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HelicopterAerobatic FAI F3C F3N Contest › Spin semi-symetrical blades for F3C ?
12-04-2011 04:08 PM  5 years agoPost 1
trillian

rrVeteran

London, UK

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Just curious what the consensus is on these Spin blades
or on semi-symetrical airfoils in general?

I am attracted to the claim about the Spin blades using
less energy so longer flight times and / or less fuel
burned etc. but have heard very little from people actually
flying them and nothing as to whether they would be any good
for FAI flying.

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12-06-2011 01:42 AM  5 years agoPost 2
Santiago P

rrProfessor

South West, Ohio

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Semisymetrical blades are a bit more efficient making lift but some react baddly when hovering in gusty conditions , and very tricky in aerobatics. Semis are not friendly to axial rolls.

I flew FAI semis for a year, not going back to them.

I found less efficient blades with shallow lift to angle of attack slope being best specially in gusty conditions. Best blades are between 220 and 235gm in weight, popular examples are the Radix FAI 710 and Rotortech FAI 720mm. There are other from Funtech and Hi-Products but hard to find.

My advice, stay away from semis for F3C

S

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12-06-2011 01:46 AM  5 years agoPost 3
GM1

rrElite Veteran

Tallahassee, Florida US

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Semis

For many years semi-symmetrical blades were used by many of us in F3C as they were very fast, which gave lots of momentum for vertical climbs and they autoed beautifully. However, they did have some issues when changing from positive to negative pitch like in rolls. If you got too much negative pitch in, the nose of the model would pitch up and the model lost much of its forward speed.
With the introduction of the newer FAI schedules that had longer and longer inverted segments, most of the F3C pilots switched to symmetrical blades which behaved nearly the same inverted as upright. The latest schedules have backwards inverted segments with rolls which would be even trickier so I don't think you will see very many pilots using semi-symmetrical blades anymore.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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