There will come a time when you good ppruners will realize that AnFI is able to counter any argument with excellently phrased pap, and make it sound scientific.
That Greek Apache was flown into the water with virtually NO pitch rate, and therefore no maneuver-induced load factor. Blade stall is certainly not a factor. A large collective pull reduced the descent and the RPM and it almost worked.

AnFI has "analyzed" it to prove his crackpot theory of how rotors work, and the result is a sausage casing of misapplied theory and mismeasured "facts".

There comes a time when you are wrestling in the mud with a pig and you realize the pig loves it.

In a former life he probably sold snake oil........

oh well at least I now know that coning angle is not the ratio of Lift to Cf apparently

and that neither lift nor Cf are proportional to RRPM^2 which is why apparently they don't cancel out (!)

furthermore courtesy of PPrune I have learnt that Vortex Ring a a condition that can be inescapable for 4000ft ! apparently

and I have learnt from Crab that if you crash then you are too low, seems obvious now, silly me.

PoF courtesy of PPrune

Normally after reading AnFI's posts I almost lose the will to live :rolleyes:

Finally, however, amazingly, I agree with something he said:

:}

haha (65789)

AnFI, this drags on. Cf falls with RPM, but lift must be a constant, because the pilot raises the collective and increases the blade angle to compensate, therefor as RPM falls, the coning angle increases immensely. Please, consider that this is just a bit more complex than your simple analysis, and that some of us have a bit of knowledge about this.

it does drag but there is a serious point in there Ascend approximately understood it in post 33

The Cl will hit it's max at the same coning angle regardless of the RRPM.
eg increase RRPM but add weight to keep Cl at max and the coning angle will be the same (as good as damn it)
get it yet?

(last go)

if only it was..........

But you follow a predictable path AnFi - you come up with an off-piste notion, get challenged on it, move the nub of the argument from place to place, confuse everyone, refute the opinions of those who have an esteemed track record in the discipline and finally claim no-one else understands you and flounce off.

And then in a few weeks you will be back to do the same again.

I was accused by Canute of not bringing anything useful on this thread - he hasn't dealt with you before so that is understandable.

However, in the final analysis, your confusing, unproven ideas are actually damaging to those seeking to further their knowledge of helicopters - fortunately we have our resident experts to guide them back on the the true path.

Sincerely, AnFI your fundamental premise relies on Lift being proportional to RRPM squared and only to RRPM squared so that you can "cancel" it out. I've posted for you the simplest equation, based on BET, for lift on an individual blade. In calculating α you need RRPM, if you choose to dismiss α as a second order effect when calculating CL then that neatly sums up my concern with your approach.

Rotor design is fascinating because each section along the blade radius is experiencing significantly different conditions due to rotor speed, then each blade experiences significantly different conditions each cyclical rotation. The lift of each blade not only contributes collectively to the total lift, but individually has to cyclically influence the orientation of the disc. Rotor design, and therefore the selection of aerodynamic qualities, has to take this and many other things in to account. The concept of a "stalled" disc is interesting, but is so much more complicated than the concept of a stalled wing - it certainly doesn't distill straight to the CLmax of each blade independent of RRPM which your initial premise implies.

All I want now is to find out you are Simon Newman or Gareth Padfield - that would be the icing on the cake of the thread!

You flatter, 212man, sadly no icing on my account. But my hat's off to you, as one of those greats was my tutor and mentor, he will be horrified :}

Was it Simon Newman? I attended a short university course at Southampton courtesy of the RAF a good few years ago and he was one of the lecturers - absolutely excellent.:ok:

It is indeed Crab :)
He has a rare enthusiastic talent for taking a complex concept and making you feel it is simple to understand, before you had to deal with the challenging maths.

I have his 'Foundations of Helicopter Flight' book....

It's a good book, mine sits on my shelf at work with many post-it notes.

It reads like he lectured. Each chapter is an individual topic and starts with an explanation. For many uses the explanation is sufficient without having to dive into the maths. I always recommend it to young graduates who join the team.

Asking two highly experienced, world renowned, chief test pilots of a major helicopter manufacturer if they "get it yet".....priceless.

ShyTorque, the quote I loved most is the above telling Nick he "is mostly correct". Left me speechless, must admit I've not seen the likes of it on Pprune previously, the sheer arrogance and unbridled condescension.

the hallmarks and calling card of AnFI across many threads...

I would sincerely love to know who AnFI is, and watch him/her work.....

I'd rather rub lemon meringue pie on my head right before going to church.
Attachment 1105

CORRECTION

In the calculation for g of the Greek machine I used a=wv (where a is accelerationn (m/s/s), w is angular rate (rad/s) and v is airspeed (m/s)) brilliant eh?

xept I FORGOT the 1g we start with on this planet. !!!!!!

So the calculation for the 'g' for the Greek machine works out at 2.7 'g' not the 1.7g I wrongly declared.

It's pitch rate is 21deg/sec and avg speed 90kts.
So that means 'g' = 1+wv/10 (a works out at 17ms^-2) or 1.7'g' PLUS 1g = 2.7g

Looks like it's fair to say that was limiting thrust after all.

AnFI, the Apache was traveling nothing like 90 knots when that unsuccessful pull occurred, as evidenced by the video. As to how much 'g' it was trying to pull at the end ... ]


I don't recall that Apache's have a 'g' meter installed, so (I mistakenly thought that ) the Greek accident board won't be able to confirm or correct your estimate when their report on this bit of flat hatting goes final.


Edit: LRP has corrected my lack of knowledge on that point. Many thanks, sir.

The 64 does have a g-meter. It is also measured by the FCC for weapon inhibits.

Lonwolf you may well be right but my working was this:
Speed 5.25 lengths in 2 secs is 58x5.2x3600/6080 = 90kts (I measured 10 times and divided by 10 for more accuracy)

Can you see this video ytCropper | Dramatic: Apache helicopter slams nose-down into sea during exercise in Greece ?

i agree it doesn't look very fast but if you measure it in aircraft lengths and time then the result is a surprising 90kts according to my calc, try it yourself see what AVERAGE speed YOU get

I can understand someone thinking it doesn't look as fast as it is. Like a Formula1 car on telly doesn't look very fast either

Angle change rate and speed is all you need to work out the 'G' strange but true (a=wv)

just sayin'

Without getting into details LRP, for obvious reasons, was that a normal g readout, I'm aware of lateral g being used.

Lonewolf, I suspect the inertials will be measuring normal g, but not familiar enough with the type to know whether it would be recorded for retrieval.

wot do they use lateral g for ? sideslip?

dCl/da are you actually a helicopter designer?

Most modern inertial systems will tend to have a triaxial accelerometer orthogonally orientated aligned to the aircraft axes. Given our previous discussion on inertial forces when a body is rotating i'm sure someone as on the ball as you can figure out how to use such an output to give a whole raft of useful information. One obvious one would be how well a turn is coordinated, perhaps?

AnFI: The Blackhawk, for example, uses accelerometers to measure lateral acceleration. The signal gets fed into the AFCS, and account for control coupling, to include an input mixed with the stabilator when lateral acceleration is sensed (gust alleviation). (From old lecture notes, Fort Rucker origin, UH-60A)

Quote:

---

(4) Provide sideslip to pitch coupling to reduce susceptibility to gusts. When the helicopter is out of trim in a slip or skid, pitch excursions are also induced as a result of the canted tail rotor and downwash on the stabilator. Lateral accelerometers sense this out of trim condition and signal the stabilator amplifiers to compensate for the pitch attitude change (called lateral to sideslip to pitch coupling). Nose left (right slip) results in the trailing edge programming down. Nose right produces the opposite stabilator reaction.

---

As to your speed estimate, OK, I see how you arrived at that. The last time I did a rotor over type maneuver was a few decades ago, so memory may not serve on how much speed is reduced going over the top and then accelerating ... maybe 90's closer than my guess.


Is your 90 kts the resultant vector in direction of travel, or is it already converted to X axis 90 kts and Y axis (some vertical speed) ? I ask because he picked up a bit of vertical velocity (acceleration even) after the turn over the top.

AnFI, what did you use as points of reference to measure the distance travelled?

Yes, normal g readout.

dCl/da

"i'm sure someone as on the ball as you can figure out how to use such an output to give a whole raft of useful information."
cut the sarcasm, it doesn't suit a helicopter designer? more like Crab's style.

"One obvious one would be how well a turn is coordinated, perhaps? " yea that why I said "sideslip?" (obviously !)

Lonewolf thank you for your informative answer, I wonder if that is to help the fact that the swashplate is not orientated it the same plane as the zero-pitch plane?
(dCl/da any view on that? Maybe try googling it?)

[ and glad you see where the 90kts comes from, some others on here found it hard to understand (surprisingly !) ]

AnFI, my suggestion was turn coordination not sideslip.
You have not answered what you are using as points of reference for distance travelled.

dCl/da "my suggestion was turn coordination" then you were wrong apparently (smartarse)
(and sideslip was right, "called lateral to sideslip to pitch coupling")

regarding refrences tail nose tail nose tail nose etc you get the idea , or as you would sarcastically say "I would have thought that would be obvious"

and if you're touchy about 'not answering questions' then you didn't answer this "dCl/da are you actually a helicopter designer?"
are you? (i'd be surprised if you are)

Tail nose with regards to what fixed points of reference?

AnFI - what you are too up yourself to see is that you are being asked how you measured the aircraft movement accurately.

If the camera was in a fixed position, you might be able to assess the movement relative to the scenery BUT the camera is panning to keep the aircraft in the middle of the frame.

So, exactly how did you do it?

Crab I refer you to the answer dcda gave "i'm sure someone as on the ball as you can figure out...." it's not that hard, I don't think you've said anything useful, you're just a troll (xept perhaps "if you hit the ground then you're too low" but then most people knew that already !!)

Excellent work AnFi - you are alienating everyone else on the thread but still not providing any information, there is only one troll on this thread..........

Keep up the insults, they are just more insight into your insecurity.

AnFI nice googling.
How would an accelerometer detect a constant velocity sideslip?
Still no hint at the reference points you used to estimate the distance.

dcda googling ? no! Lonewolf's post 108 doh
"How would an accelerometer detect a constant velocity sideslip?" there is a limit to how much basic understanding you are asking me to explain to you, the most basic accelerometer in an aircraft measures sideslip (the ball), I don't know what method they actually use in this aircraft system but it doesn't sound very hard with a "triaxial accelerometer orthogonally orientated aligned to the aircraft axes"
No hint at the reference points? I answered you. Try it. Are you serious that you think that is hard? nose tail etc (yes it does)
.... and you still didn't answer MY question !

Crab almost the only replies i ever get from you are insults, you have a damn cheeck accusing me of it, you barely ever say anything that is not an insult. I'm sorry to stoop to your level but you really are a total.... oh I can't be bothered.

So in measuring "sideslip" what physical quantity is the most basic accelerometer measuring?

Again, you have asserted that you can measure velocity from the video clip, it is central to your calculation, all I am asking is what points of reference did you use to carry out the measurement, you say you did it 10 times so it should be easy to share with us.