Zero-G

[Guest sharky]

In flight school, we''re all taught the dangers of semi-rigid rotors in zero or negative G environments...how do other rotor systems, built by different manufacturers, fare in zero or negative G?

[MINI]

Bo105 inverted,in autorotative state doing pedal turns to the right,stop,then left then pull out at 3 gs.ya fricken hooooo,what a blast!!!!!!!

[VERTICAL REF]

...that BO105 pilot is now dead...

[Guest graunch1]

If I can find it I have a great picture I took from the back of Dome''s BO105 in a near inverted turn over McKinley Bay. "Now what in **** are those drill ships doing up there?? "

 

[Winnie]

The original question was in the line of how do other helicopters "fully articulated and rigid in plane" fare in low or negative G situations?

 

The answer is this: Since these helicopters have offset flapping hinges, or no hinges at all, they will not allow you to get into mast bumping, however, you stand a great chance of getting Droop-stop Pounding, which I'm sure is not too good either! The AH-64 Apache helicopter is actually capable of -1G, but other than in an extreme push-over or bunt would it be possible to achieve that, since if it rolled inverted all the way, it would start falling (no negative pitch). Your instructor probably showed you a low-g situation, and how to recover, and the biggest concern seems to be that in a violent pushover, the tail will roll you to the right violently, and a natural reaction is to roll cyclic to the left to arrest. This has no effect on an unloaded semirigid disk, but because of the offset flapping hinges, there will be a bending moment on the hub in fully articulated machines, and this will induce some roll. In Norway (My country of permanent residence) the military actually had problems of mast bumping in their Bell 412SP's, which theoretically seemed impossible, since they are four bladed, but the system is aparently a double two bladed 'soft in plane' similar to the 222/230, and thus capable of achieving mast bumping.

Speaking of inverted flight, the British army air corps rolled and looped their Lynx helicopters, and Sikorsky barrel rolled their S-65 Super Stallion (Ch-53E).

 

Hope nobody got bored, and that somebody actually reads what I've written!!

 

Edited typos only, so the typo police wouldn't catch on!

[CTD]

Excuse me? The Norwegian military has certainly never experienced ''mast bumping'' with any of their 412s. A testiment to this fact is that they still have all the machines they bought, which would not be the case follwing a mast bumping incident.

 

What has occurred in the past have been cases of incorrect rigging, resulting in the swashplate impinging on the mast and grooving it.

 

Also, the stacked soft-in-plane rotors of the 412 and 430 have no similarity whatsoever to the 222/230, which are teetering semirigid systems, like the 206. The former behaves more like a fully articulated, but use flexing in the hub instead of hinges.

[Winnie]

CTD:

I stand corrected!

I should question my references better for sure!

What happened was that the Royal Norwegian Air Force "thought" they had mast bumping on their 412SP's, and consequently they were limited for maximum 30 degrees nose up/nose down. But I fear that they, as I was wrong in our conclusions, and I believe that you are right and I am wrong.

 

I realize now what I wrote! Had something else entered here, but just as I signed off it came to me, the AH-1 Cobra has something of a soft in plane, but then again it looks to act like a semirigid in action, somewhat similar to the head of the 214B's? Not sure anymore, and now I will shut up !

 

At least you read the post!

[Guest sharky]

So Bell''s 4-bladed soft-in-plane rotor systems have more of a semi-rigid action? Would that be to say that the blades move equal and opposite in directional flight...not unlike a teetering system?

 

####, how does EC''s 3-blade starflex behave? Is it a semi-rigid design as well? Does the starflex absorb the lead/lag or do the blades themselves hinge?

 

Is the flapping action of either of these systems absorbed by the elastomerics as well? Or do the blades hinge?

 

This is all wonderful information so far....and so for curiosity''s sake, could a rotor system say with bell''s soft-in-plane or EC''s starflex be able to tolerate 0 or negative g''s? What about sustained 0/neg g''s?

 

thanks again.

[CTD]

Winnie, no worries. I know that your dealings with RDM has distoted your normal views of the world, and thus, you can be easily forgiven.

 

Sharky, the 4-blade soft-in-plane systems behave more like fully articulated, and nothing like the teetering semi-rigid found on the two-blade Bells etc. The three-blade EC rotor heads slightly different in design, with an elastomeric spherical bearing etc., but are very are similar in function. In both systems, the function of the flapping, pitch and lead-lag hinges is performed by flexing of the yoke itself, or by elastomerics.

 

Although neither of these systems is as ''aerobatic'' as the rigid rotor on the BO-105, the Bell 680 rotor system - which is the experimental rotor from which the 430 system came - is very nimble, and when installed on an experimental 222 was able to loop and roll with ease.

[Winnie]

CTD

Yeah, RDM is the man...

At least he let me fly some, but you shoulda been there when he tried to roll the throttle the wrong way on the power recovery!!

 

To all:

There is a new book out by Shawn Coyle, who used to be in TC, it is called: "Cyclic and Collective, More art and science of helicopter flying", which is fairly expensive, but extremely informative, both for the prospective student and the advanced pilot (neither of which category I fall in, so I just have to read and keep on dreaming!)