Manifold Pressure R22
 

It seems to me that with the large amount or derating on these engines, resulting in more power available at higher altitudes etc, could the MP limitation be theoretically raised for operations at lower alts, lower disc loadings etc etc....

comments?

You can pull what you like from the engine, it's the transmission that'll suffer.
That's why the engine's limited.:ok:

The main danger is that you'll over pitch the blades, if you have an engine hiccup or a magneto cough the rotor will stop in the blind of an eye. They're de-rated for a reason !!:ok:

Words fail me!
Are you just saying this to wind us up?
Just excuse me for a short while whilst I consult Roger's Profanisaurus for a suitable reply.
Are you really saying that it's designed-in to cover the possibility of a magneto problem?
No, it's no good, I really have to lie down.

Bloody hell!

The redline on the MAP gauge, is just that, a red line on a guage. We all know it'll pull more than that:eek:

In theory, yes you can pull more power than red line on the MAP guage in an R-22, but you WILL over torque the transmission....


Oh, and if you try that trick on the R44 your going down quick!.....They have NO power left once you get to red line!

Aye, but there's the rub.
We all know that there's a red line on the gauge, but what most don't realise is that there is a graph up in the roof that doesn't have a red line. But it does have a manifold limit.
I still contend that this graph is needed to preserve the integrity of the transmission. So does Frank Robinson.
Not of significance to those backing-up into cranes and ordering bacon butties:eek:

Tosh. The 44 has a stack of power that isn't used - just read the POH. As has been said above, the red line is there for a reason and it isn't a lot to do with the engine. However, the 2200hrs of life is based on operating within manufacturer limits.

It's a question of whether you care enough about the next people to get in the heli. And the next. And the next. Most overspeeds, overstresses and exceeding of limits don't show up for a few more hours.

ELT2GO : are you really a pilot ? Your thought process is somewhat worrying.

There have been cases of blades failing in the R22 with as little as 6-700 hrs on them. Its one thing to momentarily exceed manifold pressure to get out of a bad situation.......its entirely different to do it on purpose just because its there :=:=:=

Mike

If you are talking about the ag machine in New Zealand that was a slightly different situation. He used the 'big twist and heave' t/o method. That means he opened the throttle (well ABOVE the red section on the tacho) and heaved the collective up until it's 'light on the skids' so they can do a cushion creep t/o. It's quite a standard procedure in NZ ag circles and quite nessecary when overloading by 200-300 lbs is standard practice. Only in NZ...

Basically the question is why are there red lines on the gauges, they are only blocking the vision!!!!

With an attitude like that, I highly recommend you to refrain from flying.

ETL2GO,
I'll assume your enquiry is genuine so at the risk of repeating what some have already said, here's my 2 cents worth. The manifold pressure guage gives you an indication of the torque being produced by the engine -
Yes, you can ignore the guage & pull power in any model R22 until the RRPM droops.
Yes, you will get away with it for a while.
Yes, the drive belts will shred & depart the scene eventually.

Theres no call to pull more power than the red line indicates..

With any exceedance, you can lie to your boss, and you can lie to yourself, but you can't lie to the machine...

as i expected a wide range of input, some even intelligent.....I come from a part of the world where practicality is more often required, things are not always done by the book.
I'm not saying I condone it, personally I strive to remain within any limitations, thinking about not just the transmission, but the whole machine, especially the drive train, grips, spindles, feathering bearings, blades, TR d/s...the list goes on....and obviously the future pilots and more especially the future pax who use the machine........

however, back to my original question....surely there is a great deal less stress on all these components in lower disk loading / torque manouevers than others...

i'm interested in hearing from designers perhaps who have a working knowledge of the principles here....

also it would be nice if we could act a bit like grown ups and share some opinions, instead of casting petty aspersions.....

I believe Mr. Lappos has a certain reputation in the field of design so maybe his words on
this thread will help you.

when that fails try this recipe.

an' if you still canner make sense of it even by this method

then here's the fail safe method.

do it by the book
cheers tet

ETL2GO

My grown up opinion is that if your interest is simply academic, it's interesting, but you should never knowingly exceed the gauge other than in a life-threatening situation and should disclose it every time.

If your purpose is at all to conceive of scenarios where you might, at some time in the future, use your freedom of choice as a pilot in command to pull more MAP than permitted in what you consider to be a practical and safe manner, please have the decency to leave a list of machine names you use so the rest of us can have the freedom of choice to avoid them.

That's not a petty aspersion, just a statement of fact that a lot of us who rent aircraft depend on the fact that everyone before us has acted according to the POH for their own and their passengers safety.

BW

When I had my beloved little R22 beta II my belly was a bit bigger than it is now. (Ironically now that I have lost weight I fly a 44 II).

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.

SB

R-22 manifold Pressure Limitation
 

Suggest you write a letter, or call the Chief Test Pilot at Robinson and just ask about the derivation of that limitation. He will know and will be happy, I'm sure, to pass it along.

Thanks,
John Dixson

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

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

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.

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

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...:ugh:

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.

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:ok:) and save a lot of confusion.

Cheers
TS

Just going back to the original question as below. it is a nonsense of contradiction


.

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.

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.

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.

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.

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

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

with people skills like that topend I see why you are so good with your books....:8

You need to add "whilst at sea level" to this statement.

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.

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

unbelievable!

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

:ugh:

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

Isn't it Roget's Profanisaurus? Other than that quibble, I agree completely. :ok:

roger's profanisaurus:ooh:

That's it, in a bucket.

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

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 20°C and I think, but I'm not sure, if you look at the OGE chart and see how high you can hover at 20°C then drop to 0°C 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!!