Gyrocopter Speed

On 2005-03-24 01:25:19 -0500, "Mark" mark said:

Why is there such a wide range of max/cruise speeds for gyros? I
notice a Barnett BRC540 2 place cruises at 110 with a top speed of 138.
An RAF Cruises at 70 with a max of 100.

You mean, these are the advertised speeds. Not many Barnett 540s are
flying. There are a number of gyro speed records; I recommend you go to
fai.org and look them up.

Gyro speed is limited by drag. A rotor in autorotation is a draggy
thing. Most gyro fuselages are either designed without any
considerations but function, or are styled without a thought for
aerodynamics. Aero costs money and most gyro firms are in a
hand-to-mouth mode.

Most single places seem to cruise between 45 and 80.

Why aren't there more fast single place gyros?

Take a look at the tractor Little Wing. That holds a number of speed
and distance records. It is plansbuilt, although you can purchase the
frame tack- or finish-welded.

Other than a bigger engine, why can a Barnett go 138 compared to RAF's 100?

Well, with who-knows-how-many Barnetts flying, I would like to see
proof it does go that fast before accepting the number.

IMHO an RAF at high speed -- which is around 100 -- is in a hazardous
flight regime.

What characteristics give it the stability to safely go faster?

Gyro stability is a very large can of worms, largely because one large
maker believes it's all voodoo or myth, and not a matter of science. So
forgive me if I don't go there.

And why wouldn't they design those characteristics into other gyros?

If you want speed, you don't want a gyro. It's just that simple.

If I have a design of a stable gyro that cruises at 50, what would
prevent me from safely adding a bigger engine, re-doing my hang test,
and flying at 80 (for example).

Engine is only part of your powerplant. There's the propeller. A lot of
guys got killed because Rotaxes replaced Macs as powerplants. And they
could drive a longer prop, but the prop wouldn't clear the runway. So
the whole engine was moved up. or the gearbox flipped. Raising the
thrustline relative to the vCG, and resulting in PPO (bunt over). This
is normally an unsurvivable mode.

Everything you change in a gyro affects all the other components in a
system as well as the system as a whole, and often (unless you have a
bunch of knowledge and experience, and sometimes still even then!) in
unexpected ways.

For more on gyros read:

(1) FAA's Rotorcraft Flying Handbook, including all the helicopter
stuff at the beginning (the gyro stuff assumed you understood the helo
stuff). Available for free on the FAA website as a .pdf, or for money
from the GPO and booksellers in the dead-trees edition. (google
"Rotorcraft Flying Handbook" site:faa.gov to find the .pdf).

(2) www.rotaryforum.com, which is a web based rotorcraft forum with a
strong gyro bias. There is a little bit of good information on the PRA
website www.pra.org and will soon be more (the site is being redone).

cheers

-=K=-

Rule #1: Don't hit anything big.

"Kevin O'Brien" kevin@org-header-is-my-domain-name wrote in message
news:2005033111575992791%kevin@orgheaderismydomain name...
On 2005-03-24 01:25:19 -0500, "Mark" mark said:


If you want speed, you don't want a gyro. It's just that simple.


Or any rotorcraft for that matter. Sure, some helicopters are much faster
but none (or at least, very few) of them are really close to even the
average general aviation fixed wing and certainly no contest for "many" of
the experiemental fixed wing kits around.

Fly Safe,
Steve R.