Increased takeoff performance downwind on Bell 212's
Thread Starter
Increased takeoff performance downwind on Bell 212's
At lunch a few minutes ago....a very qualified 212 pilot, with lots of mountain and sling time in the Northwest part of the USA....suggested that a Bell 212 performs better on a downwind takeoff than into wind. The suggestion that the downwash from the rotor system misses the synch elevator as a result....and a bit of aft cyclic from a stationary hover actually results in a vertical climb in situations where the aircraft will not ascend when facing into the same wind.
Anyone else experience this or have an input that might be persuasive? This technique definitely is one of maximum finesse...thus the ham handed of us might not be qualified to expound upon the merits of the issue. Makes for an interesting proposition....kinda follows up on a previous thread where Nick Lappos noted the helicopter does not know it is in or out of wind....and the power for takeoff in either case is the same....
Anyone else experience this or have an input that might be persuasive? This technique definitely is one of maximum finesse...thus the ham handed of us might not be qualified to expound upon the merits of the issue. Makes for an interesting proposition....kinda follows up on a previous thread where Nick Lappos noted the helicopter does not know it is in or out of wind....and the power for takeoff in either case is the same....
This is not unique to the 212. The difference is minimal, and is often offset when long lining by having to get turned around for departure anyway.
Much of the gain realized is in increased stability. As we know, the 212 doesn't like the pilot stirring the stick, and the most lift is achieved when the cyclic is poured in cement. The 212 (especially the VFR version) can be a handful during long line operations with an aft c/g and a slight (5 - 10 kt) wind on the nose. The downwash can start talking to the back end, and an unstable rolling moment can be created. In this case I would often turn the tail into wind for stability, especially when doing precision work. Less cyclic movement would result in better lift.
You're right though, it is a technique that requires some finesse.
Much of the gain realized is in increased stability. As we know, the 212 doesn't like the pilot stirring the stick, and the most lift is achieved when the cyclic is poured in cement. The 212 (especially the VFR version) can be a handful during long line operations with an aft c/g and a slight (5 - 10 kt) wind on the nose. The downwash can start talking to the back end, and an unstable rolling moment can be created. In this case I would often turn the tail into wind for stability, especially when doing precision work. Less cyclic movement would result in better lift.
You're right though, it is a technique that requires some finesse.
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I fly 205's so it must be about the same technique. I shall have to try that one next time I'm out. I always had the feeling that they don't like tailwinds at all especially in ground effect with a light load and lots of fuel, so I try to avoid them rather than stuffing the tail in.
Is it specific to slinging and OGE?
Is it specific to slinging and OGE?
It's more prevalent in an OGE hover, as in most machines.
Actually, the 205 and 212 have different airflow patterns over the back end, and I agree the 205 doesn't seem to enjoy being downwind as much.
The only high hover work I've ever done with a 205 is rappelling, and I've never had occasion to do that downwind, so I can't comment on how the technique works with that machine.
Actually, the 205 and 212 have different airflow patterns over the back end, and I agree the 205 doesn't seem to enjoy being downwind as much.
The only high hover work I've ever done with a 205 is rappelling, and I've never had occasion to do that downwind, so I can't comment on how the technique works with that machine.
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I can support part of that technique, SAS. The bit of aft cyclic from the stationary hover will result in a vertical climb (sometimes a very impressive climb). However, rather than perform the entire routine downwind, I quarter the aircraft into the wind to help unload the tail rotor a bit. For me (personal preference only), this works better than twisting the tail into the wind (especially when flying lots of turns). Since my approach is flown this way it’s a natural termination to a stabilized hover – hook up the load – pull in the power – let the nose come up slightly (the bit of aft cyclic) – establish a respectable vertical climb – obstacles clear – a slight drop in the nose and your flying away. A walk in the park. And, as CTD states, it’s much better than having to dance with the silly thing all day.
Now, I’m not a Norman Einstein, so I’ll leave it to someone smarter than I to come up with the explanation as to why. I just happened blunder onto the technique a couple decades back and have been happy with it since.
Now, I’m not a Norman Einstein, so I’ll leave it to someone smarter than I to come up with the explanation as to why. I just happened blunder onto the technique a couple decades back and have been happy with it since.
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This gets worse by the minute!
The helicopter does not takeoff "downwind" in this procedure.
The takeoff is initiated from a hover with a tailwind into wind i.e backwards. After all there is no such thing as a "downwind hover", it is just a poor execution of the english language.
The Bell mediums are more stable in a tailwind hover for a multitude of reasons. Think about all the connotations of where the wake from the MR is going.
As you increase the "tailwind component" the sync elevator will reduce the vertical fuselage drag component. Think Rutan aeroplane canard to point you in the right direction. This is only effective up to a certain point where it can get ugly. Have a little think about it.
Too long now but I think there may even be a little fine print that gets missed in the RFM about "rearward flight".
The helicopter does not takeoff "downwind" in this procedure.
The takeoff is initiated from a hover with a tailwind into wind i.e backwards. After all there is no such thing as a "downwind hover", it is just a poor execution of the english language.
The Bell mediums are more stable in a tailwind hover for a multitude of reasons. Think about all the connotations of where the wake from the MR is going.
As you increase the "tailwind component" the sync elevator will reduce the vertical fuselage drag component. Think Rutan aeroplane canard to point you in the right direction. This is only effective up to a certain point where it can get ugly. Have a little think about it.
Too long now but I think there may even be a little fine print that gets missed in the RFM about "rearward flight".
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I don't have a lot of 212 experience, but I do know that a 412 hates a crosswind more than a tailwind. I've come off tankers with a 90 degree crosswind, pulling 100% torque, & barely climbing. As soon as I turn into the wind, it literally jumps into the air. I've also had to come up with a tailwind, after the ship had turned while I was on the deck. It's not nearly as bad as a crosswind, at least in a 412. The S76 doesn't seem to care as much.
Mr. Bicker,
Any take-off or hover with the tail facing the wind, is a downwind take-off or hover. Every single pilot, firefighter or sailor on the planet will understand what you're talking about. If you want to nit-pick, then maybe 'take-off with a tailwind component' is technically a more accurate description, and if I were writing a flight manual (which I used to do), then that's what I would use. I wouldn't use it in conversation, not even with 10 of my favorite FTEs and Chuck Yeager, unless I wanted to sound self-righteous.
"All the connotations of where the wake from the MR is going" were addressed in my first post above.
I'd also be interested in knowing what vertical drag issues Rutan had to cope with in an airplane.
Any take-off or hover with the tail facing the wind, is a downwind take-off or hover. Every single pilot, firefighter or sailor on the planet will understand what you're talking about. If you want to nit-pick, then maybe 'take-off with a tailwind component' is technically a more accurate description, and if I were writing a flight manual (which I used to do), then that's what I would use. I wouldn't use it in conversation, not even with 10 of my favorite FTEs and Chuck Yeager, unless I wanted to sound self-righteous.
"All the connotations of where the wake from the MR is going" were addressed in my first post above.
I'd also be interested in knowing what vertical drag issues Rutan had to cope with in an airplane.
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CTD,
Gotta love your righteousness as well - would appear to protect the innocent (read stupid).
Being a) a pilot, with some experience b) a sailor, only one circumnavigation so far c) a firefighter, about 3000 hours of it with 900 of that in Bell 205/212 maybe I do understand what you are trying to say. Have also met some FTE's, FTP's and Mr Yeager twice and also Mr Hoover a few times.
The simple fact is this procedure is not a downwind takeoff. The procedure is a takeoff into wind tail rotor first i.e backwards. Not a takeoff "downwind".
You would appear to be friendly with a few FTE's. Ask about the vertical components in a "Rutan" type aircraft versus a "conventional" one. Now tell me there is no vertical drag component from the airflow from the rotor around the tailboom, fuselage and more importantly the sync elevator which is in the opposite direction to the lift component. When you fly forward in these machines the elevator component is opposite to the lift. When you fly backwards due to the way it is rigged on a Bell 205/212 the sync elevator surface provides lift. This is where the free ride comes from.
Tell me which flight manuals you wrote - maybe I could read them in a new light.
Gotta love your righteousness as well - would appear to protect the innocent (read stupid).
Being a) a pilot, with some experience b) a sailor, only one circumnavigation so far c) a firefighter, about 3000 hours of it with 900 of that in Bell 205/212 maybe I do understand what you are trying to say. Have also met some FTE's, FTP's and Mr Yeager twice and also Mr Hoover a few times.
The simple fact is this procedure is not a downwind takeoff. The procedure is a takeoff into wind tail rotor first i.e backwards. Not a takeoff "downwind".
You would appear to be friendly with a few FTE's. Ask about the vertical components in a "Rutan" type aircraft versus a "conventional" one. Now tell me there is no vertical drag component from the airflow from the rotor around the tailboom, fuselage and more importantly the sync elevator which is in the opposite direction to the lift component. When you fly forward in these machines the elevator component is opposite to the lift. When you fly backwards due to the way it is rigged on a Bell 205/212 the sync elevator surface provides lift. This is where the free ride comes from.
Tell me which flight manuals you wrote - maybe I could read them in a new light.
Ahhhh, there's the rub, we're talking about two different t/o profiles, albeit with different levels of condescension and rudeness. Nice to be anonymous huh? You seem to have some good things to say, why don’t you leave the attitude home and say it? Starting your post with “This gets worse by the minute!” is not a good beginning.
In your example, you are 100% correct. When SASless said downwind t/o I took it to mean lifting off with tail to wind, and continuing forward with the wind. Not backing up and turning (which makes more sense).
At these speeds (5-10kts), any lift, positive or negative, created by the elevator is negligible. It’s basically hanging there in the way.
During my time on the dark side, I had a hand in several RFMs, amendments and a couple of maintenance manuals. To specify would merely offer you the opportunity to say something clever like “That explains a lot”.
Hope you're feeling better today.
In your example, you are 100% correct. When SASless said downwind t/o I took it to mean lifting off with tail to wind, and continuing forward with the wind. Not backing up and turning (which makes more sense).
At these speeds (5-10kts), any lift, positive or negative, created by the elevator is negligible. It’s basically hanging there in the way.
During my time on the dark side, I had a hand in several RFMs, amendments and a couple of maintenance manuals. To specify would merely offer you the opportunity to say something clever like “That explains a lot”.
Hope you're feeling better today.
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Monsieur le CTD, 
hey I was wondering about your comment about the airflow being different around the 205 and 212 tails. Aside from the engine cowlings being different (I suppose that might change the flow), I can't see any difference betweeen the 2. Our 205's have 212 blades, and t/r's, only difference is that our 205's have the strake kits installed (I know that will make a huge difference). I guess my question really is: without the strakes, how is the airflow different ??
BTW, I noticed a difference when we added the strakes, very nice !!!
Cheers
Randy_G
hey I was wondering about your comment about the airflow being different around the 205 and 212 tails. Aside from the engine cowlings being different (I suppose that might change the flow), I can't see any difference betweeen the 2. Our 205's have 212 blades, and t/r's, only difference is that our 205's have the strake kits installed (I know that will make a huge difference). I guess my question really is: without the strakes, how is the airflow different ??BTW, I noticed a difference when we added the strakes, very nice !!!
Cheers
Randy_G
Randy,
There are several factors.
-Much higher exhaust volume and velocities on the 212.
-The cowling area is HUGE compared to a 205. You have the elephant ears, oil coolers, two exhaust stacks, etc. This causes more disruption than you'd think. During the development of the 427, small adjustments in cowling length and exhaust angle would produce completely different rides/vibration levels/stability at different speeds.
-Symmetrical 205 series blades (if installed), produce significantly different flow of air across the boom (The 412 is different again, which is why the mast cowling extends so high - to condition the air over the boom and decrease 4/rev. Interesting side note about the 412 is that if the elevators are out of rig, the 4/rev increases.
Here's an example of how much impact the change in loading may have: The 412, 212, 205B and some A1s use the same t/r blade. One would think that the 412EP, with 11,900 lb gross weight and oooodles more power would be more stressful on the tail rotor, but there is a configuration of 205 in which the t/r blade life is halved because of excessive loading. Don't ask which one because it's been too long and I don't remember
Wish I had invented the strake
There are several factors.
-Much higher exhaust volume and velocities on the 212.
-The cowling area is HUGE compared to a 205. You have the elephant ears, oil coolers, two exhaust stacks, etc. This causes more disruption than you'd think. During the development of the 427, small adjustments in cowling length and exhaust angle would produce completely different rides/vibration levels/stability at different speeds.
-Symmetrical 205 series blades (if installed), produce significantly different flow of air across the boom (The 412 is different again, which is why the mast cowling extends so high - to condition the air over the boom and decrease 4/rev. Interesting side note about the 412 is that if the elevators are out of rig, the 4/rev increases.
Here's an example of how much impact the change in loading may have: The 412, 212, 205B and some A1s use the same t/r blade. One would think that the 412EP, with 11,900 lb gross weight and oooodles more power would be more stressful on the tail rotor, but there is a configuration of 205 in which the t/r blade life is halved because of excessive loading. Don't ask which one because it's been too long and I don't remember
Wish I had invented the strake
Thread Starter
To clarify what my dear friend said....he described the aircraft being tail into wind....and a very, very, very small aft input of cyclic....not a rearwards takeoff per se...but just the very slightest aft input...which he suggests results in a vertical ascent......even when the aircraft will not ascend vertically while facing into the wind. Does this change any positions already set forth ?
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Thanks CTD, it's logical that the larger cowling area would make a difference, just never thought it would make all that much difference.
I noticed with the strake that in the hover the t/r is much more sensitive, and I didn't need as much left pedal as well.
Cheers
Randy_G
I noticed with the strake that in the hover the t/r is much more sensitive, and I didn't need as much left pedal as well.
Cheers
Randy_G
SASless, yes it will generally perform better 'tail into wind'. My comments about finesse were along this line...OK, you have lifted it vertically and are sitting in a high hover, tail into wind. Where do you go now? Do you carry on in the same direction, or let the torque turn you around and then blast off into wind? One must be careful with either for obvious reasons. But the short answer is yes.
Sorry for the misunderstanding, I went off on a bit of a tangent.
I remember doing some of the certification flying for the 407's 6000lb external gross weight upgrade from 5500lbs. I played with this nose-into-wind vs. tail-into-wind quite a bit, and she would always perform better in a hover with the tail feathers into wind. That is of course, a hover in relation to the ground, which is really flying backwards...here we go again...
Randy, I ve never flown a strake, but it makes sense that you'd require less left pedal. Not sure why they'd be more crisp, are you sure it's not you?? Is there a strake guy in the house??
Sorry for the misunderstanding, I went off on a bit of a tangent.
I remember doing some of the certification flying for the 407's 6000lb external gross weight upgrade from 5500lbs. I played with this nose-into-wind vs. tail-into-wind quite a bit, and she would always perform better in a hover with the tail feathers into wind. That is of course, a hover in relation to the ground, which is really flying backwards...here we go again...
Randy, I ve never flown a strake, but it makes sense that you'd require less left pedal. Not sure why they'd be more crisp, are you sure it's not you??
Is there a strake guy in the house??
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Rear cyclic
Hello Sassless
I KNOW that if you lift into the hover in a 212 at max auw with a fairly strong tail wind you can run out of rearward cyclic control as you try to get back into wind whatever direction you turn. No problem of course because you can land and tell them all to get off and carry on your turn. The other factor is of course the much higher engine temperatures with the wind blowing straight up the exhaust. My company recommends shutting down and starting up with the wind on the tail because of blade sailing but when it is over 30 knots it is a problem.
What is the right way to do it?
I KNOW that if you lift into the hover in a 212 at max auw with a fairly strong tail wind you can run out of rearward cyclic control as you try to get back into wind whatever direction you turn. No problem of course because you can land and tell them all to get off and carry on your turn. The other factor is of course the much higher engine temperatures with the wind blowing straight up the exhaust. My company recommends shutting down and starting up with the wind on the tail because of blade sailing but when it is over 30 knots it is a problem.
What is the right way to do it?
d/w t/o perf
As I`ve only flown Jetboxes recently,and a 212 about 30 years ago(once),otherwise vastly experienced,my suggestion would be to note Tq and pedal position facing into wind ,then 180 and note again.You may/will find that you are using less power as the t/r is in free air and has enhanced perf.,therefore less pwr.rqd., and the downwash does not "wet" so much of the fuselage,gaining a bit more performance.I don`t` know the" strakes" that have been mentioned,but if they are lengthwise along the top of the tail-boom,then we put them on S/king`s` in 1982 to improve yaw control in sideways flight/x-wind hovering and give a more linear pedal postion,and reduce control (pedal) reversals.They just "spoil" the airflow around the t/boom,particularly in right x-winds.
Great discussion.
I have also found the 212 to be good with a tailwind, but I have not really noticed a tendency to climb with a gentle bit of aft cyclic (too ham fisted perhaps??). I agree with CTD's comments re downwash patterns, and in particular, the difference with the 205. Despite a post above, I would never use this technique on a 205 unless fitted with the 212 rotor system, and I avoid out of wind ops as much as possible due to the probability of pounding the left pedal stop at higher AUW's.
I believe the downwind hover technique is good for the precision stuff, but you do get the quandry of when to turn back into wind for the departure - because I am a very strong believer of into wind ops when above translational. Perhaps when sufficiently clear of the obstacles, you could turn and go (power permitting). With such a magic tailrotor on the 212 system, I am happy to turn right and get a bit of extra verticle power as I lower the nose to translate - something I definately avoid on the 205(UH-1H) system in case I cannot stop the turn.
I have flown the 205 with and without strakes - and luckly enough, on the same day. To compare, the strake equipped machines tend to hover with a reduced left pedal, but does seem to be slightly more twitchy. This seems to give you a bit of extra TQ (although I couldn't quantify the amount, it appears to be only 1 to 2 PSI). They are now fitted to most, if not all, of the Oz Army UH-1H fleet - mainly as a result of seeing them fitted to the NZ Airforce Hueys in Bouganville several years ago. The Oz defence force test and development unit (ARDU) did test flights with them and concluded that they provide minimal extra TQ, had a quantifiable benefit by increasing left pedal margin (always a problem in the UH-1H), caused the pilot to have insufficient right pedal for engine failure situations and some left crosswind situations, and lastly, that a long term vibration analysis had not been conducted to determine any new fatigue issues on the tail boom. They were fitted despite this advice!!
I have heard a rumour that the Kiwi's were removing theirs - can anybody squash (or verify) this one?
John Bicker - the synch elevator will provide no such lift at the speeds we are talking about, and when it does produce lift, it produces a pitching moment to the aircraft rather than significantly contribute to the total lift moments (Note: significantly is the operative word here). But your point does raise an intresting question: when an aerofoil is moved backwards through the air, does it produce lift in the opposite direction as you surmise? I would have said "absolutely not", but maybe someone else can comment. I thought it would create heaps of drag and become very unstable.
Lastly Mr Bicker, I can see you are an experienced aviator by your own comments - but I have to agree with CTD here after your response here and on the "phase shift" thread - can you bring your experience and leave your attitude?
(BTW are you going to answer the questions on the phase shift thread, I would like to know what happened??)-
Edited for some crap spellung!! And again.
I have also found the 212 to be good with a tailwind, but I have not really noticed a tendency to climb with a gentle bit of aft cyclic (too ham fisted perhaps??). I agree with CTD's comments re downwash patterns, and in particular, the difference with the 205. Despite a post above, I would never use this technique on a 205 unless fitted with the 212 rotor system, and I avoid out of wind ops as much as possible due to the probability of pounding the left pedal stop at higher AUW's.
I believe the downwind hover technique is good for the precision stuff, but you do get the quandry of when to turn back into wind for the departure - because I am a very strong believer of into wind ops when above translational. Perhaps when sufficiently clear of the obstacles, you could turn and go (power permitting). With such a magic tailrotor on the 212 system, I am happy to turn right and get a bit of extra verticle power as I lower the nose to translate - something I definately avoid on the 205(UH-1H) system in case I cannot stop the turn.
I have flown the 205 with and without strakes - and luckly enough, on the same day. To compare, the strake equipped machines tend to hover with a reduced left pedal, but does seem to be slightly more twitchy. This seems to give you a bit of extra TQ (although I couldn't quantify the amount, it appears to be only 1 to 2 PSI). They are now fitted to most, if not all, of the Oz Army UH-1H fleet - mainly as a result of seeing them fitted to the NZ Airforce Hueys in Bouganville several years ago. The Oz defence force test and development unit (ARDU) did test flights with them and concluded that they provide minimal extra TQ, had a quantifiable benefit by increasing left pedal margin (always a problem in the UH-1H), caused the pilot to have insufficient right pedal for engine failure situations and some left crosswind situations, and lastly, that a long term vibration analysis had not been conducted to determine any new fatigue issues on the tail boom. They were fitted despite this advice!!
I have heard a rumour that the Kiwi's were removing theirs - can anybody squash (or verify) this one?
John Bicker - the synch elevator will provide no such lift at the speeds we are talking about, and when it does produce lift, it produces a pitching moment to the aircraft rather than significantly contribute to the total lift moments (Note: significantly is the operative word here). But your point does raise an intresting question: when an aerofoil is moved backwards through the air, does it produce lift in the opposite direction as you surmise? I would have said "absolutely not", but maybe someone else can comment. I thought it would create heaps of drag and become very unstable.
Lastly Mr Bicker, I can see you are an experienced aviator by your own comments - but I have to agree with CTD here after your response here and on the "phase shift" thread - can you bring your experience and leave your attitude?
(BTW are you going to answer the questions on the phase shift thread, I would like to know what happened??)-
Edited for some crap spellung!! And again.
Last edited by helmet fire; 31st Aug 2002 at 05:37.
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IMHO Helmetfire is right, in that the lift produced by the horizontal tail is very small, in either direction, at common hover/wind speeds. I calculate about 20 pounds of lift from an optimum angle of attack on 20 square feet at 20 mph. Peanuts.
The downwash on the tailcone and horizontal tail is not peanuts, however, and might increase hover performance by 100 to 200 pounds when the downwind hover flow pushes it away from the tail, as opposed to the head wind pushing it onto the tail. As an example, if you recall the Shadow test aircraft we built a few years back, where we grafted a new cockpit onto the nose of the S-76, that cockpit cost us 150 pounds of lost hover performance due to the vertical drag of the extra stuff.
One possible problem in generalizing the benefits of downwind hover from one type helicopter to any other is that the tail rotor wash can upset the main rotor flow if a tailwind pushes it into the main rotor, and this could cause a large increase in power required by the main rotor.
BTW, we call the situation where one hovers with one's ass into the wind as a downwind hover. I will have to tell the old test pilots at Sikorsky how very wrong they have been all these years. Just think, in 7500 hours of flight, the majority in engineering or experimental test, I have not yet got that right. John Bicker,. can you again clarify the situation?
The downwash on the tailcone and horizontal tail is not peanuts, however, and might increase hover performance by 100 to 200 pounds when the downwind hover flow pushes it away from the tail, as opposed to the head wind pushing it onto the tail. As an example, if you recall the Shadow test aircraft we built a few years back, where we grafted a new cockpit onto the nose of the S-76, that cockpit cost us 150 pounds of lost hover performance due to the vertical drag of the extra stuff.
One possible problem in generalizing the benefits of downwind hover from one type helicopter to any other is that the tail rotor wash can upset the main rotor flow if a tailwind pushes it into the main rotor, and this could cause a large increase in power required by the main rotor.
BTW, we call the situation where one hovers with one's ass into the wind as a downwind hover. I will have to tell the old test pilots at Sikorsky how very wrong they have been all these years. Just think, in 7500 hours of flight, the majority in engineering or experimental test, I have not yet got that right. John Bicker,. can you again clarify the situation?
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OK, attitude adjustment complied with. I have to live up to my surname that follows me around though.
Main Entry: 1bick·er
Pronunciation: 'bi-k&r
Function: noun
Etymology: Middle English biker
Date: 14th century
1 : petulant quarreling :
It has made this thread longer and brought a few out of the woodwork.
CTD: accept your comment. In your example, you are 100% correct. When SASless said downwind t/o I took it to mean lifting off with tail to wind, and continuing forward with the wind. Not backing up and turning (which makes more sense).
At these speeds (5-10kts), any lift, positive or negative, created by the elevator is negligible. It’s basically hanging there in the way.
If you got it wrong - what would the lurkers have made of it. Probably out there giving it a go right now. At 5-10kts airspeed I agree it would be negligible. You actually need a little more than this to see the benefit.
Nick Lappos: I calculate about 20 pounds of lift from an optimum angle of attack on 20 square feet at 20 mph. Peanuts.
The downwash on the tailcone and horizontal tail is not peanuts, however, and might increase hover performance by 100 to 200 pounds when the downwind hover flow pushes it away from the tail, as opposed to the head wind pushing it onto the tail.
I agree with your statement 20 square feet at 20 knots. This is of course if the elevator is out in clean air not living under the rotor wash. My assumptions are based on the fact that as you use aft cyclic and the aircraft is moving backwards (relatively) the sync elevator is now in a position to produce lift or put another way to have reduced vertical drag. It is now a canard and the more aft cyclic you use the more lift (or reduced drag) you get. As you get faster going backwards the pitch rate can become divergent or negative. Get a Bell 47 going backwards at 40 knots and have a play. This is placarded as "prohibited" by the way.
helmetfire: the synch elevator will provide no such lift at the speeds we are talking about, and when it does produce lift, it produces a pitching moment to the aircraft rather than significantly contribute to the total lift moments
So what is the "speed" of the elevator. Do you think that the wake from the main rotor is now in front of it? No such lift - agreed but what about less drag in the vertical plane? When it does produce lift it produces a pitching moment rather than significantly contribute to the total lift moment. Hmmm is this pitch moment not aligned with the lift vector? Take a look at a "Rutan" style aircraft where both horizontal surfaces produce lift as opposed to a "conventional" aircraft where the rear one doesn't. Maybe this is all a load of bollocks but the question in this post was why, I am just expounding a possibly flawed theory. SASless and CTD assumed that the takeoff was done in the downwind direction which was incorrect.
Nick Lappos: BTW, we call the situation where one hovers with one's ass into the wind as a downwind hover. I will have to tell the old test pilots at Sikorsky how very wrong they have been all these years. Just think, in 7500 hours of flight, the majority in engineering or experimental test, I have not yet got that right. John Bicker,. can you again clarify the situation?
(from Cambridge International Dictionary of English)
downwind
adverb, adjective_
in the direction in which the wind blows; with the wind behind_
A tail wind is a wind blowing from behind a vehicle._
Planes travelling from America to Europe usually have a tail wind rather than a head wind.
Shall we say that the difference is who is meant by we. Geographical? I like the one that refers to the vehicle. I also like to stay away from the downwind term in light of the fact as you have expounded here that the main rotor doesn't know which way the wind is blowing and in English english it refers to movement and here we are in the stationary hover. Remember the surname! For example another term that has a difference is the reference to "hover auto". I know what is mean't buy the term but where I come from it is called a power failure in the hover. Use of this terminology during a flight test with the authorities will result in failure. Geography again.
helmetfire
Will post in the "phase-shift" as to what happened.
Are we having fun yet?
Main Entry: 1bick·er
Pronunciation: 'bi-k&r
Function: noun
Etymology: Middle English biker
Date: 14th century
1 : petulant quarreling :
It has made this thread longer and brought a few out of the woodwork.
CTD: accept your comment. In your example, you are 100% correct. When SASless said downwind t/o I took it to mean lifting off with tail to wind, and continuing forward with the wind. Not backing up and turning (which makes more sense).
At these speeds (5-10kts), any lift, positive or negative, created by the elevator is negligible. It’s basically hanging there in the way.
If you got it wrong - what would the lurkers have made of it. Probably out there giving it a go right now. At 5-10kts airspeed I agree it would be negligible. You actually need a little more than this to see the benefit.
Nick Lappos: I calculate about 20 pounds of lift from an optimum angle of attack on 20 square feet at 20 mph. Peanuts.
The downwash on the tailcone and horizontal tail is not peanuts, however, and might increase hover performance by 100 to 200 pounds when the downwind hover flow pushes it away from the tail, as opposed to the head wind pushing it onto the tail.
I agree with your statement 20 square feet at 20 knots. This is of course if the elevator is out in clean air not living under the rotor wash. My assumptions are based on the fact that as you use aft cyclic and the aircraft is moving backwards (relatively) the sync elevator is now in a position to produce lift or put another way to have reduced vertical drag. It is now a canard and the more aft cyclic you use the more lift (or reduced drag) you get. As you get faster going backwards the pitch rate can become divergent or negative. Get a Bell 47 going backwards at 40 knots and have a play. This is placarded as "prohibited" by the way.
helmetfire: the synch elevator will provide no such lift at the speeds we are talking about, and when it does produce lift, it produces a pitching moment to the aircraft rather than significantly contribute to the total lift moments
So what is the "speed" of the elevator. Do you think that the wake from the main rotor is now in front of it? No such lift - agreed but what about less drag in the vertical plane? When it does produce lift it produces a pitching moment rather than significantly contribute to the total lift moment. Hmmm is this pitch moment not aligned with the lift vector? Take a look at a "Rutan" style aircraft where both horizontal surfaces produce lift as opposed to a "conventional" aircraft where the rear one doesn't. Maybe this is all a load of bollocks but the question in this post was why, I am just expounding a possibly flawed theory. SASless and CTD assumed that the takeoff was done in the downwind direction which was incorrect.
Nick Lappos: BTW, we call the situation where one hovers with one's ass into the wind as a downwind hover. I will have to tell the old test pilots at Sikorsky how very wrong they have been all these years. Just think, in 7500 hours of flight, the majority in engineering or experimental test, I have not yet got that right. John Bicker,. can you again clarify the situation?
(from Cambridge International Dictionary of English)
downwind
adverb, adjective_
in the direction in which the wind blows; with the wind behind_
A tail wind is a wind blowing from behind a vehicle._
Planes travelling from America to Europe usually have a tail wind rather than a head wind.
Shall we say that the difference is who is meant by we. Geographical? I like the one that refers to the vehicle. I also like to stay away from the downwind term in light of the fact as you have expounded here that the main rotor doesn't know which way the wind is blowing and in English english it refers to movement and here we are in the stationary hover. Remember the surname! For example another term that has a difference is the reference to "hover auto". I know what is mean't buy the term but where I come from it is called a power failure in the hover. Use of this terminology during a flight test with the authorities will result in failure. Geography again.
helmetfire
Will post in the "phase-shift" as to what happened.
Are we having fun yet?