Author Topic: I need a jet engine  (Read 893 times)

Offline Rickshaw

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I need a jet engine
« on: August 16, 2019, 01:15:52 PM »
I need a jet engine.  It must have been comparable with the J79 in service life and about 3/4 the diameter.   Any ideas? 

Offline tankmodeler

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Re: I need a jet engine
« Reply #1 on: August 17, 2019, 01:01:42 AM »
I need a jet engine.  It must have been comparable with the J79 in service life and about 3/4 the diameter.   Any ideas?
Comparable in what way? Time of service? Cost? Fuel efficiency? Thrust?

If it's thrust, you're pretty much out of luck. Thrust is governed by mass flow and for similar performance you need similar mass flows. Mechanically things that hold the engine together require a certain mount of space at the centreline of the engine and military engines have always pushed the packaging of their engines as tight as possible so the minimum diameters for a given airflow have not changed much over the years. And a more modern turbo fan, while providing more thrust at lower engine mass, usually does so by increasing the diameter to accommodate the low (or high) bypass duct of the engine.

And, because the mechanical gubbins of an engine doesn't really scale well with the airflow, even much lower performance engines don't really get much smaller than the old school turbojets. The 38" diameter of the J79 is really hard to beat unless you're willing to go down to really small jets in the 4-7,000 lb thrust category.

Paul

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Re: I need a jet engine
« Reply #2 on: August 17, 2019, 03:26:30 AM »
I need a jet engine.  It must have been comparable with the J79 in service life and about 3/4 the diameter.   Any ideas?
Comparable in what way? Time of service? Cost? Fuel efficiency? Thrust?

Yeah.  I assume you are also talking about a 'Western' engine in the same approximate era as the J79.  Given the J79 has a diameter of between 0.973 - 0.992m depending upon version, you are looking at something in the 0.73 - 0.74m diameter range.  A EJ200 (diameter 0.74m) might work, especially given the thrust (13,250 lb dry/20,000lb AB) though not sure how this stacks up for your era.  A Rolls-Royce/MAN Turbo RB.153 (diameter 0.749m) as used in EWR VJ 101D might also work though again depends upon era plus thrust is a lot less (6850 lb dry/11,645 lb AB vs ~10,000lb dry/~18,000lb AB depending upon version).  Finally, some of the RR Vipers are another option (diameter 0.74-0,75m) though again thrust much lower (~4000 lb dry/~5000lb AB).
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Offline Rickshaw

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Re: I need a jet engine
« Reply #3 on: August 17, 2019, 11:19:42 AM »
OK, just to be a little bit clearer - this engine must be around when the J79 arrives on the scene - that is what I meant by "comparable".  Thrust should be near equal or better, if at all possible.   However that is, upon reflection not going to be likely.  However it needs to be about .75 the diameter of a J79.

Offline Jeffry Fontaine

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Re: I need a jet engine
« Reply #4 on: August 17, 2019, 11:46:00 AM »
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Offline M.A.D

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Re: I need a jet engine
« Reply #5 on: August 17, 2019, 01:09:46 PM »
I need a jet engine.  It must have been comparable with the J79 in service life and about 3/4 the diameter.   Any ideas?

Oh, I smell something cooking  :P
Bring it on, I say!!


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Re: I need a jet engine
« Reply #6 on: August 18, 2019, 02:17:11 AM »
OK, just to be a little bit clearer - this engine must be around when the J79 arrives on the scene - that is what I meant by "comparable".  Thrust should be near equal or better, if at all possible.   However that is, upon reflection not going to be likely.  However it needs to be about .75 the diameter of a J79.

I don't believe you are going to find an engine (at least not a turbojet) of that era and that size that is comparable.  The GE J79 was simply groundbreaking when it arrived.  It set the new standard against which everything else was measured.
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Offline Rickshaw

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Re: I need a jet engine
« Reply #7 on: August 18, 2019, 09:56:42 AM »
Maybe this link can help in your quest: Jet Engine Specification Database - Nate Meier (jet-engine.net)


Thanks!  That is exactly what I am looking for.  Just needs the years introduced added to it! 

Offline elmayerle

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Re: I need a jet engine
« Reply #8 on: August 18, 2019, 11:49:03 AM »
OK, just to be a little bit clearer - this engine must be around when the J79 arrives on the scene - that is what I meant by "comparable".  Thrust should be near equal or better, if at all possible.   However that is, upon reflection not going to be likely.  However it needs to be about .75 the diameter of a J79.

I don't believe you are going to find an engine (at least not a turbojet) of that era and that size that is comparable.  The GE J79 was simply groundbreaking when it arrived.  It set the new standard against which everything else was measured.
I'll agree.  The J79 introduced variable compressor stators which allowed a single-spool engine to be smaller, lighter, and just as efficient as a twin-spool engine of comparable performance (compare the J79 and J57).  I did some checking, the comparably performing J52 came slightly later and has the same maximum diameter as the J79, though the afterburning version didn't come along until significantly later and then was derailed by world events.

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Re: I need a jet engine
« Reply #9 on: August 19, 2019, 01:52:35 AM »
Maybe this link can help in your quest: Jet Engine Specification Database - Nate Meier (jet-engine.net)


Thanks!  That is exactly what I am looking for.  Just needs the years introduced added to it!


It still won't help you as the engine you are looking for does not exist.  I was referencing my copy of Elodie Roux's Turbofan and Turbojet Engines Database Handbook when I did my searches for you and there is nothing that matches the spec of what you were after in the timeframe you were after.  You can also do searches on the lists on that link and you will also come up short.  Simply put, there is nothing of the size you are after with the performance wanted until much later than the J79 (e.g. the EJ200).  Everything else, such as the after burning J52 Evan mentioned (it was the PW1216 BTW) is still much larger than the size you are looking for.  I even tried looking at things that might theoretically be developed into something such as cancelled projects or the like and came up with nothing that was able to meet both the size and performance levels.
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Offline jcf

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Re: I need a jet engine
« Reply #10 on: August 22, 2019, 03:21:17 AM »
My read of Brian's request is that he's simply looking for a smaller diameter engine with
similar dates of introduction, production and service use, not of similar performance.
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Offline jcf

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Re: I need a jet engine
« Reply #11 on: August 22, 2019, 07:17:08 AM »
Viper and J52 fit the rough introduction and service parameters, although neither are 75% the size of the J79
and grew in size over time. Note that Wikipedia J52 entry giving a diameter of 38" is wrong.

« Last Edit: August 22, 2019, 07:19:50 AM by jcf »
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Offline elmayerle

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Re: I need a jet engine
« Reply #12 on: August 22, 2019, 08:23:43 PM »
Note that Wikipedia J52 entry giving a diameter of 38" is wrong.
I rather suspected that, ISTR that it has a diameter roughly similar to that of the F404.

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Re: I need a jet engine
« Reply #13 on: August 23, 2019, 01:57:51 AM »
My read of Brian's request is that he's simply looking for a smaller diameter engine with
similar dates of introduction, production and service use, not of similar performance.

Diameter, era etc is easy.  However, this part:

Quote
Thrust should be near equal or better

is not...
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Offline jcf

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Re: I need a jet engine
« Reply #14 on: August 23, 2019, 02:56:38 AM »
My read of Brian's request is that he's simply looking for a smaller diameter engine with
similar dates of introduction, production and service use, not of similar performance.

Diameter, era etc is easy.  However, this part:

Quote
Thrust should be near equal or better

is not...

Missed that part in his later post.

So he is looking for a unicorn.  ;D
"Evil our grandsires were, our fathers worse;
And we, till now unmatched in ill,
Must leave successors more corrupted still."
Horace, 65BC - 8BC. Marsh translation.