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Hacker A60 18L Prop?

Hi there, I hope someone can help me....
I have converted a BH Glasair 120 to EP, using a Hacker A60 18L and an Masterspin 99 opto which was previously underpowering a 180 size edge 540.

I am using a 12s setup, I have an 800g setup (2x2500) and 1kg setup (2x3300) and while tried out a 22x12 mejzlic prop (M, which suggested 10kg of thrust using the "tied to a tree" test.

Great performance with this, although the plane is 6.5kg with the 1kg lipos, the recommended weight is 5.2kg

However very poor ground clearance with the prop here and I snapped shaft and broke prop on a heavy landing.

I have put on an 18x8 mejzlic prop, it tachos at 9,000 rpm full tilt but only pulls 4kg on the restraint.

I see gas versions use this prop with success, not sure how it will handle an extra 1.3 kg????

I am worried about trying out the prop, can anyone guide me as the proper thrust / weight or suggest a prop? Is there an online calculator I can put in all the info?? Any help or advice would be much appreciated.

:)

http://www.wattflyer.com/forums/showthread.php?t=59706

There is mention of a calculator there, hope it is one that will help you. They say it is free for 30 days but is worth the price if you decide to keep it.

Thanks, great program, says the prop is too small alright, recommends a 20x12 or even 22x12 if I want to go ballistic.

Will need to modify undercarraige to get the clearance.

Quote:

Originally Posted by gdwyer (Post 776832)

Uh Oh
Try to find out if you can pick up an APC-E ELECTRIC prop. These electric props have a much thinner blade, and are supposed to be slightly more efficient than props for the gasoline (Petro) or alcohol engines.

But, the important part, those thing electric props will often break on a noseover before the motor shaft does. :eek:

Take a look, at least in the USA anyhow.

http://www.apcprop.com/SearchResults.asp (Click on "Thin electric props".)

http://www.aero-model.com/Hacker-Bru...60-Series.aspx

http://www.aero-model.com/Hacker-Brushless-A60-18L.aspx

glasair 120.wmv

thanks! going to stick with original 20x12 apce ( in this video ) and adjust the legs to get the clearance I need.

Data sheet attached, hope it hauls 6.5 kg around!! :)

glasair 120.wmv

Prop diameter has far more influence on thrust than RPM does.

Thrust goes up - or down - as the 4th power of the diameter but only the cube of the change in RPM.

In other words, if you go from say 4000 rpm to 8000 rpm, thats doubling the rpm you should get 2 x 2 x 2 = 8 times the thrust.

But if you double the diameter of the prop you will get 2 x 2 x 2 x 2 = 16 times the thrust.

Another more realistic example might be a 10% increase.

With rpm if you go up by 10% you get a thrust increase of 1.1 x 1.1 x 1.1 = 1.33 times as much thrust or a 33% increase in thrust for a 10% increase in rpm.

With diameter, if you do the same 10% increase - say going from a 10" to an 11" prop - you get 1.1 x 1.1 x 1.1 x 1.1 = 1.46 times the thrust.

Power usage goes up or down at the same rates.

At least, thats the theory :)