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HomeAircraftHelicopterAerial Photography and Video › symmetrical vs semi symmetrical blades for ap
03-05-2008 02:20 AM  10 years agoPost 1
abwomack

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Houston, TX - U.S.

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are there any significant advantages/ disadvantages with one of these over the other??

Allen Bryan

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03-05-2008 02:45 AM  10 years agoPost 2
KC

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WA

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all things equal between a semisym and a sym blade (chord, length, weight, balance, etc) a blade with a semisym airfoil is usually more efficient.

most pilots will say semisym are less stable but airfoil differences do not affect stability nearly as much as disc loading, chord balance, blade bolt position, materials used to make the blade, dampening, flybar, etc, etc....there are a lot of ways to get stability, but very few to get more lift.

I like semisyms for AP myself, but I know a lot of APers who use syms probably because they have found them to work better for the way they set up their copters.

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03-05-2008 03:05 AM  10 years agoPost 3
jascamera

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san francisco, ca

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I would say ideal situation is to have 2 type of blade. symmetrical for windy day and flat bottom one for heavier equipment on calmer days.

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03-05-2008 07:05 AM  10 years agoPost 4
efliernz

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Hamilton, New Zealand

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I flew the AP Trex-600 at 4.8Kg with semi-symms last Friday - 20 mph gusting 25. I even got spun around twice at 200' while tail-into-wind hovering

The lifting was incredible and required care at takeoff to avoid premature liftoff. Apart from that, they were good. I am installing an Eflite wattmeter tonight so I will do some testing. While the semi-symms are a little bouncy in gusty conditions, I couldn't be bothered changing the blades over - and I had them with me...

Pete, Trex500, Trex600E, Streched 600, DSX9, DX7, Low-volt alarms - check the gallery for my alarms

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03-05-2008 08:06 AM  10 years agoPost 5
macsgrafs

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Barnstaple, Devon, UK

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I'm looking for a set of semi syms, but cant find any anywhere!!!

Ross

Seems to me that ALL heli's beat the air into submission

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03-05-2008 08:13 AM  10 years agoPost 6
Hogster

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Surrey, UK

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I think the following sum it up:

SEMI-SYMMETRICAL

Advantages - More lift for the same power input
Disadvantages - More susceptible to translational lift in gusts of wind

SYMMETRICAL

Advantages - Less susceptible to translational lift in gusts of wind
Disadvantages - Less lift for the same power input

David

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03-05-2008 08:39 AM  10 years agoPost 7
FCM

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Surrey, England

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Disadvantages - Less lift for the same power input
for a given blade area. But you can run longer, broader symetrical blades than you can semis. It all just about evens out in the end but semi's are normally more prone to wind gusting which is okay for stills and not okay when shooting video in anything other than flat calm conditions.

Paul.

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03-05-2008 01:06 PM  10 years agoPost 8
Seablade

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earth

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I'm looking for a set of semi syms, but cant find any anywhere!!!

Ross
Try Revolution Models.

NHP make a set of 800mm, no complaints. The only ones I've used on MJ-2 aside from sym's.

"Vini, Vidi, Velcro"

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03-05-2008 08:08 PM  10 years agoPost 9
KC

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WA

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NHP makes very good blades

smaller semisyms arent always easy to come by, the best I have found so far for 600mm are Mikados, p/n 1048

for 680mm I had a pair of Leisuretechs I really liked.

for 550s, Vs have the most lift I have ever come across, they are syms but they have a large chord.....the airfoil on them doesnt really matter

I have flown V550s at 500rpm...you won't get much else from them at low rpms except mast bumping and dangerous instability, but above 15-1800rpm, they are the money ticket for making a 550 machine go faster, lift more, and auto better.

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06-19-2008 09:43 AM  10 years agoPost 10
jusrap

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Asia

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Does anyone have picture of the airfoil shapes of these diferent blades. I take it semi's are flat at the bottom.

Thanks

Jusrap

Life's sweet

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06-19-2008 09:48 AM  10 years agoPost 11
TrexRookie

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San Francisco, CA

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Semi-symmetrical blades look more like an aircraft wing, with a slight contour on the underside of the blades. Hence the "semi" part of that word. Flat bottom blades are just that. They look like a symmetrical blade virtually chopped in half.

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06-19-2008 11:51 AM  10 years agoPost 12
Griffo

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Melbourne / Canberra, Australia

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Has anyone tried semi symmetrical blades on a flybarless head with HC rigid or similar?

I'm just wondering if the HC Rigid would counteract the balooning tendancy in heavy winds, thereby providing a win win situation for efficiency and stability.

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