Governor on or off for autos? Just a matter of choice I think. I've done both with instructors; each instructor seems to have a preference. If I'm practising them alone with a power recovery, I prefer to have the governor on; it's one less thing to think about. YOU have to join the needles anyway; but then the governor takes over - no big deal.

NigD2,
I hated autos for ages. But after practising them to the ground for what seemed like hours and hours during my CPL course, I suddenly realised they could be fun, and told my instructor that. He reminded me of this during my recent LPC, when I got nervous at the idea of doing autos to the ground, since I'm a bit rusty again. Do enough of 'em, and you might come to love 'em!

"regular governor-off refresher training sounds like a very good idea, and perhaps should be part of the annual LPC"

It is where I fly. We also do a new thing on R22 and R44 - the testers pull the tacho cb as a surprise. This is related to a recent incident where a 44 was flying along happily and the tacho dropped to zero. So, the pilot decided to immediately auto. He landed hard and chopped the tail off.

Turned out there was nothing wrong with the engine. The tacho needle/spindle had failed...........

So - might be a good idea to check all pilots for hearing........generally speaking, if the cylinders sound intact, the rotor rpm OK. the airspeed is OK and the VSI isn't diving - you'd think anyone with even half a brai...........sorry. I'll stop. Don't want to get banned. :D

headsethair,

Yes, from the comfort of a desk, or probably even flying with a helluva lot of rotary hours behind you, you would think that anyone with half a.... But up there when you haven't had that much experience and something goes wrong, and you know you have to do something but you're scared and your brain's slowed down as a result...it's all too easy to make the wrong decision. I know; I've been there.:( :( :(

System failures like tachos are not peculiar to R22s of course. In fact, the inbuilt engineering redundancy in R22 RRPM control aids is very high so you will be unlucky not to get some help in RRPM control - (there are 5 separate aircraft systems).

When I did the Bell 206 factory course (which is unbeatable if you fly their aircraft) they made mention of a number of "engine failures" where a perfectly serviceable helicoper was flown into the ground because of a tacho generator failure giving a spurious indication. One of my colleagues had a torque indication failure with other failure indications in an AS355N just a couple of days ago. It all ended uneventfully, fortunately.

Experience can certainly help in these cases, but experience is expensive and difficult to obtain. However, a small part of all that time we spend on the ground waiting to go flying can be usefully spent with the AFM and technical manuals getting to understand how these things work. When something does fail you are in much better shape to intelligently assess the problem. And best of all, you can gain such knowledge at NO COST!

R22 Performance Chart Interpretation
 

OK, this one's a little complicated to explain so please bear with me. Any text book I've ever read has said that every degree of temperature deviation off a standard ISA day (15C at sealevel, temperature lapse rate 1.98C for every 1000ft) is equivalent to 120 feet. So on an ISA +10 day (ignoring humidity) a pressure altitude of 0ft should equate to 1200ft of DA. This is easily confirmed by checking a PA/DA conversion chart such as this one from the R22 manual. Pretty standard stuff and up to here no problem (I hope! :)) .

Now, if you want to calculate the IGE ceiling for an R22 Beta (at say 1300lbs for the sake of argument) using this IGE Ceiling chart (from the same manual) you will see that your ceiling is 8,500ft of density altitude (point of intersection of ISA line 'Standard Day' with vertical to 1300 lbs). Now at this stage we could stop using the graph and work out the rest in our heads: DA = 8,500ft, ISA +10 day, PA=(8,500-(10x120))=7,300ft also confirmed by aforementioned PA/DA conversion chart.

If however you decide to use the IGE Ceiling chart to calculate your PA, it will give you an answer of 8,000ft PA (intersection of interpolated ISA +10 line (not OAT +10 line!!) with vertical to 1300lbs). So for our 10 degrees of deviation from ISA we have paid a price of only 500ft which equates to 50ft for every degree and not 120ft. :confused:

Can anyone explain this discrepancy??? Or have I lost the plot and am incapable of reading a perfomance chart? :(

If at this stage you are totally lost and wish to brush up on DA and PA calculations, I recommend going to my previous post 'Want something to read?' If you are not totally lost, please enlighten me! Now, where did I leave those Tylenol?? :rolleyes:

Thanks!
Irlandés :)

Irlandes, I think it is because you have tried to interpolate from the standard day line - I understand why but since there is only one ISA line on the graph you are only guessing as to where the ISA +10 line would be.
The gradient would be parallel to the standard day line but you can only best guess the spacing using the spacing on the OAT lines.
This may or may not be reasonable but I suspect that Robinson would argue that they did not include such a line on the graph, therefore you shouldn't make one up. If there had been a series of ISA+temp lines then you could actually 'interpolate'.
To be honest the lapse rate is likely to change so much in the real world that assuming it is ISA+10 at altitude just because it is ISA+10 at sea level is asking for trouble. You are better off getting an accurate OAT from either Met reports (balloon ascents) or from the OAT gauge when you get up there.
The NZ handbook on performance is a very good guide and every operator should be made to read it. As a Mil pilot I would have to have a very good reason to operate without OGE performance plus a 5% Thrust margin. I know the light single operators will tell me they could never get the job done if they had to have this much spare performance but the accident statistics speak for themselves.
Planning to land in the mountains with only IGE hover capability is like russian roulette - you only have to get it wrong once!

Hey Crab,
thanks for your reply and for taking the time to wade through my post. On a practical level (the one that really counts!) you are of course totally right and I couldn't agree more.

On a purely theoretical level however (please indulge me here), I would suggest that I'm not really guessing where the ISA +10 line is. If you consider that the ISA line intersects the 1300 lb vertical at approx -2 degrees OAT (pretty clear on the graph) which exactly corresponds to the ISA temp at 8,500ft (15-(8.5x2)=-2) then it seems logical that the ISA +10 line must intersect the same 1300 lb vertical at + 8 degrees OAT (-2+10=+8) which on this graph corresponds to 8000 ft PA and not the 7,300 ft I believe it should be. Do you see what I mean? My worry is that the graph tells you that your ceiling is higher than it actually is for ISA + values, i.e. if there is an error, then it's not erring on the side of safety. Obviously the reverse holds true for a 'minus' ISA day where performance improves. Also the same holds true for the R22's OGE graphs. The way I see it, on a 'hot and heavy' day, the graphs are not penalising you as much as they should for non-standard temperatures. Maybe I need glasses... :rolleyes:

Ah well, back to the real world... :D

Irlandés

Irlandes, I fully understand your concern and think it is worth highlighting this anomaly on the graph. I would be very interested to see what experienced R22 operators have to say. You could always email it to Frank Robinson and ask, just don't copy it to Lu Z or there will be another conspiracy born!

Irlandes,

I think the problem is that you are expecting the hover performance of the aircraft to be driven only by the density altitude. For any helicopter, the hover performance is based upon the altitude, temperature and engine power available, as well as the ancilliary limits, such as tail rotor effectiveness.
The gain in hover IGE weight with reduction in altitude is a product of the both rotor efficiency, (which is almost entirely driven by density altitude), and the engine power available, which gains power as altitude is reduced, and also as temperature is reduced.

I believe the hover performance is more strongly influenced by engine power than by rotor efficiency, and you have deduced that from the charts.

As an experiment, look at several constant density altitude conditions, where the temperature is increased considerably, and see if the weight to hover is a constant. I believe the lower temperature conditions should have higher HIGE performance.

Well Nick I've had to rethink my original reply to your post and subsequently deleted it (I was in a dazed and confused state! ;)). I did what you suggested using the line of constant 12,600 ft DA on the graph and here are the results...

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

You said that you believed the lower temperature conditions should have higher HIGE performance. But it seems judging by these figures, that DA being equal, performance is increased at the lower altitudes/higher temperatures. This is reflected by the increase in maximum allowed all-up weight. Does that make sense?? Is the piston engine performance therefore more adversely affected by higher altitudes than by higher temperatures for a constant DA? That's the only way it seems to make sense to me. Am I still in a dazed and confused state? :(

That apart, thanks for throwing light on the error of my assumptions. As usual, it all seems so obvious in hindsight. I always took for granted that an aircraft would perform identically irrespective of the pressure altitude/temperature combination as long as the density altitude didn't change. If only life were so simple! I guess this assumption is only correct for non-powered flight, gliders etc. This for me is a real eye opener and something I thought I understood well needs a bit of reevaluation. :rolleyes:

Thanks!
Irlandés :)

Just a quick shot at a short answer.

Because of the carburator and its associated temperature drop on the engine inlet air, I would not be surprised to learn that the engine gets a little bit of a temperature-related performance benefit. Becuase the R22 is not turbo equipped, there is no associated benefit to offset lower ambient pressure.

This could explain the performance numbers.

Well- never thought I'd say this but I think Nick Lappos is wrong (there I've stuck my neck out now!)

The engine is de-rated which means that, having set the limit manifold pressure, the engine power output is the same regardless of the Density altitude. This is 124 BHP or 131 BHP depending on the limit (MCP or 5min T/O power) we are talking about. Either way the function of the limit manifold pressure chart is to set the max power the drive train can handle for a wide range of altitude/temp combinations.

This works up to an altitude/temp combination where the throttle is fully open- Robinson call this the "critical altitude". Hotter and higher than here and, yes Nick I agree, the engine cannot put out the Horse Power that it has been derated to. Below or colder than this though the power output remains steady despite changes in DA. You can see this effect best on the OGE hover charts for the R22HP and Alpha - the throttle being fully open is the cause of the "knee" in the curve and the nosediving performance.

If you take two points of equal DA on the flatter bit of the curve (use for example the OGE HP & Alpha chart, 8500' pa and -2 degrees C and 7500'pa and +8.3 degrees C) and calculate the Max weight you STILL come up with a discrepancy- despite the engine giving the same power output of 124BHP. So I don't think Nick's explanation holds.

The concept of derating is the same as a torque limit in a SE turbine. If you do the same for the Jetranger over its "Torque Limited" part of the OGE curve (constant engine power output despite different altitude/temp combinations) the performance obeys the DA calculations perfectly.

After a bit of research it seems the most likely explanation for the R22 anomalies is either-

1. The Manifold pressure charts don't accurately hold the engine power output constant or

2. Tip effects which spoil the rotor behaving according to theory. These tip effects are due to the airflow at the blade tips running into compressibility at high Mach numbers. This results in the usual density calculations no longer holding good. A quick dimensional analysis of the equations I could find predicting airfoil pressure from PA and Temp where compressibility has to be taken into account shows that while Height is raised to the power of 2.6 the temperature term is raised only to the power of 1.75. Thus changing height has a far greater effect on performance than changing temperature for the same Density altitude- this agrees with what we can tell from the charts. (I'm prepared to have my maths criticized by an aerodynamicist- but I think the basic problem of compressibilty still holds out).

It is interesting that the JetRanger charts don't show any compressibility effects (despite the 206 having a 11% higher rotor tip speed than the R22). This is either due to differing blade geometry or due to the test pilot technique of "referring the parameters" used in the 206 certification. This is when, having found a few points on the graph, the rest is predicted from theory. It may be that in the old days tip effects weren't understood or did not have to be taken into account when the performance charts were produced.

Hope this is understandable.

FoM

Or it could be a problem with assuming everything falls off as linearly as temperature in the ICAO model.
Pressure and density reduce at a greater rate at lower levels - compare the reduction from 0-5000' of relative density (2.76% per 1000') with the reduction between 5000-10000'(2.48% per 1000') whilst the temperature rigidly declines at 1.98 deg C throughout.
Therefore the effect on density of purely a change in temperature cannot be the same at all levels.
As Nick has said before on this thread - rules of thumb are not generally infallible.

You can see the R22 OGE chart (HP, Alpha and Beta) that Figure of Merit refers to here...

I'll have to think this one through... :)

Irlandes, I have come to the conclusion that the Robinson graphs are just crap! If DA is meant to be the yardstick by which aircraft performance is measured then constant DA must mean constant performance. I have looked through our Sea King Operating Data Manual and can find no such anomalies - maybe it is because the graphs all have PA, OAT and DA lines on them, whereas the R22 graph just has the 12600 DA line. This makes it easy to miss the very thing that you have spotted - ie that the performance claimed by the graph is at odds with all common sense and practice.
There may be, as FOM says, problems with MAP management and compressibility errors, especially the latter since Mach no is governed primarily by temperature and the increase in AoA required at altitude will affect the Mcrit of the blade.
But, as he also points out, the 206 has no such compensation - so is it us not understanding some crucial aerodynamic phenomenon or is it just a poorly constructed (whether by accident or design) graph?

Dear Figure of Merit,

Unlike then Pope, I don't even pretend to be infallable! Sometime it seems that way because I have seen the exact issue, measured it and experienced it, but in this case, I am as much a novice as anyone out there in cyberspace. This thread is another really good one, because from a simple question, real understanding can be pried out. Thanks to Irlandes, who provided the suspect chart, we can do some more examination. In every case, I implore Ppruners to challenge (the ground effect crowd had no such problem!) each of us, so we all learn more.

I certainly agree with you about my fallability, but (with some quibblingness) my original post was a speculation, based on what the limiting factors for rotor hover performance are, and a request for more data to seek the real answer. While the Robinson is probably derated up to the Knee of the WAT curve (the slope change at 5000 to 7000 feet), it is power limited above that. The two slopes of the curve reflect two of the several possible limiting factors:

1) Constant power section - The lower less steep slope from sea level up to about 5000 feet is the fall-off of performance of the rotor due to density altitude, while the power is a constant (this is the area where you are quite correct, the derated engine puts out constant power). The performance loss of the rotor is about 1 lb of lost hover weight per 100 feet of altitude increase (about 50 lbs per 6,000 feet, actually). This is purely the affect of the density being reduced, so the blade must be operated at an increased angle of attack, so the induced power is higher, and some performance is lost.

2) Reduced power section - The slope above the knee is the result of the performance loss due to engine power loss, PLUS the lost rotor efficiency due to density altitude. That slope is about 250 lbs per 5,000 feet, about 5 lbs lost per 100 feet of altitude gain. This is the sum of the 1 lb per 100 feet of the rotor efficiency and one would guess 4 lb per 100 feet due to other effects such as engine power decay and or loss of tail rotor thrust.

If this were not a family holiday in the States I would spend more time with the chart and try to deduce more, but that will have to wait, since a turkey waits for me!

Ooops- Ignore my last post above.

I had got the bits of the curve the wrong way around.

The correct way around is-- the portion to the LEFT of the "knee" is where the throttle is fully open. The "steep" bit on the curve is the constant power portion.

Rechecking a few figures shows that where the performance of the machine is unlimited by engine power (to the RIGHT of the knee in the R22 HP and Alpha OGE curve) the weight is constant at constant DA

For example 1000 feet at +30 is equivalent to 3000 feet (ish) at ISA and 5000 feet at -10. All have a max weight of 1340 lbs.

God-- How embarrassing!!

Off to eat Turkey (american visitors staying) and humble pie

Irlandes, further to my last post I have been very boring and used your three examples of constant DA and checked using the gas constant, temperatures in Kelvin and accurate pressures from ISA and the Density in all 3 is within 0.0001 kg/m3. So there is no mysterious change in DA caused by altitude vs temp and I can only conclude again that the Robinson graphs are crap. DA is DA is DA so the answer to why you get 3 different AUM for 3 identical DAs can only be answered by Uncle Frank.

Crab- I agree that DA is DA as far as the rotor is concerned (compressibility effects ignored) . But as the engine sees things, though, DA is not just DA.

On the bit of the graph that Irlandes was looking at the engine's throttle is fully open. The power output of the piston engine is not solely dependent on density altitude, but all kinds of thermodynamic boffin-equations. So for example- although 9000 feet and +10 degrees is the same DA as 10,000 feet at 0 (more or less) the engine is putting out less power in the latter case so the rotor can do less work.

You'll see the same thing with any helicopter once the engine starts to be the limit- in turbines it'll eventually be the TOT or N1 that limits you hot and high. If the engine can't put out the torque the rotor can't do the same work for the same density.

There's no mystery to it (despite my earlier, misguided attempts to muddy the waters) and we can't conclude crappiness at all!!

FOM,
I must admit to have being totally confused after your second-last post. Female intuition (although I am not female! ;) ) seemed to tell me that something was not quite right in the state of Denmark although I couldn't quite put my finger on it. I think however, that thanks to Nick and yourself I've been rescued from the void of confusion and this graph suddenly seems perfectly logical. It seems that there were more things between heaven and earth than were dreamt of in my philosophy.

I walk away a slightly wiser man! :)

Thanks!
Irlandés

P.S. Any humble pie left? I'm kinda hungry. :D
P.P.S. OK, ok, sorry for overdosing on the Shakespeare. :rolleyes:

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.

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. :D It's a nice day, and the sea looks inviting. I think I'll go for a swim!

Irlandés

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.

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

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.

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).

http://www.geocities.com/irlandes00/DA1.jpg

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 isn’t 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)

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.

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 £6000 Ford KA has power steering, surely your £120,000 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 £6500 (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
:cool:

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 :rolleyes: + 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?

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 ?

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 agree the others - There is no need because the controls are already light.

Added cost & weight burden for no gain

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

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. :rolleyes:

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!

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.

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.

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
:cool: