VT-50 Jr. Dragster (kindof)

[ashpowers]

Hi Feathers,

Admiration and props to your perseverance!

A few thoughts I have after going through your thread.....
(constructive mode = ON)

I recall you speaking of using an electrical approach to regulating oil pressure along the way and having some hurdles.... I also recall you saying you are using a gear pump for your lube system.

I wouldn't bother with trying to control pump pressure via a PWM speed controller - get a mechanical pressure regulator that uses a reference pressure input. Just like how a fuel pressure regulator works for an EFI system.. Johannson hit that on the head. Look at the Aeromotive EFI fuel pressure regulators - like the 1000 series they sell. Nicely machined parts with AN style ports, quality materials... This type of regulator uses a reference pressure source to control the oil pressure. Connecting this reference port to the combustor will create a system where the oil pressure will increase as combustor pressure increases, in a 1:1 relation. This configuration will allow you to adjust the regulator down to a ~40psi base pressure for startups and as combustor pressure increases it will increase oil pressure pound for pound.

Something I have found with gear pumps is that they dont produce a smooth pressure output. Might want to use a non-dampened oil pressure gauge if you dont already have one to monitor oil pressure fluctuations. This is less likely to be an issue when you go to a mechanically-based oil pressure control system as the pump will be running full speed and the regulator will also tend to buffer some of the ripple. Journal bearing turbos are very sensitive to pressure ripple in the oil feed - if you can see your oil pressure gauge jittering you should consider installing a dampener or accumulator, or both. Those VT/ST 50 turbos dont have much for a thrust bearing and you'll do it well to cover all bases on the lube side.

***** EDIT *** Bah - I see you are using a ShurFLO diaphragm pump - not a gear pump, FYI. This type of pump isn't quite as bad for ripple as a gear pump; 3 diaphragm overlap vs. 2-gear overlap. But again, that all depends on how fast you run it and what buffering you have inline between the pump and turbo cartridge.

You know, I've got like three of these turbos on hand and some additional bearing tubes as well. If it were me, I would find a set of SiN3 bearings to fit the shaft and make them fit into the cartridge. Ball bearing turbos require significantly less oil - they do not rely on hydrostatic pressure to float the rotating bits. In fact, comparatively speaking, you only want to give them just a little dash of lube. Too much lube and the balls will hydroplane and skid. With silicon ceramics you literally only have to lube them like remembering to change the central AC system's filter in your house.

...... ever start up a ball-bearing "turbo"jet engine before? Once you do, you'll never go back to journal bearing configurations.

ashspecz.com/Image%20Gallery/GasTurbineT4/Videos/GasTurbineT4Test3-384.mpg

For the love of god and all that makes a public forum great, you gotta post more pictures and videos of your work! That power turbine section got me buzzed but hardly jack for pictures for me to drool over! You have a great project going on here - SHOW IT TO US!!!

Looking forward to seeing your project come together - keep up the good work!

-Ash

[Feathers]

Ash,

Thanks for all the input!

A couple of clarifications on my part,

The oil system uses a ground-isolated DC oil pump driven by a simple, rugged, 555/mosfet PWM controller which I adjust as needed with the turn of a knob. The gear pump actually produces a very smooth, even pressure with very little ripple. I adjust a small ammount as the oil warms up, but the motor is running at about 1/4 speed to maintain 45 PSI oil pressure. In the future, I'll use an arduino to interpret oil pressure readings and P2 readings and keep a good eye on the oil pressure, as well as a redundant pressure-switch to shut off fuel below 30 PSI like the one I have now.

The fuel pump (the shurflo diaphragm pump) on the other hand is TERRIBLE at producing an even pressure. The needle on the fuel pressure guage vibrates between 10 and 50 PSI, but it works okay, and the rising-rate fuel pressure regulator does a great job adjusting pressures as P2s rise.

I've loved the idea of converting to a ceramic bearing unit! But it would be expensive, and require some high-precision machining from the looks of it. Two things that I have zero access to are precision machines and lots of money .

Are there any "drop-in" style ball bearing / ceramic B.B. kits for such a turbocharger as I have?
That would make the option alot more appealing!

You have a great looking website! Do you do alot of work on turbos?
If so, What would it cost to have one ballanced? (if you do that kindof work)

And the worst part of a journal-bearing engine is startup. TAKES TOO LONG!. Too much friction! What you've said, I belive would be very true if I could convert to Ball bearings!

And the reason I haven't uploaded any pics of the power turbine section is cause I don't have it yet! And I completely agree that there should be a picture:post ratio that should be carefully monitored to ensure all the visual people like us stay interested .

I'm working on saving up, and am working on starting a project on:

www.kickstarter.com

I'll post a link when it's finished and ready to collect funds!

I will be using the N2 stage of a JFS-100 starter unit to turn gas into torque. $1,500 in excelent condition, and I've got one tracked down thats $800 with some non-critical scratches and dings. $800 that I don't have yet .

Thanks for the post, I can't express how much I appreciate the feedback, and how its helped shape this project.

-Feathers

[Feathers]

So that gasket I made for the combustor outlet - turbine inlet coupling....

Didn't work as planned.

I wasn't expecting it to remain emaculate and unscaved operating with 800* oxygen-rich gas at 15 PSI, but the way I cranked down the 6 bolts securing the coupling, I would have at least expected the pieces to stay put...

So I ran the engine up to 15 PSI, and was suprised when my EGT started to rise, engine speed dropped, and there were hot little pieces of gasket flying everywhere... I walked around and found that half of the gasses leaving the engine were now escaping out the side of the coupling, rather than out the rear of the turbine

Heres how much "gasket" (burnt flakes of carbon that was once upon a time gasket material) was left:





So obviously this material wouldn't do.

Plan B was a crush-gasket made of thin brass holow tubing. So I just bent it into a decent-looking profile, sandwiched it in the joint, and tightened everything down.



So Far, I've had P2's up to almost 20 PSI, and the coupling has remained perfectly sealed.

Heres a video of the running engine:
(Taken awhile back, I'll post a more recent video with all the modifications from the past 3 weeks soon)



I'll keep everyone posted as work continues!

-Feathers

[Johansson]

Take a word from one who´s been there, you are in for a period of "breakdown-teardown-payup" if you go down the ball bearing route for a radial turbine...

It doesen´t have to take longer to start a brass bearing turbo than a ball bearing one, it just takes a bit more force.

You could perhaps use compressed air instead of the leaf blower if you fit a pair of impingement nozzles in the turbine housing pointed at the turbine tips, a large compressor at 10bar should spin her up nicely.

[racket]

Hi Feathers

I'll go along with Anders , for an inexpensive and reliable bearing system stick with the "brass" , ball bearings can be fun but the setting up of them is critical , preloads, external damping , etc etc . .................I wrecked a lot of rotors getting mine to work , turbo shaft dynamics are complex, and need to be "tamed" if balls are to be successful , it gets very expensive replacing rotor after rotor during development .

Fast spoolups of brass bushed engines is certainly achievable as Anders has said , my 10/98 engine which has a lot of bearing drag , ~0.5 ft lbs when stationary , can be started in 10 seconds , 0 to 22,000 rpm.
www.youtube.com/watch?v=NR0rsTbkOS4&list=UUHWNGFJ7enlzhsguJJbahyg&index=7&feature=plcp
just need enough start power :-)

Cheers
John

[Feathers]

I'd tend to agree with you guys as far as the brass (or in my case and strangely eanough, aluminum) bushing bearings go.

Ceramic bearings seem like they would be thermally indestructible, but relatively brittle...
Say an engine isn't perfectly balanced and hits a harmonic at 55,000 RPM... Bad news right? Its a cool idea, but for now I think I'm going to stick with a decent bushing bearing.

Although as Ash said, and as I've noticed, the VT-50 doesn't have much of a thrust bearing... I'll just have to see how that turns out.

Before I go any further pushing the engine, I need to have the rotors balanced, and get a reliable tachometer setup, just to be safe.

And I figure its just a matter of power

I have an 80Amp ESC and am waiting on a beefy brushless motor to come in. Its 2000KV (RPM per volt) so at 12 volts and with a relatively heavy load, it should spin the motor up to around 22,000 RPM. The 960 watts (around 300 watts more than RCDon used for the same system on the same turbo) of starting power should be eanough to spool up the engine relatively quickly, even with thicker cool oil in the bushings, and I'll machine a gentle bendix style system to engage and disengage the starter.

The great part of the motorized starting system rather than impingement, will be that I can "idle" the motor to facilitate warm-up, and cool-down with the help of my arduino mega, then go in for the punch with startup.

Like you guys said, just need MORE POWER!

-Feathers

[racket]

Hi Feathers

The SiN bearings are extremely tough , the SiN balls I used in my hybrid bearing chewed the steel raceways away whilst remaining unhurt.

Our rotors even if very well balanced will still go thru a number of "vibrations" on the way to max rpm , its just the nature of the beast .

Even full sized aero turbines can have an rpm range where its not advisable to stay within , at this early stage in your engines development I'd be leaving the turbo as standard as possible whilst feeding it with good quality filtered oil at a decent pressure, not that the VT50 needs high oil pressure to survive , but the extra lube will keep things cooler and hopefully give the thrust bearing a fighting chance :-)

Cheers
John

[ashpowers]

In my professional life we rely on weighted piezoelectric knock sensors in automotive engine tuning. I would imagine that an appropriate vibration sensor and a PC with a decent sound card to monitor the signal would allow us to keep an eye on these harmonics. I also think it would be very useful in keeping an eye on bearing condition during operation - bearings are going to make noise of their own as they deteriorate which a system like this would likely be capable of detecting. Our ears/brains can't filter out all of the compressor, turbine, and air shear noise these engines produce while they are running but a sensor like this would be able to cut right through all of that.

[Feathers]

Guys! Digging this one out of the grave for a moment.

I've started Aerospace Engineering at the University of Kansas, and am loving it.
My instructor was talking to one of our professors about the eco-hawks (diesel-hybrid vw bug team at ku), and how they are adding a very small aerocharger (pretty cool, extremely expensive self contained turbo) to the small diesel engine they use.

Professor said something to the effect of "ever seen the jet engines they make with those things?"

And I pounced.

They got a kick out of the video, and I showed them my build log.

Professor basically ordered me to write a report for the AIAA (American Institute of Aeronautics and Astronautics, which has an undergraduate chapter at KU) Undergraduate technical paper competition this winter break, regarding the design, building, function, and operating characteristics of the engine. He said I'd have a fantastic chance at 1st place, which means $1K and more or less a ticket into grad school!

This is all great, but means that I have to really finalize this engine, and put it under a microscope.

It has oil leaks, air leaks, combustion gas leaks, fuel leaks, I need a leafblower to start it, I need to spend the first 5 minutes of runtime continually adjusting oil pump speed, and the fluted turbine outlet produces no useable or accurately measurable amount of thrust.

I need to fix the leaks, get a brushless motor or impingement start, program an arduino to take care of the oil pressure (or the rest of the operation ), add an appropriately sized nozzle to produce some thrust, and poke it full of presure transducers and thermocouples.

The first thing I'm tackling is the jet pipe. I bought a 5" to 3" (4" length) 16 gauge 304 ss reducer, which I can cut at any final diameter I want, but I can't, for the life of me, find the flange that fits with a v-band to the turbine outlet. Its extremely simple, with an ID of 5", and a small ~3/8" lip at about a 75 degree angle, exactly like this:

www.paradiseracing.com/Store/components/com_virtuemart/shop_image/product/67f3dd0319fea424bfa3dbfd4dd33dae.jpg

Except I need 304 stainless!

RC Don went to burns stainless, but the lip is doubled over (which apparently doesen't fit), and its very expensive.

Does anybody know where I can get this simple but apparently non-existent part?

I'd think somebody somewhere has to be selling it, with the number of t-46, t-50, st-50, vt-50, s400, etc. turbos that use that type of turbine outlet.

Glad to be back!

[Feathers]

Racket!

Quick question.

There is an allison 250 stage 1 turbine wheel on ebay, starting at $35.

I know you lent one of these to Sal Aiello, and thought you might know a thing or two about them...

If I decided to pursue shaft power, would this wheel have an appropriate flow area for my 3" inducer dia. ST-50? Or a bit small.

I belive you used a 3rd stage wheel for your bike? But that was with your monster turbo.

I'm just not sure how this stuff adds up.

Thanks!

[racket]

Yeh , that first stage wheel would be a bit too small for a 3" inducer'ed engine ............the first stage wheel has a "flow area" of ~4.5 sq inches , the third stage has ~10 square inches , you probably need 7 or 8 . ..................or use a third stage wheel with a very shallow angled NGV .

Flanges, look here........... vibrantperformance.com/catalog/index.php?cPath=1022_1125_1338&osCsid=c5913cb283d1186d3ce90020bde04277

All the best with the mods :-)

Cheers
John

[Feathers]

So I've got the engine up on a stand to make testing, access and assembly easier.





Also mildly nervous regarding the several hot starts this engine has been through.

I've never seen an operational EGT higher than 475*C, but the turbine wheel has been glowing visibly on more than one occasion.

Does this greatly effect the structure of the wheel? Heres a pic of the present coloration:



Thanks!

[racket]

Hi Feathers

That wheel certainly looks like its been exposed to more than 475C , there shouldn't be any glowing at that temperature , I'd be checking the TOT setup .

Your turbine wheel has very little exducer angle on it, which will generally mean higher temperatures as the engine tries to compensate for the lack of gas deflection .

Did you checkout the third stage wheel on Ebay www.ebay.com/itm/Allison-Rolls-Royce-A250-3rd-Stage-Turbine-Wheel-/190762620794?pt=Motors_Aviation_Parts_Gear&hash=item2c6a56977a&vxp=mtr

Cheers
John

[Johansson]

Hi Fethers!

Looks like new to me.

The first area that will be damaged in case of overheating is the inducer tips, so you need to remove the turbine housing to inspect them. A badly designed combustor might produce a hot streak that melts the inducer tips while the EGT probe still shows ok temps, it all depends on the position of the probe.

I quote John when I say that turbine wheels are meant to glow!

Cheers!
/Anders

[sven]

Very nice setup, you have done good job, hope you figure out high EGT


Sven