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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Matt Piatkowski on November 25, 2017, 04:23:21 PM
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Hello,
How to tighten the propeller nut when the motor is front mounted but the rotor is not easily accessible?
At this moment I can hold the rotor by hand but when the motor goes into the fuselage there will be no such possibility.
Thank you,
Matt
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This happens to all of us the first go-round, Matt. On the second plane we leave access room for a pipe wrench.
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blank
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Craftsman 6" offset pipe wrench works best for me.
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What about strap wrench like https://www.amazon.ca/Multi-use-Rubber-Strap-Wrench-6/dp/B0002H338C/ref=sr_1_15/140-4849530-0013034?ie=UTF8&qid=1511694738&sr=8-15&keywords=strap+wrenches
There is enough room to wrap the strap around Cobra 3515/18 rotor but only testing will show if the idea works.
Matt
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I have found the solution.
Please see the attached.
M
"The solution is always there - the trick is to find it"
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More on the same subject....
When the spinner backplate is replaced with the AL backplate, the problem disappears. Please see the attached.
AL spinner backplate "bites" better into the carbon composite propeller, the friction is higher where it is needed and I can easily tighten the nut holding one blade only by hand.
The AL backplate comes from the Great Planes (GP) nylon spinner. The only problem: GP does not sell the spinners of this type for the 3 blade props.
Solution? Entirely AL spinner or carbon composite spinner with AL backplate. https://www.ebay.com/sch/i.html?_nkw=3+BLADE+SPINNER+RC shows possible choices.
Perhaps the GP nylon spinner's cone can be carved to accommodate the 3 blade props. The added benefit will be better motor cooling but the spinner after carving may be too weak to survive.
M
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Matt what kind of prop is that and where did you get it? Thanks
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Walter,
That is a Pol Prop. A friend thought they looked pretty good so ordered a couple. They look good in pictures but are poorly shaped with a very bad airfoil. Would be very inefficient for electric. They are hollow blades but weigh almost an ounce which is about 10 grams heavier than the props Igor sells. I sure wouldn't use one.
Alan
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The only problem: GP does not sell the spinners of this type for the 3 blade props.
I print 3-blade ABS spinners for Great Planes backplates. I drill and tap the other four spokes. There is still the problem of aligning the spinner holes with the backplate as the prop is tightened. I printed a partial spinner as a tool to align the prop
as it’s being tightened. You can search for it here.
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Here you go. Reply # 8: https://stunthanger.com/smf/open-forum/spinner-45680/msg475189/#msg475189
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Hello again,
I am attaching the results of the static tests of different propellers using Cobra 3515/18 and 5S and 6S LiPo.
The average in-flight current can be easily calculated knowing the static current and using the "3/4 Rule" .
Pol-Prop weight is 25 grams and this is 7 to 8 grams more than Igor's props. I have four Pol-Props and each weights the same. This is 11.5 x 6" propeller designed for lower RPM than Igor's propellers therefore the blades airfoil is different. The Pol-Prop blades bending stiffness seems to be higher than in case of Igor's propellers but I did not measure this important parameter yet.
Alan,
It would be really interesting to find the formula for the propeller efficiency for the C/L stunt to make the attempts to assess efficiency less subjective.
Howard,
Cool idea! 3D printing is ideally suited for such task. I wonder what is the final strength v/s weight ratio for such spinners.
Best Regards,
M
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Alan,
It would be really interesting to find the formula for the propeller efficiency for the C/L stunt to make the attempts to assess efficiency less subjective.
I'm not Alan, but coincidentally I owe him a report on a prop he made. I recommend this: https://arc.aiaa.org/doi/abs/10.2514/6.1983-190 . You could also Google Javaprop. The figure of merit you want is probably not efficiency, but a high negative rate of change of efficiency with airspeed. A local guy went to great lengths to make an airplane that would work with a very inefficient prop.
Howard,
Cool idea! 3D printing is ideally suited for such task. I wonder what is the final strength v/s weight ratio for such spinners.
I am, however, (or used to be) Howard. Beats me, but so far it's strong enough. Because my airplanes have ballast in the nose anyhow, the only adverse effect of spinner mass is the gyroscopic moment. I was constrained by wanting: the same slope at the base as the Great Planes spinner I originally used with a 2B prop, a nose radius that was FAI legal at the time, and to accommodate a backwards prop. Now that I've been using the printed prop spinner, I prefer it to alternatives. It paints nicely, too.
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This response is for Howard Rush only.
Yes..I know you are not Alan.
Please read again my response from yesterday, 05:40:14 PM. and you will find your name as the intended addressee of certain part of my response.
I know the method described in https://arc.aiaa.org/doi/abs/10.2514/6.1983-190.
The efficiency of the electric motor and propeller for the C/L stunt is, like I wrote before, a very interesting and complex subject.
I welcome all the information that is practical and possible to test while flying stunt.
Regards,
M
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The Pol-Prop blades bending stiffness seems to be higher than in case of Igor's propellers but I did not measure this important parameter yet.
The aforementioned Alan (who for medical reasons I am currently happy not to be) can fix you up with excellent, Canadian-made 3-blade stunt props with satisfactory bending stiffness.
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For Howard Rush:
I will consider the efficiency and quality of the Canadian made 3-blade stunt prop very carefully and decide accordingly.
Regards,
Matt