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Nov 18, 2019, 12:16 PM
"the analog man"
Thread OP
Question

"Rules of Thumb"?


Guys, Are there any rules of thumb useful to selecting an EDF/motor/battery cell count for an airplane? There are a few for electric conversions for prop powered airplanes like needed watts per pound of airplane, but not sure how to use the thrust capabilities of a fan system for a jet powered conversion. I'd like to find a system to power a 3.7 meter (ws) glider, and not sure how to use available info on different fans.

Help?
Larry
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Nov 18, 2019, 06:55 PM
Foam addict
4stripes's Avatar
That is a loaded question!
A glider should need 0 watts pound.
That being said, it also depends how much climb performance you will need and how will it be launched? A prop will always be the most efficient. EDF is terrible when it comes to efficiency in comparison.
How much does it weigh now (without powerplant and propulsion battery)?
Nov 19, 2019, 09:46 AM
"the analog man"
Thread OP
4Stripes, the current weight is about 13lbs, or 6kgs. The glider is about 1/4 scale of the Swift S-1. The full sized is a fast aerobatic demonstration glider.The model has a fiberglass fuse and obechi over foam wing and horizontal fin. I'd liike to launch it on it's retract wheel,, but could use a dolly. Runway is short grass (about 1") normally. Thoughts? Are there design tools guys use to select the correct size power plant?
Nov 19, 2019, 09:55 AM
That thing almost hit me
Tahoed's Avatar
You might find something here....https://www.turbines-rc.com/en/50-edf-for-gliders
Nov 19, 2019, 10:00 AM
Foam addict
4stripes's Avatar
Right, now add another 2kg for the powerplant setup to make 8kg. You have one big model that will have pretty high rolling resistance on one wheel. Because you have a glider and probably don't expect fighter jet performance, I would suggest a 6S 90mm EDF minimum. It won't climb on power but the efficiency of your plane should make it work.
Again, I think you are making a huge mistake using EDF over a folding prop. The prop is streamlined when not running, lighter and more efficient requiring smaller batteries for longer running time.
Nov 19, 2019, 10:02 AM
Foam addict
4stripes's Avatar
Quote:
Originally Posted by Tahoed
You might find something here....https://www.turbines-rc.com/en/50-edf-for-gliders
Holy cow!
Those are neat. A bit rich for my blood.
Nov 19, 2019, 10:08 AM
That thing almost hit me
Tahoed's Avatar
An example of something less expensive.
RC Jet Glider: RCRCM Tomcat with EDF Drive System (1 min 43 sec)
Nov 19, 2019, 10:13 AM
Foam addict
4stripes's Avatar
sweet sounding fan!
Nov 19, 2019, 10:35 AM
That thing almost hit me
Tahoed's Avatar
With a fixed wheel like the Swift or the Fox, unless you use a cradle for launching, there is not enough clearance for a ROG takeoff with a folding prop on the front. Something like this would work too...http://www.icare-rc.com/self_launch_...O_II_SLS_small However, it looks like LR Fitch wants to build his own. As a rule of thumb, some where between .5 and 1 thrust to weight ratio should work. Since it's an aerobatic sailplane, I'd shoot for a 1:1 ratio. (or more....)
Last edited by Tahoed; Nov 19, 2019 at 11:07 AM.
Nov 19, 2019, 11:12 AM
That thing almost hit me
Tahoed's Avatar
Darn it! Now I'm thinking about one for my Fox.....

Nov 22, 2019, 12:08 PM
Registered User
I have converted a few gliders to power gliders .
EDF fans are very inefficient and create high drag .

Best is to remove the lead in the nose cut the tip off and build a fire wall for a low kv motor with a fold back prop
This will give you much more thrust tmand the least amount of drag compared to a EDF setup


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