Retreating Blade Stall No 2

[SASless]

fijdor.....Next time you hover the aircraft with nothing hanging under it.....establish a stable hover into wind.....then start wiggling the tail using the Tail rotor pedals....gradually work them with increasing amounts of input and watch the aircraft begin to roll a bit. The high tail fin position of the Tail Rotor on the 205 provides for that kind of pedaling to cause the aircraft to react in "Roll" as well as Yaw.

A lot of the symptoms you mention are classic Bell LTE.

I wonder if you might be experiencing LTE right at the airspeed where you begin to experience the onset of RBS. As you are right up there at the very top of the charts.....you are operating in a region of flight not all that many folks do.

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And it's professor not proffessor

[topendtorque]

you are operating in a region of flight not all that many folks do.

if any with a heavy pendular load?

good one sasless, been waking up at night trying to nut this out, as you can see.

I wonder if you might be experiencing LTE

I wonder could the T/R have been intercepting some rather unusual turbulence at that point as well from the retreating blade, breaks away, then as you say rolls right?
just a thought.

did the T/R break away as well Fijdor?

[SASless]

In the second video....right at the end....it appears the airspeed goes to zero....then the attitude indicator shows a roll to the right.

My understanding of RBS is the airspeed would drop off after the pitch up and simultaneous roll to the left.

Ya'll look at the video and tell me what you see.....as my tired ol' eyes are not what they used to be...especially the right hand one with the growing cataract.

[AnFI]

crab: thanks for the spell-check

[fijdor]

No it was a stock 205, single hyd, 205 blades but -17 though. Fast-Fin, strake kit and all were not invented yet.

Ugly for sure with nobody in the left seat but not to long after that video was taken the left seat came out to save weight. I needed those extra pounds.

Sasless, Topendtorque, there is NO Retreating Blade Stalls in those videos, just simple LTE.
The banking angle you see on the Att Ind after I enter LTE is me reacting to the LTE by moving away from the mountain and trying to get some speed. You can't just hover there OGE pulling torque with full left pedal, it won't come out of it, when it goes you go with it.

JD

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An FI, since few of us have access to professor Leishman's book would you like to post the extract (in context) so we can see for ourselves how he states that blades don't flap?

[AnFI]

If I prove to you that you are wrong about one of the most fundamental aspects of helicopter PoF, will you;

a) apologise for being so dismissive of what I say
b) agree to take more seriously what I believe to be at play with VMC pilots and IIMC
c) not be so dismissive in the future.
d) agree to continue helping me with my spelling

Seems fair?

A simple a)y/n b)y/n and c)y/n would do.

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And if you don't?

[SASless]

Sounds like a Poll needs taking here......

I put my money on Crab as being "More Correct"....as an absolute may not be possible in this topic shy of some very serious Aerodynamicist getting involved.

[AnFI]

Crab: then I guess I'd have to sort out my own spelling!

[500e]

Watch through don't know what the fuss is about "simples" the answer starts 2:50
Now go play quietly boys.

[AnFI]

Crab: be nice - 'nough said? or do i still need to type out a chapter of academic explanation?

500e : "gee we're smarder efery dayee" simple and clear (but doesn't explain the process)

... can we forget about Leishman now that "Smarter Every Day" has PROVED it?



(...left a few spelling mistakes for you to correct - my attempt at an accent)

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AnFI - yes you do still need to show your workings, I don't have a Leishman nor access to one - the nearest I can get is to view part of his book on Amazon which has many, many references to flapping in the index.

[AnFI]

the amazon preview works page 208 last three sentences of 2nd chapter (from memory)

[AnFI]

... it's the only place in his book which covers that, the the rest of it is 'unimportant'.

(except perhaps the other IMPORTANT point is the one I previously mentioned about the reference for 'flapping')

[AnFI]

(which is why AC interestingly mentioned FLAPPING UP on the retreating side - which you don't believe, and did not pick up on, but claimed to agree - because you think blades flap down on the retreating side (in the cruise)) -

That's the thing about helicopters - you never stop learning.

[500e]

Hmmmm no sense of humor either,

[bast0n]

Many many years ago - drone drone in one of these,



It was a windy day. So windy in fact we had to engage in the hangar and taxy out for an SAR callout to the northwest - directly into a hooly of a wind. I flew as low and as fast (not very) as I could to keep out of the gale.

As I crossed the cliff tops near St Agnes you can guess what happened. The updraughting air whistling straight up the cliff suddenly and dramatically increased the angle of attack on the blades. The aircraft flipped left to an angle I still have no idea about but it threw the crew from sitting in the door to the otherside of the aircraft and the nose rose equally dramatically. The aircraft hurled its way sort of sideways and nose up and came out of the updraught and sort of recovered itself, whilst I played tunes on the manual throttle.

I have always thought that this was retreating blade stall.

Crab - am I correct............................?

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Baston - I think so...AnFI will surely disagree. A Valley crew had the same thing winching on Tryffan in 70 kt winds and strong updraughts, fortunately just before they put the winchman out of the door!

AnFI, just print the article and stop dancing around the issue. If you read his post, AC was talking about blade response to swashplate demand, not the blades reaction to aerodynamic forces cause by large differences in V squared between the advancing and retreating sides of the disc.

According to you (and I suspect Prof Leishman doesn't agree) selecting 10 degrees nose down from a still air hover will produce the same AoA on the retreating side (because it is all about swashplate demand and not flapping in your world) as having 10 degrees nose down to maintain (or to induce RBS exceed) VNE in the cruise. if your postulation is correct both scenarios will produce RBS when in fact only one of them does.