Entering autos: discussion split from Glasgow crash thread
.......
HC, the obvious answer was found by both EHI and Sikorsky with the Merlin and the Sea Stallion: deal with dual engine failure risks by adding a third engine. 
Simples. 
hillberg: henra made that point ages ago, in the original thread. That is what got some of this discussion about stalled rotor blades kicked off.
Thanks for your NASA/Army test info. Reaffirmation of "keep Nr in the green" if there needed to be any.
Simples. hillberg: henra made that point ages ago, in the original thread. That is what got some of this discussion about stalled rotor blades kicked off.
Thanks for your NASA/Army test info. Reaffirmation of "keep Nr in the green" if there needed to be any.
-ve G really?
Do you really not "get" that when you rapidly lower the collective in response to a complete loss of engine drive, without moving the cyclic, the g will fall to near zero or even below if you are in the cruise
Yes, with caveats. It varies by type due to the exact head geometry. It varies a lot according to speed, so at 100 kts not much effect, at 150 kts yes g will go negative. "Sustained"? - well not indefinitely, of course, but probably for long enough to allow Nr to decay to unrecoverable. Eventually g will settle at 1 when the heli reaches terminal velocity with the rotors stopped (height permitting)
OK thanks HC - yes "sustained" to mean beyond mere spikes off the back of harsh control movements if you like; but as you say its sustained enough for the Nr to decay more quickly than the re-establishment of +ve G?
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Negative g?!
It's picky and pedantic, but I assume here the "negative g" being bandied around means g<1. If it's g<0 then that's one hell of a rotor. Unless you can accelerate upwards at 9.8m/s/s under power, it seems unlikely that you can beat a cannonball to the ground just by playing with the settings of the blades without power.
I also think there's also an issue with the idea of "wind going up through the rotor". Unless the flow slows substantially during that trip, leading to a lot of drag, that change in wind direction would help to push the aircraft to the ground.
The inrushing wind is deflected down in powered flight, pushing the aircraft up.
The same holds for autorotation, but the power for the deflection then comes from gravity rather than burning kerosene.
I also think there's also an issue with the idea of "wind going up through the rotor". Unless the flow slows substantially during that trip, leading to a lot of drag, that change in wind direction would help to push the aircraft to the ground.
The inrushing wind is deflected down in powered flight, pushing the aircraft up.
The same holds for autorotation, but the power for the deflection then comes from gravity rather than burning kerosene.
Negative g ???
Let's see, rotor blades detach, initial g around zero until vertical speed builds up towards terminal. So to get zero g requires no power at all.
Or to out it another way, with rotors suddenly producing no lift at all, g will initially be zero, no effort required.
In my personal experience rapid lowering of the lever at fast cruise can take the g a little below zero - things float up from their resting place in the cockpit - though certainly not as much as -1g. Not hard to see how, with the blades at flat pitch and airflow coming down from above due to the tilt-forward of the disc and attitude pitching down causing a negative angle of attack. What's not to understand?
Edited to say that if you have only flown helicopters that cruise around 100 kts or so, you probably don't notice it much, but at 150kts+ you certainly do.
Or to out it another way, with rotors suddenly producing no lift at all, g will initially be zero, no effort required.
In my personal experience rapid lowering of the lever at fast cruise can take the g a little below zero - things float up from their resting place in the cockpit - though certainly not as much as -1g. Not hard to see how, with the blades at flat pitch and airflow coming down from above due to the tilt-forward of the disc and attitude pitching down causing a negative angle of attack. What's not to understand?
Edited to say that if you have only flown helicopters that cruise around 100 kts or so, you probably don't notice it much, but at 150kts+ you certainly do.
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
so Negative
I'm pretty sure he means negative as in g<zero - like free fall plus some additional negative thrust from relative wind from above the disk (at high airspeed with nose down attitude)
same problem happens when peeps talk about negative pressure ... meaning negative relative pressure. 1/2g is not -1/2g
Cyclic would need to come aft as lever is lowered just to maintain the same attitude - but it's obviously better to bias it towards nose up - so cyclic needs to come back - it's often useful to increase aircraft pitch attitude even at low lower speeds...
same problem happens when peeps talk about negative pressure ... meaning negative relative pressure. 1/2g is not -1/2g
Cyclic would need to come aft as lever is lowered just to maintain the same attitude - but it's obviously better to bias it towards nose up - so cyclic needs to come back - it's often useful to increase aircraft pitch attitude even at low lower speeds...
Edited to say that if you have only flown helicopters that cruise around 100 kts or so, you probably don't notice it much, but at 150kts+ you certainly do.
Yes, I've no experience of twin rotor and no idea what if any pitch attitude change you get with a rapid lowering of the collective. I guess it will depend on the front to back collective control mixing?
DB: Good call and well done for coming out 
Don't you feel better now?
The CIA will now go away and stop bullying you.
Peter (and his cronies nubian and fn1100). Here is a a little quiz for you:
1. During your departure whilst flying through 150' and 50kts, the donk stops. Do you (a) dump the collective first or (b) select aft cyclic first to contain Nr?
2. In the hover the donk stops. Do you (a) dump the collective first or (b) select aft cyclic to contain Nr?
3. You are doing aerial work and operating inside the H/V curve. The donk stops, do you (a) dump the collective first or (b) select aft cyclic first to minimse Nr decay?
4. You are a police helicopter orbiting @ 30kts over the city at 500'. As you pass through the downwind heading, one of the donks stops (or if in the USA: the only donk stops). Do you (a) lower the collective or (b) select aft cyclic to conserve Nr?
5. During a helipad departure (backwards) as you are passing up and backwards through 30 feet, the donk stops. Do you (a) select collective down or (b) select aft cyclic to conserve Nr.
Now if the aft cyclic brigade chooses (a) in any of the above, it blows your argument out of the water.
Do me a big big favour would you?
Qualify your statement to read thus:
IF in the cruise or at significant forward speed, should the Nr decay for any reason whatsoever, the pilot can select down collective and/or aft cyclic as part of the immediate leading actions.
That way Peter it leaves absolutely no ambiguity whatsoever to your american pilots as to what to do during a decaying Nr scenario. The ab initio's and naive ones amongst your fraternity cannot afford to be misled at their embryonic stage of flying training. It seems that UK pilots and the FAA are already up to speed with this recovery process.
And finally, to clear up one more ambiguity; provided the Nr remains in the green, it will never decay any further of its own volition. Thus if one was to select down collective ONLY during entry to an EOL and that selection arrested the decaying Nr such that it remained inside the green (or above min Nr)...IT WOULD NOT CONTINUE TO DECAY. And that is because you would be in autorotation.
For the hard of hearing: One doesnt have to 'flare' by selecting aft cyclic to "get air up under the disc" (
). Lowering the collective automaticlly induces air below, to go through the disc...is that too difficult for some newbies to understand.
Did anyone understand Hilberg's post
Don't you feel better now?The CIA will now go away and stop bullying you.
Peter (and his cronies nubian and fn1100). Here is a a little quiz for you:
1. During your departure whilst flying through 150' and 50kts, the donk stops. Do you (a) dump the collective first or (b) select aft cyclic first to contain Nr?
2. In the hover the donk stops. Do you (a) dump the collective first or (b) select aft cyclic to contain Nr?
3. You are doing aerial work and operating inside the H/V curve. The donk stops, do you (a) dump the collective first or (b) select aft cyclic first to minimse Nr decay?
4. You are a police helicopter orbiting @ 30kts over the city at 500'. As you pass through the downwind heading, one of the donks stops (or if in the USA: the only donk stops). Do you (a) lower the collective or (b) select aft cyclic to conserve Nr?
5. During a helipad departure (backwards) as you are passing up and backwards through 30 feet, the donk stops. Do you (a) select collective down or (b) select aft cyclic to conserve Nr.
Now if the aft cyclic brigade chooses (a) in any of the above, it blows your argument out of the water.
Do me a big big favour would you?
Qualify your statement to read thus:
IF in the cruise or at significant forward speed, should the Nr decay for any reason whatsoever, the pilot can select down collective and/or aft cyclic as part of the immediate leading actions.
That way Peter it leaves absolutely no ambiguity whatsoever to your american pilots as to what to do during a decaying Nr scenario. The ab initio's and naive ones amongst your fraternity cannot afford to be misled at their embryonic stage of flying training. It seems that UK pilots and the FAA are already up to speed with this recovery process.
And finally, to clear up one more ambiguity; provided the Nr remains in the green, it will never decay any further of its own volition. Thus if one was to select down collective ONLY during entry to an EOL and that selection arrested the decaying Nr such that it remained inside the green (or above min Nr)...IT WOULD NOT CONTINUE TO DECAY. And that is because you would be in autorotation.
For the hard of hearing: One doesnt have to 'flare' by selecting aft cyclic to "get air up under the disc" (
). Lowering the collective automaticlly induces air below, to go through the disc...is that too difficult for some newbies to understand.Did anyone understand Hilberg's post
Thread Starter
Join Date: Dec 2013
Location: Southern California
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Hello TOTD...You said
"With respect, that's not considered to be correct in UK (mil) teaching - which I believe still includes a demonstration of Nr decay caused by rolling the (only) throttle to idle in the cruise, and doing nothing with the controls. The recovery from the ensuing rapid Nr decay was always to lower the lever to prevent further decay, then flare to restore the Nr. Perhaps someone currently active at Shawbury can confirm?"
Lowering the lever does NOT by itself prevent further decay. Never. Repeating myself again, nothing but applying aft cyclic IN TIME will prevent further decay. The procedure above should be reversed: Flare first if not simultaneously with lowering the lever!
Thank you, TOTD. Pete Gillies
"With respect, that's not considered to be correct in UK (mil) teaching - which I believe still includes a demonstration of Nr decay caused by rolling the (only) throttle to idle in the cruise, and doing nothing with the controls. The recovery from the ensuing rapid Nr decay was always to lower the lever to prevent further decay, then flare to restore the Nr. Perhaps someone currently active at Shawbury can confirm?"
Lowering the lever does NOT by itself prevent further decay. Never. Repeating myself again, nothing but applying aft cyclic IN TIME will prevent further decay. The procedure above should be reversed: Flare first if not simultaneously with lowering the lever!
Thank you, TOTD. Pete Gillies
I liken it to your point about moving the cyclic back being inappropriate under some circumstances - you are right of course, and no-one is disagreeing. But to say that collective down will always induce an autorotative flow is equally fallacious.
Peter I beg you to stop spreading false statements on this web site...please!
I believe you are an Instructor - yes? I was one for many mnay years too. Several posts back someone asked how many EOL's I had actually done in a single engined helo. I estimated conservatively that it was around 2500 EOL's and they ranged from 50'/120kts to 12000'/0kts to downwind @800'. Now many of those entry into EOL manouevres required me to either lower the collective first AND flare simultaneously or just flare first and then adjust with collective.
BUT please believe this Peter for I am alive and kicking (much to the consternation of many on here
) to prove it, but all I ever ever did on several hundred+ EOL's was simply lower the collective and NOTHING ELSE. In the UK (and because I currently teach 5 other countries' pilots) several other countries, the standard response to MOST entries is LOWER THE COLLECTIVE TO RETAIN Nr. It is most definitely not, no never ever will be: ALWAYS SELECT AFT CYCLIC FIRST.
Please qualify your claims before you confuse new pilots on this site
I believe you are an Instructor - yes? I was one for many mnay years too. Several posts back someone asked how many EOL's I had actually done in a single engined helo. I estimated conservatively that it was around 2500 EOL's and they ranged from 50'/120kts to 12000'/0kts to downwind @800'. Now many of those entry into EOL manouevres required me to either lower the collective first AND flare simultaneously or just flare first and then adjust with collective.
BUT please believe this Peter for I am alive and kicking (much to the consternation of many on here
) to prove it, but all I ever ever did on several hundred+ EOL's was simply lower the collective and NOTHING ELSE. In the UK (and because I currently teach 5 other countries' pilots) several other countries, the standard response to MOST entries is LOWER THE COLLECTIVE TO RETAIN Nr. It is most definitely not, no never ever will be: ALWAYS SELECT AFT CYCLIC FIRST.Please qualify your claims before you confuse new pilots on this site
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
0g in free fall, little bit of negative g moves things.
HC, I agree: detach the rotors, and you will briefly free fall: there will be weightlessness, which then rapidly (~5s later) returns to normal conditions at the terminal velocity (c.f. AF447).
However, you're not blowing the blades off to experience this, you're pitching them down.
If your clipboard drifts up off a flat surface in the absence of any lateral acceleration to make it bounce off a projecting lip, I agree: that's (briefly) real negative g, with g~-0.0X, where X~1-5. Things "drift" at 0.0Xg; they "fly around" at -0.Xg, and at -Xg they hurt you.
I find this a very interesting discussion - there seems possibly to be a transatlantic polarization developing about old Isaac's ideas, and how air interacts with whirling blades, and that's definitely not based in physical reality. If it's not all just a mix of semantics, cultural difference, sloppy description and misunderstandings, then getting to the bottom of these differences will surely lead to greater awareness of the energetic perils of rotary wing flight, and make everyone's life safer.
However, you're not blowing the blades off to experience this, you're pitching them down.
If your clipboard drifts up off a flat surface in the absence of any lateral acceleration to make it bounce off a projecting lip, I agree: that's (briefly) real negative g, with g~-0.0X, where X~1-5. Things "drift" at 0.0Xg; they "fly around" at -0.Xg, and at -Xg they hurt you.
I find this a very interesting discussion - there seems possibly to be a transatlantic polarization developing about old Isaac's ideas, and how air interacts with whirling blades, and that's definitely not based in physical reality. If it's not all just a mix of semantics, cultural difference, sloppy description and misunderstandings, then getting to the bottom of these differences will surely lead to greater awareness of the energetic perils of rotary wing flight, and make everyone's life safer.
Thread Starter
Join Date: Dec 2013
Location: Southern California
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Hello SASless...
Hey, I'll be glad to answer your questions, but since a rock knows more than I do about writing to this forum, please help me. Tell me how to highlight your sentences or paragraphs and then to write an answer or comment immediately after them. Think I'm kidding? I'm not. Thanks, SASless - - Pete
Hey, I'll be glad to answer your questions, but since a rock knows more than I do about writing to this forum, please help me. Tell me how to highlight your sentences or paragraphs and then to write an answer or comment immediately after them. Think I'm kidding? I'm not. Thanks, SASless - - Pete
Hello SASless...
Hey, I'll be glad to answer your questions, but since a rock knows more than I do about writing to this forum, please help me. Tell me how to highlight your sentences or paragraphs and then to write an answer or comment immediately after them. Think I'm kidding? I'm not. Thanks, SASless - - Pete
Hey, I'll be glad to answer your questions, but since a rock knows more than I do about writing to this forum, please help me. Tell me how to highlight your sentences or paragraphs and then to write an answer or comment immediately after them. Think I'm kidding? I'm not. Thanks, SASless - - Pete
HC, I agree: detach the rotors, and you will briefly free fall: there will be weightlessness, which then rapidly (~5s later) returns to normal conditions at the terminal velocity (c.f. AF447).
However, you're not blowing the blades off to experience this, you're pitching them down.
If your clipboard drifts up off a flat surface in the absence of any lateral acceleration to make it bounce off a projecting lip, I agree: that's (briefly) real negative g, with g~-0.0X, where X~1-5. Things "drift" at 0.0Xg; they "fly around" at -0.Xg, and at -Xg they hurt you.
I find this a very interesting discussion - there seems possibly to be a transatlantic polarization developing about old Isaac's ideas, and how air interacts with whirling blades, and that's definitely not based in physical reality. If it's not all just a mix of semantics, cultural difference, sloppy description and misunderstandings, then getting to the bottom of these differences will surely lead to greater awareness of the energetic perils of rotary wing flight, and make everyone's life safer.
However, you're not blowing the blades off to experience this, you're pitching them down.
If your clipboard drifts up off a flat surface in the absence of any lateral acceleration to make it bounce off a projecting lip, I agree: that's (briefly) real negative g, with g~-0.0X, where X~1-5. Things "drift" at 0.0Xg; they "fly around" at -0.Xg, and at -Xg they hurt you.
I find this a very interesting discussion - there seems possibly to be a transatlantic polarization developing about old Isaac's ideas, and how air interacts with whirling blades, and that's definitely not based in physical reality. If it's not all just a mix of semantics, cultural difference, sloppy description and misunderstandings, then getting to the bottom of these differences will surely lead to greater awareness of the energetic perils of rotary wing flight, and make everyone's life safer.
Typical British method.....complicated.
I highlight the post contents....click copy....go to my post....hit paste....edit as i wish.....highlight the text....hit the Quote thingy on the tool bar....done.
More steps probably....but far easier for a Dinosaur like me to figure out.
I highlight the post contents....click copy....go to my post....hit paste....edit as i wish.....highlight the text....hit the Quote thingy on the tool bar....done.
More steps probably....but far easier for a Dinosaur like me to figure out.