Propeller torque & engine torque

[italia458]

oggers:

You accusing me of holding out info and trying to guilt trip me has been bugging me. I shared all the resources I was using throughout this discussion. You and everyone else had access to them on here. I posted the whole AfNA document section on the propellers where it talks about induced power. The reason I hadn't picked up on this earlier and put the two together is because I hadn't read the article word for word and analyzed it. I also hadn't come across the article which you posted about Figure of Merit. Once you did post that, I picked up on it right away and I think it actually backfired on you! It added more evidence to the fact that you don't know what you're talking about. I highlighted that in my last post.

But I should ask the same of you: Have you been holding out this information knowingly as I constantly repeat myself in post after post, trying to explain THP? Have you been sitting on this information? Why didn't you speak up earlier about it? What proves that you haven't just been trolling the whole time, like someone else has mentioned in this thread, and knew all along about this?

I'm not responsible to teach you everything about aerodynamics. You need to take responsibility for your learning. You can't blame me for you not thinking about the efficiency of the prop in creating the thrust. I mentioned that there were other efficiencies that can be analyzed and I agreed that the propeller is doing work on the air. Did I really have to tell you that if anything is doing work, there is a way to analyze the efficiency of the object doing the work? I'm not responsible to think of everything for you.

You finally discovered something that would add to the discussion and then you blame me for not telling you earlier. You really are a piece of work.

[oggers]

In the quote you used, I said THP is relative to the distance the aircraft moves with reference to the earth. That's incorrect. It's TAS, which is flight velocity and explicitly states as so in the Aerodynamics for Naval Aviators text. I made a mistake.

That's right. You did make a mistake. But not just in that quote (which was actually two quotes anyway). No. You reiterated it across 4 pages:

I have been very clear in describing that if the 'vehicle' is not moving...

.....the distance that the aircraft moves with reference to the earth...”

...when the helicopter is in a fixed position over the ground...

...if the aircraft isn't moving, it isn't covering distance and so the work = zero. When work = zero, Power also = zero.

etc etc.

Who are you trying to kid? You made it central to what you've been prattling on about. Now finally you've dropped it.

You accusing me of holding out info and trying to guilt trip me has been bugging me

Well, maybe it will help if you go back and read between the lines. I wasn't really accusing you of holding out info. I was suggesting that it hadn't occured to you.

But let's just be clear about one thing. After 4 pages you have now done a ma-housiv u-turn and decided that the aircraft can stay still after all and still output power from the prop.

[oggers]

blackhand:

The best thread hijack for 2012

Gets my vote

[Old Fella]

Flat Rated

Aerbat77. The Allison is not flat-rated and to clarify my comment on reaching the limiting T.I.T I was simply saying that, especially on the T56A-11 it was common to reach max permissable T.I.T before achieving limiting torque.

[italia458]

oggers:

We had never talked about a wind before and I had assumed that there would be no wind. Therefore, with no wind, TAS is the same as GS.

You hold onto it as if you 'won' or something. If you really were thinking about wind before, you would have made a comment about it the first time I mentioned a position relative to the ground. You also forgot to highlight the times when I referred to the same speed as "TAS". Of course you wouldn't want to provide an unbiased view because that would mean you don't really have a point in this case. I think its quite obvious to everyone that neither of us was thinking about wind.

I should also point out that out of the 4 quotes you posted, only 2 actually relate to what you were talking about. #2 and #3 mention earth or the ground. But #1 and #4 only mention motion.

You never addressed the recent 'issues' I brought up in my last 2 posts about what you said about induced power. It seems as though you actually can't admit being wrong at all. You would never be a good scientist or engineer.

I think the original point of discussion between us was if the aircraft velocity was zero, I said there would be zero THP and you obviously did not agree because you said this:

Not that myth again. It's disappointing to have to point out to one who calls himself an instructor that in your 'brakes on' scenario the aircraft is still producing 200 THP as well as 200 BHP because it is accelerating a mass of air rearwards in a futile attempt to turn the earth and the atmosphere in opposite directions. Come on italia, pull your socks up. These are fundamentals that instructors should have a grip on.

So, has this discussion changed your answer now, or do you still believe that the THP will equal the BHP because it's 'accelerating a mass of air rearwards'? After this discussion it's quite obvious that I have a better 'grip' on the fundamentals of aerodynamics than you do!

EDIT:

After 4 pages you have now done a ma-housiv u-turn and decided that the aircraft can stay still after all and still output power from the prop.

Where did I say that the prop does not do work on the air when the aircraft is not moving? I never said that! So, to put it bluntly, you are lying.

[barit1]

And so when a PW4000 runs up to max on a terrestrial test bed, it is actually creating ~70,000 thrust HP? Is that what we surmise?

[barit1]

Old Fella:

...on the T56A-11 it was common to reach max permissable T.I.T before achieving limiting torque.

Hmmm. Since the aircraft performance is dependent on the props being driven at some torque rating, I must ask how you determine your performance-limited TOGW??

[italia458]

barit1:

And so when a PW4000 runs up to max on a terrestrial test bed, it is actually creating ~70,000 thrust HP? Is that what we surmise?

No. THP has to do with aircraft performance. When it's on a testbed, you wouldn't be analyzing THP. The engine would be producing thrust and you could compute how efficient the engine is in making thrust (ie: accelerating air).

EDIT: However, if you were to apply the concept of THP to the testbed scenario, the THP would be zero because the testbed/engine wouldn't be moving.

[oggers]

italia:

So, has this discussion changed your answer now, or do you still believe that the THP will equal the BHP because it's 'accelerating a mass of air rearwards'?

Not changed my pov. BHP x PE = THP. [notwithstanding Tx losses obviously]

After 4 pages you have now done a ma-housiv u-turn and decided that the aircraft can stay still after all and still output power from the prop.

Where did I say that the prop does not do work on the air when the aircraft is not moving? I never said that! So, to put it bluntly, you are lying.

Well, what I wrote and what you wrote underneath it aren't the same. But taking your little statement at face value, you are clearly accepting there that there is a power output from the prop even if the plane is stationary.

An equation for PE (that you have used yourself) is power output divided by power input. An equation for THP is BHP x PE. If you acknowledge there is a power output from the prop you must acknowledge there is THP.

I look forward to reading the wriggling you will do to mitigate this conclusion. Not that I've entirely finished myself.

No. THP has to do with aircraft performance. When it's on a testbed, you wouldn't be analyzing THP

I think most people here, being aviation professionals, would feel the putting of an engine on a tested had quite a lot to do with aircraft performance. Unless you are a glider pilot.

[italia458]

oggers:

You're wrong. End of story.

There is no point explaining it anymore.

Good day!

[Old Fella]

Limiting MTOW

Barit1, I probably did not articulate my point as well as I might. All I was trying to convey was that the 19600"/lbs limiting torque was often not achievable before reaching the Max permissable Turbine Inlet Temperature, especially on the T56A-11 which from memory was limited to 971 degrees C at Take-off power and 927 degrees C Max Continuous. The T56A-15 however with a higher T.I.T limit could readily reach Max Torque below the limiting T.I.T of 1083 degrees C for Take-off. Of course, achievable Torque for the given ambient conditions and Runway length available, surface type etc all are considered to determine Max Take-off weight allowed. Hope this is clearer.

[rudderrudderrat]

Prop Torque

Hi,

In my reply (post #24), On RR Tyne with 4 bladed variable pitch props, we had to have both Prop RPM and torque within limits before we called power was set. The engine and gearbox were bolted together so it was not possible to measure their individual torques separately.
Hence the torque sensor (which was bolted between an engine mount and the airframe) simply measured the reaction to the propeller torque - so it indicated actual Prop Torque.

In order to keep passenger comfort during stepped climbs, we kept the prop RPM constant, but varied the fuel flow by "trimming" the (guarded) HP fuel levers. Power changes were called for ("50% trim" etc) and measured by observing the torque.

Since we measured both torque (force) and prop RPM (velocity) one could calculate the propeller horse power being generated (with a known p.e.) - even when stationary on the runway

Since there is no torque meter fitted on a bypass jet engine, the most useful parameters are N1 / EPR which only give an indication of thrust, not power.

Edit for Capt Pit Bull's comments below.
Rolls-Royce Tyne - Wikipedia, the free encyclopedia
"RTy.1 Mk 506
3,259 kW or 4,985 e.s.h.p"

[blackhand]

only give an indication of thrust, not power.

mmm mumble mumble walking away.
Is that because there is no electricity?

[Old Fella]

RPM & Torque

rudderrudderrat, the Allison T56 is essentially a constant speed engine/gearbox/propeller installation with propeller blade angle selectable only in the 'ground' range of throttle lever travel (except feathering or unfeathering of course). Once in the 'flight' range (flight idle to 90 degrees throttle angle) the throttle simply schedules fuel flow and the propeller is governed to 100% RPM (1021 RPM) + or - 2% in basic hydraulic governing mode. The obvious advantage in having such an engine is almost instantaneous response to throttle movement (limited to not moving the throttle from Flight Idle to Max in less than 1 second) Without getting the purists throwing stones the torque value indicated on the C130 is the load imposed on the engine torque shaft ( and thus the engine itself) by the reduction gearbox, accessories and propeller. This whole thread seems to have become the site for "ego boosting" by some, surely not what the original poster was looking for. I am sure you, barit1 and I each would understand that as a crew member our concern would be "Have I got the torque or power I expect within the RPM and T.I.T limitations applicable and, if not, why not?" I am familiar with the use of N1 and EPR (or IEPR on the RB211 engine) as a measure of thrust. Whether we call the motive force Horespower, Thrust, Torque or any other name doesn't really matter. Every aircraft I have operated has had a specific set of parameters which are to be met before and during flight.

[Capt Pit Bull]

Sorry I'm late.

Italia is correct (give or take the odd minor slip / assumed simplification e.g. zero wind etc).

Oggers, you don't understand efficiency.

An engine in a test bed does NOTHING except churn up air thereby producing heat. If the object an engine is attached to does not increase in the total of GPE +KE as a result of the efforts of the engine then no *useful* work is being done. Likewise a person straining on a wrench is just producing heat. In both cases energy is certainly used, but not usefully.

This is my one and only post on the topic. Oggers, you have a long ingrained 'alternative framework'. Unless you are at least prepared to consider that something you think you understand could be wrong I, like italia, see no point in spending any time over it.

pb

[oggers]

Oh yeah nice one Pitbull. I'll chalk that up to being 1st Apr

[oggers]

Capt Pit Bull:

The issue I’m disputing is the assertion by italia458 (note, he raised it, not me) that a plane at standstill can knock out 200 BHP and generate static thrust, yet there is zero THP.

“italia is correct.”

That’s a very definite conclusion to draw from the rather subjective argument you offer.

“Oggers, you don't understand efficiency.”

‘Power out over power in’ is pretty uncontroversial.

Unless you are at least prepared to consider that something you think you understand could be wrong I, like italia, see no point in spending any time over it.

THP = BHP x PE. If the thrust is not zero, PE cannot be zero, therefore THP is not zero. There is another equation out there based on airspeed for an arcraft in flight but it does not invalidate this one or vice versa. The trouble is Pit Bull, that italia458 is insisting it does, and you assert that he is correct. I would call that dogma and therefore I have to chuckle at the irony of your post.

“An engine in a test bed does NOTHING except churn up air thereby producing heat."

It develops thrust.

"If the object an engine is attached to does not increase in the total of GPE +KE as a result of the efforts of the engine then no *useful* work is being done..”

Well, hopefullly the engine won't "increase in the total of GPE + KE" during the test because that wouldn't be terribly "useful work". It is on the test-bed for a reason. It is developing thrust and fulfilling a purpose other than moving an aircraft. You are entitled to your opinion - in a certain context I would agree with it - but it does not lead me to the conclusion that the propeller efficiency is zero, or that static thrust = zero THP.

Applying this to the helo scenario, if I want to maintain a steady hover, the work done on the air which provides the thrust to keep me there is 100% useful work. In no sense is it wasted.

[aerobat77]

oggers ´n italia : do you not have more important things to sort out in your life?

[oggers]

I squeeze it in between the pilates and AA meetings.

[ft]

If you're not doing any useful work, you can't claim to be efficient. End of story.

As for your uncontroversial proof of understanding, it dictates that if the Joules leaving the system per time unit equals the Joules entering the system per time unit, efficiency is 100%. Any less than 100% efficiency, and less Joules leave the system than enter it.



That's pretty amazing, and proves Pitbull's point rather nicely.