heli can't lift - the solution
 

hi,
a few weeks ago i posted a thread here about my esky comanche that wasn't able to lift higher that 1 foot off the ground, despite of its good motors, batteries, blades, etc, etc.
well, i accidentally learned that the problam was the tracking.
with incorrect tracking - flybar linkage too long, in my case - the heli just won't lift.
could someone explain the physics involved?
i would expect the heli to spin in such a situation, but it doesn't. it just doesn't lift.
thanks

RE: heli can't lift - the solution
 

Hey again RTG,

I wouldn't know where to start to explain all the physics of rotary flight - it is very complex - but google search "dihedral lift" and/or rotary flight" and/or "gyroscopic progression" and/or "angle of blade attack" and it will give you an idea.....
I will try to keep it simple: At any "moment" (imagine freeze-framing a video;)) the 'angle of attack' of a blade affects its lift. If the angle of attack is in any way different from its opposing blade (opposite) the lift will be different and usually induce bad vibrations.
Gyroscopic progression is something else to factor in. It is the difference in lift from an attacking and it opposite "retreating" blade.
The upper blades on your model have a top link to adjust these angles to get a balance where both of the blades are within the same range producing a smooth "one-blade" look when viewed from the side at arm length:D
Does any of this make sense to you?:) This summary is VERY simplified - there are many factors involved in rotary flight.

Peter[sm=shades_smile.gif]

RE: heli can't lift - the solution
 

hey Peter,

Hello again. It's very nice to talk to you.;)

Jack, from Helifreak, corrected me. It seems the name for this fly bar linkage adjustment is not ''tracking''.

Actually, I'm trying to understand what ''tracking'' means. I've searched a lot and found an explanation in a article I bought from John Salt.

''Tracking'' seems to be the adjustment on the blades so that blade A and B tips will rotate at the same level. Is that correct? When they don't, the heli has vibrations, but no lift problems. Am I right?

As to the lift, it can really be affected by the incorrect length of the fly bar linkage and the explanation you gave couldn't be more right.

The guy who helped me fix my Comanche told me he had fixed the tracking, but I think what he actually did was fixing the linkage size.

Let me know your opinion.[sm=tongue_smile.gif]

Thanks.[sm=thumbup.gif]

P.S.: Do you guys in Australia like football? I mean soccer, but the right name is football:). Are you watching the World Cup?

RE: heli can't lift - the solution
 

Hey again RTG,

Yip:) I'm sitting at home watching the build up to the World Cup on my wide-screen TV!
Re. the "tracking": you have got it correct - blades A and blades B MUST make two planes that are exactly parallel to eachother.
All of these things, lift (drag) and coaxial tracking and thrust and torque and helicopter (rotary flight) physics are closely related and affect oneanother - so to say "no lift problems" bolded above (I'm sorry;)) - but it is just not correct........[sm=what_smile.gif] The lift problem that you WERE experiencing - I love saying that[sm=tongue_smile.gif] - was probably due to the pitch and dihedral of the actual blade. Put a blade A that you have now removed next to (or on top of) a blade A that is good (you may need to remove it from the bird) and notice the differences........so the correct adjustments of the top linkage (between flybar and upper head) makes the leading edges of the blades that you have installed "cut into the air" the same! The pitch and dihedral and length of the blade is supposed to be set in plastic and out of the newbies hands[sm=wink_smile.gif]

Peter[sm=shades_smile.gif]
P.S. Basically, the guy that helped you was right! He adjusted the "top link" which made it track better or perfectly![sm=thumbs_up.gif]