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        GWS Tiger Moth - A Newbie's Story Part 3

#1 The Enemy Sep 03, 2003 07:56 AM

GWS Tiger Moth - A Newbie's Story Part 3
 
Woah boys, part three. Figured I'd start this sooner rather than later after the 500ish limit.

The links:
Part one - http://www.rcgroups.com/forums/showt...hreadid=114411
Part two - http://www.rcgroups.com/forums/showt...hreadid=140767


Corey (The Enemy)

#2 The Enemy Sep 03, 2003 09:34 AM

Commodore,
While looking at replacement motors for myself, someone mentioned an M-100 motor. It will still work with my QC batteries, which are limited in amp draw, and give huge amounts of thrust at the same time. Check this out.

http://www.rcgroups.com/forums/showt...hreadid=133797

http://www.rcgroups.com/forums/showt...threadid=92050


Corey

#3 Dragonfly IIV Sep 03, 2003 10:42 AM

BC,

That was a nice, simple analogy for comparing differences in propeller pitch. I like it.

#4 Dragonfly IIV Sep 03, 2003 10:43 AM

Doug/Tas,

The physics of propulsion are quite complicated even for something as simple as a small plastic propeller/motor combination. One difference between a car transmission and a propeller is the efficiency of converting power into forward velocity. A car transmission is highly efficient at this. Propellers will have varying degrees of efficiency depending on many factors (rpm, forward velocity, shape of the blades, etc.)

When a full-sized fixed-pitch propeller is designed, its performance is "mapped" before it is put into use on an aircraft. This map shows how much power is required to drive the propeller at different rpm and forward speeds. This is then compared to the aircraft requirements. The power required to pull or push an aircraft in straight and level flight is proportional to the cube of its forward velocity (V^3). This defines a curve on the propeller map. The motor is the final variable; it sets power available for a given propeller rpm.

#5 Dragonfly IIV Sep 03, 2003 10:45 AM

At a given forward velocity for the aircraft, if there is excess motor power available, it can accelerate or climb.

Rob

#6 Dragonfly IIV Sep 03, 2003 10:52 AM

Doug,

All else being equal, a larger prop will require more amps, but here we're comparing propellers of different pitch, too. It's not a direct comparison. However, nothing will show the difference bettern than a measured test flight.

Rob

#7 The Enemy Sep 03, 2003 11:31 AM

Well today I did it. I ordered the M-100 motor and the EPS 300C 6/6:1 gearbox. I was able to get everything but the prop shaft, but I'm pretty sure I can just use one from my other GBxs. I also got a new motor for the old IPS-A box. Unfortunately I am grounded until these things arrive. The weather is already toying with me. There isn't a breeze outside to measure. :mad:

Dragonfly IIV,
When do you expect your things to arrive? Can anyone say Canadian Tiger Moth combat? I can't wait. I've even got the streamers ready. ;) Flying WITH someone is 10 times better!


Corey

#8 EcoTony Sep 03, 2003 01:56 PM

Hi guys:

Here's my story. I've gone through 2 indoor power motors on this thing so far. First time was on account of the hobby store guy saying an 8 cell 300 mah NiMh batter would be fine. Motor lasted about 4 minutes and died. Replaced motor and flew with 7 cell 300 mah NiMh.... motor lasted about 5 minutes.... died.....

I have been reading here that you guys are flying on 7 cells w/o any problems.... what's my deal? I'm afraid to put the 7 cell in it because of the last motor didn't last.

This morning I put in a 6 cell 800 mah and that tipped the scales at 9.9oz AUW... heavy. It didn't want to get off the ground. I didn't want to throw it because the wind was a bit funky and wanted to see what you folks said before I helped it into the air.

Next option... Li-Poly . . . any opinons on that?

Tony

#9 The Commodore Sep 03, 2003 02:03 PM

Corey - thanks for the M-100 information. Now I'm in info-overload mode.

(Brain siezing...)

Tony - I've been using ETEC 700mah Li-poly's in my moth, and it works great. A little pricey and you have to get a special charger, but the 40 minute flights are worth it. Haven't burned the motor yet, I figure I've probably got 6-10 hours on it.

I did put a GWS heatsink on the motor though.

Hope that's helpful,
Chris

#10 Basketcase Sep 03, 2003 02:55 PM

Thanks Dragonfly.

Tony, the 7 cell 300's are a perfect match for the IPS motors. You should easily get 15 to 20 hours form a motor with those packs. The 8 cells might cut it by half but not to less than a couple of hours. I've used 7 and 8 cell 300 and 370 NiMH packs for about two years with no unusual motor burnouts. Am now slowly converting over to LiPolys.

Either something else is wrong or by luck of the draw you got two defective motors in a row. :rolleyes:

Did you use the same gearbox? Is it turning free? Sometimes the spur gear will jam against the housing. What size prop?

As is being discussed the 9x7 is the proven best for normal outdoor flying.

Wayne

#11 Tasmania Sep 03, 2003 05:12 PM

Well had my first chance to fly my moth with the 10x4.7, I'm amazed at how much I dont know, you guys were right. The moth flies ok with the 10x4.7 it does actually climb steeper without stalling, it does seem to gain altitude faster, it also cruises with less throttle, but it definately cannot handle the wind as well as the 9x7, and when it gets close to the ground and there is turbulance it is certainly a lot more of a handful and harder to control at low speed and in tight turns.

Couldn't realy try the flight time, as after 15 mins the wind got up to a strength that I was lucky to get it down in one piece, I was tempted to quickly switch props and chuck it up again, it was then that the wind blew my cap off my head and I thought I'd wait for a calmer day. :)

thanks againfor all the input, both props work ok but I think I like the 9x7 the best out of the two, I will try the 10x4.7 again though.

theres a saying that goes "you never know how much you don't know" How true, its great finding out though. :)

Taz

#12 Morb Sep 03, 2003 06:01 PM

Taz....

Try a 10x8 prop on there, and feel the difference. You're still able to cruise along nice and slow, yet perform simple Moth tricks.

Make sure you have a heatsink on that motor, as it will get warm quite quickly.

Geof.

#13 Tasmania Sep 03, 2003 06:24 PM

thanks Morb, I'll get an 10x8 prop and try that. it amazes me though how right Basketcase was about the 10x4.7 it was just like flying with a lower gear.

#14 TooTall Sep 03, 2003 08:45 PM

I have recently obtained the dual IPS-A and an IPS_S1......the s1 dual with 10/8 prop gives me better performance than the EPS-300C setup.....but I found with the S1 a 9/7 or 8/6 gives outstanding flight performance with a 2cell 1020 lipo......has anyone else tried the S1 gearing? The whatt meter allows that with the 9x7 I am pulling 4.1 amps and with the 8x6 it lowers the amp draw to 3.2.......motors are warm but not hot to touch.....I will be using the IPSD-A in a home built flying wing ....I really like the S1 over the A for the moth .....Tom

#15 Davomatic Sep 03, 2003 08:48 PM

I'm putting together a TM now and putting in a PJS 300 w/ I don't know, several different batteries - 2s 700 E-Tec, 2S-1020 Kokam, have some NiMh 300 mah 7 cells. Will reinforce the wings with some CF rod spars.

Has anyone else done this? I usually do built-up planes but thought I'd throw this together to try out the motor and to use it all in an indoor meet in Cocoa next weekend. I won't tell 'em what's under the hood unless they ask :D.

Dave


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