Calling Nick Lappos - Blade Stall

[AnFI]

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.

[Lonewolf_50]

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.

[LRP]

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

[AnFI]

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'

[dClbydalpha]

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.

[AnFI]

wot do they use lateral g for ? sideslip?

dCl/da are you actually a helicopter designer?

[dClbydalpha]

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?

[Lonewolf_50]

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)

(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.

[dClbydalpha]

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

[LRP]

Originally Posted by dClbydalpha

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.

Yes, normal g readout.

[AnFI]

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 !) ]

[dClbydalpha]

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

[AnFI]

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)

[dClbydalpha]

Tail nose with regards to what fixed points of reference?

[[email protected]]

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?

[AnFI]

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 !!)

[[email protected]]

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.

[dClbydalpha]

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.

[AnFI]

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.

[dClbydalpha]

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.