GP Ultimate Biplane conversion - RC Groups
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Aug 24, 2002, 11:42 AM
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SoarNeck's Avatar

GP Ultimate Biplane conversion

Hi folks,

Sorry if this has been discussed before, but I couldn't find any info on this model as an electric.

I've been flyng a ModelTech Magic with good sucess, but I'd like to try something a bit smoother, and more capable of knife-edge maneuvers. The sensible thing would be to convert a Cap or Extra, but I like the looks of this kit.

Has anyone done this before? I'm thinking a Jeti Phasor on a 2:1 geabox (kept below the 15k destruction point) would be okay, but I'd like to be able to torque roll the beastie.

Any advice? I'm not opposed to brushless, but I can't afford a Lehner
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Aug 24, 2002, 12:14 PM
flying in the rain....
dave_beardsley's Avatar
I converted a Goldberg Ultimate.

Mine is about 4 years old. It worked well, would be better today on less cells with a hacker motor.

picts on my site
Aug 24, 2002, 05:10 PM
Registered User
kmashima's Avatar
I have an Ultimate from another company. Unless you can get the weight way down, it's not a good choice for doing any kind of hovering. My plane has a Hacker setup and 16cells and flies like a brick. It weighs almost 8 lbs. As long as I'm going fast, it's fine. But let off the throttle, and it sinks like a rock. It will knife edge but if that's what you're looking for there are better choices. The Venus is a much better plane all around. Light, fast and can do any trick in the book.

If you can build it to be 6.5 lbs with the batteries, then it might be fun.

Which Jeti are you thinking of? The 45-3?
Aug 24, 2002, 10:29 PM
Visitor from Reality
Hi Soarneck
Jack Sowle used to fly a MaxCim 13Y powered GP Ultimate on 18 cells, IIRC - Tom Cimato at MaxCim could probably give you the entire skinny on this one. Saw it fly a couple of times, smooth, big aeroes and pretty fast. Jack is a real good pilot though...

If you start with the GP kit, they are a tad overbuilt in places (like, the woodwork ) being intended for the shorter attention span kit builder who maybe can't spell "weight" but are good aerodynamically. Treat the kit as a pricey set of templates, replace all the sheet Liteply with sensible structures or light balsa and you can come out with a reasonable weight of model. My GP CAP232 weighs 6.25lb with a geared MaxCim 13Y - BEC, no lugging a receiver pack around with these - and 20 x 2000 nicad cells. 35A into a 14 x 10 APC makes for fun times - it will climb in KE, for one. The rudder, cowl and canopy are about all that's left of the kit bits, though it is still the same outside shape.

Beware of flogging cheap brushless motors hard. They have been known to lose their smoke under pressure.

I occassionaly consider this one myself, even if it is plug ugly, IMO. Would use a MaxCim 13D, 4:1 or deeper ratio, 16 x 2400 nicads and start with a 13 x 8 or 14 x 7 APC-E. Not fashionably coloured, but would allow me to mess with the gearing to match it to the model. A small point is that MaxCims are made some funny place called "The USA".
Aug 24, 2002, 10:42 PM
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Joe Elston's Avatar

Dave Patrick Extra

Hi Soarneck, when I talked with Sean Plummer yesterday about converting my GP Extra 300S. He told me that he has had very positive results with converting the Dave Patrick ARF Ultimate Bipe. I would give him an email or a call at
He's a real nice and knowledgable guy.

BTW: he told me that he will be flying electric demonstration flights at this years TOC. He will be flying all the aerobatics with an electric conversion. I forgot to ask which planes he will be using. Just thought it was interesting.
Aug 25, 2002, 01:20 AM
RCGroups Author
SoarNeck's Avatar
Thanks for the info guys, it's appreciated. I realize that whatever kit I'd choose would likely require a lot of modification, but I'd like to do a conversion of this sort. I tend to scratch build from my own designs, but I'd like to try a non-composite project that isn't going to take 100+ hours to complete for once! I'll probably end up making carbon fibre cowls and pants for the subject at a minimum, so I'm not opposed to a major overhaul.

I looked at the GP Extra again today (there's advantages to working in a hobby shop for the summer), and it looks like an easier candidate for conversion. Joe - could you tell me what Sean Plummer recommended, to save him having to answer the same questions twice?

The only real reason that I'd lean towards the Jeti motors is that I can get them at close to store cost. We may be importing Hackers in the next little while, so that would also be an option. The Jeti motors are pretty impressive for their price, but I'd like to be able to fly on the edge without letting all the magic smoke out! I have no problem supporting home industries, but I'm still a starving student at the moment.
Aug 25, 2002, 03:21 PM
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Joe Elston's Avatar

GP Extra 300 S

Soar, are you talking about the GP Extra 300 S ARF ? Thats the one I have and wanted to convert? Sean told me it would come out at about 8 pounds. Now I thought the plane was lighter than that but I guess not. I still am not sure if I want to convert it or not. The kit is just sitting in my shop begging to be built and flown. Anyway the recomended motor combo was the Hacker B50-L geared 3.7 to 1 and the Hacker Master 77 amp esc on 16 cells swinging an APC 13x10 E prop. I would really love to convert my Extra but I don't see how I can take some weight out short of a major rebuild and that kinda defeats the purpose. Let me know what you decide,
Sep 05, 2002, 09:07 AM
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gouda's Avatar

the site above will give you some details about the Dave Patrick 40 sized Ultimate bipe. It does have some advantages in my opinion, like being available in a RTC form. that would allow you to make any changes to the airframe you'd like for weight saving. But I 6think you'll find it lighter than the competion anyway. And it is a very good quality airplane. Semi-reasonably priced as well.
Sep 05, 2002, 10:29 AM
jprechel's Avatar

GP Cap 232

Does anyone have an idea how a Hacker B50-13s geared 6.7-1 with 16 NimH 3000HV cells and a 15-10apc-e prop would work in a GP cap 232 kit? The standard kit is supposed to weigh less than the Venus and the Venus performs well on this motor combo. I'd probably like more vertical and less speed on the Cap if possible.
Sep 05, 2002, 12:19 PM
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fbw4's Avatar
As long as you do the wood swapping and use micro equipment the weight will be about the same as the Venus and should fly great.
Sep 05, 2002, 12:27 PM
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fbw4's Avatar
My CAP is flying on 18 cells with Unlimited Vertical Performance.
Sep 05, 2002, 02:11 PM
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Joe Elston's Avatar

GP Extra 300 S ARF

Well Guys, I decided to go ahead and convert my Great Planes Extra 300S ARF to electric. I have a Hacker B50-10L Geared 5.2 to 1 and a Hacker 70-3P esc comming from Aero Model. After several phone calls with Sean he came up with this power package. I will run 16 zapped RC 2400's and a 13x10 APC E prop to start. I may up the prop to a 14x10 APC if I feel the plane needs it. I ordered two of each prop. And I also bought the trick black adjustable motor mount that Aero sells. So the conversion should be pretty easy. The only reason I am trying this plane is because I have it already. If I don't like how it flys I will put the motor in something else. I also plan to try 16 3000 NIMH's later on. Sean seems to think that I will have excellent performance as this combo puts out 6.75 pounds of thrust on the 13x10. I also got a carbon fiber landing gear and will use light wheels and the stock glass wheelpants. I also plan to cut a hatch in the top to slide the pack through. Keep you updated.
Sep 05, 2002, 02:48 PM
jprechel's Avatar

Thanks for the reply, but I was curious about your ecalc figures. I have the latest version of ecalc (2.14) and my motor constants are different from yours. For example the Kv for a B50-13s is 3277 in mine. Is there a new patch that I have missed or are those some numbers you have input manually? I think your readings may be more accurate. My venus setup is drawing about 44 amps which is where your numbers are. My Ecalc numbers put my venus setup at 53.7 amps.
Sep 05, 2002, 03:14 PM
Registered User
fbw4's Avatar
I have found MotoCalc Data to be more acurate for Hacker Motors. So yes I manually input the data from MotoCalc into ecalc.
Dec 28, 2008, 10:11 PM
Registered User

PA's Ultimate Bipe

I purchased the red PA Ultimate Bipe and the Thrust 40 and the Quantum 45AMP ESC. Great flying so far. What does AMR stand for if anyone knows. Thanks. I also have 3 PA Addictions and love those planes.

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