contra rotating blades? - RC Groups
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Jul 13, 2004, 04:58 AM
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contra rotating blades?

Is there anyone producing twisted and cambered blades for a micro heli (hornet size) that is available in both revolution directions?? The efficiency of the DF or MS composite CH46 must be verry much improved if the symmetrical blades could be replaced with cambered ones. Im waiting for the upgrade but have yet not seen it.

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Aug 30, 2004, 08:05 PM
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english please
Aug 30, 2004, 11:40 PM
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phscott's Avatar

Higher efficiency blades

If you ever find any, please let me know. I have been looking for something to lift my CH-113. The stock blades on the MSC CH-46 are symmetrical and are JUST able to lift my 880 gram creation. I'd like a little more margin.

I installed one of the new 10C LiPo batteries today and was finally able to climb out of ground effect, but it's still no rocket. The older (about 5 charges) battery is a ThunderPower 3S1P 2100mah (3C version) and it won't lift it OGE.

Aug 31, 2004, 02:53 AM
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Hi, i dont know the size of hornet blades, but the hirobo xrb lama has a twisted and simetrical opposite blades, because is a contra rotating blade heli. The stock blades are of depron, but also they are of CF and other option in wood. Maybe that could serve you.
Aug 31, 2004, 11:28 AM
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phscott's Avatar
The blades on the SeaKnight are 225 mm from bolt to tip (they would probably have adequate clearance if they were 230mm, but not longer) and have a 5mm root thickness. How do the Llama blades compare?
Aug 31, 2004, 07:03 PM
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About 6 months ago I spoke to Yukonho (Like90) about making some counter-clockwise rotating blades to match his Hummingbird replacements. He said he would do it as soon as he got a little free time. If enough people let him know that they are interested in a set maybe it will be easier for him to find some free time.
Last edited by Hooters Driver; Aug 31, 2004 at 07:10 PM.
Sep 01, 2004, 10:45 AM
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The foam blades of Xrb Lama are 155 mm from bolt to tip. I think cf blades are the same size.
Sep 01, 2004, 04:26 PM
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phscott's Avatar

More lift with symmetrical blades

I've looked all over and haven't found any flat bottom or refelex blades to fit the MSC CH-46. There are a couple of leads that may eventually pan out, but in the mean time I'm wondering if LONGER blades might help.

My questions are:
1) Does lift (increases with diameter at constant RPM) go up faster with blade length than drag (increases with blade length, but I don't know the ratio) reduces the RPM on a given motor/gear/battery combo?

2) Since I have only clearance enough to swing maybe 230mm blades with the front and back heads fixed at 90 degrees, could I change them to 45 degrees and increase the overlap? What happens when the front and back aren't at 90 degrees to one another?

If the answers to those questions seem reasonable, I may try some of the Hornet II blades, which are longer, but still symmetrical.

Sep 01, 2004, 05:38 PM
This stuff is so cool !
joe@tech-mp's Avatar
Hi Paul,

What is the head speed you are runing at? We run our Dragonfly Pro tandem at around 2200 rpm with the same blades you are using and a TP1350 pack.
With the painted JMD CH46 body is weighs in at 740 grams. The stock twin speed 300's are plenty of power for it. An Astro 20 with a TP2100 pack gives awesome vertical performance.

I mentioned this to give you a reference point. Mabey your motor/ESC are producing less than normal power.

Sep 01, 2004, 08:00 PM
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phscott's Avatar

I'm running about 2150 RPM. While I was flying it witout paint and doodads, it flew fine (or at least better). Now that I've added tanks and several coats of paint to the fuse (see my gallery for photos of the bird), it weighs about 890g ready to fly. (Which is about 100-150g heavier than the manual says this heli should weigh.)

The motor that comes with the MSC SeaKnight is an "EM-400 brushless" (I don't know the mfg nor the speed controller since they are both tagged with MSC stickers). The motor has an 1100KV rating and the MSC CH-46 uses a 14 tooth pinion with a 70 tooth main (5:1). The head turns about 2760 with just flybar paddles attached, and tach's about 2150 when hovering right now. I plan to tach it with blades fixed at zero degrees to see what the RPM will be.

With the TP2100 (3C version) it flew fine before, but now it won't get OGE. With the TP2100 (10C version) it flys better, but not much 'up'. Yesterday I checked the current draw (not very accurate execpt for an average). It hovered for 12 minutes and required 1500mah recharge (for an average of 7.5A). That seems high, but that might explain why the 3C battery didn't work so well.

I'm still chasing throttle curves and pich curves to try to see if I'm having ESC programming issues (maybe ESC is not linear from 0-100% throttle so I'm getting a shortened or dogleg curve) or maybe its just a badly matched TCV/PCV (low stick-pitch too high or throttle-curve too straight, etc.). I have about 6 degrees at mid stick and about 11 degrees at top stick. It hovers at around 3/4 stick and climbs slowly between 7/8 and full stick. Seems like too much pitch to me, but it doesn't want to fly with less. I can change mid-stick and max-stick pitch +/- a degree or so using the trims on my 9Z and it doesn't seem to change much of anything.

That's why I started looking for "better blades" and was attracted to this thread. Flat bottom maybe. Reflex maybe. Longer maybe.

Still looking for ideas though ;-)
Sep 04, 2004, 03:21 PM
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bat's Avatar
as for cambered blades that are made for both directions, I saw a very helpful forum on how to make your own fixed pitch cf blades with camber. I used his method with balsa to make my own xrb blades. search my posts to find more info on making blades. hope it helps
Dec 01, 2004, 09:05 AM
meatbomber's Avatar
woops.. was reading old post in cache... better refresh next time before posting
Last edited by meatbomber; Dec 01, 2004 at 09:07 AM.

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