A friend of mine has a notion to power his now-framed-up Sportster with an Astro 40 he has, never used the motor for anything. Also discussed the possibility of direct drive. While I've conversationally rambled around the topic with him, I have no experience with that size model or that motor that could be used for advice.

I noticed this model mentioned in the thread on the Art Chester Jeep conversion, but I didn't want to break in with this 'me, too, please' query.

So...I think trying to address these questions might help: (1) what sort of watts/lb do we want for this not-particularly-light glow model, (2) gearing/propeller suggestions, (3) comments on direct drive in this particular application. Considering the expen$e of high-capacity LiPo cells, let's assume that this aircraft will be drawing its current from a NiMh battery.

Thanks, folks.

I have the .40 glow powered version of this model. If built as-designed with heavy fabric covering, priming and painting, a sport .40 2 stroke engine had just enough power to fly the thing in a scale-like non-aerobatic manner. forget loops! My Enya .46 4 stroke was very marginal which led to it's first crash.

Anything you can do to significantly reduce overall weight would improve this model's flying ability as an electric conversion. It's a flying lumberyard. Obviously a large brushless outrunner and expensive Lipo pack would be the easiest way to cut weight and get enjoyable performance and duration. You would need to locate the lipo pack and everything else as far forward as possible and minimize weight in the tail.You might still need to add weight in the nose

I think that a geared Astro 25 on 16 Sanyo 1950AUP NiMh cells would probably fly a lightly built and covered model with maybe 5-7 minute flights. A geared Astro 40 with 16 cell 3000mah pack might improve performance but added weight might make it have to take off and land faster to avoid snappy tendencies. You would definitely need a paved runway, no tail heaviness and let it lift off when it wants to and keep climb angle shallow till you get to know it's habits. Would like to see a larger model E designed for E-power!!

What is the AUW supposed to be as a gasser? I have a 3 1/2 pound FG fuse and built up wing in the .25 size Gee Bee R-1 and fly it on an AXI 2820-12 DD with a 10x8 prop, I use 2 3s 1500 Li-Po's in parallel and it flies GREAT.

I also fly my Sureflite PT-19 at 4 1/2 pounds on the same motor with a 12x6 prop and 2 3s 2100's in parallel

A rough guestimate and rule of thumb is 100 watts per pound for an aerobatic plane.

I think my .40 glow powered Model E weighs around 5 pounds fueled. I would want it to be closer to 4 pounds or less with brushless outrunner and lipo pack. The 16 cell 3000mah NiMh pack with a large brushed motor would probably push the plane over 5 pounds. I would want to err on the side of excess power and light weight if you want to do easy take offs, scale-like loops, inverted flying, and land easy on the unsprung landing gear.

That Coverite is nice stuff. I'm assuming it has the Coverite covering on it. I just used it on my Zero build. Applys and shrinks beautifully at 1 low temp. Easiest stuff ever to use. Only not that dark, so I used white Econokote on the fuse. I saw a picture of Nelson light film, on Pat Tritle's Waco bipe in Flying Models (I believe Waco). It looked to be less transparent, like a heavier film. Have you used the Nelson stuff? Is it darker than Coverite? Sorry to be a bit off the topic.

Hi peter,I did some test tonight.
astro 40 geard(1.68 to1)= 14.8oz
16cell NimH hsr2600=34oz,or 2lbs 2oz
16cells 23v,13.6/5 apc prop @22.5amps =465 watts
apc 14/7 @25.4amps= 502w down to 480w
apc 15/7 @31.5amps=540w down to502w As for the plane its bigger than 1/6 scale but a little smaller than 1/5 scale.Not knowing the full scale prop size,I assumed it would have been around 6' or 72" I scaled it to 1/5 which is 14.4" I was just reading astro bob's motor hand book and he list to use a 13/8 with18 cells with the 40g.That one thing I don't like about bob is that he likes high volts and low amp draw.Anyhow thats my 2cents .Pete you can email me if you want to talk more about this off the air.Scratchandbash nelson lite film is a product from the U.K. very LITE and takes some time to get use to useing it.When the clear back is peeled off you need to put baby powder on it or it sticks to its self.Then you throw it out I use160 degrees to tack in place 180 to 200 to seal in place . I love using this stuff.But be patient.stefanP

Hi Peter

Agree with a bunch of the advice that you've got-

1) The motor is fine, but needs a gearbox- DD is right out.
2) Nickel cells can work but require a light by glow standards airframe.
3) Li-poly is the way to go- I gave up on most of my nickel cell powered aircraft.
4) Astro Bob likes high V, low A solutions which plays well with li-polys- some of the packs can hit 30A on a single cell. ESCs may not be a trivial problem though, but you can probably get away with 5S on a Pegasus 35. (need to be checked though)

The simple answer is that larger electrics are more expensive than glow. I've got the Jeep kit stashed somewhere- haven't popped the box IIRC. Sounds like some judicious lightening is in order on the structure.

Sam Brauer

Stamford, CT

Sam I have the jeep kit also.It is a serious lumber yard that needs lightning up.Another way is to replace heavy wood with lite wood.

stefanP

Hi Stefan

Have to admit, that one's not even in the foreseeable build queue, but that's pretty variable. Having done a bunch of conversions- I'm pretty firmly convinced that li-polys and brushless if needed (I'd go to li-polys and cobalts before brushless and nickel cells) can come up with performance that's basically glow drop in if not a little more on occasion. It's also no longer necessary to go nuts with an e-conversion- I've built several airplanes close to glow stock with kit wood and had no trouble. Often the glow kits are beefy enough so that they do better in service than the airplanes designed as hyper lightweight electrics. The problem you get into is when you start with a glow kit which was known to be heavy.

Sam

Sam, Stefan, I'm reading your responses at one time, i hope that a common reply is all right... Thanks for going to the trouble to consider the question. I'll try to make sure that the project's owner sees all this. Sounds like a typical aviation problem fix - - bring money. I infer that this airplane, by virtue of its smallish size and mass-market-kit origin is just gonna be too 'dense' to do well by electrifying it without labor-of-love infusions of cash.

I, too, have a 'Jeep' in the box, never thought to electrifying it. A long time ago the design was originally a freebie plan in (I think this is the title) 'R/C Sportsman' newsprint magazine. I later was offered a kit at a reasonable price. 'someday', but nothing to do with electric flight.

Peter

Let me summarize

Stefan's findings- 3 lb powerplant using nickel cells- (2 lb powerplant using li-polys) for 500 watts- decent performance on a 5 lb airplane, but not vertical rolls out of sight. For this airplane, I'd be happier with a 13 x 10 prop (a bit higher top end which befits a racer) which adds a couple of extra ounces unless you go to 2000 size cells. Flight times are marginal- you've got around 4 minutes at full throttle, and with that power loading, you're going to have a heavy throttle stick.

The airplane can fly on nickel cells at an empty weight of 2 lbs- no motor or battery, but everything else- you can go to 3 lbs empty weight with li-polys. Brushless buys you less than 0.5 lbs-probably not that noticeable. 2 lbs empty weight on li-polys gets to be much more fun. If the airframe is really that heavy- start cutting holes until the airframe makes weight or falls apart.

Sam

Big ring cowl and fake radial engine, fat fuselage but normal moments and wing area built to make money by the Granville brothers to finance building the racers. They were not fast but "sporty" and reasonably good at 30's aerobatics. With the model, the prop has to reach past the large ring cowl to provide thrust but not touch the runway during takeoffs and landings. Flying with cowl/fake engine off looks dorky. The fat fuselage has some lift itself at certain angles giving it a blimp-like feel . It looks "stately" flying by . I landed mine on the mains like a P51 as smoothly as possible. The only cushioning is from the balloon tires.

I have a built coverite model E that i bought at a bring and buy, so lightening is out the window. I was considering fitting a Twister 29 (.60 glow equivilent) and 4s lipos, anyone out there agree that this should fly it well?..........Martin

Martin

500 watts from a healthy 4s li-poly pack is not the equivalent of a good .60- doesn't matter what the motor says. On the other hand- if the airplane weighs in at 3.5 lbs with radio but sans motor and battery, you've got a prayer. As EC points out- swinging a large prop really matters.

Sam

Well i`m biting the bullit and putting the gear in, it`s going to be a bit of a porker but my pals ARTF Corsair weighs similar with only 4" more wingspan and fixed gear/radial cowl etc and that flys great on 4 cells!
Can anyone give me the balence point for the E and the recommended control throws?............Martin