Pre-1980 VW Beetle Gas Turbine - Episode IV - A New Hope

Electronic only please. Will be relying on fuel flow to dial in rpm for idling/noise testing etc.

For the next test session we're going to be concentrating on rpm measurement and noise reduction.

RPMs

Leaving the idea of measuring fuel flow we're going to just use the fuel tank valve fully open to measure max compressor turbine rpm (60k rpm nominal)and then try to find a reasonably stable 'tickover' speed by reducing fuel flow. Won't be far short of 20k if we're lucky. At the free turbine end the volute puts out 88 lbs/min of air at 43psi. According to 'classic horsepower required to compress air' calculations that little lot takes a theoretical 88hp with an additional 10-20% due to frictional losses. This way we will see the actual rpm at the output shaft under load and that will allow us to tune our reduction box ratio.

At the volute end we can use my Facebook Marketplace £10 mechanical tacho which goes up to 50k rpm.





At the compressor end we take off the oil pump end plate



where we have a hollow shaft that I can make up a temporary plug for with a white mark on the circumference for my cheapo handheld optical tacho



Moving on

Noise

Dragging some pics from the Restricted files we can see that turbine was fully enclosed. The covers were titanium and so all have disappeared down the scrapyard.





Now we get to the 'Please don't judge me' section. We needed some trial, temporary and mostly cheap sound reduction panels and the bodge is strong in me. If we get a worthwhile noise reduction then we can invest in metal panels with high temp insulation.

First up, need to move the Lucas high power ignition exciter.





Side panels out of some old 10mm ply as they won't see much heat





Got the ignition cable touching an oil return. Chance of it abrading to a dangerous point nearly zero but why risk it.



Moved.



Cut the other ply side panel and then scratched my head over what to use for the hot top panel. Bingo (don't judge me) I found a bit of plasterboard. It will smell but won't burn.



Cut a bit of stainless sheet to go over the exhaust to be able to balance the diffuser on top



Drat, diffuser bore is just too small so Colin the Sheetmetal King is knocking up a short length of 330mm diameter ducting and I turned a bit of strip into a band clamp.



Next up, obviously the testing, but also pull the spare turbine out of its transport frame to weigh the frame and see how we can reduce the weight that I reckon is 40 kilos. My original idea of building a frame out of aluminium extrusions may not be suitable.

It's been a month and it's not stopped raining long enough for the field to be firm enough to do the next noise and rpm testing. The rolling 4WD chassis will turn up when it turns up so all I've got to be carrying on with is some fiddle faddle and lightweight frame work.

The noise and rpm measurement is important to future developments because after delving into even more very dry documents there are tantalising hints that the project may become simpler than I could even dream. The two bits of information are

(1) that at free turbine stall the residual torque may be only 4 ft lbs which means no N₂ brake is needed. This level of parasitic torque might make the car creep but could be easily controlled with the car brakes.

(2) that under load the free turbine can be turning at only 22,000 rpm and not the rated 46,000 rpm. That means we could only need a single stage reduction and we have a bit of a cunning plan if that is so.

Otherwise Colin the Sheetmetal King got me the 330mm collar and by 'eck can he size something accurately.





It fits



Now to do something about the horrible rectagonal sheet and utilising an old woodworking trick to get a larger concentric circle marked





Then a combination of tinsnips and RSI got me this and the sense of achievement when the two ends met to millimetre precision just like the channel tunnel



I'll make some hold-down tags so the exhaust doesn't blow the diffuser off and now to remove the the spare turbine from the humongous transport frame. I was supposed to have help with the 160lbs of reasonably delicate turbine.

First off the rigid mounts



Oopoh look the overspeed sensor output for the free turbine. I have some plans for this.



Can't use the lifting eye because it's well shrouded by the Nimrod inlet, So it's going to be wrestling a lump of metal.



Much cursing and skinned knuckles later it's on the high tech wooden pallet



And there's the transport frame ready for weighing and downsizing



Fingers crossed for a week of fine weather

High praise from a builder like you Sir.

Picture(s) please

Sadly this is a familiar tale where the low life scum in society can basically do what they like and the police don't want to stop them, its much easier for them to deal with the decent people in society and control them to temper the situtation.  Ultimately they don't care who is right and who is wrong, they just want everyone to shutup so they can go back to eating donughts and drinking coffee.

We used to have one of those on the last rig I worked on, used it a few times ( but never at your kind of rpm) always seemed accurate and very stable.

Something in my mind, about spooling up to get the speed needed,...... Nick Mann (he of Morris Minor fame) has a 4wd Mallock style car with a BDG? which used a constant speed turbo, powered by a helicopter starter motor. which was spun up with a big CO2 cylinder so it could be started.

It's my fault for recycling old batteries. Plan is to have a paddock start cart along with two of these in series giving the required 24V for onboard starting. It should be 28V but who's counting?