Nf-ID: #R:mlb.semi.harris.com:13803:trsvax:1195667328:000:3744
Nf-From: trsvax.tandy.com!earl    Dec 11 16:54:00 1992



/* ---------- "Please Explain Helicopters" ---------- */
After browsing through the articles relating to helicopters, you
folks have stirred my curiosity regarding how the heck they fly.
More importantly, how do you CONTROL them?
What do the 4 or 5 channels control?  
As a helicopter moves faster through the air (suppose in a straight 
line), how do you account for the needed dynamic changes in pitch 
of the blades and rotor?  Doesn't it continually want to bank and 
turn as speed increases? Please explain in less than 10,000 words.
..amazed they can fly at all....
Mark.
***********************************************************

How do you control them?...
   Basically you use 5 RC channels:
      1.  Left-Right Cyclic   ( eg ailerons)
      2.  Forward-Back Cyclic ( eg elevator)
      3.  Tail Rotor Pitch    ( eg rudder)
      4.  Engine Throttle     (eg  throttle)
      5.  Main Rotor blade Pitch Control (no normal airplane correllation)
          Collective Pitch.

      Normally in modern RC helicopters, the throttle is mixed in with the
  main rotor pitch servo to adjust pitch (collective) as engine speeds and
  rotor speeds increase.

How do you account for the dynamic changes...that occur?...
    Basically, you feed in more or less tail rotor pitch as needed when your
changing collective pitch, engine speed, et cetera. Most RC helicopter
flyers use a "tail rotor" gyro in series with the tail rotor servo to help
compensate for rapid 'dynamic' changes. The "gyro" slows down the rapid
tail rotor movements to give time for the pilot to be able to control the
chopper better and easier. It is not impossible, but it is real hard to
fly a RC chopper without a "gyro".

SPeed, bank and angle changes?...
   Sure it does change a lot in the air, depending on what you're doing.
Basically after getting up to normal flying speeds a helicopter starts to
behave more like a real fixed wing aircraft. After taking off and transitioning
from hover to forward flyight, you'll decrease your angle of attack as the
chopper gets going faster and faster. Plus as you increase speed, you may or may
not be able to increase or decrease collective pitch, it depends on what your
doing and the chopper's design. Normally, to increase speed you can increase
main rotor RPM and increase collective pitch to get more speed and bite out of
the air. Now getting back into a hover for landing, that's the real trick.


Doesn't it want to bank and turn?...
   It sure does...But that's what the tail rotor and gyro help compensate for.
Plus at speed the little tail fins act as stabilzers in forward flight too.
Minor trim changes are handled on the transmitter with trim tabs for the
four main channels. The collective pitch channel usually has a low speed
versus high speed throw adjustment too. Plus you can control and adjust the
amount of mixing from throttle to the pitch channel too. A number of the
"gyros" also can take advantage of a "sixth" channel and gives you a high
versus low sensitivity to movement through the tail rotor pitch servo.

It's amazing they fly at all?...
     It sure is, it's all magic you know. Lot's of money, lots of practice,
     and lots of luck. (Most important lots of LOCKTITE.)


***********************************************************************


<This information is provided by an individual and is not nor should be
 construed  as  being  provided  by  Radio  Shack or Tandy Corp.  Radio
 Shack/Tandy Corp has no obligation to support the information provided
 in  any way. > 
						
						Earl W. Bollinger
						@ <earl@trsvax>


"You were in the Clone Wars!", said Luke excitedly.
"Yes", replied Obi Wan, "I was a DOS programmer. But that was before the dark
 times, before OS2."