What motor would YOU use?

[MYC]

Hey gang,

I'll probably get banned from the ducted fan board when they find out i'm doing this :p but I have decided to build a Park Pilots/EJF F-18 as an electric pusher. If you haven't seen it, its a big bug, 44in W/S and 68in Long

http://www.kmp.ca/product_info.php?cPath=35&products_id=134&osCsid=987d1185c6069d53ac2f9a00089a7cd3

There's a ducted fan build thread at

http://www.rcgroups.com/forums/showthread.php?t=551569

but it doesn't seem like they could get the performance that we can get as a pusher. From watching the video, if I can keep it light ~4lb range it may even make a decent park flyer.

OK, so this all considered... What motor / prop would you use?

Mark

[beanie]

hey mark,
you might want to give the AXI 2820/12 with APC-E 10x7 or 11x7 a try. J Morgan has a very similar sized scratch built F-18 that just looks absolutely amazing. i believe his bird was 48"WS, 62"L. he ended up with 68oz AUW i think with a 4s-4000mah and CC45 esc. there were some initial lauching problems off of a bungee that i think was attributed to too weak of an elevator servo. when he went to hand launch and a stouter elev servo, she flew beautifully. it had gobs of power and i think he said that it should eve be able to handle 7 lbs without problems. here is his thread :
http://www.rcgroups.com/forums/showthread.php?t=453549
there are some great pics on post #188 and #189
hope that helps. please let us know which motor you chose and how it turns out.
-beanie

[MYC]

Thanks beanie, just got back from reading through that thread. The Axi is now on the list. I just can't help but think though that there may be something with a bit more KV to get more than 62 mph prop speed. Also, is 58 oz thrust is enough for jet performance on a 4-5lb plane?

[birdlives1955]

How wide is the exhaust area on that plane? I don't think I know as much about motors as beanie does, but here's a suggestion. If you can fit two 7" props back there somehow, you might be interested in the new motor that CustomCDR is working on. It's a jet motor and with a 7x5 APC E prop and a 4S pack it makes the following data:

4s
25 amps
12.5 volts
15,600 rpm

That's about 37.1 oz. of thrust using a free calc on the internet. I really don't know what the speed is, but I think Jon told me that on 3S the 7x5 makes around 70mph, so with 4S I don't know how much more it would be but according to the rpm difference it should be more.....
http://www.rcgroups.com/forums/showthread.php?t=728505
Actually, if you are really looking to save weight, it looks like 3S makes around 30 oz. of thrust and 70mph with the 7X5 on that motor. So, using two 3S 2100's with the twin CCDR motors and 7x5 prop set-up might get you around 60 oz. of thrust and ~70mph (this is all just from what I can gather from the data that has been posted here.... I actually bought one of these from Jon but that was only a few days ago and it hasn't been delivered yet so I can't give ya first-hand experiences yet...the motor sounds cool though)

I was just thinking that 3s packs might save a little weight over 4s packs....
However, 4s would probably be the way to go, and if you wanted to use one big pack you could go with something like a 4S ~4000mah like beanie listed. Or two TP 3S 2100's would probably be fine if run in parallel.

Other than that, the only thing I can think of that would probably make faster pitch speed is the micrdan 2505 speed motor. The motor weighs 36g and here is the data on 3s:

Microdan 2505 Speed with a Zagi Carbon 5.1x4.9 - 28.90oz @ 108mph from 28.60A (321W) on 3s.

This would probably be pretty cool, but I guess if the plane weighed more than 58-59 oz. the power might be sligthly insufficient. However, the low weight of those motors might help with the overall weight situation enough that the plane might come in under your estimated weight projection. Plus if you use TP 3S 2100 prolites, your talking about 10 oz. total battery weight. (That 10 oz. weight is for two 3S 2100 prolites wired in parallel, I think they weigh 5 oz. a piece or so....)

By the way, the Little screamers super parkjet might also be a really good choice, they are supposed to be ready for people to buy pretty soon. it seems pretty similar to the CCDR motor listed above except lighter.... I don't know what the real differences are but they seem fairly close to my relatively motor-data-naive eyes. :)

Well I hope you find what you are looking for. Have fun, and take care.

[MYC]

Thanks birdlives, but I think you are being too modest!

It looks like each exhaust is ~2in wide and theres about 1.5in between them. Would like to do it as a twin but these rough numbers seem to indicate that I've got ~3.5in shaft to shaft. If I stagger the motors, how much overlap could I get away with?

[MYC]

OK, just playing with motocalc and a new option may be the Medusa Research
MR-036-050-1000 on 10x6e and 4s 4400
I'm looking at 663.1 watts at 47.38 amps and 90.96% efficiency

With 85.29oz thrust and top speed of 74.4MPH this almost seems to be too good to be true! Does anyone have any experience with this motor? It appears to be an inrunner but I spec'd 1:1 (no gearbox) to get these #'s