Maximum G in a helicopter ???
Andrzej Jesmanowicz
On airplanes it's easy. Divide actual speed by minimum one
and square. Everything above stalls a plane.
I made my license on 300CB, and transitioned to R22 recently
(Yea, SFAR 73), and never found the G number in a POHs.
The Robinson video warns about rotor stalls but doesn't
give any number too. Wouldn't like to be surprised in
a steep turn :-).
Thanks,
Andre
Squeaks
have POH's) will prohibit any aerobatic manouevres for helicopters. Usually
it's a function of the head construction, which on teetering or articulated
heads will let you get away with about +1.5g (maybe) and NO negative G at
all. If you're lucky enough to fly a rigid rotor the game changes, although
the manufacturer will still prohibit any G. The BK117, for instance, will
pull +3/-1 g, but don't even think of loading a rotor head unless you really
know what you're doing. IMHO, of course :-)
John
The Helicopter Service Australia
Andrzej Jesmanowicz wrote in message <6sk4qe$l...@wiscnews.wiscnet.net>...
cbateman
to fly Gazelles and they did rolls and loops. Now they fly the Lynx (mostly
I understand). Any you can do negatives too. And if you bank at 60deg. in
level flight you will be pulling more than 1.5g.
Squeaks wrote in message <6skcoj$b...@sleipnir.iaccess.com.au>...
Richard Williams
For those of us(me) who do not know, exactly what is a 'articulated head' and how
does it differ from other heads?
R. williams
Mark Chapman wrote:
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Squeaks
IMHO.
FWIW, the RN 705 NAS had a display team with Gazelles back in the early
seventies, and they used to throw the aircraft around somewhat. Still not a
good thing in a fully articulated head, unless you know what you're doing.
John
Mark Chapman wrote in message <35F6A56F...@ibm.net>...
Agcatman
>how
>does it differ from other heads?
>
>R. williams
>
An articulated head is one in which each blade is allowed freedom of movement,
i.e. they can flap, lead and lag independently of the other blades.
A semi-rigid head is a 2 bladed system in which the blades feather and teeter
as a unit. There may be semi-rigid systems with more than 2 blades but I'm not
aware of any.
The fully rigid head is magic. It has little elves that move the blades as
necessary. Seriously, I'm not experienced enough with fully rigid to post on
the subject. Not without a probable flaming anyway. :^)
Stephen Austin
Austin Ag Aviation
Comm. Rotorcraft/Helicopter, CFI and CFII Helicopter
Comm. SEL and MEL
Instrument Airplane and Helicopter
Agcatman
>movement,
>i.e. they can flap, lead and lag independently of the other blades.
>
Errr, forgot to mention. Articulated heads usually have 3 or more blades.
Once again, there may be an articulated head with 2 blades, but I'm not aware
of any.
RotorDyne
contributer was looking for more on a subject that really interested me when I
first got into rotorcraft design (and flying). If I'm mistaken.. oh well.
I used to wonder if it was possible to reach a G-loading in a helicopter that
would cause a permanent deformation or structural failure in the rotor blades
that would cause a catastrophic failure. None of my professors or flight
instructors could give me an acceptable answer other than "no".. so I came up
with some theorys myself. But yes.. the short answer is 'no"..hehe.
Each helicopter has a unique ability to generate "g" forces in turns, vertical
accelleration, and yes vertical decelleration (as in loops) based on it's
lifting capability, which is a product of horsepower, blade area, chord, and
aircraft weight. Forget for a moment stuff like settling with power, HOW the
loop is performed.. etc.
The greater the margin of power, the higher the g-loads.. in other words the
more lightly loaded aircraft (all other factors being equal) will be able to
attain higher g-loads.
So what happens when you attemp to exceed the rotorcrafts lifting power by
going into say a tighter turn than power and loading will permit? Nothing..
well nothing serious.. unless of course you are trying to avoid another
aircraft or an obstacle in flight. The aircraft simply slips through the
airspace dispersing the maximum amount of lift that the situation will allow.
Like in a quickstop.. the higher the speed.. the longer it takes to stop.. you
are still loading up the rotors with the maximum remaining lift available.. but
the distance depends on the amount energy the rotor system has to dissapate.
One final example. What happens to a helicopter that is attempting to takeoff
from the tarmac at a loading that is greater than its hover capability?
Nothing.. except lots of wind. Otherwise we would have lots of "L" shaped
blades laying around out there.
I hope this helps the original poster.
Mark Chapman
the bank angle and the speed. (assuming still air and no vertical accelerations
of course)
The applicable formulae are:
G = 1/cos(Bank)
t = 0.0055 TAS/tan(Bank)
Diam = TAS^2/34208 tan(Bank)
Stall = Nstall x Root(G) [Not applicable to Helos]
Where-
Bank = bank angle in degrees
Diam = turn diameter in naut miles
TAS = true airspeed in knots
t = time to complete 360 deg of turn (minutes)
Nstall = normal (1 G) stall speed
G = G force
Gary Allen
Mark Chapman wrote in message <35F94826...@ibm.net>...
>Ummm.. No it doesn't quite matter. The ONLY factors that are of substance
is
>the bank angle and the speed. (assuming still air and no vertical
accelerations
>of course)
>
The formula also assumes a coordinated turn.
Gary
Agent 86
altitude, and no "knife edge" flight).
Speed and turn rate relate to each other, bank and G's relate to each
other.
Mark Chapman
only mentioned the speed issue to point out that it is important if you consider turn
RATE. The previous posters contention was that turn rate influenced G, which of
course it does not.
Agent 86
formulae, and there wasn't enough verbiage to allow me to follow your
argument.
George Schneider
> >An articulated head is one in which each blade is allowed freedom of
> >movement,
> >i.e. they can flap, lead and lag independently of the other blades.
> >
>
> Errr, forgot to mention. Articulated heads usually have 3 or more blades.
> Once again, there may be an articulated head with 2 blades, but I'm not aware
> of any.
articulated heads, as mentioned, start with three bladed rotors. each blade is
free to lead/lag, flap, and pivot about the feathering axis. semi-rigid heads
(also called teetering heads) consist of two blades that are rigid together in
lead/lag and flapping, but can individually pivot about the feathering axis
(pitch change).
many teetering heads are limited in their low g capability because when the rotor
becomes unloaded, the aircraft is free to pivot beneath the rotor mast. this can
result in mast bumping, which is ultimately very painful.
in level flight (no altitude gain, no airspeed change), g's are directly related
to angle of bank. turn radius, turn rate, and angle of bank are all related to
each other as a function of airspeed.
so when you start looking at the power available/power required curve, you can
find the bucket airspeed (best rate of climb, best endurance), and try your max
bank angle turn here because you will have the most margin or excess power
available...that is, you can sustain the turn without losing altitude.
> --
George Schneider
PP-H
page: http://wwp.mirabilis.com/9154574
J.C. Johnson
>
> How much G force one can pull in a helicopter?
Definitely depends on the helicopter's rotor system. In the Apache
(which has a fully articulated four-blade main rotor system) we perform
a demonstration maneuver called high/low G flight where we reach and
hold +2.0g and +0.2g. I know the rotor system can tolerate more, at
least I've been told so, but that was enough to gain my full confidence
in it's rotor system!
--
Attack!
Jon Johnson
LT type, 1 each, AH-64A Apache (soon to be Longbow) Aviator
"Blessed be the Lord my strength, which teacheth my fingers
to fight and my hands to war." - Gen. Robert E. Lee, 1863
Agcatman
>semi-rigid heads....but can individually pivot about the feathering axis
>(pitch change).
Hmmm, not sure I agree with that. Or maybe I'm misunderstanding you.
BH206B
>>semi-rigid heads....but can individually pivot about the feathering axis
>>(pitch change).
>
>Hmmm, not sure I agree with that. Or maybe I'm misunderstanding you.
They have to, Steve, or else there wouldn't be any collective pitch capability.
Agcatman
>
>They have to, Steve, or else there wouldn't be any collective pitch
>capability.
>
>
I guess I'm misunderstanding the post. Hehe, "Thou shalt not think about
semi-rigid blade pitching after 1 AM lest thy brain play tricks on thyself".
Agcatman
>>>semi-rigid heads....but can individually pivot about the feathering axis
>>>(pitch change).
>>
>>Hmmm, not sure I agree with that. Or maybe I'm misunderstanding you.
>
>capability.
>
>
>
>
>
>
I've got many hours in semi-rigid systems but I'm afraid it's of no avail.
Here's what I'm thinking, maybe I'm just clueless.
When you say that the blades pivot individually about the feathering axis,
aren't you in essence saying that the blade can change pitch without the other
blade moving? A semi-rigid rotor head's blades move together in all respects.
In other words, if one blade pitches the other pitches also. Due to the
linkages one blade cannot move independently of the other. If one blade
changes pitch the other must also. If it doesn't you got a problem. Big
problem. Like broken pitch change horns, control rods or tubes, etc.
I really don't understand the reference made to the collective pitch.
Collective pitch always refers to pitch which changes *all* blade's pitch
equally (or "collectively"), even on fully articulated and fully rigid rotor
heads. Hence the term "collective". So really it seems to me that collective
pitch capability has more to do with the blades acting as a unit not
individually.
Hehe, for the record, if I'm screwing the pooch here, take it easy on me. I
need a break. :^)
BH206B
Steve,
As I understood the post, the original writer was just differenting between a
semi-rigid helicopter head and a gyrocopter head, where the blades have NO
feather capability at all and the hub handles all cyclic pitch changes. So in
that regard, a 47 blade does pivot "individually" about the feathering axis,
even it if does do it simultaneously with the other blade. See now?
Agcatman
Okay, now I have another question. Which is the proper terminology: gyrocopter
or gyroplane? Is there a difference? Does it have to do with whether the prop
is fore or aft on the ship? Do you hardcore gyro guys get rankled when a
gyrocopter is called a gyroplane? Or vice versa? Kinda like helicopter guys
when someone calls them choppers? Hehe, is this a stupid question?
Rhodesst
>Okay, now I have another question. Which is the proper terminology:
>gyrocopter
>or gyroplane? Is there a difference? Does it have to do with whether the
>prop
>is fore or aft on the ship? Do you hardcore gyro guys get rankled when a
>gyrocopter is called a gyroplane? Or vice versa? Kinda like helicopter guys
>when someone calls them choppers? Hehe, is this a stupid question?
>
Hi Mr. Austin,
I'd like to take a stab at this one if I may and I don't think it's a stupid
question.
As I understand it, Juan de la Cierva's original gyro was called an "autogiro".
Note the spelling. He trademarked (if that's the correct phrase??) the name
so that only he could use it. Later developers used (as I understand it) the
word "autogyro", hense the two different spellings. The word "gyrocopter" was
created by Dr. Bensen when he developed his pusher design. The word
"gyroplane" is used by the FAA (here in the States) to discribe a rotorcraft
that flys with a free spinning rotor instead of a powered one.
I've not personally met any gyro fan who cares what you call the machine. The
words, autogiro, autogyro, gyrocopter, gyroplane, or just gyro are pretty much
interchangable and can be used properly for any gyro whether it be a pusher or
tractor design. The above statements are how I've come to understand this but
I could be wrong on some points. I'm sure someone out there will correct me
if I am. :-)
Fly Safe,
Steve Rhodes
Dennis McGuire
> Okay, now I have another question. Which is the proper terminology: gyrocopter
> or gyroplane? Is there a difference? Does it have to do with whether the prop
> is fore or aft on the ship? Do you hardcore gyro guys get rankled when a
> gyrocopter is called a gyroplane? Or vice versa? Kinda like helicopter guys
> when someone calls them choppers? Hehe, is this a stupid question?
I think we need a full-time evangelist to straigthen this out!
(No, I'm not volunteering!) I believe the correct term, and the one which
is used by the FAA is gyroplane. "Gyrocopter" was trade nme owned by
Bensen. "Autogiro" (with an i) was a also a trade name (Pitcairn,
Cierva, or Kellett?)
RotorDyne
> Which is the proper terminology: gyrocopter
>or gyroplane?
I personally like autogyro....
EJGelsone
>
>When you say that the blades pivot individually about the feathering axis,
>aren't you in essence saying that the blade can change pitch without the
>other
>blade moving? A semi-rigid rotor head's blades move together in all
>respects.
>In other words, if one blade pitches the other pitches also. Due to the
>linkages one blade cannot move independently of the other. If one blade
>changes pitch the other must also. If it doesn't you got a problem. Big
>problem. Like broken pitch change horns, control rods or tubes, etc.
>
> I really don't understand the reference made to the collective pitch.
>Collective pitch always refers to pitch which changes *all* blade's pitch
>equally (or "collectively"), even on fully articulated and fully rigid rotor
>heads. Hence the term "collective". So really it seems to me that collective
>pitch capability has more to do with the blades acting as a unit not
>individually.
>
Don't leave out what the swashplate does to each blade with cyclic input. Just
untie the blades, shove the cyclic full forward (or any diresction for that
matter) and slowly rotate the blades. Each blade will seek the pitchchange
induced by the swashplate independently. This pitch change is not collectively
made. It is indepent and in the form of a "cyclic" input. Without this
ability we would have no directional control except in the verticle plane.
BTW, I do mean to try this WITHOUT the use of the engine. :-)
One thing to think about, the need for lead, lag, feather and flap are to
correct for dissimilar lift caused by horzontal airflow through the rotor
system. You will never get that airflow (other than wind) through the rotor if
you don't use the feather axis to tilt the disc in the desired direction of
flight.
Ed