501K History

Topics for the Marine & Industrial 501 Units

501K History

Postby j79guy on Tue Jan 20, 2009 10:39 pm

Interesting engine this.
Started out as the T38 turboprop engine, designed in 1949 as a lightweight, high specific output engine. (Type-I engine) As all turbine designs at the time were in their infancy, there was a lot of corporate espionage, and cross pollination between manufacturers going on, as the dearth of good information and real experience with turbine engines led to a few innovative designs springing forth, which would quickly be copied and show up in a completely different engine line and manufacturer. Allison having enjoyed the position of selling as many piston aircraft engines they could possibly make during war time, and the subsequent contracts they picked up from GE to manufacture the early single stage centrifugal compressor turbojets, were flush with cash and wanted to scratch build their own turboprop engine line.
The T38 had a tremendous amount of great ideas incorporated, but for a few shortcomings. Mainly, fixed geometry compressor stators, and to a minor degree, external "flame tube" type combustors. Well, they certainly could not be looked down on for these two less than stellar design details as everybody else were building their engines with the same two poor features.
Early flight trials were moderately successful, but the industry demanded more power. Solution? bolt two T38s together onto a cojoining gearbox, and call it the T40! It was a nightmare, and quickly died a natural death. Allison re-grouped, and did a re-design of the T38, using a couple new fangled ideas that seemed to be working for the competition. They added compressor bleed valves at the fourth and tenth stages of the compressor, jacked up the overall compression ratio, and put the combustors within the outer engine case. Perfection. (Well, perfection in the late 1950's) They went on to sell several thousand in Military T56, and Commercial 501D guise. (Type-II engines.) Later major upgrades included incorporation of air cooling the first & second stage turbine nozzles, and first stage turbine blades. (Type-III engines.) Introduction of single crystal first stage turbine blades, improved cooling regimens, and honeycomb type gas path sealing led to the current Type-IV engines.

Industrial applications started out in the early 1960's and really received popularity in the mid to late 1960's as reliable, tidy packages that delivered the goods. Allison had quite a few different model designations at the time and as I sift through the archives, I will try to list them here.
Some of the initial industrial engines were designated as 501K13C (Circa 1966) were based on the early T56-15 engines. (Type-III), which a few years later were re-named 501KB
501K13C were rated at 3,800 shp @ 1700 Degrees F. TIT. Very conservatively rated, they would chug away for years and not hurt the hot section. Over the years, I've purchased a couple of these units, inexpensively, as no one was quite sure what they were. We increased the first stage turbine blade cooling plate holes to modern 501KB sizing, and jacked the TIT up to 1830 Degrees F. TIT, with no ill effects, or reduction in overhaul life. Tough engines.
Other 501K13 models at the time were Series-II units, which led to considerable confusion. To alleviate this, Allison in the late 1960's started designating the Series-II engines as "501KA", and the Series-III engines as "501KB"

Some time ago I bought some "T56" overhaul tooling. What arrived had T40 stamped into each tool. I was dismayed at first, until I discovered that each and every tool fit the 501KB engine I had perfectly. Close lineage or what?

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