Relation between Rotor RPM and IAS during Autorotation
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Relation between Rotor RPM and IAS during Autorotation
For the majority of you this could be an as simple as silly question but ... I'm discussing with some colleagues of mine about the relation between RPM and IAS during autorotation.
I'm sure that as long as I increase IAS, RPMs slow down and viceversa but I'm not able to convince my colleagues about this theory more than telling them go and try!
Any clues from some aerodynamic enthusiast?
... or am I dead wrong !!?!
Thanks a lot you all,
Sax
I'm sure that as long as I increase IAS, RPMs slow down and viceversa but I'm not able to convince my colleagues about this theory more than telling them go and try!
Any clues from some aerodynamic enthusiast?
... or am I dead wrong !!?!Thanks a lot you all,
Sax
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Normally as your increase TAS your RRPM will be higher
A simple way of understanding this is that as you go faster (ignoring lower speeds, say more than 50 kts) your ROD increases this means you have more air driving your rotor system therefore it spins faster.
What can make this confusing is that if you push the cyclic forward fast you will lose RRPM as you are essentially performing the reverse of a flare. It will not take long for this to recover though as ROD increases.
A simple way of understanding this is that as you go faster (ignoring lower speeds, say more than 50 kts) your ROD increases this means you have more air driving your rotor system therefore it spins faster.
What can make this confusing is that if you push the cyclic forward fast you will lose RRPM as you are essentially performing the reverse of a flare. It will not take long for this to recover though as ROD increases.
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Generally, the rpm peaks at or just above normal auto speed (min ROD). With fixed collective, if you go faster or slower, the rpm decreases somewhat (after the initial rpm disturbance from the pitch attitude change).
For the S76, at zero knots in auto, the rpm is low (bottom of the green) and the ROD gets to be about 6000 fpm. Same at auto Vne.
For the S76, at zero knots in auto, the rpm is low (bottom of the green) and the ROD gets to be about 6000 fpm. Same at auto Vne.
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... Actually I've tried this many times but not till the moment the RRPMs start to increase back again accordingly to the higher ROD.I've always been supposing that RRPMs decrease when you change the helicopter's attitude in order to accelerate because of the smaller amount of air passing through the rotor and, to be honest, I' have never waited so much to allow the ROD to increase RRPMs back again.
I will try ... hoping not to have to wait that long
!!!Thank you very much for sharing.
Sax
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Mr. LAPPOS, I've been hoping to receive your point of view. Many thanks.
What you are stating is related just to S76 or is quite a rule of thumb for whatever the helicopter?
Assuming we are considering just the velcity spread between MAO and MAK and not from zero to VNE, with a fixed collective, how will the RRPMs vary and, possibly, why?
Thanks a lot again,
Sax
What you are stating is related just to S76 or is quite a rule of thumb for whatever the helicopter?
Assuming we are considering just the velcity spread between MAO and MAK and not from zero to VNE, with a fixed collective, how will the RRPMs vary and, possibly, why?
Thanks a lot again,
Sax
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It holds true for a H300 but they are not the fastest of machines so perhaps it all changes in the higher speed ranges you would get on say a s76.
The 300 has a pretty forgiving RRPM range so please dont get into trouble in a r22.
At 40 kts in a 300 you need to have collective on floor but at 70 you need alot of collective to prevent overspeed. When students try for 80 you need a s*&t load especially when they pull cyclic back to slow down
The 300 has a pretty forgiving RRPM range so please dont get into trouble in a r22.
At 40 kts in a 300 you need to have collective on floor but at 70 you need alot of collective to prevent overspeed. When students try for 80 you need a s*&t load especially when they pull cyclic back to slow down
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conceptual chaos: momentary vs steady state
One doubts you'll get clear resolution of this one, either with your mates or on this forum. Even in the few posts thus far, we're beseiged with references to "it" and "this" and other vague substitutions--we can't really tell who's referring to what flight regime or how long that regime persists or . . .
The first thing to get clear is, perhaps, the distinction between transitory effects (as in pulling BACK on cyclic, causing 20-90 second increase in RPM as rotor disc intercepts more air at same airspeed) vs steady state conditions (stabilized descent, constant cyclic/collective positions, constant airspeed, thus constant RPM).
Draw diagrams. Sketch graphs of RPM vs time. Establish that you have common points of reference. Be specific.
An interesting corollary conversational practice exercise in a less technical, easier-to-demonstrate arena: when you perform a turn on a bicycle, which way do you first turn the handlebars? [Answer: AWAY from the direction of turn. Very briefly. Because you FIRST have to establish the bicycle's angle of bank, disrupting its balanced straight-ahead motion, and THEN you turn the handlebars into the turn to maintain angle of bank, and balance. But nobody actually LEARNS it that way, so they never have to think about the details!]
The first thing to get clear is, perhaps, the distinction between transitory effects (as in pulling BACK on cyclic, causing 20-90 second increase in RPM as rotor disc intercepts more air at same airspeed) vs steady state conditions (stabilized descent, constant cyclic/collective positions, constant airspeed, thus constant RPM).
Draw diagrams. Sketch graphs of RPM vs time. Establish that you have common points of reference. Be specific.
An interesting corollary conversational practice exercise in a less technical, easier-to-demonstrate arena: when you perform a turn on a bicycle, which way do you first turn the handlebars? [Answer: AWAY from the direction of turn. Very briefly. Because you FIRST have to establish the bicycle's angle of bank, disrupting its balanced straight-ahead motion, and THEN you turn the handlebars into the turn to maintain angle of bank, and balance. But nobody actually LEARNS it that way, so they never have to think about the details!]
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I think Nick has it right, generally. The maximum rotor RPM will be seen near the minimum ROD airspeed, which will be different for different aircraft of course. There is also a maximum autorotation airspeed, which should be shown on the airspeed indicator or on a placard. This is also different for each model. All this should be available in the RFM, in the performance and limitations sections.
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The 300 has a pretty forgiving RRPM range so please dont get into trouble in a r22.
Establish autorotation at about 65 kts, and get RRPM right in the middle of the green. Gently push cyclic forward to decrease disc loading - RRPM drops, then as speed increases, it goes up again. Then gently flare to increase disc loading, RRPM goes up even more, then comes down as speed decreases. You can demonstrate it convincingly without it being remotely scary, and keeping the RRPM in the normal range the whole time, despite the R22's relatively 'unforgiving' RRPM range. I have to think hard to explain the reasons, but I know this works.
Montana 407 engine failure at 350ft
Other reports indicated an engine chip light:
ALERT ’copter crashes at helipad
Posted: Friday, Nov 03, 2006 - 12:31:01 am MST
By DAVE REESE and CHERY SABOL
The Daily Inter Lake
The ALERT air ambulance crashed at the Kalispell Regional Medical Center helipad shortly after takeoff Thursday around 9 p.m. No one was injured.
ALERT chief paramedic Chuck Curry, who was on the flight, said a helicopter warning light went off just after takeoff in a snowstorm around 8:55 p.m., and the crew returned immediately to the helipad next to Kalispell Regional Medical Center.
Curry said the engine died on the return flight near the water tower on Buffalo Hill, only about 300 yards from the pad and about 350 feet in the air.
As it landed, without power, the helicopter struck a parked vehicle next to the helipad, clipping the vehicle’s side mirror. The helicopter also tore out about 50 feet of chainlink fence before skidding about 40 feet to a stop just at the edge of the pad.
Sparks could be seen coming out of the top rear of the helicopter as it returned to the helipad.
The Federal Aviation Administration will investigate the crash, according to hospital administrator Jim Oliverson.
He and Curry praised the skill of pilot Addison Clark who made a hard landing, but kept the plane upright.
“What an incredible job” Clark did, Oliverson said.
The helicopter’s protocol is to land immediately if a panel indicator light goes off as it did Thursday night.
“The protocol is, don’t think about it. Set it down,” Oliverson said.
Clark, Curry and nurse Megan Hamilton were the only people on board.
Kalispell Fire Department was dispatched to the crash. Captain Dave Dedman said a small fire was extinguished before the crew arrived.
“The pilot did an awesome job,” Dedman said.
Oliverson said FAA officials should arrive this morning. The hospital will contact flight programs in Missoula, Great Falls, and Spokane to cover for the ALERT helicopter while it is being repaired.
The flight program has a nearly spotless record for accidents.
The crew struck a tree on a flight in July 2001. Then, pilot George Taylor was also able to return the craft safely.
Thursday night, Oliverson said everyone was relieved that the helicopter landed safely.
“We’re all very sad, but appreciative,” he said.
ALERT ’copter crashes at helipad
Posted: Friday, Nov 03, 2006 - 12:31:01 am MST
By DAVE REESE and CHERY SABOL
The Daily Inter Lake
The ALERT air ambulance crashed at the Kalispell Regional Medical Center helipad shortly after takeoff Thursday around 9 p.m. No one was injured.
ALERT chief paramedic Chuck Curry, who was on the flight, said a helicopter warning light went off just after takeoff in a snowstorm around 8:55 p.m., and the crew returned immediately to the helipad next to Kalispell Regional Medical Center.
Curry said the engine died on the return flight near the water tower on Buffalo Hill, only about 300 yards from the pad and about 350 feet in the air.
As it landed, without power, the helicopter struck a parked vehicle next to the helipad, clipping the vehicle’s side mirror. The helicopter also tore out about 50 feet of chainlink fence before skidding about 40 feet to a stop just at the edge of the pad.
Sparks could be seen coming out of the top rear of the helicopter as it returned to the helipad.
The Federal Aviation Administration will investigate the crash, according to hospital administrator Jim Oliverson.
He and Curry praised the skill of pilot Addison Clark who made a hard landing, but kept the plane upright.
“What an incredible job” Clark did, Oliverson said.
The helicopter’s protocol is to land immediately if a panel indicator light goes off as it did Thursday night.
“The protocol is, don’t think about it. Set it down,” Oliverson said.
Clark, Curry and nurse Megan Hamilton were the only people on board.
Kalispell Fire Department was dispatched to the crash. Captain Dave Dedman said a small fire was extinguished before the crew arrived.
“The pilot did an awesome job,” Dedman said.
Oliverson said FAA officials should arrive this morning. The hospital will contact flight programs in Missoula, Great Falls, and Spokane to cover for the ALERT helicopter while it is being repaired.
The flight program has a nearly spotless record for accidents.
The crew struck a tree on a flight in July 2001. Then, pilot George Taylor was also able to return the craft safely.
Thursday night, Oliverson said everyone was relieved that the helicopter landed safely.
“We’re all very sad, but appreciative,” he said.
