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Manifold Pressure R22

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Manifold Pressure R22

Old 9th Sep 2008, 13:56
  #21 (permalink)  
 
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As some people have already stated you should be very careful of pulling too much power. It's not a case of "every machine has a bit more" I'm sure in any helicopter there will be more power available past the limit on the gauge but once you have exceeded it you are getting into the bounds of major inspections leading to the scrapping of transmission components. There for it is vital that any overtourque situation is reported and dealt with properly.

NST
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Old 9th Sep 2008, 20:34
  #22 (permalink)  
 
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I would ernestly suggest that you stay within the KNOWN limits especially with the R22.

I once SFH'd a nice looking R22, that a Fi had just allowed his student pilot to exceed its limits during a practice auto down to power recovery, despite my absolute keeness for everything being right and where it should be on my pre-flite( you cannot see the overstretched rotor bearings) I started up and after all I could do I flew off to pick up my friends 12yr old son to give him a special birthday treat!!

Imagine my horror when I discovered I had a machine that was totally out of kilter and trying to shake itself to pieces but all this only realy kicked it at around 60 knots and at the critical take of stage.

I wont bore you with details for it still makes me go cold when I think about it, but with the brilliant help of the EGNH ATC that day I was blessed and managed to land in one piece, later to find I was given the excuse that the young Fi hadnt really though it was a problem exceeding the limits, and hadnt thought even to write it in the tech log (which I always read before any flight).

Simple really the limits are there to stop other or further problems, due to a complete idiot who DID'NT KNOW WHAT LIMITS WERE THERE FOR, I was
handed a Helicopter that could quite easily have finished up a heap of wreckage with me and my friends precious son wrapped up in in it.

STAY WITHIN THE LIMITS, AND STAY ALIVE!!

Peter R-B
VfrpilotPB
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Old 10th Sep 2008, 00:48
  #23 (permalink)  
 
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IMHO one of the major issues with MP limits in the Robbies is that there is no maintenance actions required if the limit is exceeded.

It is not helped in some way that the aircraft will easily perform above MP limits, so often an inattentive pilot is none the wiser. Of course it all catches up one day.

It is poor lead in training as far as power management goes when progressing onto turbines where red lights, HUMS etc etc tell the tale. Going from looking at only 1 'power' limiting (MP) instrument to possibly 3 (T4, Ng, Tq) is a big leap. And we all know the expense when one of these is exceeded.
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Old 10th Sep 2008, 01:55
  #24 (permalink)  
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I do not, and am not endorsing exceeding limitations.

None of what follows addresses the very valid concerns related to transmission overloading. Do not discount those. As for the engine....

The manifold pressure on a gasoline aircraft engine is partially a measure of how much power is being developed, but more to the point, how the power is being developed. If you have high manifold pressure, you have lower RPM, (because the rotor is limiting it). If the RPM were not limited, it would increase, and the manifold pressure would decrease. High manifold pressure and low RPM is the combination needed for detonation. The manifold pressure limit is there is part to provide a margin of safety against damaging detonation.

Very minor detonation can be tolerated by the enigne for very short periods of time (the margin part), but even when the operating conditions which caused it are removed, it will continue for a while, and continue to cause damage. And before someone jumps on me for how I know, I have successfully conduted Transport Canada testing for detonation margins in aircraft engines. I have seen pistons from enignes in service with a 2" diameter hole in the middle, from detonation. Lycomings in particular, are intolerant of metal chunk contamination inside the case. It is the possiblity of damaging detonation that is the reason we do not run constant speed propeller piston engines "over square" in airplanes (unless their turbo'd), and why we don't run lower octane fuel than specified for the engine.

The damage to an engine from detonation may show up at overhaul, long after (if you're lucky) or may show up minutes later as that hole in the piston. That will be very dramatic. It could show up as that hole in the piston for the next guy who gets near the limits 'cause the last guy exceeded them. Unlike a car, the pilot will have zero awareness of detonation occuring until either the engine disintegrates, or a mechanic later tells him it nearly did. The helicopter is not instrumented to tell the pilot detonation is occurring, and he cannot hear or feel it. Trust me on this.

As I said, the manifold pressure limit gives a margin of safety. It is not the pilot's business to know how big that margin is, or try to work into it. As is the case with nearly all limitations in aircraft design and certification, a margin is given. Approved testing should be the only time that margins are explored, other than the previoulsy mentioned life threatening event, which is then followed by honest reporting and inspection. A piston engine overhaul shop knows how to inspect for damage resulting from possible damage from detonation.

Those who wish to know more about this subject would learn well by reading FAR 27 and 33. Then you'd understand why we place operating limitations, to tell pilots how to stay safe!

It was well said that "regulation is for the guidance of wise men and the obedence of fools". It applies here.

Pilot DAR
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Old 10th Sep 2008, 08:34
  #25 (permalink)  
 
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Can anybody tell me why they don't use torque meters in pistons? surely this would immediately cancel out the massive misunderstandings about MAP limitations. The red line is only there as a legal requirement and indicates the maximum that could be used at certain alt/temp combinations. Most of the time (in my experience) the limit is something lower than the redline so using the red line as a limit would have meant continually exceeding the limitations of the TRANSMISSION...
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Old 10th Sep 2008, 12:56
  #26 (permalink)  
 
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Actually - the red line is at 25" and is NEVER allowed under ANY alt/temp combinations according to the POH. If you get anywhere near the red line you can guarantee you've busted a limit no matter what the ambient conditions.

The maximum according to the checklist in front of me here is 23.2" continuous and 24.1" maximum at sea level if it is 40C outside. So why isn't the red line at 24"?
I don't have a POH with me but I'm pretty sure that you can find a combination of alt/temp which reaches the redline, maybe you are mixing up the R22 models, I can't remember as its been a while.

I recall taking off one day from my garden with 2 fat boys on board when I was faced with a choice - it was either trim the rotor blades on a telegraph pole or exceed the limitation. I chose to exceed the limitation.

A chat with the engineer later on reassured me that all was well.

Both the 22 and 44 have more power available than the red line indicates.

It is there on the rare occasion that you need the extra power to prevent rolling the machine up into a ball.
Your last sentance is correct but is NOT to be used in the example you gave as you were fully aware before takeoff that you were overweight and were therefore willingly over torquing the transmission. Again, the MAP guage is not there for engine limitations but is to show you how much engine power you can use for the current ambient conditions in order not to exceed the TRANSMISSION limitations. Exactly the same rules apply to your new R44. The red line on the MAP guage is not to be used as a limit except when certain conditions exist, I wish they'd just get rid of the damn thing (the red line, not the R22) and save a lot of confusion.

Cheers
TS
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Old 10th Sep 2008, 12:58
  #27 (permalink)  
 
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Just going back to the original question as below. it is a nonsense of contradiction


could the MP limitation be theoretically raised for operations at lower alts, lower disc loadings etc etc...
.

Raise the MAP at a low disc loading and only one thing will happen, the blades will be spinning so fast that they will disappear faster than any boomerang.

the checklist in front of me here is 23.2" continuous and 24.1" maximum at sea level if it is 40C outside
That suits the 0-360-J2A, a la beta 11, however the rest are different with the 0-320 donk in the HP and Alpha it's just a tad more and quite a bit more in the Standard and Beta.

The easy answer is, once again, refer to the book, or at least the placard on your forehead.

You know Frank puts the placard pretty much right on your forehead, obviously its not close enough for the dumbos. duh.
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Old 10th Sep 2008, 15:59
  #28 (permalink)  
 
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The R-44 Raven 2 is rated at 205hp MCP & 245hp TO/5 min. It is derated from approx to 293 HP per the instructor that I had at the Robinson Factory Course.

In the factory course, they showed us the main rotor head from an R-44 where the owner routinely exceeded the MP & did external loads well over the R-44's max gross of 2500 pounds. How that rotor head stayed together is a mystery.
The course gave me a better understanding of why the limitations are in place. Yeah, the R-44 has power well beyond the MP limitations. When you exceed it you run the risk of a catastrophic failure of components especially in the transmission and main rotor system at some future date.

I agree with those who say "don't let a red line kill you" however, you don't over torque or over temp a turbine. You don't fly past the VNE. Most of understand those red lines are there for a really good reason.
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Old 10th Sep 2008, 21:25
  #29 (permalink)  
 
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the R-44 has power well beyond the MP limitations
This has been a puzzler for me but i've not been there.

The secondary reason not to exceed any flight manual limitations would be insurance cover.

Can anybody tell me why they don't use torque meters in pistons?
It's a good question, my guess would be that the information isn't supplied for 'free' by the engine and MP + rrpm droop had become the industry standard. I believe the turbine measurement is derived from an oil pressure effect/sensor. I'm sure someone who knows will explain this? One curious, random-internet-found diagram follows!

http://www.aircav.com/img/cav/inlet.gif
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Old 10th Sep 2008, 21:47
  #30 (permalink)  
 
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the R-44 has power well beyond the MP limitations
It is not just the potential for damaging the drive train.

Several years ago I was doing some pinacle approaches with a very experienced instructor to a peak at 5500' and around 30degrees (it wasn't in the UK :-) I was amazed how the power just ran out exactly like the limit charts said it would. It was almost like a brick wall and there was absolutely no margin - a very salutory lesson.

John
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Old 11th Sep 2008, 07:33
  #31 (permalink)  
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The easy answer is, once again, refer to the book, or at least the placard on your forehead.

You know Frank puts the placard pretty much right on your forehead, obviously its not close enough for the dumbos. duh.
with people skills like that topend I see why you are so good with your books....
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Old 11th Sep 2008, 08:44
  #32 (permalink)  
 
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the R-44 has power well beyond the MP limitations
You need to add "whilst at sea level" to this statement.

Several years ago I was doing some pinacle approaches with a very experienced instructor to a peak at 5500' and around 30degrees (it wasn't in the UK :-) I was amazed how the power just ran out exactly like the limit charts said it would.
One of the reasons for derating the engine is to gain acceptable high-altitude performance without turbo- or super-charging the engine, both of which result in reduced reliability.

It's actually quite easy to work out mathematically, no test pilot required.

The Lycoming IO-540-AE1A5 engine in the R44 Raven II develops 300bhp full throttle at sea level. The maximum continuous power allowed is 205bhp - so during normal everyday operation assuming you observe the MAP limits this is all you will use and you'll be operating somewhere below full throttle. You can pull a bit more for five minutes but that's basically all you've got.

A normally-aspirated piston engine loses approximately 3% power per 1000ft increase in density altitude.

If your pressure altitude was 5500 feet at 30C that gives a density altitude of 8620 feet, and full throttle engine power is reduced to approximately 209bhp. So now you're operating on the same power limit in terms of available bhp, but this time at full throttle and you certainly do not have "power well beyond the MP limitations".

I designed a spreadsheet to examine the effects of weight, balance, and density altitude on flight performance during my training to help myself understand what effect the different parameters had. Anyone interested can download it here.
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Old 11th Sep 2008, 12:21
  #33 (permalink)  
 
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with people skills like that topend I see why you are so good with your books....
Thanks for the compliment, you better believe it, we start with the book and the basics, like being able to hover inside a cricket pitch when you arrive with a brand new worthless CHL. The people skills pail well into the shade when we start examining the pilots skills I can tell you. Keep reading, and you'll learn lots more.
cheers tet
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Old 11th Sep 2008, 19:23
  #34 (permalink)  
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unbelievable!

you make a good case for giving up reading my friend (on here anyway)

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Old 12th Sep 2008, 12:59
  #35 (permalink)  
 
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gauge, (guage)

Hey tet I'm back!
Can you tell me why pilots; and engineers; cannot spell the simple word gauge?
My theory is that because any word starting with q is always follows by a u, gauge, gauge is often misspelt guage.
Any thoughts?
thekite
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Old 12th Sep 2008, 13:05
  #36 (permalink)  
 
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Isn't it Roget's Profanisaurus? Other than that quibble, I agree completely.
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Old 13th Sep 2008, 11:56
  #37 (permalink)  
 
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roger's profanisaurus
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Old 13th Sep 2008, 12:32
  #38 (permalink)  

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The people skills pail well into the shade when we start examining the pilots skills I can tell you. Keep reading, and you'll learn lots more. cheers tet
That's it, in a bucket.
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Old 13th Sep 2008, 13:03
  #39 (permalink)  
 
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Hey tet I'm back!
Can you tell me why pilots; and engineers; cannot spell the simple word gauge?
My theory is that because any word starting with q is always follows by a u, gauge, gauge is often misspelt guage.
Any thoughts?
thekite
Yes,
I am thinking, thinking deeply now that this bloody mosquito turnout might not be such a good idea if'n the good book that came with it canner even spell! We're holding our breath to see just what may be on the dashboard. up, down etc, This way, that way??
cheers tet
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Old 2nd May 2014, 05:45
  #40 (permalink)  
 
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Manifold Pressure (Again) R22

I was ask a question recently that really I couldn't answer:

How much does 1 inch of manifold pressure lift?

I later found out that for the R22 (helicopter taken for the example) the answer is 50lb (roughly), but why, and how do you come up with that number?
It's something you have to estrapolate from the OGE or IGE chart, bigger more complex helicopter have this kind of charts already but not small helicopters like robinsons.

Another question was also, how much temperature is 1 inch of manifold pressure equivalent to?
The answer is 20C and I think, but I'm not sure, if you look at the OGE chart and see how high you can hover at 20C then drop to 0C you'll see that you gain 1000 ft which is around 1 inch of MP. "I THINK" this is how it works but if not and someone knows the right answer please jump ahead.


Thank you all!!
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