The gyroscopic forces on the blades when changing changing axes are
minimal
as it is
done over a relative long period of time. In contrast a propeller
changes
axes
in an airplane at about 60 degrees per second during a stall or
spin. The
tilt
rotor does 90 degrees change in 20 or 30 seconds.
Perhaps a small electric motor could be added to orient the blades
in an
impending
crash.
It is not just that it flies 100 MPH faster. It flies much much
higher and
much much further
than any helicopter.
http://www.rotaryeng.net/VTOL.html
"No discussion on the controversial V22 tilt rotor would be complete
without a discussion
on Vortex Ring State or VRS for short. An issue has been made about
the V22
Osprey's 47
degree blade twist and how it affects the Vortex Ring State. Unlike a
helicopter high
blade twist is necessary in a tilt rotor to get good propeller
efficiency
at high speed.
This high twist can cause blade stall in the vertical landing mode.
I also
suspect it
affects the ability of the V22 to auto rotate.
The V22 can roll over if one rotor stalls and the opposite side
rotor does
not stall.
Special landing techniques have been devised to overcome the problem
namely
by limiting
the decent rate to 1000 FPM.
What the V22 Osprey critics don't realize is an off the shelf variable
twist rotor
blade such as we are proposing above is already on the market and
has been
proved
to work. Namely the IVO. Thousands have been sold over the past ten
years.
Contact IVO and see if they will build a variable twist rotor for your
needs.
http://www.ivoprop.com/ if I were Bell/Boeing I would be looking
long and
hard at
this option for the V22 rotors.
We are not affected to the same extent as the V22 is to VRS as we
have only
one rotor axis. However blade twist negatively affects the
efficiency of
the
rotor in the vertical take off mode. Never the less Boeing is
working on
their
own system of variable blade twist. Here is a graphic that gives some
estimated performance improvements."
I believe for every proplem there is an answer. Just like the Wright
brothers.
--
Paul Lamar ...No rotor no motor.
Keith,
What is your favorite source of data on the V22?
Do you believe Wikipedia is materially in error?
http://en.wikipedia.org/wiki/V-22_Osprey
They say that the combat operating _radius_ is 416mi - 830mi
out-back.. I would presume that would include at least some mission
load.
They show a max speed of 316mph for the V-22 and a cruise speed (at a
sub-optimum sea level alltitude) of 246mh. I'd guess that the long
range at-altitude cruise is going to be more like 270mph.
One of the craft that the V-22 is to replace is the CH-46:
http://en.wikipedia.org/wiki/CH-46_Sea_Knight
With a combat radius of 184mi - less than half. 165mph is the max
speed allowed.
100mph faster is really useful. Being faster can definitely save
lives for many kinds of missions.
There are all sorts of things you can do with a normal helicopter
which are completely fatal. For instance many helicopters can sever
the tail boom with the main rotor under certain maneuvering
situations. The CH-46 suffers from a problem (as do all twin rotor
designs) where the transmission can have a mechanical failure which
causes the two rotor systems to get out of sync - causing loss of
blades or at least loss of control. There are lots of other problems
with helicopters. Engineers come up with ways to mitigate the
issues..
The BA-609 is a much smaller vehicle than the V-22...
http://en.wikipedia.org/wiki/Bell/Agusta_BA609
It's a real flying airplane that is going through FAA certification -
supposed to be completed in 20011.
Matt-
To start with, the V-22 CAN autorotate, the problem is that it has a 5000
foot per minute sink rate in this configuration. The problem is not that
it's a tiltrotor, the problem is an extremely high disc loading; the
Osprey
isn't as much a rotary wing aircraft as it is a powered lift vehicle.
Since the rotors aren't intermeshing, getting out of sync is not a
problem
but any condition that would do this would probably mean a destroyed
transmission. In the Osprey, a total loss of power is dealt with by a
forced landing same as a fixed wing aircraft.
A smaller vehicle can do things in a much simpler manner, look at the
differences between the BA-609 and the Osprey. If the Osprey didn't
have to
fold up to fit on a ship, the systems could be much simpler. The wing
could
have been longer and it could have bigger rotors. Remember that
weight goes
up as the cube of increase in linear dimension. A two or four seater
may be
able to use a two blade rotor with a teetering hub. A ballistic chute
system would be usable. A 2000 lb vehicle with two twenty-foot rotors
might
auto-rotate very well. A two-blade rotor with the blades feathered in
horizontal position might glide reasonably well.
I don't care is this thread may not be specific to rotary engines. The
rotary engine is an enabling technology and the more new vehicles that
are
designed around them, the more this system will be developed.
Discussion of
new applications enabled by rotary engines is not irrelevant.
Steve Brazil
The Vega and the Pinto were the future - at the time, nearly all US cars
were frame on body. The Vega and Pinto were the first serious attempt to
compete with the Japanese unibody sub-compact. For the Vega with the
aluminum block (my first car :-) it also was the future. Yes, they had
many problems, but when you break ground you always do... Just like the
Fiero - problems with fires solved, but too late. I think if you compare
any car from 1972 to any car in 2008, you'll see how flawed all were in
safety in 1972. The Pinto was just more visible. Look at how many Crown
Vic police cars had the same problem with gas tank rupture.
Many helicopters can't have you unload the rotor disc in flight - that
is go to negative G even briefly. The tilt rotor certainly does not have
this problem.
-dave
Any system is a series of engineering compromises. The Osprey's design is
driven by the need to stow it on or below deck and carry a large load. It
is also the first of its kind to be produced in numbers. Considering the
stretches they made with existing technology, they are bound to have a few
problems, but they are being overcome and what they learn will benefit us
all.
My interest is a helicopter that weighs about 1200 to 1300 pounds empty and
will lift about 2200 pounds with a two-blade, 30 foot rotor, be able to
cruise around 120 and cost no more to operate than a four-cylinder Mooney.
This may be enabled by the new 16B engine. Ron Willocks has come close to
some of this already with his Pawnee Helicopter:
http://www.pawneeaviation.com/
It may look crude but it works and it's using a ALL-IRON small block Chevy!
The next iteration will be much cleaner, right now, his focus is on system
reliability.
I don't have the time or resources to design and build a small tilt-rotor,
but I have no doubt that it could be done. Check this out:
http://www.aviastar.org/helicopters_eng/bell_xv-3.php
This thing flew in the fifties and it didn't have computer aided control.
One of the pictures show it flying with two blade rotors. If I had
unlimited time and money, I would be very tempted to look into a two to four
seat tiltrotor.
Steve Brazil
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