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Sep 29, 2001, 07:55 PM
Most Exalted Windbag

GWS 10 x 4.7 prop gives more thrust than APC


Using 3 x 800 Tadrian Li battery with nominal 9V and a GWS DX-A motor I got:

5.2 oz static thrust with an APC 10 x 4.7 prop and
6.2 oz static thrust with a GWS 10 x 4.7

I don't know if it's due to the heavier weight of the APC or the design, but I like the GWS.

My numbers are a bit low since I measured the thrust by tying my scale to the tail of my GWS Tiger Moth. I have fat foam rubber tires with toe in. That gives some drag.

When I measured a 10 x 4.7 GWS prop, same battery and motor on a plane with light, free running wheels I got 6.75 oz thrust.

RB
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Sep 29, 2001, 09:58 PM
MKH
MKH
Registered User
Did the amp draw change as well? That would tell alot about the prop(s) efficiency. Interested to hear, if you had a chance to measure current.
Marcus
Sep 30, 2001, 12:09 AM
Most Exalted Windbag
No. I didn't measure the current on the Moth and I'll probably never put the APC on again. It's a bit of trouble what with Loc Tite, different washer set up etc. Maybe if I break the GWS and have to replace it I'll put the APC on briefly.

I do have values on the GWS 10x4.7 from the time I measured it on the other plane.

That was 2.0A, 16W, 8V, 6.75 oz. thrust I also got:
9x7" prop 1.9A, 15W, 8V, 4.50 oz.
8x6" 1.4A, 11W, 8V, 3.50 oz. all GWS

In looking at the data I see that I also measured thrust of a 9x7" GWS on the Moth. I got 4.5 oz. The same as on the "free wheeling" plane. I guess I have some experimental error.

RB

I had everything in columns, but the BB software throws away more than one space and doesn't allow the use of tabs.
Last edited by Red Baron 47; Sep 30, 2001 at 12:14 AM.
Sep 30, 2001, 08:24 AM
Registered User
It is not uncommon for two props from different manufacturers with identical dimensions to have different characteristics due to the airfoil design of the blades. For instance, one can have higher static thrust while the other may produce more thrust when unloaded in flight. Also, a prop that provides less thrust can provide more airspeed, which may or may not be more important depending on the particular application. So basing prop decisions on static thrust alone may or may not get you the best prop for the flight characteristics of a particular aircraft.

Personally, I have no problem with the larger (10-inch and higher) GWS props. However, the smaller GWS props (9-inch and lower) are fragile. I broke a bunch of 9x7 GWS props in relatively soft grass landings on my GWS Tiger Moth. I've since gone exclusively to the use of 8x6 and 9x6 APC props on my TM and have yet to damage one. I have not tested static thrust on any props because I am more interested in how they fly than how they test, and don't want to be misled by static thrust figures that may or may not relate to flight characteristics. Both the 8x6 and 9x6 APC props give fine performance on the TM, and I still haven't decided which one I like best.

Slowflyer props are cheap enough that it makes sense to me just to buy many different sizes and try them all in the air to see how they perform. Those that don't work on one of your current aircraft will probably wind up being useful on a future one.