Dynamic rollover

[brett s]

When I learned to fly the R22 they actually used to demo low g flight & recovery, was a Robinson requirement at that time - scary stuff.

They don't do that anymore, not sure when they quit - don't think too many CFI's were sad to see it go!

 

[Kandace]

When I learned to fly the R22 they actually used to demo low g flight & recovery, was a Robinson requirement at that time - scary stuff.

They don't do that anymore, not sure when they quit - don't think too many CFI's were sad to see it go!

Eeek! I'm glad they don't do that anymore! Sound scary to me!

Kandace

 

[helipaddy]

I remember when SFAR 73 required a "demonstration" of low G and recovery.
It stopped soon after four flight instructors were killed in Germany ( IIRC) in a R44 "Demonstrating" low G recovery.

 

[brett s]

This was prior to the SFAR existing, in the late 80's in my case - I remember it was Robinson requiring it prior to solo, maybe it was tied to their insurance at the time?

 

[Al_Hammer]

Kites are another thing that can lead to mast bumping- as a result of jamming the stick forward to avoid impact. There was just such an incident not far from me a few years involving an R22. it is discussed in this thread on Pprune.

 

[Walter]

A similar thing can happen, in my view, in gyros, and an accident here in Germany seems to have been due to this. Low g in a slow pushover, and a resulting roll along the longitudinal axis due to full power (high propeller torque). Guess that in case of low g (e.g., gusts, turbulence) the best is to load the rotor and reduce power.

 

[WaspAir]

I remember when SFAR 73 required a "demonstration" of low G and recovery.
It stopped soon after four flight instructors were killed in Germany ( IIRC) in a R44 "Demonstrating" low G recovery.

This was prior to the SFAR existing, in the late 80's in my case - I remember it was Robinson requiring it prior to solo, maybe it was tied to their insurance at the time?

I kept all my old training materials from my R-22 student days. See attached scans - this is from the "Robinson R22 Flight Training Guide", "R22 Maneuver Guide" section and "RHC Safety Notices".

According to the "Flight Training Syllabus" of the same vintage, Lesson 11 (after 10 hours of dual) includes an introduction to "Recognition and recovery of low G conditions", to be reviewed in Lessons 12 and 13.

The current language in SFAR 73 2(b)(3) includes this:

The dual instruction must include at least the following abnormal and emergency procedures flight training:

(i) Enhanced training in autorotation procedures,

(ii) Engine rotor RPM control without the use of the governor,

(iii) Low rotor RPM recognition and recovery, and

(iv) Effects of low G maneuvers and proper recovery procedures.

 

[RotoPlane]

Stan - Of course this explains how the thrust of the tail rotor will roll the fuselage around the cg when the fuselage has low to 0 g's on the mast.

Thanks Stan....I wasn't quite understanding the airframe action due to the tail-rotor at low G's. Now I see it....it's the relationship between the thrust of the tail-rotor and its height above the CG! If the tail-rotor could have CLT, much of that airframe rolling would go away....makes me wonder if the NOTAR causes less airframe roll to due to its thrust being closer to the CG.....

 

[Vance]

I am proud of you Stan!

I feel that expecting the unexpected and knowing how to respond to it is one of the ingredients for a safe pilot, particularly when the best response is counterintuitive.

I also like your best and second best response and the down side of the second best because it will allow you to have choices and prioritize them when things aren’t going well.

You sharing you musings here on the forum makes us all better pilots.

Luck favors the prepared.

Thank you, Vance

 

[helipaddy]

Good stuff Stan!

Now with this in your head remember the Dynamic rollover scenario...

With the helicopter (be it semi-rigid teetering, fully artic., or rigid head) in normal flight, the lateral thrust from the tilted head "torques" the fuselage around the aircraft's centre of mass in the required direction. This is a tilting moment which is the lateral thrust of the main rotor multiplied by the distance between the rotor head and the helicopter centre of mass.

force X arm = moment

On the fully artic and rigid head there are other forces trying to align the fuselage to the disc as well, discussed in a previous thread, but most of the turning moment is lateral rotor thrust X distance between rotor head and Centre of mass.

Now consider the Dynamic rollover situation:

Now the skid is touching something, the point of fuselage rotation is the skid contact point. The rotor lateral thrust is the same, but the Arm is much longer, being the distance between the rotor head and the skid, so the force, multiplied by the longer arm, creates a much quicker rotating moment.

This rotating moment if allowed past the point of no return will not be reduced with cyclic, no matter what type of rotor head. reducing the total rotor thrust with collective is the only way ( as you know already)

You have the low G in your head spot on, remember in a low G situation the helicopter will roll at a rate of around 90 degrees a second!!
If you feel weightless always reload the rotor head with aft cyclic.


If I could think of things that would help you to enjoy the R22 it would be these:

1. NEVER EVER give someone that is not a rated helicopter pilot a "go" on the controls EVER!

2. Always take the controls out of the pax seat if you do not have a rated helicopter pilot in the left seat.

3. wires wires wires.

ENJOY!

 

[helipaddy]

Its all magic Stan. This stuff never ceases to amaze me. I've learned so much from this forum about gyros and helis. I honestly think that this forum has educated people (myself included) in ways that gives them the knowledge to make the correct decision, and has saved their lives. Long may it last

Paddy

 

[tyc]

... this forum has educated people (myself included) in ways that gives them the knowledge to make the correct decision, and has saved their lives. Long may it last
Paddy

If you want an education - with emphasis on what NOT to do - have a look at some of the aircraft salvage pages, helicopters.

Most include a brief printed description of what was going on up and including what happend during the accident. With that in mind I can't help thinking of the "classic", one in which an idiot did a quick pre-flight (not that he was paying too much attention while engaged in that part of his work) as he undid the restraint lines on the right skid, climbed in, "lit the fires, lifted the tires" and immediately rolled the Hughes 500 over on it's left side - the "cowboy" (who didn't own the machine) never bothered to untie the left skid and completely destroyed an almost totally new machine ...

Then there's the one where on a windy day, the pilot of Bell 206, landed and taxied over to and settled very near the hanger, a metal pre-fab building and while ingaged in the two minute cool down of the turbine, with the rotors still spinning at a good rate at the time, a gust of wind picked up the helicopter and blew it into the side of the building. Another nice Bell 206 good for parts, as well repairs which were needed to replace the side of the building where the rotors went thru it.

Then there are those who like to practice autorotations and take it to the extreem - completely destroying the helicopter in the hard landings which do end the flight, as well a the use of the machine, save for salvage sales of scrap parts and pieces ... and the proverbial "beat" goes on ... and on ... and on ...

tyc

 

[Arnie Madsen]

Here is a good 1:27 minute video of a Brantly helicopter coming as close as you can to dynamic rollover without actually going over. And just to keep things exciting he does it twice. Then to top it all off he sticks his leg out the door ....

There has been some discussion on this thread regarding the narrower CofG of a 2-blade teetering rotor vs the slightly wider CofG range on an articulated rotor head.

It is my guess that the Brantly 3-blade system (slightly wider CofG) helped saved the day for this pilot along with a whole bunch of luck.

http://www.youtube.com/watch?v=n6P51PWvTQo

As far as I know this happened at a Homer Bell fly-in a couple of years ago. Apparently the tail rotor was set up wrong and was short 2 degrees of pitch. Other factors were tail/cross wind with hot/heavy conditions.

 

[SamL]

Gyroplanes, and Dynamic Roll Over

Gyroplanes, and Dynamic Roll Over

Hi All
Dynamic Rollover is something that can occur to gyroplanes as well.
The effect and outcome are the same. The cause is the only difference.
I usually explain it to my students while flying low over undulating ground.
If you were to land a gyroplane on side of a slope (90 degrees across it) and the gradient is greater than your heads movement (usually 9 degrees from centre) The gyroplanes blades would be still be tilted down the hill and they would simply fly you over onto your side.
For this reason whenever having to land across a slope you should always try landing up, down, or oblique to the slope.
Its a simple case of not enough head movement.

Regards SamL.....................

 

[tyc]

It is my guess that the Brantly 3-blade system (slightly wider CofG) helped saved the day for this pilot along with a whole bunch of luck.

http://www.youtube.com/watch?v=n6P51PWvTQo

With the years of experience I've had in Brantlys, I've never had that happen. I have seen videos of individuals learning to fly the Mosquito Air - on their own - come close to doing this. Operating low and slow and smoothly when in ground effect is not something new rotorwing pilots are used to and it is my guess that the individual was/is a very low time Brantly pilot ... and that "a whole bunch of luck. " was definatly involved.

If I'm right regarding the pilot's lack of experience with the B2B (the right leg all the way out the door and his apparent marginal control while simply hovering suggests I may be right in this assumption), it won't be the first time a novice took someone up (probably illegally) and either came very close to killing himself and the passinger as the video shows or did.

tyc

 

[Kicking Skids]

I have to agree with Helipaddy,
I fly EC120 with a Spheriflex rotor head and I also fly the Schweizer 300 with a fully articulated rotor head.

When a skid gets stuck or if you have sideways movement on takeoff or landing, you will definitely get dynamic rollover if it is not corrected. In both cases the corrective action is to lower the collective smoothly until weight is put back on both skids. You MUST NOT correct with the cyclic. It is possible for the momentum of the roll to keep the helicopter rolling and no amount of cyclic or collective input will prevent the helicopter from rolling over.