vortex ring alt + vsi
Joined: Apr 2004
Posts: 483
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From: The Dark Side
Aaaaah - overpitching - I wondered when this would raise it's ugly head! Overpitching is simply when you top out the N1/Ng whatever of a gas turbine (merely using gas turbine because most are familiar with terminology - happens in pistons as well) - in other words engine can give no more but you as a pilot keep pulling lever - drag on rotor system increases - blades slow down - lift is lost.
GAGS,
E86
PS I trained through the US Defence system - aerodynamics was over simplified to suit the "sausage machine" process. It wasn't 'til I attended the "School" that I gained a clearer understanding of helo aerody.
GAGS,
E86
PS I trained through the US Defence system - aerodynamics was over simplified to suit the "sausage machine" process. It wasn't 'til I attended the "School" that I gained a clearer understanding of helo aerody.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,110
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From: Wandering the FIR and cyberspace often at highly unsociable times
I've until now refrained from getting drawn into the argument about ROD of 200 ft/min at less than 30 kts being "VRS" territory, but seeing as it keeps on being mentioned.....
The Flight Manual for my aircraft states, in the "Normal Procedures" section:
STEEP APPROACHES AND VERTICAL DESCENT MANOEUVRES
Low speed steep approaches (up to 20 kts) and vertical descent manoeuvres should be performed with a maximum descent rate of 900ft/min.
That is copied verbatim. I expect the manufacturer also allows a bit for safety, as per the term "should", and so gives a conservative figure.
Nick, thanks for your patience on this subject
The Flight Manual for my aircraft states, in the "Normal Procedures" section:
STEEP APPROACHES AND VERTICAL DESCENT MANOEUVRES
Low speed steep approaches (up to 20 kts) and vertical descent manoeuvres should be performed with a maximum descent rate of 900ft/min.
That is copied verbatim. I expect the manufacturer also allows a bit for safety, as per the term "should", and so gives a conservative figure.
Nick, thanks for your patience on this subject
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
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From: EGDC
Shy, I would guess that your aircraft is a modern, high disc loading machine so the downwash velocity is higher than an R22 or Schweizer and therefore the RoD would have to be much higher to encounter VRS on yours than theirs. However, I think the 2-300 fpmin is far too conservative and belongs in the days of ultra low disc loading like sycamores and similar.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,110
Likes: 1,083
From: Wandering the FIR and cyberspace often at highly unsociable times
Crab, correct on all counts.
I think we now need to forget the Sycamore, even I can't remember seeing one airborne. I recall RAF teaching was 30kts & 300 ft/min for the Whirlwind; that type used to be taken up to 10,000 ft on the basic course (pilots wearing parachutes) to demo it, the climb taking most of the sortie. I was never convinced by the demo I saw; I must have blinked and missed it.
The later inadvertent developed VRS in the Puma over Forkhill after a long night hovering at Flight Level Nosebeed was much more interesting....
)
Chalk and cheese for a decent modern helicopter. Even the little R-22 has a relatively high disc loading.
I think we now need to forget the Sycamore, even I can't remember seeing one airborne. I recall RAF teaching was 30kts & 300 ft/min for the Whirlwind; that type used to be taken up to 10,000 ft on the basic course (pilots wearing parachutes) to demo it, the climb taking most of the sortie. I was never convinced by the demo I saw; I must have blinked and missed it.
The later inadvertent developed VRS in the Puma over Forkhill after a long night hovering at Flight Level Nosebeed was much more interesting....
)Chalk and cheese for a decent modern helicopter. Even the little R-22 has a relatively high disc loading.
Joined: Nov 2001
Posts: 298
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From: Norfolk
Mention of the Sycamore reminded me that it demonstrated all the symptoms and unpleasant effects of vortex ring better than any type I've flown since. Probably why the exercise was discontinued for a while. As an aside it also demonstrated ground resonance pretty repeatably as well. But then it was the first British designed useful helicopter.
