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Jan Jurek
11-15-2005, 03:09 PM
Hi,
I have just got a set of four bladed prop(24cm dia) from Hobby lobby which Iam planing to use on my from the scrach build P-47 (about 900m/m wingspan, weight 880g and using AXI 2820/10 motor. Anybody have some input on the performance of this set up? I have been flying Grumman TBM (real aeroplane and I know that the initial take off torque might present some problems . Sure like to know what the community might add to this.
Thanks,
Jan Jurek

jrb
11-15-2005, 10:19 PM
It will perform similar to a 27.6cm two diameter of the same pitch; will that give you enough performance w/o using too may amps/watts?

Glacier Girl
11-15-2005, 11:09 PM
Jan are you running it direct drive? Is this the FS400 prop? 9.5 x 7 x4
Motocalc shows on 3s set up, 32.2 amps, 45.0 thrust,52.2prop speed
4s set up, 40.9 amps, 57.7 thrust, 59.1 prop speed
Might want to look at a gear box set up to drop the amps, if this is the case.
I run a Mega 16/15/6 on a 3:1 box, swinging that prop, in my Stang. I use 6s1320 TP pro lites(2 3s packs series wired)
My specs. 18.1 amps, 54.1 thrust, 57.3 prop speed.

Jan Jurek
11-16-2005, 02:50 AM
Hi,
Thanks for answering. The prop is GWS EP 1080x4. Did you ever heard of this propeler? I will be using Thunder power Li Polimer 2100mAh7.4V(8/4/04). Now , I have also purchased with the Jetti 40 controller a small computer and I have no idea how to use it. I would like to programe it for a gradual power reduction. (I now I must sound like an idiot). This is a brand new ball game for me. Sure can use some help,
Thanks Jan

Glacier Girl
11-16-2005, 10:39 AM
Jan your set up specs out as follows.
24 amps, 29.8 thrust, 43.0 prop speed.
Too many amps for the pack to handle.
Plus hands off flight is borderline.
The Jeti, I believe uses a programming card, to set it up. Did you get that too? As for "the gradual power reduction" I'm guessing you mean a soft cut off? If so yes it can be programmed in.

Matt Kirsch
11-16-2005, 04:27 PM
The GWS prop is meant for low-RPM geared motors, specifically for the smaller, lighter park flyers. That AXi 2820/10 will be spinning too many RPMs, and the prop won't take the abuse.

rcers
11-17-2005, 04:15 PM
What Matt said, I would not use the GWS prop anywhere over about 8-9 amps. If you do those light blades will flatten out, not to mention the option of shearing a blade off.

Mike

Jan Jurek
11-22-2005, 06:00 PM
To all these smart people which answered my question, thanks a lots. A lots of wisdom and accumulated experience . Iam sure I will be back with some more questions. Thanks again guys!
Jan

Bil2
11-29-2005, 02:30 AM
I've read that 3- and 4-bladed props are inherently less efficient, because one blade interferes with the next blade's airflow, as it is following so closely behind. Any truth there? They sure do look cool though...Bil

olmod
11-29-2005, 04:51 AM
No truth at all ,as the prop screws through the air it is moving forward ,so how can it be in disturbed air.

jrb
11-29-2005, 01:38 PM
No truth!

Check out the photos below, they clearly show no interference by one blade to the next.

Also, the best indicator of efficiency is Mother Nature.

If something was less efficient, it wouldn’t be quieter!

Adding blades on prop driven planes or helicopters makes them quieter, and improves their performance. Look at the latest aircraft being produced.

Here’s a graphic from Mark's Mechanical Engineers' Handbook (6th addition, pg 11-109) that shows more blades are better.

rcers
11-29-2005, 02:30 PM
No truth!

Here we go again!

Bil2
11-29-2005, 04:16 PM
Well, my question would be why don't all planes use 3 or 4 blades if they're quieter & more efficient? I'm not sure if I read that turbulence is the reason, but I did read that they were less efficient. Bil

rcers
11-29-2005, 04:38 PM
Bil you can find arguments on both sides, JRB fights the Multi-blade and others say single or two blade is better.

Here is what I know when it comes to models and my very un-scientific tests.

I have never found a 3 or 4 blade prop that pulls my airplane better than a 2 blade. By my own admitance, much of that may be because we simply don't have many multi-blade choices.

I suspect if APC or GWS used the thin-e blade or HD blade series on a 3 blade prop I would be interested in "playing" with them.

Full scale aircraft would all use 2 blade props if they could. Why - because of one simple reason, cost. But the powerful engines/turbines they use would require blades that would be HUGE. In military applications it was not only the power absorbing ability, but the landing gear clearance that were an issue as well.

Another factor is the RPM's we use vary significantly from full scale aircraft that is also a factor on blade efficiency. I have never been in a Cessna yet, that will turn a prop at 15K RPM! (or 5k for that matter...)

Mike

jrb
11-29-2005, 06:01 PM
Mike are you still comparing vastly different props?

Would anyone expect an APC sport prop to compare favorably with a Zinger wood prop of the same size?

Or, an APC “E” with an SF.


So your experiment comparing a GWS HD and EP are of absolutely no value; but if that’s what you want to base you opinion on, so be it.

Others have been fooled by equally bad comparisons; while those who have done exacting, precise and repeatable comparisons know the truth!


BOL!


Jim

rcers
11-29-2005, 06:33 PM
Jim I am not going to fight with you - re-read my post carefully.

I am saying we dont' have enough choices, why do you still fight and attack me?

You get me a 3 blade GWS HD blade profile 9x7x3 prop and I will test that.

What do you suggest I test? By the way since we lasted talked I had a buddy playing with the vario prop - guess what!?!!!!

Mike

jobu
11-30-2005, 03:48 AM
hehe
that's rich
good read

jrb
12-01-2005, 12:18 PM
Success of course as has been reported elsewhere with 3, 4, & 5 blades.

One gent had a bit of an issue; but an exchange of a few posts lead him to similar success saying Vari Props “rock”.


With your tutelage, I’d say similar to yours – you just can’t swap a prop w/o some thought!

rcers
12-01-2005, 03:15 PM
you just can’t swap a prop w/o some thought!

You crack me up.

Mike