the throws and CG from the manual. The throws are perfect, the CG is a little conservative, I'll try backing it 1/8" next time. I did use a little washout as the manual suggested, the turns can be very tight and the plane still tracks well. With powered stalls the wings don't even seem to rock, the nose goes down smoothly. 7 out of 10 for the building, 9 of 10 for the flying, and I think it'll get 10 of 10 with a brushless set up!

Rounding up, a very nice parkflyer. Easy to fly and buid if you know how to. I wouldn't use it as a trainer and if building for the first time I'd recomend a little advice and supervision from some experienced fellow flyer to make sure you don't mess it up!!!

Regards,
Paul
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Old Apr 18, 2005, 06:57 PM
one game away...
PerfectStranger's Avatar
Willoughby, Ohio
Joined Apr 2004
3,891 Posts
Good job and a very nice, concise and informative review.

matt
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Old Apr 20, 2005, 08:04 AM
What power line?
PoudreDerf's Avatar
Rocky Mountains
Joined Aug 2004
3,507 Posts
Neat-o. Always liked the look of the RV-4.
Was that picture taken in the early morning or late evening. Just curious.
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Old Apr 20, 2005, 09:15 AM
Account closed
Joined Oct 2002
35,016 Posts
Quote:
Originally Posted by J.Paul
Hello there!

I just built a Greatplanes RV-4, this is my first electric plane after more than ten years on glow.

I'm using a Sagami 280BB, 5:1 BB MPJet gear and APC10x4.7SF. With a 9.6V 650mah Nimh it has 10 minutes of part-throttle power and it spins the APC at 4750RPM.

The pane flyes slowly very well at 1/4-1/3 throttle and at full power it has a nice steady climb. However, I can't get a decent loop or stall turn from level flight.

The airframe is very stable and precise, rolls well, has a good rudder and glides smoothly. Because of this, I think with a "little" more power it would perform solid scale-like aerobatics. (that is loops, point rolls, cuban8, split-s, immelmans, stall turns, etc for you "3D-only" flyers out there!) If I get good feedback on the power systems forum I'll get a MPJet 28/7-35D outrunner.

The picture is at a site "just discovered" less than a mile from where I live. Our club has a nice tarmac strip, short grass but lots of wind!!!!

It took me 1-1/2 months from box to air.

Paul
Señor Paul:

You have too much reduction gearing on that gearbox with the BB280 brushed motor. Your AMPs are maintained low because of the high gearbox ratio but, your motor RPM's are high because of it and explains the low RPM at the Propeller.

Loop from level flight and other in-flight performance increases can be sought by reducing the reduction gearing and your RPM at the propeller will significantly improve with the cost of some AMP (Current draw).

I would reduce the Gear reduction and go with a 9 inch propeller with a high pitch such as the APC "Slow Flyer" 9 X 7.5

Try it before you go and spend $$$ for brushless.

Carlos
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Old Apr 20, 2005, 05:32 PM
Balsadust Everywhere!!!!
Concepcion, Chile
Joined Jan 2005
106 Posts
Hi there!
The picture was taken at late afternoon.

I also have a 4.1:1 gearbox, maybe I'll order an APC9x6SF to try. If I get 10 minutes with my current set up, how much do you think I'll loose??


Saludos,
Paul
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Old Apr 20, 2005, 05:50 PM
Don't cut the Yellow Wire
dr.E's Avatar
Ridgewood ,NJ
Joined Jan 2000
3,509 Posts
The sagami motor is sold as the Simprop acro drive as well as the Kyosho DMC series. Try going to a larger diameter prop and higher pitch (gws HD prop).
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Old Apr 20, 2005, 05:55 PM
Don't cut the Yellow Wire
dr.E's Avatar
Ridgewood ,NJ
Joined Jan 2000
3,509 Posts
Quote:
Originally Posted by J.Paul
Hi there!
The picture was taken at late afternoon.

I also have a 4.1:1 gearbox, maybe I'll order an APC9x6SF to try. If I get 10 minutes with my current set up, how much do you think I'll loose??


Saludos,
Paul

You have to check your amp draw to figure your run time. The sagami 5:1 combo would fly the Simprop Sukoi with great authority. At its time it was the strongest s280 power plant (before brushless came redily available)
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Old Apr 21, 2005, 07:53 AM
Balsadust Everywhere!!!!
Concepcion, Chile
Joined Jan 2005
106 Posts
Quote:
Originally Posted by dr.E
The sagami motor is sold as the Simprop acro drive as well as the Kyosho DMC series. Try going to a larger diameter prop and higher pitch (gws HD prop).
I bought it as a "Greatplanes" motor, a lot cheaper than the simprop!!!
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXAHK6&P=ML

Tower doesn't carry replacement brushes though, but Hobby-Lobby does; I don't know yet how may flights they last.
http://www.hobby-lobby.com/speed280.htm

I'll have to get a Wattmeter to figure the load on the motor, I don't want to burn anything, and I wouldn't accept less than 8 minutes with power.

Thanks for the replies!

Saludos,
Paul
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