Trex700 F3C

[trillian]

That's interesting. I thought the big horizontal fin was just for some stability in FF flight. I'm sure it deflects some of the rotor downwash but have never thought too much about what this may do. So the net result then is slightly less air being blown straight down over the tail vs over the nose.

[Steve]

That's interesting. I thought the big horizontal fin was just for some stability in FF flight. I'm sure it deflects some of the rotor downwash but have never thought too much about what this may do. So the net result then is slightly less air being blown straight down over the tail vs over the nose.

Big flat fin also helps in forwards flight as well - it helps to keep the boom true while rolling by resisting skewing - unless of course your thumbs are as bad as mine!

[GravityKills]

>> It's all about the energy required to accelerate / decelerate a given mass
well, that's the problem. it takes 10x more energy to accelerate 0.1 "mass" at 10 "distance" than 1 "mass" at 1 "distance" to the same angular velocity, because E ~m v^2.
The leverage to the COG is the same for both, mass*distance. Whether or not it would be a problem in a heli, I don't know.

[trillian]

>> It's all about the energy required to accelerate / decelerate a given mass
well, that's the problem. it takes 10x more energy to accelerate 0.1 "mass" at 10 "distance" than 1 "mass" at 1 "distance" to the same angular velocity, because E ~m v^2.
The leverage to the COG is the same for both, mass*distance. Whether or not it would be a problem in a heli, I don't know.

Hmmmm, there's no problem. What you're saying is true but any way you slice it the energy required (and thus inertia) is the same. We don't need to be concerned with angular velocity or moment of inertia because the arc each mass travels in is also perportional. So all we need to worry about is E=1/2M times V squared.

The point was about using a smaller mass mounted farther forward vs a larger mass closer in (for example inside the canopy). A smaller mass mounted farther forward will have the exact same net effect as the larger mass closer in for all the purposes we're discussing (so long as the distance and mass is adjusted in the right perportion).

Without needing to get into the maths at all (I can but I'm saying it's not needed here) the weight that balances the heli will create the same results to the C of G and everything that goes with it, whether it is 500 grams inside the canopy or 50 grams on a 30 cm rod extending in front (these are just figures plucked as an example not meant to be real numbers but you get the idea).

Think about it this way: gravity is essentially the same as a constant rate of accelleration. So if a given weight at a given distance balances against another weight at another distance it means the two share the same effective inertia / kinetic energy. You can adjust the weights and distances all you want, you are just trading velocity / distance for mass or vice versa.

The difference is that the heavier weight contributes more to the overall disc loading, but sometimes this might be desireable. The downside of a smaller weight on a carbon pole is it will look strange (and might possibly have a negative drag effect)