Jump Takeoff Gyrocopter
Dave Jackson
Groen Hawk, etc., that is performing true jump takeoffs, without any ground
roll and at maximum gross weight?
Is this ability to jump takeoff a reality or a targeted objective?
This inquiry is for gyrocopters that have their source of propulsion inside
the fuselage, not on the rotor disk such as tip jets.
--
Dave J
Project: http://www.SynchroLite.com
MICHEAL GASPARD
at all.
GyroMike
www.geocities.com/gyromike
Dave Jackson <dave_j...@ultranet.ca> wrote in message
news:39ef4...@axion.net...
William Scott
weight (jump-take-off-gross-weight?) and it needs a roll at weights above
and upto the gross-gross weight.
William
Owen Davies
> I would be interested in knowing if there is a gyrocopter, CarterCopter,
> Groen Hawk, etc., that is performing true jump takeoffs, without any
ground
> roll and at maximum gross weight?
>
> Is this ability to jump takeoff a reality or a targeted objective?
>
> This inquiry is for gyrocopters that have their source of propulsion
inside
> the fuselage, not on the rotor disk such as tip jets.
There was a home-built gyro several years ago that would do it. I've
forgotten the details and probably never had any idea about its gross
weight, but it shouldn't be too hard to find the article in Sport Aviation
or EAA Experimenter. No doubt the PRA covered it as well.
Owen Davies
George Vranek
performed perfect jump take offs in 1937 !!!!
George
"Dave Jackson" <dave_j...@ultranet.ca> schrieb im Newsbeitrag
news:39ef4...@axion.net...
> I would be interested in knowing if there is a gyrocopter, CarterCopter,
> Groen Hawk, etc., that is performing true jump takeoffs, without any
ground
> roll and at maximum gross weight?
>
> Is this ability to jump takeoff a reality or a targeted objective?
>
> This inquiry is for gyrocopters that have their source of propulsion
inside
> the fuselage, not on the rotor disk such as tip jets.
>
Michael Prentler
> I would be interested in knowing if there is a gyrocopter, CarterCopter,
> Groen Hawk, etc., that is performing true jump takeoffs, without any
ground
> roll and at maximum gross weight?
>
> Is this ability to jump takeoff a reality or a targeted objective?
>
> This inquiry is for gyrocopters that have their source of propulsion
inside
> the fuselage, not on the rotor disk such as tip jets.
>
> --
> Dave J
> Project: http://www.SynchroLite.com
>
>
designed himself. I met him at the fly-in this year in Napolean, MI where
he is based and saw the gyro do a jump takeoff: Absolulty no ground roll.
I videotaped the whole episode...very spectacular.
I belive his gyro is a one of a kind design, it has a lever that looks like
a collective but is set up like a regular gyro - pusher propeller, no
tail rotor and no cheaters on the blades. I believe that he accelerates the
blades in a flat pitch to about 150-200% of flight rpm, and then uses the
lever to snap and lock the blades to full flight pitch at the exact instant
that the rotors are disconnected from the pre-rotator drive - thus using the
stored energy in the rotor to shoot the gyro straight up into the air
without any adverse effect on the handling of the ship.
It's called the rhino gyro, and he's been to Mentone with it.
Dave Jackson
There are some questions about his gyro that I would be very interesting in
knowing, if you can help. They are;
1/ The ground clearance at the top of his jump?
2/ The minimum ground clearance during the transition from hover to
forward flight?
3/ Does he lower the 'collective' as the craft achieves forward flight
speed and the rotor rpm slows to 100% of flight rpm?
Thanks for your response.
And if you don't know the answers - thanks again for your original reply :-)
Dave J
Project: http://www.SynchroLite.com
"Michael Prentler" <ford...@hotmail.com> wrote in message
news:39f12a20$0$30013$2c3e...@news.voyager.net...
Geoff Sjostrom
load them to the point where you couldn't do a jump takeoff, though.
john martin
do they jump before they have to nose over?
John
Rod Buck
<jo...@internetnorth.com.au> writes
up the rotor to well above flight rpm WHILST THE GYRO IS STILL ON THE
GROUND.
Such gyros, of course, need blade pitch control, either in the normal
collective manner, or by using a delta-3 hinge.
This hinge reduces blade pitch to zero (or thereabouts) whilst torque is
applied to the rotor hub on the ground.
(Or the pilot does it manually).
So, the blades are spun up to maybe 150% of takeoff rpm, in low or zero
pitch. (This reduces yaw reaction as well, of course)
Then if manual collective, the pilot disengages the engine clutch
from the rotors (it's still driving the propellor, of course), and
increases pitch to normal autorotational setting.
If delta-3 hings are used, the declutching of the rotor drive causes the
blades to swing forward relative to the hub attachment points, which
increases the pitch automatically.
The gyro jumps off the ground, with NO yaw reaction, because it's only
using the power stored in the rotor.
I've seen a film of a Pitcairn (I think) jumping maybe 200ft in the air,
using the inertia in the rotors.
There is no noseover, because ANY gyro that noses over is in deep sh*t,
negative G and all that - the disk must be angled UP slightly with
respect to the direction of flight to allow the airflow to pass UP
through the disk - NOT down, as in a helicopter.
All that happens is that the propeelor satarts to drive the gyro forward
as soon as it leaves the ground, and this process accelerates it
forwards during the jump, shortly after the thing reaches the top of the
jump, it's moving forward fast enough to permit autorotation to maintain
rotor RPM in the normal gyro manner.
Interestingly, the delta-3 hinge produces a takeoff situation rather
like the Shuttle after the boosters light off - it's no longer a
question of:
"Are we going?"
- but only:
"which way?"
Think about it. Once rotor rpm gets over takeoff level in autorotation
pitch setting, you have built up excess energy in the rotor.
As soon as you either reduce engine power, or declutch the engine from
the rotors, the torque on the blade roots reduces, they swing forwards
in the direction of rotation, and the pitch increases as they do so....
You HAVE to take off, there is no way out, once rotor RPM is above the
flight value....
Nothing you can do can abort the jump.
Remember, the pilot has No control over blade pitch - only applying
torque to the rotor hub cause the blade root hinges to drag back, which
reduces blade pitch. (In a delta-3 hinge, the blade yaw hinges are
offset at an angle, not vertical, to give this effect)
Interesting!
- Rod Buck
Walter Hawn
have time to produce yaw?
180 Walt
Dave Jackson
takeoff. The use of delta-3 is of particular interest and I would like to
pursue this phenomenon further with you.
I am under the impression that delta-3 is a Pitch-Flap Coupling and that it
can be achieved by 1/ flap hinge geometry or by 2/ control system geometry.
In a normal helicopter configuration, when a blade flaps or teeters upward
the delta-3 causes the pitch of this blade to be decreased. Conversely
downward flapping or teetering will cause an increase in the blade pitch.
Most, if not all, gyrocopters use a teetering hinge hub. If the teetering
hinge is rotated clockwise about the mast's axis to give delta-3, as per #1
above, then the introduction of teetering will cause the two blades to pitch
in opposite directions. If offset flapping hinges are used then these
hinges can be called a Pitch-Flap Couplings or a Pitch-Coning Couplings.
I am assuming that you are referring to the use of conventional delta-3
offset hinges. As I see it, if the blades start out with an autorotative
pitch setting of around +1 degree, and there is no pilot induced collective
increase, then the only way that blade pitch will increase is if the rotor
disk goes into negative (tip down) coning.
This is a legitimate question, because of a project that I am currently
working on. A definitive conclusion will be much appreciated.
--
Dave J
Project: http://www.UniCopter.com
Project: http://www.SynchroLite.com
Rod Buck wrote in message
try_c...@my-deja.com
>
If the delta-3 hinge is turned 90 degrees from what is normally used
then it makes sense. The lag of the blades (from torque) would cause a
pitch decrease. When the torque was removed the blades would swing
forward and increase pitch. The delta hinge would be vertical like a
lead lag hinge plus an appropriate angle to get the effect.
I am not aware of this use of the delta-3; instead of pitch-flap
coupling it is pitch-lag coupling- interesting.
> I am under the impression that delta-3 is a Pitch-Flap Coupling and
that it
> can be achieved by 1/ flap hinge geometry or by 2/ control system
geometry.
Sent via Deja.com http://www.deja.com/
Before you buy.
Dave Jackson
pitch axis is interesting.
It appears that 3 scenarios would be involved:
1/ During pre-rotation the engine is driving the blade and the blade root
will be leading.
2/ During jump start the heavy tip weight will be driving the blade and
blade tip will be leading.
3/ During autorotation (flight) the root end of the blade will be driving
the blade and the root will have a *slight* lead.
As an example, if 1/ gives a pitch of 0 degrees, 2/ gives a pitch of 10
degrees and 3/ gives a pitch of 1 degree. This would seem to be an
excessive amount of pitch change for relatively little lead-lag change.
--
Dave J
Project: http://www.UniCopter.com
Project: http://www.SynchroLite.com
<try_c...@my-deja.com> wrote in message
news:8ti3tr$3h6$1...@nnrp1.deja.com...
Rod Buck
<weave...@worldnet.att.net> writes
>Interesting and informative post. I'm guessing frictional forces don't
>have time to produce yaw?
>180 Walt
over the rudder due to forward airspeed can be used to counteract any
yaw that may develop through bearing friction - just as in normal gyro
flight....
- Rod Buck
Rod Buck
>
>>
>
>If the delta-3 hinge is turned 90 degrees from what is normally used
>then it makes sense. The lag of the blades (from torque) would cause a
>pitch decrease. When the torque was removed the blades would swing
>forward and increase pitch. The delta hinge would be vertical like a
>lead lag hinge plus an appropriate angle to get the effect.
>I am not aware of this use of the delta-3; instead of pitch-flap
>coupling it is pitch-lag coupling- interesting.
>
>
- Rod Buck
Rod Buck
<dave_j...@ultranet.ca> writes
>Rod; thanks for your very detailed explanation of the gyrocopter jump
>takeoff. The use of delta-3 is of particular interest and I would like to
>pursue this phenomenon further with you.
>
>I am under the impression that delta-3 is a Pitch-Flap Coupling and that it
>can be achieved by 1/ flap hinge geometry or by 2/ control system geometry.
>In a normal helicopter configuration, when a blade flaps or teeters upward
>the delta-3 causes the pitch of this blade to be decreased. Conversely
>downward flapping or teetering will cause an increase in the blade pitch.
>
>Most, if not all, gyrocopters use a teetering hinge hub. If the teetering
>hinge is rotated clockwise about the mast's axis to give delta-3, as per #1
>above, then the introduction of teetering will cause the two blades to pitch
>in opposite directions. If offset flapping hinges are used then these
>hinges can be called a Pitch-Flap Couplings or a Pitch-Coning Couplings.
>
I'm not aware that a true gyro delta-3 hinge for jump takeoff can be
used with a 2-blade teetering rotor.
I think it can only be used with conventional 3- or 4-blade articulated
rotors.
For jump takeoff, the blade pitch , as you say, NORMALLY reverts to the
usual 1 deg or 1.5 deg positive pitch.
However, the delta-3 hingein this application is NOT affected by the
blades flapping up or down at all - what it IS affected by is torque
applied to the rotor hub.
In other words, the hinge we are speaking of is NOT the up-and-down
blade flapping hinge, but the back-and-foward (more or less vertical)
DRAG hinges at the blade roots.
When power (torque) is applied from the engine to the rotor system (when
the gyro is on the ground), the hub tries to drive the blades round. The
aerodynamic drag on the blades causes them to drag back on the drag
hinges.
If the drag hinge is a normal, truly vertical hinge, then no pitch
change occurs.
However, if this hinge is offset to become a delta-3 hinge, then it can
be arranged that, as the hub twists forward in the direction of
rotation, and the blades drag back, then pitch is reduced, removing
lift, so the gyro stays put.
As soon as the engine is declutched, and torque removed, the centrifugal
force on the blades pulls the hub back into line, and the hing resumes
normal position, and the normal pitch of 1-1.5 deg is re-established.
Lift commences, and the Gyro jumps.....
This is why I don't think it can be used in a 2-blade teetering rotor
system....no drag hinges....
- Rod Buck
Rod Buck
<dave_j...@ultranet.ca> writes
>The idea of rotating this offset 'angled' hinge by 90 degrees about the
>pitch axis is interesting.
>
>It appears that 3 scenarios would be involved:
> 1/ During pre-rotation the engine is driving the blade and the blade root
>will be leading.
Correct
> 2/ During jump start the heavy tip weight will be driving the blade and
>blade tip will be leading.
No - centrifugal force of the blade will not make the tip "lead" - the
blade is freewheeling as far as the hub is concerned. There is NO torque
reaction on the drag hinge - so it is at 90 deg to the hub.
> 3/ During autorotation (flight) the root end of the blade will be driving
>the blade and the root will have a *slight* lead.
>
No, as above - as far as the hub hinge is concerned, the blade is again
freewheeling - whether driven by inertia or autorotation - the hub
doesn't care. All the hinges know is that there is NO torque being
applied, and twisting the drag hinges back by blade drag.
>As an example, if 1/ gives a pitch of 0 degrees, 2/ gives a pitch of 10
>degrees and 3/ gives a pitch of 1 degree. This would seem to be an
>excessive amount of pitch change for relatively little lead-lag change.
>
No - just two states - torque applied, drag hinges move back, pitch
reduced to zero.
No torque applied, autorotatation, or inerta frewheeling, matters not,
no torue reaction - normal pitch.
>--
- Rod Buck
Dave Jackson
> >and blade tip will be leading.
>
> No - centrifugal force of the blade will not make the tip "lead" - the
> blade is freewheeling as far as the hub is concerned. There is NO torque
> reaction on the drag hinge - so it is at 90 deg to the hub.
The energy for rotation in a jump start gyro is primarily coming from the
oversize tip weights.
The drag (and the balance of the energy, for that mater) is distributed
along the full length of the blade. Therefor the tip will be "dragging the
rest of blade around. Granted, the lead will be very small.
___________________
> > 3/ During autorotation (flight) the root end of the blade will be
> >driving the blade and the root will have a *slight* lead.
> >
> No, as above - as far as the hub hinge is concerned, the blade is again
> freewheeling - whether driven by inertia or autorotation - the hub
> doesn't care. All the hinges know is that there is NO torque being
> applied, and twisting the drag hinges back by blade drag.
In autorotation, the inner part of the blade is providing the driving force
and the outer part is providing the "lift'. Therefor, as in case 1/, the
root will be leading the tip. Again, the lead will be very small.
__________________
> >As an example, if 1/ gives a pitch of 0 degrees, 2/ gives a pitch of 10
> >degrees and 3/ gives a pitch of 1 degree. This would seem to be an
> >excessive amount of pitch change for relatively little lead-lag change.
From previous calculations, it appears that the in-plane angular change of
a helicopter blade between power-on and autorotation is very small. I would
think that in might be too small to control +/-12 degrees of pitch change.
Do you or anyone know of a specific gyrocopter that has used this method of
control?
Thanks;
Dave Jackson
Thanks for your reply.
The following comments are submitted as a contribution to clarifying the
current topic.
> The ones I have seen HAD no extra tip weights - autorotation not
> requiring them. They might help in increasing blade inertia, but they
> are not strictly necessary - so I don't know where you get the idea that
> they MUST be present.
I don't think that the engine can produce enough power nor the landing gear
has enough friction with the ground to obtain the necessary energy in the
rotor by high RPM alone. The CarterCopter uses 56 pounds of depleted
uranium for tip weights. The resident guru on www.rotorcraft.com recommends
using an extra 10 pounds per blade for jump takeoff with the average
recreational gyrocopter.
_______________
> I must persist: Your assumption that the blades being forced forward in
> the direction of rotation by autorotation or inertia being somehow
> different is wrong.
There is no argument about the centrifugal force being FAR stronger then any
of the others, but:
When the hub is rotating the blade, the blade tip have a slight lag only
because of the profile air drag on the blade. By the same token, when the
tip weight is rotating the blade, the blade root will have a slight lag,
because of the profile drag.
For example; if a hub 'arm' was swinging a thin string with a weight at the
end, then the string and hub arm would be at an angle of 180 degrees to each
other. In the previous example, if the string was then total enclosed by a
12" diameter Styrofoam cylinder, then the cylinder would lag behind the tip
weight and the angle between the string and hub arm would no longer be 180
degrees.
_______________
BOTTOM LINE
> >From previous calculations, it appears that the in-plane angular change
of
> >a helicopter blade between power-on and autorotation is very small. I
would
> >think that in might be too small to control +/-12 degrees of pitch
change.
> >
> Well collective levers do it quite well..... Don't see why delta-3 hinge
> can't do it either.....
I had to calculate the lead-lag, on my SynchroLite project [see
http://www.synchrolite.com/0736.html]. IF MY CALCULLATIONS ARE CORRECT, the
angular lead-lag change between powered rotor and autorotative rotor is only
0.08 degrees.
This is probably not enough to move the pitch through approximately 12
degrees.
_______________
If you're interested, there's some very 'dry' information on delta-3 at
http://www.synchrolite.com/0433.html
Dave J
Project: http://www.UniCopter.com
Project: http://www.SynchroLite.com
----- Original Message -----
From: "Rod Buck" <rod...@telespeed.demon.co.uk>
To: "Dave Jackson" <dave_j...@ultranet.ca>
Sent: Tuesday, October 31, 2000 10:25 AM
Subject: Re: Jump Takeoff Gyrocopter
> In message <006f01c042ea$fcc62b40$2e33...@ultranet.ca>, Dave Jackson
> <dave_j...@ultranet.ca> writes
> >Rod;
> >
> >> > 2/ During jump start the heavy tip weight will be driving the blade
> >and
> >> >blade tip will be leading.
> >>
> >> No - centrifugal force of the blade will not make the tip "lead" - the
> >> blade is freewheeling as far as the hub is concerned. There is NO
torque
> >> reaction on the drag hinge - so it is at 90 deg to the hub.
> >
> >The energy for rotation in a jump start gyro is primarily coming from the
> >oversize tip weights.
>
> The ones I have seen HAD no extra tip weights - autorotation not
> requiring them. They might help in increasing blade inertia, but they
> are not strictly necessary - so I don't know where you get the idea that
> they MUST be present.
>
>
> In any case, whether the tip is driving the blade, through inertia, or
> the inner 1/3 is driving the blade through autorotation, the DRAG HINGE
> DOES NOT CARE, as NO torque is applied to it from the hub.
>
>
> This business of the tip or the root is totally irrelevant - the blade
> is being driven by forces inherent to the blade itself, either
> aerodynamic or inertial. Centrifugal force alone will determine the
> angle of the drag hinge, which, in the absence of hub torque, will
> oscillate cyclically round the 90 deg point (to allow for changes in
> blade airspeed round the circle as it rotates whilst the gyro moves
> forward into wind...)
>
> So, to simplify, and average things round 360 deg of blade rotation, in
> the absence of hub torque (engine drive) the blade will be at right
> angles to the hub.
>
> Engine torque to the hub will attempt to drag the blades around by their
> roots, and aerodynamic blade drag force RELATIVE TO THE HUB will cause
> the drag hinges to drag back.
>
>
> This is the only effect that we are interested in. Apply torque, drag
> hinges move back. No torque (autorotation or freewheeling blades), and
> drag hinges move forward to 90 deg point. (Assuming no significant hub
> drag from friction, etc.
>
> Obviously, if there is hub friction, then the blade forces (either from
> autorotatation or inertia) may cause the blade roots to move forward
> from the 90 deg point.
>
>
> I must persist: Your assumption that the blades being forced forward in
> the direction of rotation by autorotation or inertia being somehow
> different is wrong.
>
> Imagine this:
>
>
> Lock the hub on your articulated rotor. (on the ground!)
>
> Tie a piece of string to the blade tip, and pull in the direction of
> rotation. The blade drag hinge will allow the blade to move forward, no?
> This is the same as inertia keeping the blades spinning during jump
> start, no?
>
> OK, now untie the string, and retie it to the blade 1/3 the way out from
> the hub, and pull the blade forward in the direction of rotation. This
> simulates the blade being driven by aurorotation, no?
>
> In both cases, the drag hinge allows the blade to move forward.
>
> These forces act on the blade in the SAME direction!
>
> Now use the string to tie the blade tips to a handy tree or girder.
>
> Now crank the rotor hub round by lever, to simulate engine torque
> attempting to spin up the blades.
>
> The blade drag hinges will move BACK, as the hub attempts to drive them
> round, but the string (taking the place of aerodynamic drag) holds them
> back.
>
>
> So ,we have a simple case:
>
> 1) Either autorotation or inertia moves the blades FORWARD on the drag
> hinges.
>
> 2) Engine torque moves the blades BACK on the drag hinges.
>
>
> That's all there is to it!
>
>
> So, all you need is a delta-3 hinge that, as the blades drag BACK in
> response to engine torque, reduces pitch to zero.
>
>
> Then, when torque removed, and either autorotation or freewheeling
> inertia keeps them spinning, the blades move FORWARD on the drag hinges,
> increasing pitch to normal 1-1.5 deg autorotation value.
>
> >In autorotation, the inner part of the blade is providing the driving
force
> >and the outer part is providing the "lift'. Therefor, as in case 1/, the
> >root will be leading the tip. Again, the lead will be very small.
> >
>
> NO!
>
>
> In EITHER case, the blade is driving itself round, and the drag hinge
> doesn't care - all it knows is that there is NO torque being applied
> from the hub!
>
> >__________________
> >
> >> >As an example, if 1/ gives a pitch of 0 degrees, 2/ gives a pitch of
10
> >> >degrees and 3/ gives a pitch of 1 degree. This would seem to be an
> >> >excessive amount of pitch change for relatively little lead-lag
change.
> >
> >From previous calculations, it appears that the in-plane angular change
of
> >a helicopter blade between power-on and autorotation is very small. I
would
> >think that in might be too small to control +/-12 degrees of pitch
change.
> >
> Well collective levers do it quite well..... Don't see why delta-3 hinge
> can't do it either.....
>
>
> >Do you or anyone know of a specific gyrocopter that has used this method
of
> >control?
>
> No modern one that I know. Pitcairns used to, all the time.
>
Stephen Austin
There may not be yaw induced by frictional forces but there is a whole new can
of worms with which to deal, mainly p factor from the prop. I was over at Don
Farrington's just a couple of weeks ago and I flew the Air and Space 18A for
several hours. When a jump takeoff is performed the p factor is such that if a
cyclic correction due to p factor is not made properly one will quickly find
oneself in the weeds.
>as well as airflow
>over the rudder due to forward airspeed
From the standpoint of a jump takeoff, however, there is little or no airflow
from forward speed, at least none of consequence. It takes several seconds
before forward airspeed increases airflow to the point it actually helps.
A jump takeoff in an 18A can be done and it is a really cool maneuver. I
definitely had to sit and think about what I was gonna do though because once
you hit that button you're committed and things start happening real fast.
However, with full fuel, near max gross weight and any density altitude at all
then fuggedaboudit. It's not gonna happen.
Stephen Austin
Austin Ag Aviation
Charleston, Missouri
Rod Buck
Austin <agca...@aol.com> writes
>
>There may not be yaw induced by frictional forces but there is a whole new can
>of worms with which to deal, mainly p factor from the prop. I was over at Don
>Farrington's just a couple of weeks ago and I flew the Air and Space 18A for
>several hours. When a jump takeoff is performed the p factor is such that if a
>cyclic correction due to p factor is not made properly one will quickly find
>oneself in the weeds.
>
>From the standpoint of a jump takeoff, however, there is little or no airflow
>from forward speed, at least none of consequence. It takes several seconds
>before forward airspeed increases airflow to the point it actually helps.
>
Correct.
>A jump takeoff in an 18A can be done and it is a really cool maneuver. I
>definitely had to sit and think about what I was gonna do though because once
>you hit that button you're committed and things start happening real fast.
>However, with full fuel, near max gross weight and any density altitude at all
>then fuggedaboudit. It's not gonna happen.
>
>
>
>Stephen Austin
>Austin Ag Aviation
>Charleston, Missouri
Interesting! I've never done one - nice to hear from someone who has!
- Rod Buck
Rod Buck
<dave_j...@ultranet.ca> writes
>Rod
>
>Thanks for your reply.
>
>The following comments are submitted as a contribution to clarifying the
>current topic.
>
>> The ones I have seen HAD no extra tip weights - autorotation not
>> requiring them. They might help in increasing blade inertia, but they
>> are not strictly necessary - so I don't know where you get the idea that
>> they MUST be present.
>
>I don't think that the engine can produce enough power nor the landing gear
>has enough friction with the ground to obtain the necessary energy in the
>rotor by high RPM alone. The CarterCopter uses 56 pounds of depleted
>uranium for tip weights. The resident guru on www.rotorcraft.com recommends
>using an extra 10 pounds per blade for jump takeoff with the average
>recreational gyrocopter.
The Pitcairn of old (which had jump start) probably used wood for the
blades - very heavy by today's standards - maybe that helped.
There is a hell of a lot of inertial energy in a spinning rotor system -
look at the devastation that occurs if they hit something! So I don't
see that it wouldn't have enough energy to perform jump start.
However, older gyros of the Pitcairn era used heavier blades, rotating
slower (I read somewhere that they would take off at 120 rpm or so! - I
may stand corrected).
Now it would have been easier to generate surplus lift in such a system
by overspeeding it.
Todays gyros use smaller, lighter rotors, turning much faster. It may be
inherently more difficult, as you say, to generate the lift necessary by
purely overspeeding them - and the addition of tipweights may be
necessary, now I come to think of it.
>here is no argument about the centrifugal force being FAR stronger then any
>of the others, but:
>When the hub is rotating the blade, the blade tip have a slight lag only
>because of the profile air drag on the blade. By the same token, when the
>tip weight is rotating the blade, the blade root will have a slight lag,
>because of the profile drag.
Yup. Agree with that.
>For example; if a hub 'arm' was swinging a thin string with a weight at the
>end, then the string and hub arm would be at an angle of 180 degrees to each
>other. In the previous example, if the string was then total enclosed by a
>12" diameter Styrofoam cylinder, then the cylinder would lag behind the tip
>weight and the angle between the string and hub arm would no longer be 180
>degrees.
>_______________
>
Well, the cylinder would, by air drag, resist, and drag back the tip
weight, and the whole shebang would drag back on the drag hinge.
>BOTTOM LINE
>
>> >From previous calculations, it appears that the in-plane angular change
>of
>> >a helicopter blade between power-on and autorotation is very small. I
>would
>> >think that in might be too small to control +/-12 degrees of pitch
>change.
>> >
>> Well collective levers do it quite well..... Don't see why delta-3 hinge
>> can't do it either.....
>
>I had to calculate the lead-lag, on my SynchroLite project [see
>http://www.synchrolite.com/0736.html]. IF MY CALCULLATIONS ARE CORRECT, the
>angular lead-lag change between powered rotor and autorotative rotor is only
>0.08 degrees.
>This is probably not enough to move the pitch through approximately 12
>degrees.
You're forgetting something, Dave, there is the aerodynamic drag of the
(zero-pitch) rotors, not very great until you get a lot of rpm's, to be
sure.
However, there is another factor that will cause a LARGE force which
will definitely cause the drag hinges to move back quite a bit - inertia
of the rotor system.
Try spinning up the system from rest, and all the time the engine is
accelerating the system, there is a LOT of resistance to the torque
applied via the hub.
This will cause a large movement (lag) in the rotor drag hinges, which
can work the pitch change mechanism.
Handily, this force is at max when the rotor are at rest, and the engine
is working hard to start them turning.
Then, as the rotors speed up, and approach flying speed, the torque
difference is less, and the force on the drag hinges reduces. However,
as this happens, conveniently, air drag and tip losses on the blades
become more significant, at the higher blade speeds, thus maintaining
the drag hinge force.
I don't think it is such a problem as you maintain.
>_______________
>
>If you're interested, there's some very 'dry' information on delta-3 at
>http://www.synchrolite.com/0433.html
>
Have a look. Cheers.
- Rod Buck
Dave Jackson
> Then, as the rotors speed up, and approach flying speed, the torque
> difference is less, and the force on the drag hinges reduces. However,
> as this happens, conveniently, air drag and tip losses on the blades
> become more significant, at the higher blade speeds, thus maintaining
> the drag hinge force.
> I don't think it is such a problem as you maintain.
Rod;
Thanks for the very clear description.
I agree with what you are saying. I did not consider the overspeed of the
rotor, plus the fact that drag increases as a power of 2 (or 3)
Thanks again
Dave Jackson