Lifting capacity and power requirements

[Tyson Marchuk]

Ok first off I'm new to RC planes so some of these questions may be a bit stupid and I would appreciate any and all explanations of why something I ask is a stupid question. :)

I'm looking into (with a few other people) the feasibility of making a UAV system and I'm hoping to go mostly COTS for the parts with a custom component here and there where a suitable (and/or affordable) commercial part doesn't exist.

While I think I have an ok handle on what I need in terms of antennas, autopilot, GPS, attitude sensing, etc. I'm fairly deficient in RC knowledge so I'm looking for advice on picking the airframe/powerplant.

The things I think are important (and again maybe I'm missing stuff?) are:
1) Easy to fly. I don't intend to do stunts with this thing I want stable flight that's relatively easy to control from the autopilot. (I think this means it should probably be a trainer but maybe not?)
2) Can safely fly for at least 30 min. (By safely I mean I can land under power and I'm not cutting it close or something.)
3) Can carry all the normal stuff a plane needs (engine, fuel/batteries, servos, receiver, etc.) plus at least 3.5 lbs of payload. More later would be nice but for now I'd be happy with 3.5-4.5 lbs.
4) Reasonable price. I understand I'll probably have to pay to get the above 3 things but I don't want to go all out on what's meant to be a test of feasibility.

I was originally just going to buy a starter kit with a gas engine from a local hobby store. The wingspan was 4' and the guy at the store said it could carry around 4.5lbs but in hindsight this might have been including the engine, fuel, receiver, servos, etc. I have a friend with a lot of RC flying experience and he didn't think it was likely that kit could carry that much payload. He suggested a Senior Telemaster electric for a variety of reasons.

Does anyone have experience flying this plane? Can it carry 3.5-4.5 lbs of payload? How much battery power (mAh) would I need to sustain 30 min of normal flight? Alternatively how many amps does it take on average for stable flight with this kind of load? Not sure how much it matters but it would be mostly contained in the fuselage so it shouldn't increase air resistance.

Would using LiPoly batteries instead of the NiMH provided by Hobby-Lobby save me a lot of weight such that it would be worth the cost increase?

What about the glow model? Would it make hitting the 30 min mark easier or help with the payload weight or is it just cheaper and messier?

Is there a better plane for what I want to do?

Well I have a lot more questions but maybe it's best to start with that.

Thanks for any advice anyone can provide,
-Tyson

[workshop]

Check out :

http://www.rcgroups.com/forums/showthread.php?t=511550

Jeff

[Tyson Marchuk]

Check out :

http://www.rcgroups.com/forums/showthread.php?t=511550

Jeff

Wow thanks for the link. Lots of useful information there and it seems like you've definitely proved the usability of the vehicle for this kind of work.

I noticed early on (Post 6) you had a bunch of specs on the vehicle but I didn't see any after the addition of the video mount, camera and TX. Would you be willing to tell me the final take off weight (plane with batteries, camera, etc.) and how long you were able to stay up?

Also what batteries did you end up using for the motor? 4200mAh 6s2p LiPoly?

In any case thanks again for a ton of useful information,
-Tyson

[Tyson Marchuk]

I'll throw out a calculation of power requirements. If someone can tell me if it seems reasonable (or if I'm missing something) that would be awesome.

Plane weight without payload = 10.5 lbs
Payload weight max = 4.5 lbs
Average level flight power requirements (found this on a website maybe it doesn't apply to this plane?) = 30W/lb

So the power I need for level flight is 30 W/lb * 15 lbs = 450 W.

Assuming I use a 6 cell LiPoly pack (3.7V * 6 = 22.2V) then the current I need is 450W / 22.2V = 20.27A continuous.

If I want to fly for 30 min then I need 20.27A * 0.5 h = 10.14 Ah or 10140 mAh.

So I basically need 6s3p 3400mAh or better... ouch.

Of course this doesn't include the fact that 6s3p probably weights a bit more than the 16 cell NiMH that comes with the ARP complete kit and I'll need more power on take offs. Of course I've also read that this plane can just float on no power for hours if you can get it to ride the thermals. (No idea how to do that of course.)

Thoughts?
-Tyson

[Tyson Marchuk]

Using the weights of the 4800 mAh LiPoly batterys (6s3p => 14400mAh)
3*741g = ~5lbs.
Weight of the 'standard' 16cell NiMH is 2.5lbs so now...

Full weight = 17.5lbs
Power required = 525W
Energy for 0.5 hours = 525/22.2*0.5 = 11.824 Ah => 11824 mAh

So 4800 mAh LiPoly 6s3p would be enough... at around $900 CDN. Ouch. At least it seems technically possible. :)

-Tyson

[SoarNeck]

Hey Tyson - Adam here.

If you can keep it to 3.5 lbs payload, a smaller Telemaster will do fine, but for much else the versatility of the Senior will be quite welcome. 4.5 lbs on a Senior will be barely noticable in the air.

Examples attached...two ST's.

The yellow one is pretty close to the HL setup, with the same AXI and 16 GP3300 NiMH cells. 10 lbs, thereabouts, and the thing is so stable I don't even notice the camera out on the wing (placed there for unrestricted view along the flight path panning down to vertical). Doubled the spar to handle expected increase in weight later on, remodelled the nose to provide more prop clearance for a lower-pitch drive.

The fancier one was a glider tug...massive Aveox motor and 30 cells, pulling somewhere between 1500-1800W depending on the prop. Obviously not a stock structure. 14.5 lbs, and not particularly different in the air. Takeoff run measured in single-digit feet, of course.

Calcs look about right, though your pricing is a bit off (could probably do it for a bit cheaper then $900). The thing to consider is that you can always test fly the model on a 5/6S1P pack (assuming the current rating is good) and still get good duration, then add parallel packs later as you get further from the launch spot. The odds of the first flight being perfect aren't great considering the level of complexity involved, and so staying close to home for a while isn't the end of the world.

[Tyson Marchuk]

If you can keep it to 3.5 lbs payload, a smaller Telemaster will do fine, but for much else the versatility of the Senior will be quite welcome. 4.5 lbs on a Senior will be barely noticable in the air.
Ok that's a good point. I'll have to look at it and crunch some numbers but a smaller one for testing with 3.5 lbs (that's actually our current estimate of payload weight assuming the autopilot, GPS, etc. run off a single 1 lb battery) might be a good idea and if/when we need to scale we could get into a senior. Of course if the price is only like 20% different then it's probably not worth it to bother with the smaller one.

Calcs look about right, though your pricing is a bit off (could probably do it for a bit cheaper then $900). The thing to consider is that you can always test fly the model on a 5/6S1P pack (assuming the current rating is good) and still get good duration, then add parallel packs later as you get further from the launch spot. The odds of the first flight being perfect aren't great considering the level of complexity involved, and so staying close to home for a while isn't the end of the world.
Cost=> Hmm.. well at Zebra Hobby (http://www.zebrahobby.ca/cgi-bin/cp-app.cgi?pg=prod&ref=LiPower4800-6S&cat=blithium&catstr=HOME:blithium) it says the 4800 mAh 6s1p is regularly: $384.00, on Sale: $288.00. I assume the prices are CDN. So 3 x $288 is $864. I guess I should have said closer to $850 but I was trying to get more worst-case numbers. :)

Scaling flight time=> I agree and intended to do that all along but just trying to get an idea of overall costs and weights, etc. I'd rather be pleasantly surprised than miserably. :) I guess if we decide to go the smaller telemaster route we could probably still buy a 4800 mAh 6s1p pack and potentially even the same motor controller, etc. and then reuse those parts in a move to a senior.

Thanks for all your help,
-Tyson

[workshop]

My Sr. Telemaster weighed 15lbs. and could fly 20min. on one 6s2p 4200mAh pack (40min. with two).

Don't get a smaller plane... I wish I had the Sr. now that I'm working with the 40. :rolleyes:

Jeff

[Tyson Marchuk]

My Sr. Telemaster weighed 15lbs. and could fly 20min. on one 6s2p 4200mAh pack (40min. with two).

Don't get a smaller plane... I wish I had the Sr. now that I'm working with the 40. :rolleyes:

Jeff
Ok thanks Jeff. That's roughly the same weight I'm looking at so the real numbers are appreciated. Looks like the power requirements I'm listing are about 20% too low. I guess take-off and maneuvering probably account for that.

Thanks again,
-Tyson