section of tail blades

[moyesboy]

The tail is always pushing mostly one way, when the throttle is open.
The blades are symetrical section.
Why are they not a cambered section? There should then be less drag throughout the normal flight envelope.

The operation with symetrical blades is difficult to get even one side to the other because the main rotor torque makes it all one sided. with cambered tail blades it might actually be easier.

The only down side I see would be during an auto when operation would then be lop sided - but if you have everything set up for even piroette speed in the hover it wil be lop sided engine off anyway.

[helidriver]

well,

i think u are going down a rabbit hole really. saying more lift gives u less drag is a bit off the mark.
more lift = more drag.
we have enough pitch movement to overcome any lift advantages so it makes sense to save the power for flight conditions that require 0 or -ve pitch ( this is where a cambered blade will use more power).

look at the size of the fin on a full size , it is like a huge rudder. it is designed to allow the tail blades to give minimun drag ( zero lift ) at cruise speed. it also gives a fighting chance of being able to maintain straight flight in the event of a tail failure.

also for us a symetrical blade is easyer to develop and produce i should think. (cheeper).

not all models have the tail on the same side, would we need left or right sided tail blades ??

its getting a bit geeky for me now so i'm off.

coefficient of Drag.... drag = 1/2pV2S

p (rho) is air density
V is velocity squared
S is surface area of aerofoil

[moyesboy]

True its probably not worth it or it would have been done already.
for example even all the guys who don't do aerobatics are flying their electrics with symmetric mains and complaining about the duration

however, in most of the situations where the tail blades need 0 or -ve angle of attack, the main rotor is off loaded - so there is oodles of power available. where the tail rotor is loaded a lot in both directions, such as a ripper, the load is higher against the torque than with the torque as illustrated by the difference in max pitch you end up with on the tail rotor to get the piro rate the same.

to my way of thinking the cambered airfoil will have less drag for a given amount of lift. If that wasn't the case then there wouldn't be any reason to have cambered sections at all.

So when you have a lot of positive or negative pitch on the main rotor, and the tail blades are lifting in the normal direction, then cambered tail blades should sap less power.
Its a question of if that amount of power saving is noticable or not.

As regards different helis, if you can cover raptor and trex600 you probably covered 50% of all nitro helis. Dunno if they have the tail the same way round or not!

[BobJ]

Hi Gordon

It has to be a symetrical section on tail blades really as anything else is not as stable as the blade transitions from negative to positive pitch.
I did a lot of testing of blade section when I was with NHP and the section made surprising little difference and it really seems blade weight and area are the two things that make the most difference.
Bolt hole position also makes a little difference and a thinner section will have less drag up to a point, at high angles of attack a thin section does not work as well, tail blades get to very high angles of attack at times.

Cheers
Bob

[moyesboy]

Hi Bob.

With a symetrical section the only way to stop is stalling at high angles of attack is with a thick section and fairly forward max thickness with a bluntish entry (which is how the exsiting tail blades are). It might be worth having a rough surface like the TST...

However the tails seem to work pretty well really, and there is probably little to gain there compared to the main blades.

I was thinking of cutting down some of my stock of broken 450 carbon main blades as 50 tail blades, but I guess the thin slim entry section on them will brobably make them stall early.

[helidriver]

go for it

let us know