Entering autos: discussion split from Glasgow crash thread
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ANFI
Hmmm no never heard either HP or bananas referred to on the VSI ...even in soviet helicopters...because it's irrelevant depending on what the aircraft is doing. A zoom climb requires less HP even though you are bleeding energy.
My point is you have to frame the discussion in a way a pilot can relate to. HP.sec is meaningless to the average pilot and even the experienced pilot because it is not something we use when flying - for anything, there is no frame of reference . I have been taught by 3 different militaries and several civilian companies and have never heard anyone refer to a power demand in terms of hp.sec. Might be technically correct but it's practically useless as it has no relation to anything I am doing in a cockpit that I can reference. Sorry nobody works in HP anymore outside of the US, it doesn't mean anything outside of a design department.
If your talking generalities in energy management hmmm appropriate for basic flight training but assumed for a commercial pilot.
If your referring to a specific energy demand and its effects then yes there is a different discussion helo pilots use to correlate effects of a power demand to various issues encountered in Helos but it is specific to a type and varies by rotor design. But it ain't in terms your using.
My point is you have to frame the discussion in a way a pilot can relate to. HP.sec is meaningless to the average pilot and even the experienced pilot because it is not something we use when flying - for anything, there is no frame of reference . I have been taught by 3 different militaries and several civilian companies and have never heard anyone refer to a power demand in terms of hp.sec. Might be technically correct but it's practically useless as it has no relation to anything I am doing in a cockpit that I can reference. Sorry nobody works in HP anymore outside of the US, it doesn't mean anything outside of a design department.
If your talking generalities in energy management hmmm appropriate for basic flight training but assumed for a commercial pilot.
If your referring to a specific energy demand and its effects then yes there is a different discussion helo pilots use to correlate effects of a power demand to various issues encountered in Helos but it is specific to a type and varies by rotor design. But it ain't in terms your using.
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I think you are right - not so widespread but simple and useable nonetheless - you know how many Horspower you use to fly at different speeds - right? You know how long you can fly for using only the energy from airspeed from 100kts to 90kts? It doesn't take too long to work out the figures and you might like it.
The unit of VSI is in 100fpm
A HorsePower is 330lbs raised at 100fpm
So every 330lbs you weigh is 1Hp for 1unit on the VSI
If you weigh 3300lbs then its 10Hp per unit of the VSI ... not essential but interesting.
'Soviet units' km, m, m/s don't work so well for flying.
The unit of VSI is in 100fpm
A HorsePower is 330lbs raised at 100fpm
So every 330lbs you weigh is 1Hp for 1unit on the VSI
If you weigh 3300lbs then its 10Hp per unit of the VSI ... not essential but interesting.
'Soviet units' km, m, m/s don't work so well for flying.
Waiting 2 secs before reacting is a certification criteria. Look it up.
“The knee of the curve separates the takeoff portion from the cruise portion and is defined as the highest speed point on the low speed portion of the HV envelope. Altitudes above this point are considered cruise, or “fly-in,” points, and these test points require a minimum time delay of 1 second between throttle chop and control actuation (reference § 27.143(d)). Altitudes below the knee represent takeoff profile points. For test points in the takeoff portion, takeoff power (or a lower power selected by the applicant as an operating procedure) and normal pilot reaction time for corrective control actuation will be used.”
I believe the 2 second delay is that specified for military certification whilst the 1 second is the norm for civil certification. Possibly why we don't see low inertia rotor systems on modern military helps.
.....or quick thinking pilots evidently
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Crab, that sounds right. SASless: speak for yourself, soldier.
The point raised about low inertia heads (which are popular in design for a variety of reasons) and energy management of a low inertia head get me to three core points:
1. If you are flying somewhere at "best cruise" or "max conserve" airspeed, it would seem that one needs to ensure one's transit airspeed is some knots above best auto speed because anyone will have a slight delay in reaction, and need some energy in the bank to not get behind the problem. With a low inertia rotor head, delay can be fatal. Know your aircraft.
2. FH1100 had a point a few pages back that I agree with: when flying somewhere, where possible plan to give yourself as much altitude to cruise at as you can. That is a form of energy that gives you choices that low altitude flying won't.
3. Your Nr is your life, until you get back to Mother Earth, so you have to control Nr, know how to control Nr (see energy management), fly with two hands, and stay ahead of your aircraft. That last point gets a severe test when a surprise loss of power compresses your time, energy, and decision timeline.
A few extra knots, or a few hundred extra feet may save your chili.
The point raised about low inertia heads (which are popular in design for a variety of reasons) and energy management of a low inertia head get me to three core points:
1. If you are flying somewhere at "best cruise" or "max conserve" airspeed, it would seem that one needs to ensure one's transit airspeed is some knots above best auto speed because anyone will have a slight delay in reaction, and need some energy in the bank to not get behind the problem. With a low inertia rotor head, delay can be fatal. Know your aircraft.
2. FH1100 had a point a few pages back that I agree with: when flying somewhere, where possible plan to give yourself as much altitude to cruise at as you can. That is a form of energy that gives you choices that low altitude flying won't.
3. Your Nr is your life, until you get back to Mother Earth, so you have to control Nr, know how to control Nr (see energy management), fly with two hands, and stay ahead of your aircraft. That last point gets a severe test when a surprise loss of power compresses your time, energy, and decision timeline.
A few extra knots, or a few hundred extra feet may save your chili.
It's 5 seconds for Army pilots apparently
AnFI, I don't seem to be able to find the hp gauge in the cockpit so is my VSI calibrated in hp, brake hp or shaft hp?
Of course you know that hp is derived from torque at various rpm so you will need to know the exact rpm of the engine at any moment to calculate the hp - that's a lot of extra stuff to think about when you are flying but I know how brilliant you are
For those not stuck in the Dark ages - one hp equals 0.76 Kw (that is a kilowatt an FI, the watt being the SI term for power) Or shall we just use the torque gauge that the nice man who made the helicopter gave us? (yes I know not every helicopter has a Tq meter but which RFM has limits based on hp????)
RotorIP - don't worry, he has got lots of stuff like this that he believes everyone should teach
Of course you know that hp is derived from torque at various rpm so you will need to know the exact rpm of the engine at any moment to calculate the hp - that's a lot of extra stuff to think about when you are flying but I know how brilliant you are
For those not stuck in the Dark ages - one hp equals 0.76 Kw (that is a kilowatt an FI, the watt being the SI term for power)
Or shall we just use the torque gauge that the nice man who made the helicopter gave us? (yes I know not every helicopter has a Tq meter but which RFM has limits based on hp????)RotorIP - don't worry, he has got lots of stuff like this that he believes everyone should teach
Too much knowledge can be a dangerous thing.
We increased the thru-put of a Saw Mill by reducing the number of choices the Head Sawyer had after the Log Optimizer did its scan of the Log. Thru-put went up....production went up...Grade went up....and most importantly....profitability and Crew Bonus went up!
I would suggest the same concept works in helicopter flying.....narrowing the options to those that are necessary and appropriate is the wiser path.
We increased the thru-put of a Saw Mill by reducing the number of choices the Head Sawyer had after the Log Optimizer did its scan of the Log. Thru-put went up....production went up...Grade went up....and most importantly....profitability and Crew Bonus went up!
I would suggest the same concept works in helicopter flying.....narrowing the options to those that are necessary and appropriate is the wiser path.
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Correction for RotorIP
I thought I was referring to the ~200kg rotor of the Glasgow crash aircraft, assuming it operates at ~200rpm. Its rotational energy should then have corresponded to ~3s of full power.
However, in post #995 (http://www.pprune.org/rotorheads/528...ml#post8197441), I'd overestimated the energy in the rotor (at 2MJ).
Trying again: Four 5-m-long 50-kg blades, give a moment of inertia of 4 x 1/3 x 25 x 50 (~1500) kg.m-squared). At 200rpm (~20 radians/s), the energy - 0.5 x 1500 x 400 J ~ 0.3MJ. With up to a MW of power available, that's indeed a very brief reserve. The airflow complicates things, and makes it different from a spinning object without air, but the energy stored in the rotors is substantially less than I'd assumed.
However, in post #995 (http://www.pprune.org/rotorheads/528...ml#post8197441), I'd overestimated the energy in the rotor (at 2MJ).
Trying again: Four 5-m-long 50-kg blades, give a moment of inertia of 4 x 1/3 x 25 x 50 (~1500) kg.m-squared). At 200rpm (~20 radians/s), the energy - 0.5 x 1500 x 400 J ~ 0.3MJ. With up to a MW of power available, that's indeed a very brief reserve. The airflow complicates things, and makes it different from a spinning object without air, but the energy stored in the rotors is substantially less than I'd assumed.
Last edited by awblain; 27th Dec 2013 at 17:05. Reason: Link to earlier numbers
I know I am a simpleton on these matters but so f--king what the Hp of the rotor is ! All you have to know is the bit that turns it whether it be a piston, turbine or a donkey stops what you need to do !
I can certainly vouch when Mr Lycoming threw his toys out the pram at 30 kts and 80 ft I didn't give a flying f--k for the hp on the rotor in fact I had never heard it spoken about so what does that tell you ? By the way I didn't hurt myself and only put a smile on a 300's rear cross beam ( Thank you Mr Hughes )
I can certainly vouch when Mr Lycoming threw his toys out the pram at 30 kts and 80 ft I didn't give a flying f--k for the hp on the rotor in fact I had never heard it spoken about so what does that tell you ? By the way I didn't hurt myself and only put a smile on a 300's rear cross beam ( Thank you Mr Hughes )
awblain - you might want to do your sums again as the RRPM won't be 200 - I'm not 135 qualified but I suspect it is in the high 300s at normal RRPM.
Whatever your maths tells you, there will be a very rapid decay in Nr if both engines fail in the high hover and the ONLY option is a rapid lowering of the collective lever - this will allow continued flight but only in a downward direction to the scene of the accident.
Whatever your maths tells you, there will be a very rapid decay in Nr if both engines fail in the high hover and the ONLY option is a rapid lowering of the collective lever - this will allow continued flight but only in a downward direction to the scene of the accident.
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Re Crab...
Agree. If the rrpm is twice as high as I stated, then there's about 4 times the energy, but it's still only a matter of seconds before that would be spent if the power stops and nothing else changes.
A safe return to earth certainly needs the engines' contribution to be replaced by gravity or exchanged with forward speed in short order.
A safe return to earth certainly needs the engines' contribution to be replaced by gravity or exchanged with forward speed in short order.
"Just a pilot"
Autogyros, autorotations...
Look up autogyro "buntovers", not direcly applicable, although they are in an established autorotaional state. Quote from here:
Popular Rotorcraft Association :: Gyroplane Stability
"Power Push-Over is just one form of what is also called a "bunt-over". These typically refer to the gyro pitching rapidly forward to inverted. This typically results from an unbalanced propeller thrustline that tends to rapidly rotate the gyro forward once the rotor looses significant lift and drag (thrust).
A "bunt-over" is typically considered to occur from any or all of several factors:
Pilot rapid forward cyclic stick motion causes reduced rotor lift and drag, allowing the rotor to slow, perhaps too much!
A strong wind down-gust disturbance which also "unloads" the rotor - reduces rotor lift and drag.
Upon severe and/or extended loss of lift, the rotor slows below its ability to autorotate and support the gyro's weight.
An unbalanced propeller thrustline offset pitches the airframe rapidly nose-down upon loss of rotor lift and drag.
The unstable airframe, pitching rapidly nose-down results in moving the rotor thrustline forward, relative to the CG, causing further nose-down pitching in reaction to reducing or negative rotor thrust."
Popular Rotorcraft Association :: Gyroplane Stability
"Power Push-Over is just one form of what is also called a "bunt-over". These typically refer to the gyro pitching rapidly forward to inverted. This typically results from an unbalanced propeller thrustline that tends to rapidly rotate the gyro forward once the rotor looses significant lift and drag (thrust).
A "bunt-over" is typically considered to occur from any or all of several factors:
Pilot rapid forward cyclic stick motion causes reduced rotor lift and drag, allowing the rotor to slow, perhaps too much!
A strong wind down-gust disturbance which also "unloads" the rotor - reduces rotor lift and drag.
Upon severe and/or extended loss of lift, the rotor slows below its ability to autorotate and support the gyro's weight.
An unbalanced propeller thrustline offset pitches the airframe rapidly nose-down upon loss of rotor lift and drag.
The unstable airframe, pitching rapidly nose-down results in moving the rotor thrustline forward, relative to the CG, causing further nose-down pitching in reaction to reducing or negative rotor thrust."
design idea: prevent unrecoverable rotorspeed
Maybe a stupid questions, may be already answered (pls. link to it) but why do manufacturers not add a springloaded "minus section" to the bottom end of pitch level travel?
As currently "pitch fully down" is ~ 0° blade angle, we can stall blades due too low an RRPM, and lacking any negative angle we - even theoretically - cannot recover from that situation w/o engine power.
I'd like to suggest to provide us with - from the "current bottom" of pitch lever travel - an additional 1" travel, for which one has to overcome a strong spring, where no friction would hold the lever, which turns blade angle to say -20° with respect rotorplane.
That way one could (at FL100) let the RRPM deliberately reach today "unrecoverably low values", when switch engine to idle.
THEN one could bring the (stalled) blades to -20°, even while falling w/o laminar flow over any section of the blades they'd windmill, thereby increasing RRPM, till the combination for say ~5000ft/min "freefall" and the increasingly regained RRPM create an angle of attack that produces laminar flow again. At that point one should bring the pitch lever back into normal range and could commence a std. autorotational landing.
That helicopter would be autorotational fool proved, lacking "unrecoverable rotor speed".
I'm pretty sure there is some good reason why we don't get the negative blade angles the RC-Helis do. (They have rigid heads with +/- 15° balde angle linear on the RC stick, normal flying happens on upper half of pitch stick travel, upside down fly is down using the lower hlaf of pitch stick travel)
Maybe stuffing 20° blade angle in a rel. small section of pitch lever tavel is mechanically tricky, but certainly not impossible, methinks.
comments anyone?
As currently "pitch fully down" is ~ 0° blade angle, we can stall blades due too low an RRPM, and lacking any negative angle we - even theoretically - cannot recover from that situation w/o engine power.
I'd like to suggest to provide us with - from the "current bottom" of pitch lever travel - an additional 1" travel, for which one has to overcome a strong spring, where no friction would hold the lever, which turns blade angle to say -20° with respect rotorplane.
- from 0 up to full pitch blades would be at 0° till 5-8ish°, as we are all used to.
- from 0 down to the new "hard stop" we'd get 0° to -20°
That way one could (at FL100) let the RRPM deliberately reach today "unrecoverably low values", when switch engine to idle.
THEN one could bring the (stalled) blades to -20°, even while falling w/o laminar flow over any section of the blades they'd windmill, thereby increasing RRPM, till the combination for say ~5000ft/min "freefall" and the increasingly regained RRPM create an angle of attack that produces laminar flow again. At that point one should bring the pitch lever back into normal range and could commence a std. autorotational landing.
That helicopter would be autorotational fool proved, lacking "unrecoverable rotor speed".
I'm pretty sure there is some good reason why we don't get the negative blade angles the RC-Helis do. (They have rigid heads with +/- 15° balde angle linear on the RC stick, normal flying happens on upper half of pitch stick travel, upside down fly is down using the lower hlaf of pitch stick travel)
Maybe stuffing 20° blade angle in a rel. small section of pitch lever tavel is mechanically tricky, but certainly not impossible, methinks.
comments anyone?
Reely, you mean as fitted to the Wasp and Naval Lynx..? Keeps the a/c nailed to a ship`s deck...
reely, one reason may be the potential for ground resonance. (Model dependent). The other is that control rigging adjustments, particularly seasonal adjustments for autorotational NR, might run crosswise with a sort of "negative pitch" default blade pitch on the head that you are proposing.
I'd need to do a bit more asking around, but I also think that a negative pitch provision like that might unload the head and lead to some undesirable blade performance ... a bit of guess there, some of our aerodymanically bright folks can probably expand on that.
As to the ground resonance:
Some decades ago, we were doing a post maintenance check flight. Bird had a fully articulated head, and wheels not skids. Helo was on the ground, flat pitch (collective on the bottom). My boss and I were observing the operation, and his eyes got big. He motioned frantically and gave the cut signal. Engines shut down. He told me: "Oleo struts compressed, shoud not be compressed at flat pitch. We have a flight control rigging problem." He made reference to a bird that had gotten into ground resonance due to a crap rigging of this sort some years prior.
He was right. Rigging problem. It had to be corrected before we were going to try and put that bird into the air.
Not sure how viable your suggestion is.
@ sycamore: do Wasp or Lynx run into ground resonance in that mode very often?
I'd need to do a bit more asking around, but I also think that a negative pitch provision like that might unload the head and lead to some undesirable blade performance ... a bit of guess there, some of our aerodymanically bright folks can probably expand on that.
As to the ground resonance:
Some decades ago, we were doing a post maintenance check flight. Bird had a fully articulated head, and wheels not skids. Helo was on the ground, flat pitch (collective on the bottom). My boss and I were observing the operation, and his eyes got big. He motioned frantically and gave the cut signal. Engines shut down. He told me: "Oleo struts compressed, shoud not be compressed at flat pitch. We have a flight control rigging problem." He made reference to a bird that had gotten into ground resonance due to a crap rigging of this sort some years prior.
He was right. Rigging problem. It had to be corrected before we were going to try and put that bird into the air.
Not sure how viable your suggestion is.
@ sycamore: do Wasp or Lynx run into ground resonance in that mode very often?
LW50, it`s over 40 yrs since I last flew both..officially,and never to a deck,but I`m sure someone will correct me,and add knowledge.
It also brings into asking the question about auto-revs setting after blade changes/tracking,and how often is that checked,as blade condition can deteriorate..
The other occasions that we used to adjust the basic/minimum pitch setting was doing icing(real)trials..no heated blades, and the possibility of having ice on the blades in the event of either engines failing(due ice damage/surge,etc),or a transmission failure,which did happen(oil filter came adrift), going to the ultra low pitch would hopefully keep one safe( and a lot of spiral descent for good measure)..We also wore parachutes...
It also brings into asking the question about auto-revs setting after blade changes/tracking,and how often is that checked,as blade condition can deteriorate..
The other occasions that we used to adjust the basic/minimum pitch setting was doing icing(real)trials..no heated blades, and the possibility of having ice on the blades in the event of either engines failing(due ice damage/surge,etc),or a transmission failure,which did happen(oil filter came adrift), going to the ultra low pitch would hopefully keep one safe( and a lot of spiral descent for good measure)..We also wore parachutes...