R22 Corner
FOM, you have not answered Irlandes original question - if the engine was performing less well at higher OAT then no -one would be surprised, as you say it is thermodynamic boffin stuff.
BUT, the problem is that at ISA+10 in Irlandes original post the helicopter seemed to be performing too well ie it could hover at at a higher DA according to the graph than you would expect from doing the DA=PA+/- 120t calculation.
BUT, the problem is that at ISA+10 in Irlandes original post the helicopter seemed to be performing too well ie it could hover at at a higher DA according to the graph than you would expect from doing the DA=PA+/- 120t calculation.
Join Date: Jun 2002
Location: Dun Laoghaire
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
Crab,
if I understood things properly, Nick and FOM between them have already answered that question. On the left hand side of the curve (left of the knee) we have established that the throttle is wide open so that we are not capable of producing our 124hp. If we come from an ISA situation to an ISA +10 situation we have dramatically improved the operating conditions for the engine as the engine benefits much more from the lower pressure altitude than it suffers from the higher temperatures (thermodynamic boffin stuff). This increased engine performance has the effect of 'cushioning' the effects of a change in density altitude so that we pay a price of 50 feet for every degree of deviation from our standard day rather than 120 feet. As Nick points out it's not just a question of rotor performance, you also have to take the engine into account. This cushioning effect disappears to the right of the knee where engine performance becomes constant below the critical altitude producing a steady 124hp. Now we see that for every degree of deviation from our standard day there will be a loss/gain of 120 feet. It becomes purely an aerodynamic issue (more or less). At least, that's my understanding of the issue. Continued enlightenment always welcome however.
It's a nice day, and the sea looks inviting. I think I'll go for a swim!
Irlandés
if I understood things properly, Nick and FOM between them have already answered that question. On the left hand side of the curve (left of the knee) we have established that the throttle is wide open so that we are not capable of producing our 124hp. If we come from an ISA situation to an ISA +10 situation we have dramatically improved the operating conditions for the engine as the engine benefits much more from the lower pressure altitude than it suffers from the higher temperatures (thermodynamic boffin stuff). This increased engine performance has the effect of 'cushioning' the effects of a change in density altitude so that we pay a price of 50 feet for every degree of deviation from our standard day rather than 120 feet. As Nick points out it's not just a question of rotor performance, you also have to take the engine into account. This cushioning effect disappears to the right of the knee where engine performance becomes constant below the critical altitude producing a steady 124hp. Now we see that for every degree of deviation from our standard day there will be a loss/gain of 120 feet. It becomes purely an aerodynamic issue (more or less). At least, that's my understanding of the issue. Continued enlightenment always welcome however.
It's a nice day, and the sea looks inviting. I think I'll go for a swim!Irlandés
Last edited by Irlandés; 30th Nov 2002 at 20:58.
Irlandes, before I disappear up my own backside with this, your original post pointed out that at 1300 lbs AUM in ISA conditions your hover ceiling would be 8500 DA. Then you compared an increase in OAT (worsening conditions for the engine with the throttle wide open) between what common sense told you (7300' DA) and what the graph told you (8000'DA). The performance graph allows you to operate only 500' (not a great deal)below your ISA state when the OAT has increased by 10 deg(quite a lot). I am afraid I just cannot believe dropping 500' in PA compensates for an increase in OAT of 10 degrees, even in a crappy old piston engine - I am just going to have to go into the loft and find all my old piston notes ad there must be formula for this somewhere.
Join Date: Jun 2002
Location: Dun Laoghaire
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
Crab, you said...
I assume that you meant to say...
"Then you compared an increase in OAT (worsening conditions for the engine with the throttle wide open) between what common sense told you (7300' PA) and what the graph told you (8000' PA)."
As far as my 'common sense' is concerned it wasn't common enough to take into account the improved engine performance at lower pressure altitudes which somewhat compensates for the change in temperatures ( by 58% if my reading of the graph is correct). As for calculating it manually, I'll leave that to a braver man (you!
) It'll be interesting to see what results you get.
As an aside, is it not logical that if performance drops off radically with increased height above the critical altitude (obvious from the graph), that the converse is also true, that performance increases drastically for decreased altitude above the critical altitude?
Irlandés
Then you compared an increase in OAT (worsening conditions for the engine with the throttle wide open) between what common sense told you (7300' DA) and what the graph told you (8000'DA).
"Then you compared an increase in OAT (worsening conditions for the engine with the throttle wide open) between what common sense told you (7300' PA) and what the graph told you (8000' PA)."
As far as my 'common sense' is concerned it wasn't common enough to take into account the improved engine performance at lower pressure altitudes which somewhat compensates for the change in temperatures ( by 58% if my reading of the graph is correct). As for calculating it manually, I'll leave that to a braver man (you!
) It'll be interesting to see what results you get.As an aside, is it not logical that if performance drops off radically with increased height above the critical altitude (obvious from the graph), that the converse is also true, that performance increases drastically for decreased altitude above the critical altitude?
Irlandés
Last edited by Irlandés; 30th Nov 2002 at 22:08.
Irlandes, your correction of my PA instead of DA in the last post prompted me to start the whole thing again and I have discovered we have been arguing about an anomaly that doesn't in fact exist.
In your first post you used 1300 lbs AUM and got to 8500'PA on the ISA line which was an OAT of -2 deg. Because it was on the ISA line the PA was the same as the DA. Roger so far over?
What you then did was to use the performance chart to calculate DA which it does not do. If you had drawn your interpolated ISA+ 10 line and then read across at 8500' PA you would have got a reduced AUM at the same PA because the OAT was higher. Stay with me here..
If on the other hand you had entered a PA/DA graph at 8500'PA @ +8 degrees (ISA+10) you would have got a DA of 9759' - an increase of almost exactly the 1200' that the +/- 120T formula would have given.
What I am saying is that there is no mystical bias in engine performance with pressure vs temperature as engine performance IS determined by Density Altitude. The only problem was that the performance graphs do not indicate DA, they give a maximum PA at a specific OAT and it is left to you to equate this to the level playing field that is Density Altitude.
In hopping from one PA at one temp to another at a different temp (especially when you are using ISA+10 when the oat changes each time you change PA) you are never comparing like with like.
I withdraw my criticism of Uncle Frank's graph, it is not crap because it gives the correct information when used correctly!
Mines a slice of humble pie as well then.
In your first post you used 1300 lbs AUM and got to 8500'PA on the ISA line which was an OAT of -2 deg. Because it was on the ISA line the PA was the same as the DA. Roger so far over?
What you then did was to use the performance chart to calculate DA which it does not do. If you had drawn your interpolated ISA+ 10 line and then read across at 8500' PA you would have got a reduced AUM at the same PA because the OAT was higher. Stay with me here..
If on the other hand you had entered a PA/DA graph at 8500'PA @ +8 degrees (ISA+10) you would have got a DA of 9759' - an increase of almost exactly the 1200' that the +/- 120T formula would have given.
What I am saying is that there is no mystical bias in engine performance with pressure vs temperature as engine performance IS determined by Density Altitude. The only problem was that the performance graphs do not indicate DA, they give a maximum PA at a specific OAT and it is left to you to equate this to the level playing field that is Density Altitude.
In hopping from one PA at one temp to another at a different temp (especially when you are using ISA+10 when the oat changes each time you change PA) you are never comparing like with like.
I withdraw my criticism of Uncle Frank's graph, it is not crap because it gives the correct information when used correctly!
Mines a slice of humble pie as well then.
Join Date: Jun 2002
Location: Dun Laoghaire
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
Crab,
I can't help but feel that you are trying to put me back into that confused state that Nick and Figure of Merit pulled me out of.
I'm not sure if I understand your reasoning but if as you say DA is DA is DA then how on earth to you account for the difference in performance demonstrated by my previous example??? Here repeated... I'm not inventing anything, it's what the graph says.
12,000ft PA, OAT -4 degrees = DA 12,600ft, MAUW = 1100 lbs
10,000ft PA, OAT +17 degrees = DA 12,600ft, MAUW = 1150 lbs
8,000ft Pa, OAT +40 Degrees = DA 12,600ft, MAUW = 1200 lbs
And here's the graph to make things easier (if the graph doesn't load automatically, let me know).
I can't help but feel that you are trying to put me back into that confused state that Nick and Figure of Merit pulled me out of.
I'm not sure if I understand your reasoning but if as you say DA is DA is DA then how on earth to you account for the difference in performance demonstrated by my previous example??? Here repeated... I'm not inventing anything, it's what the graph says.12,000ft PA, OAT -4 degrees = DA 12,600ft, MAUW = 1100 lbs
10,000ft PA, OAT +17 degrees = DA 12,600ft, MAUW = 1150 lbs
8,000ft Pa, OAT +40 Degrees = DA 12,600ft, MAUW = 1200 lbs
And here's the graph to make things easier (if the graph doesn't load automatically, let me know).
Last edited by Irlandés; 2nd Dec 2002 at 07:55.
Irlandes, this is what I think happens:
When the throttle is not fully open then the pilot observes the limiting MAP according to the placard in the cockpit.
When you climb above the critical altitude, the throttle is wide open and because there is no supercharger with boost control to maintain the Manifold Air Pressure, the power of the engine reduces. So far pretty much as FOM suggested .
But, whilst I stand by my DA is DA is DA and that the density of the air is the major player in the efficiency of the engine (the weight of charge in each induction stroke to be more precise) the problem is that as you go higher, the static air pressure decreases because there is less weight of air above you as you climb.
Although all your combinations of PA and OAT give the same DA, the actual measured pressure is reduced at higher PA.
Therefore since the MAP is dependent on static pressure, the MAP and therefore the amount of air going into the engine is reduced. The density of the air is the same but there is just less of it going in the downstroke of the piston on the induction still produces the same vacant space in the cylinder but the pressure outside isnt sufficient to fill it with as much air/fuel as it was at lower altitudes.
Therefore your max AUM decreases due to PA despite the DA remaining the same.
Does that make sense?
If the R22 was supercharged it would be very different as the Automatic Boost Control would maintain the MAP by squeezing more air and fuel mix into the chamber to compensate for the loss of static pressure.
BTW I am not sure why the limiting DA appears to be 12600 since my (old) copy of the R22 handbook says it is cleared to 14000 DA (maybe it is only for forward flight)
When the throttle is not fully open then the pilot observes the limiting MAP according to the placard in the cockpit.
When you climb above the critical altitude, the throttle is wide open and because there is no supercharger with boost control to maintain the Manifold Air Pressure, the power of the engine reduces. So far pretty much as FOM suggested .
But, whilst I stand by my DA is DA is DA and that the density of the air is the major player in the efficiency of the engine (the weight of charge in each induction stroke to be more precise) the problem is that as you go higher, the static air pressure decreases because there is less weight of air above you as you climb.
Although all your combinations of PA and OAT give the same DA, the actual measured pressure is reduced at higher PA.
Therefore since the MAP is dependent on static pressure, the MAP and therefore the amount of air going into the engine is reduced. The density of the air is the same but there is just less of it going in the downstroke of the piston on the induction still produces the same vacant space in the cylinder but the pressure outside isnt sufficient to fill it with as much air/fuel as it was at lower altitudes.
Therefore your max AUM decreases due to PA despite the DA remaining the same.
Does that make sense?
If the R22 was supercharged it would be very different as the Automatic Boost Control would maintain the MAP by squeezing more air and fuel mix into the chamber to compensate for the loss of static pressure.
BTW I am not sure why the limiting DA appears to be 12600 since my (old) copy of the R22 handbook says it is cleared to 14000 DA (maybe it is only for forward flight)
Join Date: Jun 2002
Location: UK
Posts: 62
Likes: 0
Received 0 Likes
on
0 Posts
Crab: you've 'got it'!
Normally aspirated piston engine is 'charged' by atmospheric pressure.
Therefore at Full Throttle (FT) it would be preferable to achieve a DA by a combination of HIGH pressure (LOW PA) and High temperature rather than Low pressure and Low Temperature.
Since the atmosphere, as far as most helicopter pilots is concerned, is 30000ft high and 30"Hg pressure it must reduce at 1"Hg per 1kft.
Therefore at Full Throttle (FT) it would be preferable to achieve a DA by a combination of HIGH pressure (LOW PA) and High temperature rather than Low pressure and Low Temperature.
Since the atmosphere, as far as most helicopter pilots is concerned, is 30000ft high and 30"Hg pressure it must reduce at 1"Hg per 1kft.
Hydraulic R22!!!
One of the most interesting points in the press release that accompanied the lauch of the R44 Raven was that the Hydraulic system weighed NO more than the electric trim system it replaced.
If this is so, then considering that the S300 and the Enstrom helicopters use coolie hat electric trim systems how much of an benefit do you think going to hydraulics on entry level helicopters would be? After all, a Ł6000 Ford KA has power steering, surely your Ł120,000 helicopter should.
If we take the R22 as a case in point:
Assume:
Weight & Payload unaffected
Stick-shake elliminated
Hands-off flight for a limited time is possible (as in R44 & JR)
Control Forces in high-speed flight elliminated
Current 'CLUNK-BOING' trim system removed
System is a simplex system with manual reversion.
Hydraulic System will make it to 2200hr overhaul without significant maintenance.
......and.........
List price is increased by Ł6500 (USD 9750)
Would this system be more appealing to the industry, would you prefer an R22 with this system over the standard system?
I look forward to your responses!
CRAN
If this is so, then considering that the S300 and the Enstrom helicopters use coolie hat electric trim systems how much of an benefit do you think going to hydraulics on entry level helicopters would be? After all, a Ł6000 Ford KA has power steering, surely your Ł120,000 helicopter should.
If we take the R22 as a case in point:
Assume:
Weight & Payload unaffected
Stick-shake elliminated
Hands-off flight for a limited time is possible (as in R44 & JR)
Control Forces in high-speed flight elliminated
Current 'CLUNK-BOING' trim system removed
System is a simplex system with manual reversion.
Hydraulic System will make it to 2200hr overhaul without significant maintenance.
......and.........
List price is increased by Ł6500 (USD 9750)
Would this system be more appealing to the industry, would you prefer an R22 with this system over the standard system?
I look forward to your responses!
CRAN
Last edited by CRAN; 10th Dec 2002 at 13:00.
Join Date: Apr 2002
Location: Hartford, CT USA
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Admittedly, I have limited experience, but my first impression is that its not needed. Got light stick forces now anyways, and the extra weight would not be welcome 
+ more money.
Anyways, I just dont think it would sell. R22s are low cost, relatively uncomplicated machines, why add this?
+ more money.Anyways, I just dont think it would sell. R22s are low cost, relatively uncomplicated machines, why add this?
Thanks Qmax, I knew those old piston notes would come in handy one day.
Irlandes - have I managed to enlighten you or confused you again?
Irlandes - have I managed to enlighten you or confused you again?
PPRuNe Enigma
Join Date: Feb 2001
Location: Scotland
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Baran's right: since the R22 does not have a weighty electric trim system to replace (just a boingy spring) there would be a significant weight penalty.
R22 control forces are so light anyway, why complicate things ?
R22 control forces are so light anyway, why complicate things ?
Join Date: Apr 2002
Location: Hartford, CT USA
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Regarding Electric trim systems, how exactly do they work?
I would also like to clear up my understanding of hydraulics as well. A pump; driven by various means(are any electric?) provides pressure to pistons which suppliment the actions of the pilot. Where and how the movements are boosted im not sure of. Thanks again.
I would also like to clear up my understanding of hydraulics as well. A pump; driven by various means(are any electric?) provides pressure to pistons which suppliment the actions of the pilot. Where and how the movements are boosted im not sure of. Thanks again.
Join Date: Jun 2002
Location: Dun Laoghaire
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
Well that depends, are you still defending this statement you made earlier...?
"What I am saying is that there is no mystical bias in engine performance with pressure vs temperature as engine performance IS determined by Density Altitude."
It seems to me that their definitely is a bias and that density altitude as a yard stick is not as straightforward as you are suggesting with this statement. Aren't you both in fact saying the opposite, that DA is not DA is not DA. That it all depends on the PA/Temp combination for a given DA, supported by your 'charge' theory which to my limited intellect seems to make sense.
Otherwise, everything's just fine! Thanks for all your help!
Irlandés
"What I am saying is that there is no mystical bias in engine performance with pressure vs temperature as engine performance IS determined by Density Altitude."
It seems to me that their definitely is a bias and that density altitude as a yard stick is not as straightforward as you are suggesting with this statement. Aren't you both in fact saying the opposite, that DA is not DA is not DA. That it all depends on the PA/Temp combination for a given DA, supported by your 'charge' theory which to my limited intellect seems to make sense.
Otherwise, everything's just fine!
Thanks for all your help!Irlandés
Join Date: Jun 2002
Location: Dun Laoghaire
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
And I don't think that the power steering on a Ford Ka is comparable to a hydraulic system on a Robby if only from an economical point of view. How many Ford Ka's are manufactued a year?? Compare this to an R22 prodution run. More research and develpment costs (this is aviation afterall) and a lot less machines to spread that cost over. It's not so much a technical quesion as one of numbers. As for control forces, after an hour of confines, my shoulder's about ready to drop off.
Join Date: Oct 2002
Location: Bristol UK
Posts: 47
Likes: 0
Received 0 Likes
on
0 Posts
I think a hydraulic r22 would be quite nice - certainly help get students hovering earlier.
That said if the r22 was to put on a bit of weight, I think I'd rather it went into the rotor blade tips than a hydraulic system!
That said if the r22 was to put on a bit of weight, I think I'd rather it went into the rotor blade tips than a hydraulic system!
Join Date: Apr 2002
Location: UK
Posts: 45
Likes: 0
Received 0 Likes
on
0 Posts
I have to agree with the majority opinion that hydraulics are not needed on such a light helicopter. The stick forces are so light anyway, so what would the hydraulics be doing.
I dissagree with WB who suggests that hovering would be made easier.
What the Robbo needs is a fuel injection system to reduce the carb icing problem. But this is a UK problem and highly unlikely to get into the R & D cell.
A super little helicopter spoilt by the 'Barb of the Carb'
Hydraulics are normally fitted to reduce pilot input loads at the controls. I understand in the case of the R44 they were introduced to banish the feedback forces and cyclic vibrations that are evident on the original model.
I dissagree with WB who suggests that hovering would be made easier.
What the Robbo needs is a fuel injection system to reduce the carb icing problem. But this is a UK problem and highly unlikely to get into the R & D cell.
A super little helicopter spoilt by the 'Barb of the Carb'
Hydraulics are normally fitted to reduce pilot input loads at the controls. I understand in the case of the R44 they were introduced to banish the feedback forces and cyclic vibrations that are evident on the original model.
The R-22 and -44 have such completely different rotor systems that they don't really compare. The -44's is more like that of a 206. Flying it without the complicated and heavy trim system would be miserable and give you arms and an upper body like that cinema star Arnold Schwollenpecker.
On the other hand, the little R-22 does quite nicely with its light feedback forces. (Side note to Irlandes: get off the sofa and do some pressups! How do you ever expect to handle a Squirrel with the power steering gone?)
Having said that, boosting the controls of the R-22 is an intriquing idea, especially if it could be done with no weight penalty. But that is doubtful, given the weight of the pump, lines and servos as opposed to the existing spring thing.
Barannfin asked:
There is a pump (universally driven by the transmission for logically obvious reasons) which supplies fluid under pressure to two hydraulic servos located in the control runs (three servos if the collective is boosted too). On each servo is a little "pilot valve" that senses the tiniest movement of the control tube as initiated by the, er, pilot. When it does, it directs fluid pressure to the appropriate side of the servo to help "push" in that direction. Failure of any component does not compromise the connection between the cyclic grip and the swash plate.
Some aircraft (Squirrels, or fenestron-equipped machines) also provide hydraulic boost for yaw control.
All twin-engine helicopters (and one or two single-engine ships that I know of) use dual hydraulic systems. However, the secondary (or "Aux") system may not power all of the control channels. In other words, lose the primary (or "Main") system and you'll have cyclic but you may not have any tail rotor boost.
Finally, some aircraft probably should have dual systems. The Squirrel is so peculiar that Aerospatiale saw fit to include an accumulator in the system, so in the event of a hydraulic failure the poor pilot would have half a chance of maintaining control while slowing the beasty down from cruise airspeed.
On the other hand, the little R-22 does quite nicely with its light feedback forces. (Side note to Irlandes: get off the sofa and do some pressups! How do you ever expect to handle a Squirrel with the power steering gone?)
Having said that, boosting the controls of the R-22 is an intriquing idea, especially if it could be done with no weight penalty. But that is doubtful, given the weight of the pump, lines and servos as opposed to the existing spring thing.
Barannfin asked:
I would also like to clear up my understanding of hydraulics as well. A pump; driven by various means(are any electric?) provides pressure to pistons which suppliment the actions of the pilot. Where and how the movements are boosted im not sure of.
Some aircraft (Squirrels, or fenestron-equipped machines) also provide hydraulic boost for yaw control.
All twin-engine helicopters (and one or two single-engine ships that I know of) use dual hydraulic systems. However, the secondary (or "Aux") system may not power all of the control channels. In other words, lose the primary (or "Main") system and you'll have cyclic but you may not have any tail rotor boost.
Finally, some aircraft probably should have dual systems. The Squirrel is so peculiar that Aerospatiale saw fit to include an accumulator in the system, so in the event of a hydraulic failure the poor pilot would have half a chance of maintaining control while slowing the beasty down from cruise airspeed.
Some very interesting points have been fielded so far, Thank you.
As the majority of people have stated, the control forces in R22 and other light helicopters are very small and do not justify hydraulically boosted controls in that sense. However, I feel that it would be a major advantage to elliminate stick-shake and allow for hands-free flight.
All of the light helicopters currently on the market use very simple aerofoils (R22 - NACA 63-012, S300 - NACA 0015) etc and at low speeds these aerofoils produce very small pitching moments.
It we wanted to bring light helicopters up to the standards of performance of bigger machines, without requiring bucket fulls of power then more efficient rotor systems would be required which will inevitabley drive the control loads up and require at least an electric trim system but more appropriately. hydraulics.
One of the major gripes about helicopters, especially the small one is the lack of stability. Introduce hydraulics and you then have the capability to add a stability augmentation system (as an option) - this in my view would be a major advantage to low-timers who inadvertently find themselves in cloud or otherwise disorientated.
With regards SAS, we have lot's of Permitted Gazelle pilots on Rotorheads, many of which are low time, would any of them be prepared to comment on the reduced workload and increased safety offered by this system.
An addtional point, I think it is wrong for people to keep asking for 'simple' light helicopters when fundementally that is not what is required for training. Simple helicopters in the foreseeable future will be underpowered, and poses dubious handling qualities ~ it's a fact of life. A training helicopter sould be suitable for its purpose and not necessarily simple. It is my opinion that the market requires a platform with lower operating cost and increased performance........but this will not be achieved without and substantial change in approach.
Keep it coming!
CRAN
As the majority of people have stated, the control forces in R22 and other light helicopters are very small and do not justify hydraulically boosted controls in that sense. However, I feel that it would be a major advantage to elliminate stick-shake and allow for hands-free flight.
All of the light helicopters currently on the market use very simple aerofoils (R22 - NACA 63-012, S300 - NACA 0015) etc and at low speeds these aerofoils produce very small pitching moments.
It we wanted to bring light helicopters up to the standards of performance of bigger machines, without requiring bucket fulls of power then more efficient rotor systems would be required which will inevitabley drive the control loads up and require at least an electric trim system but more appropriately. hydraulics.
One of the major gripes about helicopters, especially the small one is the lack of stability. Introduce hydraulics and you then have the capability to add a stability augmentation system (as an option) - this in my view would be a major advantage to low-timers who inadvertently find themselves in cloud or otherwise disorientated.
With regards SAS, we have lot's of Permitted Gazelle pilots on Rotorheads, many of which are low time, would any of them be prepared to comment on the reduced workload and increased safety offered by this system.
An addtional point, I think it is wrong for people to keep asking for 'simple' light helicopters when fundementally that is not what is required for training. Simple helicopters in the foreseeable future will be underpowered, and poses dubious handling qualities ~ it's a fact of life. A training helicopter sould be suitable for its purpose and not necessarily simple. It is my opinion that the market requires a platform with lower operating cost and increased performance........but this will not be achieved without and substantial change in approach.
Keep it coming!
CRAN