Post by racket on Dec 19, 2014 18:23:29 GMT -5
Hi Guys
A decision has been made to construct the ..... "Fat Boy" 12/118 thrust engine ...... 12 inch diameter casing , with a 118mm compressor intake hole in the front .
Mass flow ~3.6 - 3.8 lbs/sec with a Pressure Ratio of ~3.5 to 3.7:1 , I've designed "conservatively" for the lower flow and PR but if things perform a tad better than expected , maybe I'll get closer to the higher figures...........I can dream
Turbine wheel will be the trusty TV94 wheel with 129mm inducer and ~106mm exducer ...................yeh yeh ,I know , I've been telling everyone for years that the turb exducer has gotta be a lot bigger than the comp inducer rather than being 12mm smaller as in this case , but theres going to be severe clipping of the turb exducer to increase its flow potential by ~50%.
Now normally a lot of clipping of the exducer reduces the turbines power producing capability, but this billet wheel at modest Pressure Ratios should be getting efficiency levels near 80% if combined with a good vaned diffuser, this then reduces the power required from the turbine wheel allowing me to remove a big chunk of the exducer , leaving just enough to provide a tad of gas deflection when outflow velocities are up near 1,500 ft/sec , lotsa expansion within the turb wheel where it can be done efficiently , leaving minimal pressure ratio across the jet nozzle ...........the velocity triangles for the turb stage look OK on paper at 60,000 rpm
Standard brass bush turbo bearings will be used.
With a bit of luck and a few minor mods ,I should be able to use the wooden patterns I made for my 12 inch cased FM-1 engine , I designed that engine with a very wide radial vaneless space between comp exducer and diffuser vane leading edge to hopefully produce an engine that coped with fast throttle changes , that extra wide radial space now becomes a pleasantly normal space with the new larger exduced compressor wheel.
Actual diffuser vane axial height can be "adjusted" ( machined off) to suit the design requirements of rpm , tip speed, air velocity and density , again I made the patterns with plenty of vane height ............LOL, I must have had a premonition of what was coming a decade down the track .
The FM-1 flametube dies for making the end pieces/cap have been machined to suit the new 12/118 engine's flametube , I made the FM-1s flametube "oversized" diametrically as I was unsure of any potential combustion problems that might have occurred with having a very short flametube , subsequent flametubes for the 9/94 and 10/98 showed me there wasn't anything to worry about , so I've trimmed down the dies to produce more generous flow areas around the 12/118 flametube and in the process maybe lower some losses .
Possibly having 27 evaporators in a couple of concentric rings , 18 in the outer with 9 evaps in the inner , I want to use up the evaporator tubing I already have which was left over from my other engine builds .
Thrust calcs give ~210 pounds "dry" with close to 300 "wet"
Thats about all to report at present , I'm waiting on getting the FM-1 patterns back so that I can modify them with a view to having castings done in the new year .
Cheers
John
A decision has been made to construct the ..... "Fat Boy" 12/118 thrust engine ...... 12 inch diameter casing , with a 118mm compressor intake hole in the front .
Mass flow ~3.6 - 3.8 lbs/sec with a Pressure Ratio of ~3.5 to 3.7:1 , I've designed "conservatively" for the lower flow and PR but if things perform a tad better than expected , maybe I'll get closer to the higher figures...........I can dream
Turbine wheel will be the trusty TV94 wheel with 129mm inducer and ~106mm exducer ...................yeh yeh ,I know , I've been telling everyone for years that the turb exducer has gotta be a lot bigger than the comp inducer rather than being 12mm smaller as in this case , but theres going to be severe clipping of the turb exducer to increase its flow potential by ~50%.
Now normally a lot of clipping of the exducer reduces the turbines power producing capability, but this billet wheel at modest Pressure Ratios should be getting efficiency levels near 80% if combined with a good vaned diffuser, this then reduces the power required from the turbine wheel allowing me to remove a big chunk of the exducer , leaving just enough to provide a tad of gas deflection when outflow velocities are up near 1,500 ft/sec , lotsa expansion within the turb wheel where it can be done efficiently , leaving minimal pressure ratio across the jet nozzle ...........the velocity triangles for the turb stage look OK on paper at 60,000 rpm
Standard brass bush turbo bearings will be used.
With a bit of luck and a few minor mods ,I should be able to use the wooden patterns I made for my 12 inch cased FM-1 engine , I designed that engine with a very wide radial vaneless space between comp exducer and diffuser vane leading edge to hopefully produce an engine that coped with fast throttle changes , that extra wide radial space now becomes a pleasantly normal space with the new larger exduced compressor wheel.
Actual diffuser vane axial height can be "adjusted" ( machined off) to suit the design requirements of rpm , tip speed, air velocity and density , again I made the patterns with plenty of vane height ............LOL, I must have had a premonition of what was coming a decade down the track .
The FM-1 flametube dies for making the end pieces/cap have been machined to suit the new 12/118 engine's flametube , I made the FM-1s flametube "oversized" diametrically as I was unsure of any potential combustion problems that might have occurred with having a very short flametube , subsequent flametubes for the 9/94 and 10/98 showed me there wasn't anything to worry about , so I've trimmed down the dies to produce more generous flow areas around the 12/118 flametube and in the process maybe lower some losses .
Possibly having 27 evaporators in a couple of concentric rings , 18 in the outer with 9 evaps in the inner , I want to use up the evaporator tubing I already have which was left over from my other engine builds .
Thrust calcs give ~210 pounds "dry" with close to 300 "wet"
Thats about all to report at present , I'm waiting on getting the FM-1 patterns back so that I can modify them with a view to having castings done in the new year .
Cheers
John
