Thread: Helicopter ground resonance

Originally Posted by Old Farang

In small helicopters, such as the Hughes 300 shown here, the onset is very rapid and requires instant response from the pilot.

I believe my instant response would be not to get in the damn thing in the first place. I have seen similar footage before, but had no idea that it was caused by engineering seeking a problem rather than a solution.
OF, do such birds require separate endorsement? Seems to me that a higher level of training would be required.

Originally Posted by Tins

I believe my instant response would be not to get in the damn thing in the first place. I have seen similar footage before, but had no idea that it was caused by engineering seeking a problem rather than a solution.
OF, do such birds require separate endorsement? Seems to me that a higher level of training would be required.

had no idea that it was caused by engineering seeking a problem rather than a solution.

Ah, rather the other way around. The problem is induced by the pilot (mostly), the C of G of the rotating mass gets displaced and the engineering attempts to rectify it.

do such birds require separate endorsement? Seems to me that a higher level of training would be required.

All helicopters require an individual endorsement, as compared with group endorsements for fixed wings. Ground resonance is covered in theory studies, but as you cannot demonstrate it, even in an incipient stage, some folks just don't get it!

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

Originally Posted by Hugh Jars

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

Yeah, not sure just what they are up to there, John. After all, they are probably Americans! What I first thought were test monitoring lines running off, a closer look at the lines show they may just be tether lines to prevent it flying off into the ether by itself.

But I do think it was some type of testing, and I doubt that anyone was on board.

Originally Posted by Hugh Jars

Wouldn't have liked to be sitting in the back of the CH-47 when the rear mast came off. I think that one was flight testing/demonstrating ground resonance, wasn't it?

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...

Originally Posted by Tins

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...

They were just rattling your chain mate!

Originally Posted by Tins

Had a couple of rides in a Chook back in the day. Didn't know a thing or I might have risked being disciplined for disobeying a lawful command.... I was silly enough to ask the crew about its auto rotational capabilities. Got told that the "****er has all the auto rotational capability of a housebrick". I look back in horror...

I went for a ride in a Huey when on a promotion course in Amberley with the ATC cadets, way back when. The loadmaster sat me at the left door gunner position, which had the best view in the house.

I was lucky and had a helmet and headset on, and could hear the crew talking over the intercom. We spent most of the flight chasing roos at treetop level. When the captain announced his intent to do a practice autorotation, I had no idea

When the engine spooled down I got the idea. My life flashed before my eyes, but of course the manoeuvre was well executed.
It was one of my most memorable flights as a sprog in a Service aircraft
Sadly, the crew were lost in a prang a few months later. I was shocked to read it in the RAAF News.

John R.

I have flown a Huey (while working offshore), but I am not endorsed on them. Auto rotations (successful ones!), depend a lot on the inertia in the rotor system. It is said of the Huey that there is enough inertia in the rotor system that; if sitting on the ground at flight idle you cut the engine it is possible to lift off the ground and turn a full circle and land again without damage.

The first helicopter that I owned was a Robinson R22. A very low serial number and one of the first imported into Australia.
Now that DID auto like a brick! It had about as much inertia as a paper bag. So much so that one of the first mods carried out by the factory was to install weights in the tips of the main rotor blades. (from Serial number 200 on if I recall correctly).

That did improve it, but it was still a delicate manoeuvre! It was also very easy to overspeed the rotor system, so it took a LOT of practice to become proficient.