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Old Jul 12, 2003, 06:43 PM
Registered User
Walled Lake, MI, USA
Joined Feb 2000
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GWS Hyper Drive Prop Testing

As many of you know, I've been touting the performance and efficiency of the GWS Hyper Drive props over the more common GWS Reduction Series props for some time now. I first noticed that the HD props appeared to be more efficient when GWS first published the table for the EPS-400, which was the first GWS table to include HD props in addition to the RS props. It was obvious from every comparison that the HD props were more efficient because they produced more static thrust per amp than RS props. When I bought my first HD prop, a 10x6, my own experience showed that it was a superior performer.

Now that I have a static thrust test stand rigged up on my Sunbeam "precision electronic postal scale," as well one of the Sears Craftsman DC/AC clamp meters, I'm finally able to generate good static testing numbers to prove my point. So I'd like to dedicate this thread to comparing the static test stand performance of HD props against RS and other types of props. I ran all of the following tests several times, zeroing out the postal scale and clamp meter and switching battery packs to eliminate any variables.

Since the only identically sized HD and RS props are the 12x8s, that seems to be a logical place to start. I had an IPS with D gearing (9.66:1) set up with a 12x8 RS prop, and had been running it on a pair of Panasonic 830mAh Li-ion cells from an old Qualcomm cell phone pack. After running it up and getting results, I then switched to the 12x8 HD prop and ran it up. The current was reduced so much that I also went ahead and tried it with an 8-cell 720mAh AAA NiMH pack. Here are the results:

IPS * 9.66:1 * 7.4V * 1.5A * 5.8 oz. static thrust * 12x8.0 Reduction Series prop
IPS * 9.66:1 * 7.4V * 1.1A * 5.1 oz. static thrust * 12x8.0 Hyper Drive prop
IPS * 9.66:1 * 9.6V * 1.5A * 7.1 oz. static thrust * 12x8.0 Hyper Drive prop

Note that with the same 7.4V Li-ion pack, the HD prop uses 73% of the current to create 88% of the static thrust of the RS prop.

Interestingly, the 8-cell NiMH pack pushes the current with the HD prop back up to the same 1.5A observed with the RS prop on the 2 Li-ions. But the 7.1 oz. static thrust represents a 22% increase in static thrust at the same current. I don't recall anyone else ever measuring more than 7 oz. thrust from a single 7.2V IPS motor at a safe 1.5A. The only problem with this combo is that you wouldn't want to carry a heavy 8-cell AAA pack in place of 2 much lighter lithium cells. So the question is, how to achieve 7.1 oz. thrust at 1.5A with a pair of lithium cells in place of the 8 AAAs?
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Old Jul 12, 2003, 09:40 PM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
4,564 Posts
Since the voltage is going to be lower on 2 Li cells compared to 8 nimhs, you will have to run greater than 1.5 amps to get the same watts with 2 Li's.

Wonder what a C drive would do?

Also, if only 1.1 amps on D and two cells, 3 cells should still be well under the 2.5 amp limit, probally only 2.0 amps or so. Thrust should jump to about 10 oz or so. ( 9 watts becomes about 22)

Any chance you'de try 3 cells on your test stand?


Dean in Milwaukee
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Old Jul 12, 2003, 10:06 PM
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Walled Lake, MI, USA
Joined Feb 2000
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Test #2: The old reliable IPS with A gearing (5.86:1) that has powered so many different GWS aircraft, from the original Lite Stik to the Tiger Moth and beyond. Recommended Reduction Series props are the 10x4.7 for indoor flying and the 9x7 for outdoors. I compared them to the 10x6 and 11x7 Hyper Drive props. Same test method as the previous one (I did edit the first table to identify the motor in the first column).

IPS * 5.86:1 * 7.4V * 1.7A * 5.1 oz. static thrust * 10x4.7 Reduction Series prop
IPS * 5.86:1 * 7.4V * 1.5A * 4.3 oz. static thrust * 09x7.0 Reduction Series prop
IPS * 5.86:1 * 7.4V * 1.3A * 4.8 oz. static thrust * 10x6.0 Hyper Drive prop
IPS * 5.86:1 * 7.4V * 1.8A * 5.7 oz. static thrust * 11x7.0 Hyper Drive prop
IPS * 5.86:1 * 9.6V * 1.9A * 6.7 oz. static thrust * 10x6.0 Hyper Drive prop

GWS recommends the Hyper Drive props for outdoor use due to their generally higher pitch. In this case, the 10x6 HD prop is a great compromise between the 10x4.7 and 9x7 RS props, with the diameter of one and nearly the pitch of the other. It's also real easy on the motor and battery pack, drawing 23% less current than the 10x4.7 with only 6% less thrust. However, thinking of it more as an outdoor prop, it provides 12% more thrust than the 9x7 with almost the same pitch speed, and still draws 13% less current.

Since the 10x6 was so easy on the motor, I decided to try the next larger HD prop, the 11x7. For a 6% increase in current over the 10x4.7, you gain 12% static thrust. But looking at the 11x7 as an outdoor prop, the better comparison is with the 9x7. The current increase is significant at 20%, but the increase in static thrust is even more significant at 33%. With identical pitch speed to the 9x7, an 11x7 HD could make a potent outdoor prop.

Finally, because the 10x6 HD had such a low current draw, I tried it with the 8-cell AAA NiMH pack just to see how it would respond to more voltage. As in the first test, more voltage works very well, indeed. This tends to verify Dean in Milwaukee's experience of running an IPS on a 3-pack of LiPo cells along with a smaller prop to hold current down. In this case, you'd probably need to drop down to a 9x5 HD prop with the A gearing, or perhaps use the 10x6 HD with B gearing (7.0:1) to handle the 11.1V of 3 LiPos without over-stressing the motor.

But the continuing lesson here is that you will always be ahead by using a prop that provides more thrust per amp, as the HD props do consistently when compared with the RS props.
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Old Jul 12, 2003, 10:12 PM
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Walled Lake, MI, USA
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Hi, Dean. I just mentioned you in my second test without realizing that you had posted here! I think the 3-cell LiPo pack is the way to go, based on your testing and what I'm seeing here with the 8-cell NiMH pack. I'll definitely be doing some 3-cell testing just as soon as I receive my SC2 charger from Troy. Right now, I'm limited to only being able to charge 2-cell packs with my old faithful -- a modified Qualcomm cell phone charger.

I also plan to do some prop comparisons here with larger motors, such as the M-100 and 280.
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Old Jul 12, 2003, 11:26 PM
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Albuquerque Intl, New Mexico, United States
Joined Jun 2003
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Thank you for the great data! I will be very interested in the 3-cell data.
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Old Jul 13, 2003, 01:30 AM
Random Flier
Oxford (UK) and Mtn View CA (USA)
Joined Nov 2002
1,404 Posts
Thanks Dave for the interesting data.

Any advice on "prop adapters" for running these props on standard GWS gearboxes? It seems the GWS adapters are not so much "prop adapters" as "shaft adapters" ie they adjust the shaft to suit the prop not the otherway round - a bit of a pain if you want to swap around prop types. Same presumably for using heat shrink on your gearbox shaft - OK until you want to try a reduction prop...

Also, any idea who stocks the larger HD props in the US? They seem to be as popular as hens' teeth
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Old Jul 13, 2003, 05:48 PM
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Walled Lake, MI, USA
Joined Feb 2000
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I bought all of my HD props from Balsa Products except for the 12x8s, as they did not yet have them in stock. I bought my 12x8s from Maxx Products International.

http://www.maxxprod.com/mpi/mpi-29a.html (last 5 props near bottom of page)

http://www.balsapr.com/common/listV...291317152003381

I've used a number of adapters to adapt the HD props to the 3mm IPS and EPS gear shafts. The first thing I used was a short length of fuel tubing stuffed into the hole in the prop hub and then screwed onto the threaded section of the gear shaft. Then I tried the GWS black rubber adapters in the same way -- stuffed into the prop hub hole and then screwed onto the gear shaft.

More recently, I've bored out the prop hub hole to 5mm and used one of the MP Jet 3mm prop adapters. I'm sure that one of the 3.2mm prop adapters would also work, as the 3mm adapter is a very tight fit on the 3mm GWS gear shafts. I may have to start a separate thread on this, as more people want to use the HD props with the EPS and IPS gearboxes.
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Old Jul 13, 2003, 08:53 PM
MKH
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Ohio
Joined Mar 2000
2,597 Posts
Dave, I didn't see a single HD prop on a plane at Mid-Am, but I spoke with people turning the SF props at up to 8000 rpm. Thats gotta be way past their best efficiency point, wouldn't you think? One thing I've found, is that switching to the HD props and enjoying the lower amp draws, I no longer need to chase the lipoly train, and get the latest and greatest high C discharge cells. 3 ET1200s and a small brushless setup will take any parkflyer I know of straight on up, at amps that all the gear is quite happy with. I also expected the HD props to be much heavier, but they are not. And, per your HD mounting thread, I'm glad you're sharing all your techniques. My vote is for the 'long' MPJ 3mm collet adapter. Simple and sweet, $3 well spent.
Marcus
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Old Jul 13, 2003, 09:10 PM
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Walled Lake, MI, USA
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Marcus, I missed a chance to meet you if you were at Mid-Am today (Sunday). I agree with all of your observations about the HD props. The one thing I waver on is the long vs. short MP Jet 3mm collet adapter. The long one is easier, for sure. But when you heat and sink 5mm nuts into the hubs of HD props, then you can twist the props on and off without needing a wrench or other tool. So, after the initial setup work, switching props is quicker and easier. Oh well, be sure to read the following thread and add your comments:

http://www.rcgroups.com/forums/showt...hreadid=133457
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Old Jul 13, 2003, 09:35 PM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
4,564 Posts
Dave: I'm now convinced 3 cells is in all but the most weight sensitive situations the way to go for IPS's.

I posted this in powertrains, but my first C drive finally died at 19 hours. Disection showed that the comm looked decent and the brushes were worn EVENLY, but not quite gone yet. The failure was due to some very fine steel looking wire gumming up the works. Not sure where it came from.

I swapped a new motor into the GB and got a 50 minute flight on the new one before I simply ran out of power to stay up. The cells were warm and had 9.52 volts. (3s etec 700's)

This bears testimony to your statement a while back that Li's are very unlikely to damage themselves by discharging too low as the plane just won't stay up long enough.


Dean in Milwaukee
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Old Jul 13, 2003, 10:08 PM
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Walled Lake, MI, USA
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Dean, I saw your message in the other thread. I always like to keep up with your experiments. The whole concept of balancing motors, gearing, props and battery packs is fascinating, and constantly changing. It's really just taking a systems approach rather than looking at individual components by themselves. Everything I see leads me to believe that 3-cell LiPo packs are the way to go, with gearing and prop size adjusted to compensate.

I've made a big deal of the GWS Hyper Drive props because their increased efficiency in supplying more thrust per amp could result in being able to go to a smaller, lighter pack. When you're using a 3-cell instead of 2-cell LiPo pack, it really helps when you can go to the next size smaller (lighter) cell. So I'm constantly looking at all of the variables and mentally evaluating new combinations.

Just to correct the record, I was repeating what someone else had said about lithium cells being unlikely to damage themselves by discharging too low as the plane just won't stay up long enough. However, another person noted that certain floaters that require little power to stay aloft could, indeed, remain airborne long enough to overdraw the cells. So it pays to be careful if you are flying a floater on Li cells.
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Old Jul 14, 2003, 11:50 AM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
4,564 Posts
Agreed about a true floater plane being able to run li's down to far.
Your typical TM or such though won't have that problem.

I would like to try out the 11x7 hd prop in place of my favored 10x8 rs, but I really need a way to mount it with a prop saver, instead of solid with a collet. ( belly landers you know).

Maybe gwsceo will make a press in adapter to make hd props fit rs shafts. Sure would simplify things.


Dean in Milwaukee
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Old Jul 14, 2003, 12:49 PM
Senior Moment Member
Virginia Beach, Va.
Joined Jan 2002
1,233 Posts
Dave,
After reading your posts I started checking into the HD props. But I am really confused now.

On the GWS prop page the hyperdrive props look like the ones we're already using, and the reduction series look like direct drive props. I was trying to come up with some part numbers for the HD props, but apparently I need a coffee or something, maybe an expresso would help......

GWS Props

Lost in a sea of EP #'s........

Jimmy
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Old Jul 14, 2003, 04:20 PM
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Walled Lake, MI, USA
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Jimmy, I noticed that during the recent revision to the GWS site, they transposed the HD and RS props. The curvier ones are really the RS props, and the straighter ones are really the HD props.

The identification numbers of the props are simple. They're all EPXXYY, where X = diameter and Y = pitch. Thus, the EP0840 is an 8-inch-diameter HD prop with a pitch of 4. The RS is not available in an 8x4. Likewise, there's no RS duplication in sizes with the EP0950, EP1060 and EP1170. There is duplication with the EP1280. It is the only size in which there are both RS and HD versions. So, when you order EP1280 props, you have to be sure that you specify Hyper Drive props or you will most likely get Reduction Series props.

Here are a couple of links to separate lists of the Hyper Drive ("direct drive") and Reduction Series sizes:

http://www.balsapr.com/common/listVi...91317152003381

http://www.balsapr.com/common/listVi...91319332003670
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Old Jul 14, 2003, 07:44 PM
Senior Moment Member
Virginia Beach, Va.
Joined Jan 2002
1,233 Posts
Thanks Dave, I got it now.

I had thought the direct drive was what I was looking for, but when I went to the GWS site to check it out it wasn't what I expected.

So I thought I better ask before I went shopping.

Jimmy
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