Test run 14 Dec 2000 Cone On/Cone Off, to 1.0 Bar


After several attempts to properly calibrate the stand, I feel I have finally arrived at some valid numbers. Additionally, I have been putting off making the cones because basically, I was being chicken. I could see no way to accurately roll the tiny inner cone with a pretty aggressive taper. In the end, a quick call to Dennis solved the problem, and a set of ready-made cones was here in a couple of days.

The cones Dennis supplies are devoid of tabs... these were up to me. I decided to depart from print by making the supports which connect the inner and outer cones to consist of four 0.625" SS cap screws, with a sheath of 316 SS protecting the screws in the hot exhaust stream. Once snugged tight, the inner cone was firmly fixed. This method requires a total of 8 drilled holes, and provides a neat appearance.

Remember please that these tables are only up to 1.0 bar until I can fit a reliable rev counter! Extrapolation of the cone-on numbers to ~1.4 bar shows my engine will easily deliver in excess of 12 lb thrust. Yay!

Cone Off, OAT 5 C.
PSI BAR EGT Thrust - lb
5.0 0.34 464 2.19
7.5 0.52 452 3.76
10.0 0.69 448 4.94
12.5 0.86 444 6.19
15.0 1.03 454 7.56
The finished cone assembly. Note the round stand-offs which support the inner cone rather than tabs. Four tabs were spot-welded to the cone outer and are secured to the case rear.
Cone On, OAT 5 C.
PSI BAR EGT Thrust - lb
5.0 0.34 537 2.56
7.5 0.52 508 4.25
10.0 0.69 492 5.56
12.5 0.86 500 7.00
15.0 1.03 506 8.50
This side of the newly-run cone shows even temperatures. The other side has one spot at 10:00 (facing the turbine) which is slightly hotter, and which is where the EGT is measured.

Interestingly, the ratio of thrust cone-on vs. cone off is a relatively constant 1.125

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