Hi Luc
I'll have to disagree about roller bearings being better , the GT6041 is used on a lot of BIG CAT diesel engines of >2,000 hp that vibrate like hell for thousands of hours on end ................the oil damping effects increase life of a turbo , all the huge ABB ship turbos run brass bushes for 30,000 hour TBOs.
Springer ..........bloody Springer , he's been the bane of my life, I've spent countless hours helping guys who've read Springer and constructed engines that won't work .......Springer knows "shit all" about turbine engines .
Lets take an example ..... a 4" inducer ............ yes his area is correct at 12.57 sq ins and 0.087 sq ft , but thats where it stops being correct ....................with an average turbo inlet velocity of ~475 ft/sec for good efficiency , the static pressure has dropped from 14.7psia to ~12.7 psia , that 475 ft/sec is worth ~2psi of dynamic pressure which when added onto the 12.7psia restores us to the 14.7 psia total pressure we had in the ambiant air before it was accelerated thru the nozzle ( bellmouth) into the compressor wheel, the compressr wheel doesn't suck the air in , ambiant air " forces" its way in by changing some static for dynamic pressure .
Now air at 12.7 psi has a density of ~0.066 lbs/cu ft, and with say 475 ft/sec through an area of 0.087sq ft , thats ~41.3 cubic ft /sec , multiplied by our 0.066 lbs/cu ft gives us a mass flow of 2.72 lbs/sec , nowhere near Springers 6.67 lbs/sec figure , a Garrett GT6041 has a mass flow of ~2.75 lbs/sec thru its 4.16" dia inducer ..................there is some inlet choking of a GT6041 at high rpm due to the relative air speed at the inducer tips going supersonic because of the wheels 56 Trim , most high pressure wheels are <50 Trim , preferably low 40s Trim .
So we can now say Springers figure from here on will all be incorrect .
A well built DIY engine will produce a jetpipe total pressure of ~24.7 psia or ~10 psi on a the gauge supplied from a pitot tube in the jetpipe. ....................10psi indicates a potential Pressure Ratio across the jet nozzle of ~1.68 :1 and will produce a jet velocity of ~1650 ft/sec , thrust = mass flow times velocity , 2.75 X 1650 div by 32.2 =140.9 lbs of thrust for a GT6041 nowhere near Springers 269 lbs for a 4 incher.
If we were to use Springers mass flow of 6.67 lbs/sec that would produce a thrust of 341.8 lbs .......................he knows bugger all about the maths .
As for his flametube design, it doesn't work , far too small a cross section resulting in too high an airspeed for the combustion of kero , also the hole areas are all wrong , and the fact that he uses an annular dilution ring at the bottom of the flametube , an area which will change due to both axial and radial expansions of the metal parts resulting in a change in dilution area percentages ..........I could go on and on and on
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DO NOT USE SPRINGER'S PAPER, ITS CRAP .
Cheers
John
