Another question about horsepower

[xouper]

The other horsepower thread (http://www.randi.org/vbulletin/showthread.php?s=&threadid=28060) has inspired me to post a related question. This is not a trick question and I do not currently know the answer, but would like to.

How much horsepower is required to spin the first stage fan of a typical small jet engine, such as the AlliedSignal (Garrett) TFE731? Assume the engine is stationary at sea level. To ask the same question another way, how much torque is required at say 10,000 RPM (which is near 100% for the TFE731-5)?

[Iamme]

xouper---Why don't you e-mail the tech department at say Pratt & Whitney, if you are truly interested?

[Iamme]

....or, Allied Signal.

[xouper]

Iamme: xouper---Why don't you e-mail the tech department ...I tried that once before, but got no reply. But I can try again. Here is the email I just sent to Joe Hough, Customer Service Product Manager:

<div style="border: solid black 1px; margin: 0 32px 0 0; padding: 24px; background-color: #fff8f0;">Greetings,

Where can I find rpm and torque data for the TFE731 family of engines? I am interested specifically in the data for the first stage fan only. How much torque is required to spin the fan at 100 percent rpm, stationary at sea level, and also at typical cruising altitude? Torque vs rpm curves would be even more useful. Thank you for your attention to my question.

Sincerely,</div>

[Iamme]

xouper---I have posted this before on these threads: For tech info there is a lot of interesting stuff...and MORE people that like to show you up:D at "alt. energy" There are message boards there. Try it. Challenge someone there to help you directly, or indirectly. Plyus..you might get hooked on those boards. i was over there for a while...but I don't know about EVERYTHING:roll: ...but it's fun reading what others have to say about the various subject matter there. You could maybe learn how to run your jet on french fry oil or something.:D

In fact...now that I brought it up...I think I'm going to pay that place a visit and refresh myself as to what is all being offered over there.

[Iamme]

Ask Google "jet + engines"

The threads there look like they are going to be up your alley. Somebody maybe could help you there.

[xouper]

Iamme: alt. energyI am tempted to think I might get better results in the rec.aviation newsgroups where there is quite a bit of aviation related expertise, but an answer is certainly not guaranteed, if my previous experience there is any indication.

I just thought I'd take a shot at posting it here in JREF because 1) I hang out here more often, 2) there are some aviation savy people here, 3) it is somewhat related to the other horsepower thread here, 4) sometimes ya never know what topic may be interesting or lead to an interesting thread drift, and 5), I am testing out questions for the upcoming JREF "stump the experts" contest.

Ask Google "jet + engines"That seems a bit too broad for my question. I have already been googling for TFE731 and can't find the torque info. I have been googling for years and have learned a few tricks, but sometimes I still get stumped, like now. To me, a better google search is "turbofan + torque" but even that doesn't narrow it down enough. But thanks for the suggestions, they are always welcome.

[Iamme]

But xouper....did you actually try going to that last Google site and scroll down. It looks like somebody there should be able to help you, or steer you to who could. There are people there making homemade jet aircraft. These types must really be into this stuff and you'd think they would be 'savvy' on things, or be able to have a good dialogue with you on any other related matter.

Hey...get that stump the stars thing going. Everyone here likes to THINK they are fairly intelligent, and they will fall into your lair.:D

[Skeptoid]

There's probably an article in a back issue of Aviation Week containing everything you'd ever want to know about the TFE731.

[NWilner]

You are asking for the power required to drive the compressor section in a free turbine. No one in aviation would approach it from the torque times RPM angle, because torque is typically not measured at the compressor section. (In fact I don't know that anyone in aviation would approach this question at all). The answer lies in treating the compressor as a pump and in computing the work of compression per unit time. The work of compression is taking a weight of air at such and such a temp and compressing it. Immediately many complications arise. Do you wish to include a momentum term for the oncoming air; is the compression close enough to adiabatic to use that approximation? What's happening with the power section? Is the prop fixed and we're flowing gas around the stalled power turbine blades? Are we driving the compressor through the endstage turbine (normal) or by some external means? Probably a complete analyitical solution will not be possible and approximations or even numerical modeling will be required. Standing back from the details, it remains true that for most combustion engines, including gas turbines, work on the world represents about 20% of available energy into the system. 80% is lost in waste heat, which is where the energy used to compress the gas generator (your question) eventually goes, joined by waste heat from the exhaust and other heat sources.

[xouper]

NWilner: You are asking for the power required to drive the compressor section in a free turbine.To clarify, I am just asking about the bypass fan, which could theoretically be driven by an electric motor instead of a gas turbine. The TFE731 has a bypass ratio of 3:1 so most of the air is not being compressed for the turbine, but contributes directly to thrust.

[xouper]

NWilner: No one in aviation would approach it from the torque times RPM angle, because torque is typically not measured at the compressor section. (In fact I don't know that anyone in aviation would approach this question at all).Well, an obvious question comes to mind. Without knowing the torque load, how can the engineers know strong to make the shaft connecting the LP turbine stage and the bypass fan?

Interestingly, the Compressor Research Facility at Wright-Patterson Air Force Base has a test stand for testing "fans and compressors under operating conditions similar to an actual flight profile. ... The facility can handle most compressors from operational engines and can be used to obtain updated compressor performance maps."

This test stand is rated for testing fans at 3,000 to 16,000 rpm and up to 30,000 hp (or up to 30,000 rpm at 15,000 hp). That's a big honkin' motor they have on that stand for spinning fans or compressors. Obviously I could be wrong, but I infer from this that among other data, they measure rpm and torque curves for various fans they test. That's the data I am trying to find for the TFE731 bypass fan.

[Rocky]

On a turbo-shaft motor they have Total HP and Shaft HP, compressor HP would be T-S = C (you knew that) which is perhaps 25-60% of the total. I think what you are looking for would be the same as shaft HP since that is the amount of work that the motor actually provides. If you want a rough guess of the power required to spin the "Fan" part of the TFE731, take 60-70% of the total HP. ( I haven't been able to find total TFE731 HP yet) (I bet you knew all of this already) :)

[xouper]

Rocky: If you want a rough guess of the power required to spin the "Fan" part of the TFE731, take 60-70% of the total HP.Curiously, I hadn't thought to derive a ballpark estimate from that direction. Thanks.

The turboprop equivalent of the TFE731 is the TPE331, which as I understand it shares a common core with the TFE731. The TPE331 family (depending on model) ranges from about 700 to 1100 shaft horsepower. This would suggest that the power required to spin the bypass fan of the TFE731 would also be in the range of 700 to 1100 hp (depending on model). As a rough estimate.

[Rocky]

Originally posted by xouper
Curiously, I hadn't thought to derive a ballpark estimate from that direction. Thanks.

This would suggest that the power required to spin the bypass fan of the TFE731 would also be in the range of 700 to 1100 hp (depending on model). As a rough estimate.

Glad to help. I've seen motors listed as say 3000 HP but when you look close they are 2000 SHP, the rest is just to keep the motor running. Still, lots of HP in a small box.

Are you looking to build a piston powered Mach plane? :D

[xouper]

Rocky: Are you looking to build a piston powered Mach plane? :D Shhhh. Actually, I'm looking at building a single seat, mach .7 airplane with a 1600 hp rotary engine using Mazda parts (w/ eight rotors).

[Rocky]

Originally posted by xouper
Shhhh. Actually, I'm looking at building a single seat, mach .7 airplane with a 1600 hp rotary engine using Mazda parts (w/ eight rotors).

I had some friends that were running multi rotor Mazda motors in land speed cars. Very small frontal area and lots of power.

Good Luck.

Oh BTW most people (perhaps you as well) consider Mazda motors to be piston. Some people say they are not.

[NWilner]

I meant no one in aviation would probably try to calculate the required torque based on predicting the individual l/d of the airfoil sections in the fan....I think they would assume a certain percentage of total hp is used to compress the gas and, knowing the rpm, could derive the torque.

To hear that the work of compression per unit time is 60% or so of the total hp does not surprise me but I don't really have a ref for that.

[xouper]

Rocky: I had some friends that were running multi rotor Mazda motors in land speed cars. Very small frontal area and lots of power. Rotary engines for aircraft use have many significant advantages over traditional aircooled piston engines.

Oh BTW most people (perhaps you as well) consider Mazda motors to be piston. Some people say they are not.The rotary is a four stroke, Otto cycle engine, same as a piston engine. The rotary also qualifies as a piston engine under the terms of the Reno Air races.

[xouper]

Yesterday, I got an answer from Ron Ashby, Manager, Customer Service Engineering, Business Aviation Customer Support, Honeywell Engines and Systems:

<div style="border: solid black 1px; margin: 0 32px 0 0; padding: 24px; background-color: #fff8f0;">Richard, we do not have torque and rpm charts readily available. What we do have for you is for the TFE731-60. I have attached a PDF chart from a sales brochure that lists thrust vs mach and a page for calculating horsepower. N1 speed, thus the fan speed is dependent on altitude and air temperature, thus it is rarely at 100% speed, but on a cold day you will be getting 100% thrust. Below are two points with torque: Sea Level Static, ISA +17 Deg C day at take off the engine is generating 2330 ft-lbs of torque at the fan. 40K feet, Mach 0.8, ISA cruise the engine is generating 840 ft-ilbs of torque at the fan.</div>

2330 ft-lb * 10,000 rpm / 5252 = 4336 hp.

That seems high. However, if that torque number is for less than 100% rpm, then the hp is correspondingly less. In any case, my earlier guesstimate of 1100 hp was way off. Other models of the TFE731 produce less thrust than the model -60 (not to mention a smaller bypass ratio), so I assume the hp to spin one of those bypass fans would also be less.

[ceptimus]

The interesting argument I saw about the wankel engine is how you calculate its displacement (swept volume). For each rotor, should you take into account one, two, or all three chambers? Should you check for one revolution of the 'crankshaft' (power output shaft) or one rev of the rotor?

Norton did well with a wankel engine powered racing bike a few years back, but many people I spoke to said they were cheating. Norton claimed the engine was (IIRC) 500cc, but using some other formulas it was double that or more.

[xouper]

ceptimus: Norton did well with a wankel engine powered racing bike a few years back, but many people I spoke to said they were cheating. Norton claimed the engine was (IIRC) 500cc, but using some other formulas it was double that or more.Mazda lists the displacement of their 13B rotary as 1308cc, but as I understand it (no cite handy), most racing organizations that allow rotaries to race against pistons classify Mazda's engine at twice the listed displacement.

When Mazda entered their 4-rotor car (2616cc displacement) in the 1991 Le Mans 24 hour endurance race (in category 2, no displacement limit), it won handily and rotaries were subsequently banned from racing in the Le Mans.

But this is a quibble about how to classify the effective displacement of a rotary, an issue which is not relevant to airplanes or airplane racing (yet).

Compared to traditional piston engines, rotaries have excellent power to weight ratios, are pretty much bullet-proof, they don't wreck the airframe with excess vibration, smoother power pulses allow for a lighter and thinner (and thus higher performance) propeller, and they have a benign failure mode. The only downside is a small penalty in fuel consumption and the requirement to inject 2-cycle oil into the combustion chambers for cooling and for lubricating the rotor seals.

[LFTKBS]

BORRR-ING!

Just kidding - whatever floats your boats (or powers your jets).

[Rocky]

Originally posted by xouper

2330 ft-lb * 10,000 rpm / 5252 = 4336 hp.

That seems high. However, if that torque number is for less than 100% rpm, then the hp is correspondingly less. In any case, my earlier guesstimate of 1100 hp was way off. Other models of the TFE731 produce less thrust than the model -60 (not to mention a smaller bypass ratio), so I assume the hp to spin one of those bypass fans would also be less.


Can you get a fuel consumtion (GPH) value and compair it to known motors?

BTW I just got back from the Bonneville Salt Flats, I drove at 199.7 mph. I wanted to go over 200 :mad: