First use of percentage Nr/N1?
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First use of percentage Nr/N1?
Can anyone tell me the history of the use of percentages to calibrate Nr? What was it originally 100 per cent of? When did we first get to do the impossible and exceed 100 percent?
And why don't they make all limits the same? For example, absolute max EGT/ITT/TOT/TGT, N1, N2, Nr, Tq, OEI Tq, Oil Press, Oil temp, Trans oil t/p, etc, should all be 100. And I dont necessarily mean percent. It could be 100 bananas, elphants, whatchymacallits, or percent, or even just "100" period. Why do we care that it was a 2 psi overtorque, or a 12 degree overtemp? Surely the overtorque/overtemps actual values are irrelevant to the driver (though not the engineer), so why not just call it an overtemp? Why have to remember so many different numbers? Why cant they all be calibrated to read max at 100, next at say 95 and so on?
Imagine only needing one set of figures to fly all helicopters.....Engine failure on any twin? Always pull to 100 bananas Tq, 100 bananas N1, 100 bananas N2, and 100 bananas turbine temp. What is the max oil temp in this aircraft? 100 bananas, always is. What is the max transmission temp I am allowed in the hover? 100 bananas of course! What is the max generator load? It is always 100 bananas!!
Pilot to Engineer.." I've just overtemped the engine" Engineer: "By how much?" Pilot: "By a few bananas, is that serious?" Engineer looks up table: "A few bananas equals 15.256 degrees celcius!" Pilot: "yeah, but is it serious?"
AHHHH Nirvana....??
[ 25 August 2001: Message edited by: helmet fire ]
Imagine only needing one set of figures to fly all helicopters.....Engine failure on any twin? Always pull to 100 bananas Tq, 100 bananas N1, 100 bananas N2, and 100 bananas turbine temp. What is the max oil temp in this aircraft? 100 bananas, always is. What is the max transmission temp I am allowed in the hover? 100 bananas of course! What is the max generator load? It is always 100 bananas!!
Pilot to Engineer.." I've just overtemped the engine" Engineer: "By how much?" Pilot: "By a few bananas, is that serious?" Engineer looks up table: "A few bananas equals 15.256 degrees celcius!" Pilot: "yeah, but is it serious?"
AHHHH Nirvana....??
[ 25 August 2001: Message edited by: helmet fire ]
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This is amazing I just logged on to discuss the same thought. I was actually going to ask Nick why we have 107%NR on the 76. It interesting that we all consider it normal to have limits that exceed 100%?!?
I understand on the 76 with the first models the NR % was less and as they fitted other engine types the performance and spec's changed.
I bet Nick has an answer.....
I understand on the 76 with the first models the NR % was less and as they fitted other engine types the performance and spec's changed.
I bet Nick has an answer.....
Without getting into the merits/demerits of the R22, it flies normally at 104% Nr.
I heard that this was due to the initial design calling for a certain RPM, but flight testing required 104% of that, and to change everything to be based on 100% Nr would have cost too much.
Seems reasonable to me.
I heard that this was due to the initial design calling for a certain RPM, but flight testing required 104% of that, and to change everything to be based on 100% Nr would have cost too much.
Seems reasonable to me.
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I'm one of the dunderheads that helps set the percents, so heap on the blame! Really, we have to simply understand that the thing you are reading/using/controlling to is % of a REFERENCE, not % of a LIMIT. Wanna see someone get more than 100% out of a fixed value, look at my checking account.
While it would be convenient to simply make 100% always the max, we'd have to rescale all gages every time we upped a rating or a speed. Since we design the gages and transducers before we test the system to set the limits, we'd have to re-design the stuff after test. That would cost even more, both to us when we make the stuff, and you when we send out the re-certification paperwork that allows you to operate to new limits.
If we rerate a system to higher limits now, all we do is mail out the paperwork, and all you have to do is paint on a new red line. If we tore out all the gages, you'd have to buy the new stuff at your expense.
Computers make it easier, so you'll see more consistant limits in the future. With the S-76 Turbomeca installation, rather than have folks try to keep up with limits that change with ambient temperatures and atmospheres, we used a computer to always reference to the same percentage, making it much more likely the we would all obey the limit.
The S-76 rotor speeds were set by a team that I was on, and we used the "reference" logic. 100% is 675 feet per second tip speed, and 107 is 725. We intended to allow free selection within that range, so the pilot could optimize the performance. At low altitude, the 100% was better for speed and range (about 4 knots) and by about 5000 feet the 107 was better. Growth in gross weight for the B, C and C+ made it necessary to grab the extra main and tail rotor thrust by setting the Nr up to 107% for all operations.
While it would be convenient to simply make 100% always the max, we'd have to rescale all gages every time we upped a rating or a speed. Since we design the gages and transducers before we test the system to set the limits, we'd have to re-design the stuff after test. That would cost even more, both to us when we make the stuff, and you when we send out the re-certification paperwork that allows you to operate to new limits.
If we rerate a system to higher limits now, all we do is mail out the paperwork, and all you have to do is paint on a new red line. If we tore out all the gages, you'd have to buy the new stuff at your expense.
Computers make it easier, so you'll see more consistant limits in the future. With the S-76 Turbomeca installation, rather than have folks try to keep up with limits that change with ambient temperatures and atmospheres, we used a computer to always reference to the same percentage, making it much more likely the we would all obey the limit.
The S-76 rotor speeds were set by a team that I was on, and we used the "reference" logic. 100% is 675 feet per second tip speed, and 107 is 725. We intended to allow free selection within that range, so the pilot could optimize the performance. At low altitude, the 100% was better for speed and range (about 4 knots) and by about 5000 feet the 107 was better. Growth in gross weight for the B, C and C+ made it necessary to grab the extra main and tail rotor thrust by setting the Nr up to 107% for all operations.
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Nick: Understood, and thanks for the reply. Did the early helicopters like the R4 have instruments calibrated in percentages? Or did they read in RPM? Do you know which helicopter first used percentages as a unit of calibration? I presume that on that machine, 100 per cent would have been max, and subsequent upgrades would have given us our current happy situation.
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t'aint natural:
The early recip stuff was all in actual rpm, but I don't know when the percent thing kicked in. The Huey was in rpm for rotor and N2, and percent for N1. We used to read the engine rpm at 6600 ("plus 50 for each dependent" according to legend).
This is where Lu might remember and help out.
The early recip stuff was all in actual rpm, but I don't know when the percent thing kicked in. The Huey was in rpm for rotor and N2, and percent for N1. We used to read the engine rpm at 6600 ("plus 50 for each dependent" according to legend).
This is where Lu might remember and help out.
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Vorticey, made the comment about "all Greens", would it not be easier for the Pilot to be able to scan Green, Red or Amber instead of trying to look for a line of percentage, after all most pilots are experienced enough to know where and what there machine is doing, but a quick glimpse at colours would be easier, would'nt it?
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Some observations on limit displays
The use of colours for display is useful with parameters such as oil pressure where all the pilot is realy interested in is "is the oil pressure OK" ie in the green with possibly an amber section so that a drop in pressure can be noted (as per Lynx eng oil pressure indications). Using colours for changing parameters such as Tq or Ng is less ideal as the pilot needs an indication of how much green (Tq) he has available so this brings in an element of parameter assimilation which is generally quiker with some sort of analogue display. Colour is useful on a Tq indicator, particularly a digital one where the displayed digits change colour as a limit is reached (eg EH 101). The EC120 uses a First Limit Indication (FLI) which combines engine and transmission parameters and presents the pilot a figure (I think its up to 10) that he can "pull" to and, while the actual limit may change from Tq to Ng as the conditions change, the pilot still flies to their FLI of 10.
Ay observations, or corrections to the above gratefully received
The use of colours for display is useful with parameters such as oil pressure where all the pilot is realy interested in is "is the oil pressure OK" ie in the green with possibly an amber section so that a drop in pressure can be noted (as per Lynx eng oil pressure indications). Using colours for changing parameters such as Tq or Ng is less ideal as the pilot needs an indication of how much green (Tq) he has available so this brings in an element of parameter assimilation which is generally quiker with some sort of analogue display. Colour is useful on a Tq indicator, particularly a digital one where the displayed digits change colour as a limit is reached (eg EH 101). The EC120 uses a First Limit Indication (FLI) which combines engine and transmission parameters and presents the pilot a figure (I think its up to 10) that he can "pull" to and, while the actual limit may change from Tq to Ng as the conditions change, the pilot still flies to their FLI of 10.
Ay observations, or corrections to the above gratefully received
