Qs about turbofans

jetman · July 30th, 2003, 23:47

How fast [RPM] does the fan [N1] and the the turbine [N2]turn in a turbofan engine at full power?
Do the blades go supersonic?
If they do is there a shock wave and sonic boom inside the engine?
Thanks for input jetman

Eagle · July 31st, 2003, 05:40

The N1, N2 are read in percentages, not in RPMs.

So as for what the actual speed is... who knows?

Mr_Creepy · July 31st, 2003, 06:38

Well you're supposed to know!!! It's in your FSI training I hope! Although I suppose it doesn't matter much.

The Beech 1900 turns 104% at 39,000 rpms. 100% is something like 37,842 I believe.

Of course, I would have to ground the airplane if I see it only turning 38,999 at 104 % !!!!!

NOT!

Yeah you're right. Who knows? And who cares?

Doug Taylor · July 31st, 2003, 12:07

I dug around a 727, 737-200/300 and my MD-88/90 flight manuals and I couldn't find any reference to an actual number.

But alas, a quick telephone call to Juegen Badura who is the MD-88/90 Technical Manager for Delta says that at 100% on the MD-88 engine (Pratt&Whitney JT8D-219), the RPM is about 8,900 or so and the compressor/turbine blades do not go supersonic.

Hey, how's that for customer service!

PhotoPilot · July 31st, 2003, 19:26

Wow! 39,000 RPM is 650 rotations per second! I'm not yet a pilot and won't even pretend to know anything in-depth about a turbine engine, but MAN that sounds fast.

Doug's numbers seem a bit more possible to my internal-combustion-on-the-ground brain, but I suppose that there could be a large difference in RPMs between two engines. Where did you get the higher numbers from?

Just curious!

(And who knows! Maybe I'll need to know in 5 or 10 years when I might actually be flying a turbine aircraft!

)

FlyChicaga · July 31st, 2003, 20:47

In the Saab, our gas generator is around 44,720 RPM at 100%, and the propeller is around 22,000 RPM at 100%. 1750 SHP.

Baronman · July 31st, 2003, 21:05

[ QUOTE ]
22,000 RPM at 100%. 1750 SHP

[/ QUOTE ]

Those some fast moving blades!!

Might wanna check that before your next test!!

PhotoPilot · July 31st, 2003, 21:10

My internal-combustion-on-the-ground brain is humbled! Even though I look at them every time I fly commercially, I am VERY impressed that someone can build engines that withstand the heat, rotational speed, and structural stresses encountered every day by turbo-fans. 44,000 RPM! Dang!

And I think I'm hot stuff for learning to work on my own car . . .

Alchemy · July 31st, 2003, 22:32

39,000 RPM ????

Let's say the compressor blades are 4 feet in diameter. That means a circumference of about 12.6 feet. So they're moving 12.6 feet 39,000 times every minute, that's 490,088 ft per minute, 8,168 ft per second, or 5,569 miles per hour, roughly mach 7.3 at sea level under standard conditions. Wouldn't the engine disintegrate at these speeds?

Doug Taylor · July 31st, 2003, 23:35

[ QUOTE ]
39,000 RPM ????

Let's say the compressor blades are 4 feet in diameter. That means a circumference of about 12.6 feet. So they're moving 12.6 feet 39,000 times every minute, that's 490,088 ft per minute, 8,168 ft per second, or 5,569 miles per hour, roughly mach 7.3 at sea level under standard conditions. Wouldn't the engine disintegrate at these speeds?

[/ QUOTE ]

Yup, I remember those numbers from Beech 1900 training.

I failed to ask Juergen at what point the engine is running at 8,900 -- which seems pretty low if you ask me.

Alchemy · July 31st, 2003, 23:51

wow, I didn't realize they moved that fast.....impressive stuff. So is a lot of the noise from jet engines the result of mini-sonic booms from the fan blades or am I way off.

I've read "The Turbine Pilot's Flight Manual" per doug's reccomendation and they didn't delve too deeply into shaft rotation speeds......

Doug Taylor · July 31st, 2003, 23:54

[ QUOTE ]
I've read "The Turbine Pilot's Flight Manual" per doug's reccomendation and they didn't delve too deeply into shaft rotation speeds......

[/ QUOTE ]

Primarily because it really doesn't matter that much.

Even N1 and N2, in a real basic sense, don't really matter as much as ITT or "Inter Turbine Temperature". The engines can almost spin themselves to light speed, but if the temperature gets too high, party over.

jetman · August 1st, 2003, 00:34

Thanks guys for replies ,Doug it was very nice of you to dust off the old manuals and make the phone call, the service is EXCELENT

thank you.
About the 8900 RPM i guess that is the speed of the high pressure turbine NOT the speed of the fan[if the fan is 7 or 8 feet in diam. turning about 150 RP second the blades would travel at about 3750 feet per second kind of supersonic ////////
Take care guys jetman

FlyChicaga · August 1st, 2003, 05:11

[ QUOTE ]
[ QUOTE ]
22,000 RPM at 100%. 1750 SHP

[/ QUOTE ]

Those some fast moving blades!!

Might wanna check that before your next test!!

[/ QUOTE ]

Nope, that's correct. Plus, we have overspeed protection at 25,000 RPM (1573 Np, which is read as RPM but is divided by a computer to give us that number... divided by 15.9 I believe). Our normal Flight range of prop RPM is 1150 to 1396, multiply that by 15.9 and you get the actual RPM.

Mr_Creepy · August 1st, 2003, 06:32

PT67 (Beech 1900D engine) turbines are much smaller than 4 ft in diameter. I doubt they are even a foot. I used to show them in my ground school. Even the centrifugal compressor turbine fit pretty well in my hand. Probably about 9-10" in diameter.

Alchemy · August 1st, 2003, 08:02

ahh, okay, that makes more sense. with 10" blades the rotational velocity at the tips is only about mach 1.46 I think.

Buzo · August 1st, 2003, 11:33

The 1900C with PT6-65B's puts out 1100HP. The turbine speed like John said is 39,000 at 104%, and 37,468rpm at 100%. The prop rpm is reduced through a reduction gearbox to a max of 1700rpm. Above 1768 rpm a governor kicks in to prevent it from going faster.

A300Capt · August 1st, 2003, 11:49

[ QUOTE ]
In the Saab, our gas generator is around 44,720 RPM at 100%, and the propeller is around 22,000 RPM at 100%. 1750 SHP.

[/ QUOTE ]

I would think that reduction gear system would reduce the engine's high internal rotation speeds to something far lower for the propeller. I find 22,000rpm for the propeller much too high. Seems to me the the tips would go supersonic.

Mr_Creepy · August 1st, 2003, 12:31

I am sure he means the rpm before the gear ratio reduction. I know the 1900 has something like 17.6:1 reduction.

Let me do the math here. The Props turn at 1700 rpm when the Power Turbine is doing 29,920 rpm. 29,920 / 1700 = 17.6. Wow I was right!
Notice that the Power section does 29,920 and the compressor section can be going as fast as 39,000.

That is the "free turbine" principal, also known as the "air clutch" of the Pratt & Witney design.

Anyway in what I hope will be a final answer (Regis, is that your final answer?) to this thread:

No the turbine blades do not go supersonic. The shock wave would surely cause compressor stalls and probably serious damage to the engine.

FlyChicaga · August 1st, 2003, 12:33

Yeah, I was trying to say that. Take a look at what time I posted that... ugh

jetman · August 1st, 2003, 12:44

i guess the reason for me to ask about RPM was to figure out if the fan blades went supersonic and if so how is the problem of increased drag,shock waves,noise were solved.Same applies to compressors and turbine blades for they are all airfoils of some kind and have similar caracteristics to wings.
As for the smaller size of the turbine and compressors in turboprop engines,compare to turbofans, the power turboprops developed is much less than a turbofan engine also turbofans do not have a reduccion gear to power the fan that sares the same shaft with the low pressure compressor and probably is much slower than N2.
OK guys i did not mean to be a smart a........./// asking so many questions that are probably irrelevant to the everyday ops but i like to know and i found in this forum people MUCH MORE SMARTER than im and i hope toe learn something////

but ..............
Could the fan blades be made like a variable pitch prop to increase efficienciy?

maybe thats a topic for another day

.
regards jetman

ERAU_Intern · August 1st, 2003, 17:31

Actually jetman, there are a few engines in developent right now that have variable geometry fan blades. The problem is that this presents EXTREME complexity increases in already complex engines. You would need something to power the movent of the blades (pneumatic, hydraulic, or electric), and you would need a more sophisticated engine control system (FADEC), in order to accomplish this. The 777's fan blades actually break the sound barrier slightly at the tips, and if you listen to one go buy you, you will hear a growling sound as it passes. That is the sound of a bunch of little sonic booms in the engine housing, from the fan!

FlyChicaga · August 1st, 2003, 18:18

The technology for variable vanes doesn't need to be THAT elaborate. I mean, our Saab has them, so it can't be THAT complex!

hehehe

We have variable inlet guide vanes/variable stator vanes. The first three stages of stator vanes (between compressor blades) vary in pitch thanks to mechanical movement from the Hydromechanical Unit.

CF6_rep · August 2nd, 2003, 01:15

Looks like the others have answered for commercial engines, but I used to be a rep on the F110 engine that powers the F-16 C/D aircraft. That engine turned about 8,000 RPMs for the N2 and about 15,000 for N1 at full throttle. As a little side note, when we went into augmenter (afterburner) it was pumping about 55,000 lbs/hr.

Doug Taylor · August 2nd, 2003, 08:59

Here's a spot of trivia for you guys:

"What was the PT6 turbine engine originally designed to do?"

July 30th, 2003, 23:47	#1
jetman Junior Member Join Date: Jul 2003 Posts: 188	Qs about turbofans How fast [RPM] does the fan [N1] and the the turbine [N2]turn in a turbofan engine at full power? Do the blades go supersonic? If they do is there a shock wave and sonic boom inside the engine? Thanks for input jetman

July 31st, 2003, 05:40	#2
Eagle Banned Join Date: Oct 2000 Posts: 1,272	Re: Qs about turbofans The N1, N2 are read in percentages, not in RPMs. So as for what the actual speed is... who knows?

July 31st, 2003, 06:38	#3
Mr_Creepy Old Skool Join Date: May 2003 Location: In the O-zone Posts: 5,807	Re: Qs about turbofans Well you're supposed to know!!! It's in your FSI training I hope! Although I suppose it doesn't matter much. The Beech 1900 turns 104% at 39,000 rpms. 100% is something like 37,842 I believe. Of course, I would have to ground the airplane if I see it only turning 38,999 at 104 % !!!!! NOT! Yeah you're right. Who knows? And who cares?

July 31st, 2003, 12:07	#4
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 40,430 Blog Entries: 1	Turbofan ANSWERS :) I dug around a 727, 737-200/300 and my MD-88/90 flight manuals and I couldn't find any reference to an actual number. But alas, a quick telephone call to Juegen Badura who is the MD-88/90 Technical Manager for Delta says that at 100% on the MD-88 engine (Pratt&Whitney JT8D-219), the RPM is about 8,900 or so and the compressor/turbine blades do not go supersonic. Hey, how's that for customer service!

July 31st, 2003, 19:26	#5
PhotoPilot Senior Member Join Date: Jun 2003 Location: Indianapolis, IN Posts: 902	Re: Qs about turbofans Wow! 39,000 RPM is 650 rotations per second! I'm not yet a pilot and won't even pretend to know anything in-depth about a turbine engine, but MAN that sounds fast. Doug's numbers seem a bit more possible to my internal-combustion-on-the-ground brain, but I suppose that there could be a large difference in RPMs between two engines. Where did you get the higher numbers from? Just curious! (And who knows! Maybe I'll need to know in 5 or 10 years when I might actually be flying a turbine aircraft! )

July 31st, 2003, 20:47	#6
FlyChicaga Old Skool Join Date: Dec 2001 Location: Chicago, IL Posts: 4,801	Re: Qs about turbofans In the Saab, our gas generator is around 44,720 RPM at 100%, and the propeller is around 22,000 RPM at 100%. 1750 SHP.

July 31st, 2003, 21:05	#7
Baronman Senior Member Join Date: Dec 2001 Location: NEWARK Posts: 1,041	Re: Qs about turbofans [ QUOTE ] 22,000 RPM at 100%. 1750 SHP [/ QUOTE ] Those some fast moving blades!! Might wanna check that before your next test!!

July 31st, 2003, 21:10	#8
PhotoPilot Senior Member Join Date: Jun 2003 Location: Indianapolis, IN Posts: 902	Re: Qs about turbofans My internal-combustion-on-the-ground brain is humbled! Even though I look at them every time I fly commercially, I am VERY impressed that someone can build engines that withstand the heat, rotational speed, and structural stresses encountered every day by turbo-fans. 44,000 RPM! Dang! And I think I'm hot stuff for learning to work on my own car . . .

July 31st, 2003, 22:32	#9
Alchemy Old Skool Join Date: Aug 2001 Location: Austin, TX, USA Posts: 1,752	Re: Qs about turbofans 39,000 RPM ???? Let's say the compressor blades are 4 feet in diameter. That means a circumference of about 12.6 feet. So they're moving 12.6 feet 39,000 times every minute, that's 490,088 ft per minute, 8,168 ft per second, or 5,569 miles per hour, roughly mach 7.3 at sea level under standard conditions. Wouldn't the engine disintegrate at these speeds?

July 31st, 2003, 23:35	#10
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 40,430 Blog Entries: 1	Re: Qs about turbofans [ QUOTE ] 39,000 RPM ???? Let's say the compressor blades are 4 feet in diameter. That means a circumference of about 12.6 feet. So they're moving 12.6 feet 39,000 times every minute, that's 490,088 ft per minute, 8,168 ft per second, or 5,569 miles per hour, roughly mach 7.3 at sea level under standard conditions. Wouldn't the engine disintegrate at these speeds? [/ QUOTE ] Yup, I remember those numbers from Beech 1900 training. I failed to ask Juergen at what point the engine is running at 8,900 -- which seems pretty low if you ask me.

July 31st, 2003, 23:51	#11
Alchemy Old Skool Join Date: Aug 2001 Location: Austin, TX, USA Posts: 1,752	Re: Qs about turbofans wow, I didn't realize they moved that fast.....impressive stuff. So is a lot of the noise from jet engines the result of mini-sonic booms from the fan blades or am I way off. I've read "The Turbine Pilot's Flight Manual" per doug's reccomendation and they didn't delve too deeply into shaft rotation speeds......

July 31st, 2003, 23:54	#12
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 40,430 Blog Entries: 1	Re: Qs about turbofans [ QUOTE ] I've read "The Turbine Pilot's Flight Manual" per doug's reccomendation and they didn't delve too deeply into shaft rotation speeds...... [/ QUOTE ] Primarily because it really doesn't matter that much. Even N1 and N2, in a real basic sense, don't really matter as much as ITT or "Inter Turbine Temperature". The engines can almost spin themselves to light speed, but if the temperature gets too high, party over.

August 1st, 2003, 00:34	#13
jetman Junior Member Join Date: Jul 2003 Posts: 188	Re: Turbofan ANSWERS :) Thanks guys for replies ,Doug it was very nice of you to dust off the old manuals and make the phone call, the service is EXCELENT thank you. About the 8900 RPM i guess that is the speed of the high pressure turbine NOT the speed of the fan[if the fan is 7 or 8 feet in diam. turning about 150 RP second the blades would travel at about 3750 feet per second kind of supersonic //////// Take care guys jetman

August 1st, 2003, 05:11	#14
FlyChicaga Old Skool Join Date: Dec 2001 Location: Chicago, IL Posts: 4,801	Re: Qs about turbofans [ QUOTE ] [ QUOTE ] 22,000 RPM at 100%. 1750 SHP [/ QUOTE ] Those some fast moving blades!! Might wanna check that before your next test!! [/ QUOTE ] Nope, that's correct. Plus, we have overspeed protection at 25,000 RPM (1573 Np, which is read as RPM but is divided by a computer to give us that number... divided by 15.9 I believe). Our normal Flight range of prop RPM is 1150 to 1396, multiply that by 15.9 and you get the actual RPM.

August 1st, 2003, 06:32	#15
Mr_Creepy Old Skool Join Date: May 2003 Location: In the O-zone Posts: 5,807	Re: Qs about turbofans PT67 (Beech 1900D engine) turbines are much smaller than 4 ft in diameter. I doubt they are even a foot. I used to show them in my ground school. Even the centrifugal compressor turbine fit pretty well in my hand. Probably about 9-10" in diameter.

August 1st, 2003, 08:02	#16
Alchemy Old Skool Join Date: Aug 2001 Location: Austin, TX, USA Posts: 1,752	Re: Qs about turbofans ahh, okay, that makes more sense. with 10" blades the rotational velocity at the tips is only about mach 1.46 I think.

August 1st, 2003, 11:33	#17
Buzo Junior Member Join Date: Jan 2001 Location: Rockford, IL Posts: 256	Re: Qs about turbofans The 1900C with PT6-65B's puts out 1100HP. The turbine speed like John said is 39,000 at 104%, and 37,468rpm at 100%. The prop rpm is reduced through a reduction gearbox to a max of 1700rpm. Above 1768 rpm a governor kicks in to prevent it from going faster.

August 1st, 2003, 11:49	#18
A300Capt Senior Member Join Date: Oct 2000 Location: Louisville, Kentucky Posts: 709	Re: Qs about turbofans [ QUOTE ] In the Saab, our gas generator is around 44,720 RPM at 100%, and the propeller is around 22,000 RPM at 100%. 1750 SHP. [/ QUOTE ] I would think that reduction gear system would reduce the engine's high internal rotation speeds to something far lower for the propeller. I find 22,000rpm for the propeller much too high. Seems to me the the tips would go supersonic.

August 1st, 2003, 12:31	#19
Mr_Creepy Old Skool Join Date: May 2003 Location: In the O-zone Posts: 5,807	Re: Qs about turbofans I am sure he means the rpm before the gear ratio reduction. I know the 1900 has something like 17.6:1 reduction. Let me do the math here. The Props turn at 1700 rpm when the Power Turbine is doing 29,920 rpm. 29,920 / 1700 = 17.6. Wow I was right! Notice that the Power section does 29,920 and the compressor section can be going as fast as 39,000. That is the "free turbine" principal, also known as the "air clutch" of the Pratt & Witney design. Anyway in what I hope will be a final answer (Regis, is that your final answer?) to this thread: No the turbine blades do not go supersonic. The shock wave would surely cause compressor stalls and probably serious damage to the engine.

August 1st, 2003, 12:33	#20
FlyChicaga Old Skool Join Date: Dec 2001 Location: Chicago, IL Posts: 4,801	Re: Qs about turbofans Yeah, I was trying to say that. Take a look at what time I posted that... ugh

August 1st, 2003, 12:44	#21
jetman Junior Member Join Date: Jul 2003 Posts: 188	Re: Qs about turbofans i guess the reason for me to ask about RPM was to figure out if the fan blades went supersonic and if so how is the problem of increased drag,shock waves,noise were solved.Same applies to compressors and turbine blades for they are all airfoils of some kind and have similar caracteristics to wings. As for the smaller size of the turbine and compressors in turboprop engines,compare to turbofans, the power turboprops developed is much less than a turbofan engine also turbofans do not have a reduccion gear to power the fan that sares the same shaft with the low pressure compressor and probably is much slower than N2. OK guys i did not mean to be a smart a........./// asking so many questions that are probably irrelevant to the everyday ops but i like to know and i found in this forum people MUCH MORE SMARTER than im and i hope toe learn something//// but .............. Could the fan blades be made like a variable pitch prop to increase efficienciy? maybe thats a topic for another day . regards jetman

August 1st, 2003, 17:31	#22
ERAU_Intern Junior Member Join Date: Apr 2003 Location: Knoxville, Maryland Posts: 244	Re: Qs about turbofans Actually jetman, there are a few engines in developent right now that have variable geometry fan blades. The problem is that this presents EXTREME complexity increases in already complex engines. You would need something to power the movent of the blades (pneumatic, hydraulic, or electric), and you would need a more sophisticated engine control system (FADEC), in order to accomplish this. The 777's fan blades actually break the sound barrier slightly at the tips, and if you listen to one go buy you, you will hear a growling sound as it passes. That is the sound of a bunch of little sonic booms in the engine housing, from the fan!

August 1st, 2003, 18:18	#23
FlyChicaga Old Skool Join Date: Dec 2001 Location: Chicago, IL Posts: 4,801	Re: Qs about turbofans The technology for variable vanes doesn't need to be THAT elaborate. I mean, our Saab has them, so it can't be THAT complex! hehehe We have variable inlet guide vanes/variable stator vanes. The first three stages of stator vanes (between compressor blades) vary in pitch thanks to mechanical movement from the Hydromechanical Unit.

August 2nd, 2003, 01:15	#24
CF6_rep Newbie Join Date: Jan 2002 Location: Asia Posts: 5	Re: Qs about turbofans Looks like the others have answered for commercial engines, but I used to be a rep on the F110 engine that powers the F-16 C/D aircraft. That engine turned about 8,000 RPMs for the N2 and about 15,000 for N1 at full throttle. As a little side note, when we went into augmenter (afterburner) it was pumping about 55,000 lbs/hr.

August 2nd, 2003, 08:59	#25
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 40,430 Blog Entries: 1	Re: Qs about turbofans Here's a spot of trivia for you guys: "What was the PT6 turbine engine originally designed to do?"

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