Ultralight strap-on helicopter
Roger Williams
might raise some interest here, too.
If you read the series of notes under this title on the ultralight mail
list in February/March of this year you might want to skip down to the
last couple of paragraphs of this posting--I've added some new stuff there
but the first part is a rather lengthy recap. for new readers.
I was at the Tokyo Aerospace Exhibition last February and saw what looked
like a canvas-webbing chair with a small two-stroke engine on the back and
supporting twin rotors above it. It was billed as a strap-on helicopter.
The two rotors are contrarotating, so torque is balanced--no need for tail
boom/rotor, etc. Pitch is fixed, so ascent/descent are throttle
controlled. I've kept in touch with the developer and here is a summary
first of what I learned then and what I heard recently after six months of
further development. The rotors were only 3m across (about 10 feet for the
metrically challenged) and close together. As you can imagine, they were
completely rigid! They use some ultrahigh-tech carbon-fiber winding
technique and are by far the most expensive part of this machine. Well,
the contrarotating drive is not cheap, either, and pretty high-tech
itself.
The engine then was basically two, horizontally opposed two-cylinder
two-stroke engines running on 25:1 gas:oil mixture. Each had independent
fuel lines and was separately linked to the drive shaft by a centrifugal
clutch arrangement so that either could fail while the other continued to
drive the shaft. The basic engine has quite a long development history
(over 25 years) but is a very high-tech implementation of the original
design, which was created by one of Japan's top post-war auto-engine
designers, a Tokyo University graduate who has acted as a consultant for
much of Japan's post-war auto industry development. In the two-cylinder
version it weighs 2.8kg and develops 10PS (one PS very nearly equals one
HP).
The engine on the current version is not a highly tuned version, so
further tuning could make a bit more power available. It uses THREE pairs
of cylinders, i.e., three essentially independent engines. It generates
30PS from something under 10kg (22.4lb), and power can be taken off it at
either end. (An aside: that makes it look to me as if it might be nice for
true FAR103 ultralights in either pusher or dragger configuration.) The
developer says it is very fussy over the oil to be used with the gasoline.
The simple webbing chair has been replaced by a rudimentary kind of
undercarriage. Difficult to explain without a diagram (I'm going to get
some videos of it maybe next week) but when you stand up, you lift the
whole thing including undercarriage off the ground. When you sit down, the
undercarriage bears your weight. This configuration is to get it classed
as a foot-launched device, virtually unrestricted in Japan, but to allow
you to land on the undercarriage wheels if you'd rather THEY took any
landing shock. I would certainly prefer this (!)
The weight of the whole thing is about 55kg (subject to confirmation, but
that's what I recall), so it's well within FAR103.
New in the last six months is not only the extra pair of cylinders, which
allow it to lift a 160kg weight and to provide a controlled descent when
one engine has failed and a "reasonably soft landing" (whatever that
means) when two out of the three have failed. The "softness" depends on
the weight of the pilot... <grin> So 245lb guys who want to fly an
ultralight helicopter should be OK as long as two of the three engine
units are firing.
Also new is the, er, rudder. The original idea was to gently brake one of
the rotors, unbalancing the torque as to rotate the craft. This is too
slap-bang. The thing spins like a top without much control over the
eventual direction it points. The idea now is to have a vertical tail fin
attached to the back of the "chair" in the downdraft from the rotors.
Slight angling of a control surface on the fin performs nicely to change
direction.
Control is by handlebars hanging from the rotor assembly. Pull back to
move forward, push forward to move backwards. OK, the guy knows that's
counter-intuitive but he says flying this thing is so unlike anything else
he's ever flown (and that's a lot, including helicopters, gyrocopters and
various fixed wing) that habits don't seem to get carried over to it.
Others with less variety of experience might feel differently. (I didn't
find many habits carried over from a de Havilland Tiger Moth to a
Paraplane.)
Max non-redline revs are 8,500, and the thing lifts strongly at anything
above 6,500rpm (could require higher for someone heavier than the slightly
built Japanese test pilot). There is an automatic idle-advance function so
that if an inexperienced pilot throttles right back he or she won't drop
out of the sky. This is set at 6,000rpm--a gentle sink--and there is, of
course, manual overide so you can lose height quickly if you really,
really want to.
There is a ballistic parachute attached to the tail fin which at the
moment unfortunately means that if it deploys, you're going to be hitting
the earth face down. There is also a rotor brake that goes into action
immediately after the parachute has deployed, and one thing the developers
are considering is making the tail assembly hinged so that it and/or the
parachute lines can pass through the now stationary rotors and enable a
parachute landing in proper seated position with the undercarriage taking
any shock. I just hope they get the safety interlocks between parachute
deployment and rotor brake right!
He greatly disappointed me by saying they would probably sell this in the
US before attempting to sell it in Japan, which is where I am. He's had
over 100 people wanting to buy one (one 747 captain wanted to buy a set of
four, one each for his entire family including two kids--he said it would
be cheaper than buying a four-seater helicopter and give them independent
mobility into the bargain), but many of them are saying crazy things like
"Yeah, I could take off from my back garden and be at the golf club in
less than an hour" neglecting the fact that this would involve flight over
cities. And Japanese cities, in case you didn't know, are very, very
closely built up (try finding a park or open site big enough to land in?
you'd have to be very lucky!). Must say it had occured to me that it would
be a lot more fun--and faster--than my own one-and-a-half-hour's commute
into central Tokyo. But at least *I* know that's impractical!
On the other hand he has concerns that people in the U.S. wouldn't believe
his warnings about the need for specific types/grades of oil for the
two-stroke mixture and might experiment with disastrous results. How about
it, readers? The mean-time between overhauls on the engine is
conservatively set at 300 hours but he thinks this might be increased to
500 by the time they are selling these things.
Next week I'm dropping by the office with my daughter to see some video
footage and maybe help with making an edited version to send people who
show interest, so if you have any questions and I get them either via this
newsgroup or E-mail, I'll ask'em. Replies will go to the group, not
individually (I have a business to run).
I have no personal financial interest in this project, and I know very
little more than I've posted here. I do know it's not going to be cheap.
How about list price of 30,000 US dollars? <gulp> However, it really
excites me and I'm determined to be a customer. Anybody else interested?
Roger
Roger D. Williams
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