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Old Oct 12, 2012, 02:34 PM
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Actually, a carefully matched set of motor, prop, battery, and airframe can give a 10 second climb that uses less current than a 30 second climb. It doesn't necessarily mean a bigger motor or over taxing an existing motor. Simply going to a prop with a more efficient design or, better yet, more blade area without bogging down the motor, can give much better climb performance.

Most people make the mistake of swinging a smaller prop with a greater pitch than needed. Because one has a higher theoretical top speed one is led to believe one is developing more thrust. However, that's not the case. One will get the best thrust per watt by swinging the largest prop, usually at a lower pitch, that one's motor can handle. For a glider, other than hotliners or very large models, there's no reason for a pitch of over 6 inches. I wish there were more folding props available with a 4 or 5 inch pitch. In my case, going from a 9.5X8" prop to a 10X6" prop resulted in around 30% faster climbs without raising the current draw or costing me in the number of total climbs on a charge. An 11X6" prop seemed to give an even better climb but I landed on a rock and broke it before I had a chance to thoroughly test it.
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Old Oct 12, 2012, 03:54 PM
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Originally Posted by peterlngh View Post
Actually, a carefully matched set of motor, prop, battery, and airframe can give a 10 second climb that uses less current than a 30 second climb. It doesn't necessarily mean a bigger motor or over taxing an existing motor. Simply going to a prop with a more efficient design or, better yet, more blade area without bogging down the motor, can give much better climb performance.

Most people make the mistake of swinging a smaller prop with a greater pitch than needed. Because one has a higher theoretical top speed one is led to believe one is developing more thrust. However, that's not the case. One will get the best thrust per watt by swinging the largest prop, usually at a lower pitch, that one's motor can handle. For a glider, other than hotliners or very large models, there's no reason for a pitch of over 6 inches. I wish there were more folding props available with a 4 or 5 inch pitch. In my case, going from a 9.5X8" prop to a 10X6" prop resulted in around 30% faster climbs without raising the current draw or costing me in the number of total climbs on a charge. An 11X6" prop seemed to give an even better climb but I landed on a rock and broke it before I had a chance to thoroughly test it.
Those are sizes in the assortment I purchased and I will report my results as well. I got 10x8, 11x6, 11x8 and 12x6.5
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Old Oct 12, 2012, 04:16 PM
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Old Oct 12, 2012, 04:31 PM
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Originally Posted by Eastcoast78 View Post
Soooo do you want to know what HH are doing with your returned RP's? LOL
No disrespect to you Eastcoast78 and I understand the humour in your post but I find the whole concept of "wargames" disgusting. Showing my age...maybe...but I cannot see anything good coming out of encouraging the use of guns, whether it be in a video game or for real.
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Old Oct 12, 2012, 04:36 PM
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No disrespect to you Eastcoast78 and I understand the humour in your post but I find the whole concept of "wargames" disgusting. Showing my age...maybe...but I cannot see anything good coming out of encouraging the use of guns, whether it be in a video game or for real.
Same here. Smacks of people with too much money and time.
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Old Oct 12, 2012, 04:37 PM
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I just added a couple more pictures to the end of this build to show how changing a spinner can dramatically change the prop characteristics - diamater.
Hadn't even considered the flange pin separation Good catch! I may try the stock blades in the aluminum spinner just to get a realistic perspective on what the blades differences really add. Apples to apples. Might be that you just need the spinner upgrade
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Old Oct 12, 2012, 04:41 PM
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[QUOTE=Radio.Active;22984494]I just added a couple more pictures to the end of this build to show how changing a spinner can dramatically change the prop characteristics - diamater.

Is there a big difference in weight between the HK 50 and the Graupner 55 with collets?
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Old Oct 12, 2012, 04:44 PM
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Just at a guess, coreman, I would predict that the 11X6 will be the best unless the 12X6.5 doesn't bog down the motor. Whether it's an electric motor or a glow engine I have almost always found that a lower pitch gives better vertical performance. Greater pitch just increases the load.

I should qualify that when one is using bigger props at a lower kv then increased pitch can prove a benefit but, if you are getting anything over about 8,000RPM, the flat prop will perform better.
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Old Oct 12, 2012, 04:48 PM
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I've played with different yokes too, RA. One can get a bit more thrust, in theory, by moving the blades out. This makes the prop, which is just a wing, have a higher air speed. On the other hand, it also seems like it costs a few RPM so that the difference is just about canceled out. I haven't tried a much longer yoke though and that might make more difference.
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Old Oct 12, 2012, 04:58 PM
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Old Oct 12, 2012, 05:02 PM
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Originally Posted by peterlngh View Post
Just at a guess, coreman, I would predict that the 11X6 will be the best unless the 12X6.5 doesn't bog down the motor. Whether it's an electric motor or a glow engine I have almost always found that a lower pitch gives better vertical performance. Greater pitch just increases the load.

I should qualify that when one is using bigger props at a lower kv then increased pitch can prove a benefit but, if you are getting anything over about 8,000RPM, the flat prop will perform better.
When I fly combat with my OS .32 I prop it with an 11x4 (provides tons of torque) and I get unlimited vertical and no loss of speed around the turns. as we say, speed is for running away! Unless you are flying close to the pitch speed to unload the prop you're not going to get the best efficiency and since these aren't hotliners, there isn't really a point. BUT, I have seen more than a few props to be "optimistically sized" for pitch and so I figured I would get a selection
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Old Oct 12, 2012, 05:13 PM
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Originally Posted by Radio.Active View Post

The 55mm is the Multiplex Easy Glider spinner. The 50mm is the HobbyKing Aluminium spinner. The Graupner is the prop. The 2 spinners are about the same weight. The Al 3 g heavier. The larger Graupner Cam 11 X 8 is actually lighter than the stock 9.75 X 7.5 Parkzone. 14 vs 13 g

More info here for comparisons buried in this image dumpster

https://skydrive.live.com/?cid=DBDE7...5DDCB92%211366



.

Thanks for putting all the parts on the scale! It helps to know that upgrading the spinner is not going to add much to AUW.

I have an 50 mm aluminum Turbo spinner swinging 11 x 8's on my RP and have noticed a huge difference here at my elevation, but I don't have a scale to really check that combo. I'm going to try to borrow a wattmeter and use a set of 12 x 6's and see if I stress the powertrain.

--Jason
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Old Oct 12, 2012, 05:34 PM
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Old Oct 12, 2012, 06:21 PM
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Originally Posted by Radio.Active View Post
A wattmeter is a must when you start playing with prop combos although the free Drive Calc software will give you a relative difference as you consider changes and is cheaper than buying the real props You immediately know if it is better or worse as you change props and most importantly you see where the amps go. That is one reason I switched to a 40A Turnigy HK Cheapo because I max out at 26A on a fresh charge. However the software emulates a 45mm spinner when selecting something like a 11 X 8 Graupner Cam prop but no indication of the distance between yoke pins. Oh well, if it wasn't a freebee I could complain but regardless it still is a relatively accurate comparison to the logs I get out of my ESC.

You certainly have some unique issues as I suspect you are flying a mile high before it leaves your hand and a little extra power would be welcome. But you also probably get to do real slope soaring like Jovanx while we prairie types watch in envy.
My ice lite 50 logged less than 25 amps peak when used on the stock motor with the 11 x 8. Right before I biffed it in a high wind. My real slope soaring career has had an ignoble start here at around 5700 ft. I'm not in the same class as Jovanx. Although I might to try to go up to the top of Vail next summer.

I hope to get some real sloping in at a few sites just south of Boulder. Need to buy a few rabbit's feet on the way up.

--Jason
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Old Oct 12, 2012, 10:49 PM
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Originally Posted by Watdazit View Post
No disrespect to you Eastcoast78 and I understand the humour in your post but I find the whole concept of "wargames" disgusting. Showing my age...maybe...but I cannot see anything good coming out of encouraging the use of guns, whether it be in a video game or for real.
No worries, none taken. It seems these days, they'll make a "reality show" out of anything...

I'm was more surprised that HH sponsored it to tell ya the truth!
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