Maximum Transient G in Helicopters

[Shawn Coyle]

What's the maximum transient G that anyone has developed (even for a few seconds) in a helicopter that is cruising at 100-140 KIAS, with no change in power from the engines? Killing airspeed is allowed.
In other words, how much G can you pull, even for only a few seconds?

[wg13_dummy]

2.5G in a Lynx. (Someone once pulled 9G in one but I think the G Meter was fooked ;))

[NickLappos]

3.7 in a Black Hawk, on many occasions. Trimmed steady at 2.6 and did 3 turns, climbing! Both at 14,000 lbs GW, nominal 2000 ft DA

[Graviman]

3.7 in a Black Hawk, on many occasions.

Some machine!

[430EMSpilot]

3.5 in an AH-64A when I was young...the operators manual said that was the limit and I wanted to see it. I was bold then, now I'm just old...and alive:O

[InducedDrag]

Set the elt off once in a R44 on a real tight 180 auto. :eek:

I'm not sure where that is but I've heard it takes about 3 g's.

I was not trying to do it.....I was flying with my instructor when I was prepping for my commercial and he gave me a throttle chop when there was no where to go in front of me. Right behind me was the only place I had to go......

Yea...I know.....It's no blackhawk

[SASless]

Nick,

3.7G....girl scout loading that....my smoothest landings approach those numbers.

[NickLappos]

Yea, I hit 4 g's landing during an HV curve test program, but I think Shawn was thinking about g's the ROTOR created!

[Farmer 1]

Maximum Transient G in HelicoptersPositive or negative?

I used to fly the BO105, but never with a g-meter. It grabs your attention when your shoulder harness suddenly gets very tight, and you see the oil pressures fall to zero because the oil has shot up to the top of the tanks.

I seem to remember a limit of +5g, but I sit to be corrected. Long time ago.

"Even the birds are jealous."

[NickLappos]

Shawn knows this, but for operational pilots, it is probably confusing:

The load factor limits that are published for helicopters are almost never the real limits that can damage the rotor or consume the lives of the rotating parts. The published g limits that are in some military helicopter flight manuals (and therefore get into some civil manuals) are actually the limits of the airframe, so that they measure the strength of the engine mounts and the transmission feet but have nothing to do with the stress on the rotor blades or on the rotating components. Therefore it is quite possible to see a published 4.0 G limit and yet have helicopter that can get into serious trouble by overstressing the blades or the rotating components at as little as 2.5 G's.

This is because few of the qualifying agencies rarely understand how the rotor develops load factor, how it stalls, and the resultant stress on the blades and rotating components. Often the folks who set the G limit on the fuselage are in a different section than those who understand the rotor! Also, because the stall stresses on the rotor vary greatly by the density altitude, gross weight, rotor rpm, and maneuver severity, it is very hard to give the pilots one number of load factor that will keep the aircraft safe. There are several indicators on some helicopter models that get close. The limit light on some of the Eurocopter models and the cruise guide on some Sikorsky models get close because they measure the stresses on the servos which are the resultant of the rotor stall forces coming down through the stationary control system.

The net result is that it's very hard to tell a field pilot what are the actual maneuver limits of his aircraft. It also means that the published load factor limits in the flight manual are often deceptively high and do not indicate how much trouble the pilot can be an before he gets to that G limit.

BTW, the stall factor that creates the stresses on the blades and controls is the same stall factor that causes "jack stall" ion those helos with servos that are underdesigned.

[slowrotor]

Nick,
If I read your post correctly, you said the G limit in an FAA approved flight manual may be higher than the rotor can withstand!
That is rather disturbing.
Therefore it is quite possible to see a published 4.0 G limit and yet have helicopter that can get into serious trouble by overstressing the blades or the rotating components at as little as 2.5 G's.

[NickLappos]

Yes, and it is something that helicopter people really don't appreciate.

The G limit for flight manuals in never an aerodynamic one, it is not based on what the rotors can do, it is always based on what the airframe can stand. In high gross weight conditions, at high density altitude, the rotor will go into stall and stress the blades and controls long before that G limit can be reached.

[eagle 86]

Always amuses me when some amateur galah who aerobats a helo is lauded on these pages as some kind of ace - when really they know stuff all about what they are doing!
GAGS
E86

[Shawn Coyle]

Not sure I've ever seen a civil helicopter with a G meter to observe any G limits that may have been applied.
Few enough military machines have 'em either.
Assumption seems to be that you normally wouldn't be pulling that much G for long enough to do (structural) damage to the machine.
For most civil helicopters, doing more than +/- 0.1 G from level flight will result in being allowed to find a new job....