100-150 Hp turboshaft thoughts

[racket]

Hi Monty

30 lbs/sec , thats very similar to the numbers I was working with when I thought about "fans" for my Solar T62 engine ~15 years ago , anywhere between 25 and 30 lbs/sec is good with 150 HP , efflux at ~350 ft/sec and 350 lbs of thrust ...............yep, any residual pressure from the gas producer can be used effectively.

I was concerned about starting power requirements , the T62 has a big 24V "truck starter" but I still felt the direct drive to a fan would be too much for even it .

As I had access to a Multiwing fan au.multi-wing.com/ like the hovercraft guys use , I was going to cut it down to size but when I did the "numbers" for the T62's 6,000 rpm output speed the "plastic" fan wasn't happy , so I considered other options , in the end it all became too "messy" considering the physical shape of the T62 , so went onto other projects and started making my "micro" type engines .

An interesting project you've undertaken , the ~10 inch dia gas producer part shouldn't be a problem , the PTO and gearbox will be challenging :-)

Cheers
John

[monty]

John,

I've been dreaming/scheming about this silly thing for about 20 years. I have abandoned it multiple times for the same reasons you list. But I keep doodling and running numbers. I've tried other approaches: rotary engines, two strokes....it all winds up in the scrap heap. The one thing I've figured out about fans: RPM is your friend. The problem with the T62 is the output speed is not high enough. 6KRPM is too low. The fan in that pic was designed for 10K rpm. For this engine I'll up the rpm to 13K. It makes the gearing easier, and the fan much smaller. You could make a fan work at 6K, it would just be about 2ft in diameter. You need a high enough tip speed to make it work. That said, it's still less than half the tip speed of your average propeller. I'm planning to make carbon/Kevlar blades. I think I've got that all worked out.

It's not until the last couple years that I feel I have the skills, tools, and the technology has become available to make this thing happen.

I thought I had the gearbox figured out, then I ran the pitch line velocity numbers. YIKES!....Back to the drawing board, but I still think I can make it work. The input RPM is the same as the Solar, and the overall reduction is only about 5, instead of 10!

Regarding the starting power. What rpm do you think I"ll need to reach self sustain??

This is one area where things have gotten a LOT better recently. I just replaced the starter and alternator on my biplane with things that looked like toys...and a battery that was closer to the size and weight of a pack of cigarettes than a car battery. I really didn't think it would work until I pushed the start button and the darn thing flipped over like it never has before!! I still don't quite believe it.

Monty

[racket]

Hi Monty

You probably need at least 20,000 rpm ~30% N1 capability to be on the safe side for a reliable and safe self sustain/idle, yep theres some good electrics around these days .

One problem I found with higher fan rpm/tip speed was the energy levels going into the air started making for less "efficiency" , the thrust vs HP required , theres a "sweet spot" , which in your case will be strongly influenced by "vehicle" speed , mine was for a "slower" land based setup .

I've looked at some of the larger 120 mm EDF setups , beautiful bits of gear , good for scaling up from :-)

LOL, pitch line numbers , heh heh , what are they when it comes to turbines , I think there must be another set of "numbers" just for them .

Cheers
John

[monty]

John,

Yes, pitch line numbers and bearings are in a whole different world with turbines....certainly outside what the catalog says! And the speed will absolutely influence both the diameter and RPM. I'm looking at operating around .25-.32 mach, so the fan is sized for inlet flow of around .35 mach. Amazingly the tip speeds are actually quite low.

I estimate about 4.5 hp to spin the fan up to N1 of 20,000. What do you think the core will need worst case with a hydrodynamic thrust bearing?

Monty

[racket]

Hi Monty

Probably another 2-3 HP for spooling up the gas producer , we're able to get them spooled up with a garden leafblower.

At your projected "vehicle " speeds theres going to be a good bit of ram air contribution , I was planning on ~600 ft/sec tip speeds , not high by the usual fan speeds but considering the low pressure ratio , still a bit too high for my "material" .

Cheers
John

[monty]

John,

That's about what I was thinking. My plan is to use a 60V starter/generator derived from the EV world. It is capable of about 7KW, so it "should" do the job.

For the gearing, my plan is to just copy the pitch, dia, and face width of the Solar pinion, and then work out from there. The numbers on that thing are ridiculous! Pitch line velocities have to be up around 50-60 M/s!! My pitch line velocities on the ring gear will be half what the Solar is.

I actually don't plan to use any ram air effect. I am planning to accelerate the air all the way from the inlet to the exit. That keeps the boundary layer under control. The big boys use a diffuser for the inlet, but they are traveling at ~ M.8 and need to slow the air down ~ M.5 so the fan can work at that speed. The fans on the big engines ingest air at a higher speed than my nozzle exit!

What is the best way to buy from KTS? The US sales rep email doesn't work.

Monty

[racket]

Hi Monty

Maybe get in touch with KTS head office to find/verify their US distributor , thats what I did to get my local one .

"No ram air" ..........mmm, I haven't done much thinking on this subject but won't you have a problem with Gross vs Net thrust once up to cruise speed ?

Cheers
John

[monty]

John,

RE gross vs. net thrust: It's purely a momentum change like a propeller. You don't get an increase in pressure ratio like using a diffuser, but you also don't have any ram drag. A propeller is more efficient at this speed, but I don't particularly like propellers! Plus the prop would have to be a very complex and expensive constant speed unit to work with a single shaft turbine. The fan acts like a CS propeller if you vary nozzle area.

I've sent an email to KTS.......waiting for a reply. I ordered the Turbine. This site seems to show the -0003 wheel as being the "G" trim wheel

After thinking about the gearbox, and in the spirit of off the chart design...... I've decided to try the Chinese air tool approach first. I'm trying not to take the aerospace approach, because that means EXPENSIVE. My plan is to use a coarser tooth that does not require such precise location, and mount the pinion and planets on hydrodynamic bearings. The fan-shaft will be mounted on roller bearings. This should allow the pinion and planets to self center and move a bit. If this fails, I'll reverse engineer the Solar Unit. Unfortunately, I can't get off the shelf ring gears in odd tooth numbers, so I can't make it a "hunting tooth" design. Should be less of a problem with a planetary set than a standard spur and pinion. I also can't get stock modified addendum ring gears, so I can't use the smaller diameter pinions. We shall see how it goes....

I'm also thinking about going with a more modern thrust bearing design. Any models you can recommend to look at?

Monty

[racket]

Hi Monty

LOL..........I'm no clearer on this thrust business , I've been having a look at my various texts and they all indicate there could be a problem with your reasoning ..........momentum drag seems to be the culprit , trying to get the air to the fan ,.......... without ram compression ( and even with it) thrust drops with forward speed for a while until "recompression" from forward speed starts to counter that.

Normally the ram compression adds to the pressure ratio downstream of the fan and the exhaust velocity increases , but not to the extent that it counters the velocity "loss" to the fan.

You may need to elaborate somewhat on your theory ,.......Please , Fans 101 for us land based guys who haven't had to consider it :-)

Cheers
John

[monty]

How can I make this clear in a few words!?

In an aircraft you are moving through the propulsion medium, so the relative things matter. You only get momentum drag if you take the air onboard and slow it down. It's like being in a boat at speed and putting a bucket in the water to bring it on board. You're gonna feel that! Then you do some stuff to it, and manage to squirt it out the back faster than you brought it on board. The difference is net thrust. BUT! If you can suck it in and throw it away without slowing it down or changing direction too much, it's all thrust. The negative term disappears. Problem is fans and turbine equipment in general need to ingest air at a certain speed to keep the tip flow at the design point. It's all part of a thermodynamic cycle: you compress, heat it up, and expand it. The overall pressure ratio greatly effects the thermodynamic efficiency of the cycle and thus fuel burn. This all diminishes the slower you go. There is less dynamic pressure to play with. That, plus, the slower you go, the more bypass to core flow you design in to minimize the exit velocity vs flight velocity. This increases propulsion efficiency. (helo vs Harrier!) In my instance I have 30 lbs/sec bypass to 2.3 or so core....13/1 It's really just a terrible turbo prop. If I tried to increase the pressure ratio using ram air, I would just increase the exit pressure for the core nozzle...so it doesn't really help much. In fact I get better performance with a separate fan and core nozzle exhausting to ambient. There isn't really enough heat content in the core flow to get any boost from heating the bypass air by mixing, and I'm not going fast enough for the pressure rise from ram air to help much with the cycle efficiency.

The fan drives the inlet, so if you never go fast enough to need to slow the air down for the fan, you don't need a diffuser. The inlet area is larger than the fan face, and the exit nozzle is smaller still. The air accelerates all the way through the system. In fact the more boundary layer air you ingest the better! exactly the opposite of a typical jet intake. Since the air is not diffusing, the boundary layer ingestion is a positive for propulsion efficiency and it doesn't effect the inlet by causing separation due to adverse pressure gradients.

I fat fingered my calculations earlier, the tip speeds on my fan are about the same as a prop. It may please you to know that I am looking at increasing my reduction ratio to 6.66 ;-) That will give me a 10krpm fan, with a tip speed around 720 ft/s. If I keep the 13K rpm gear ratio, I'm probably going to have to reduce mass flow to get the diameter down. I don't want tip speeds higher than 800ft/s. Static thrust and propulsion efficiency would suffer. In addition, the pressure ratio would be bumping up against technical limits, that while possible, I don't feel competent to challenge in my garage.... I'd like to keep it safely under 1.1 to keep the diffusion through the fan manageable. That's where the deltaP that drives the inlet comes from. The fan is the only diffuser in the system. It converts shaft power to pressure rise that drives flow through the inlet. You can think of it as gross power vs net fluid power. The fan has an efficiency. That may be what you are missing. It took me a looooong while to get that one. A fan is just an inside out diffuser.

[monty]

And yes, my net thrust (thrust-drag) will decline in almost a straight line from static to top speed. It's definitely not a ram jet!!

[racket]

Hi Monty

Thanks for that .

LOL.......clear as mud .

I'll digest it and see how I can fit it into the info in my texts, it must be nearly 15 years ago that I was toying with the T62 and trying to understand what the experts were writing .

I'm looking forward to watching your journey :-)

Cheers
John

[monty]

Oh well, I barely understand it...If I had a napkin and an adult beverage, maybe I could do a better job!

I've tracked down the major overhaul kit Melett# 1101-090-755. It doesn't look like it has the actual thrust plate. Any other parts missing? I need a good manual for the TV91-94.

[racket]

Hi Monty

The actual thrust plate is riveted to the comp stage back plate in the turbo and would be replaced with the backplate that generally is damaged by the time a turbo needs an overhaul.

The TV91 overhaul kits we purchased from World Turbo www.worldturbocharger.com/Product/Repair-Kits.html came with all of the thrust bearing components , they also do the F Trim turbine wheels all at very good prices .

I think I got my spec sheet from www.turbomaster.info/eng/turbos/technical_data/garrett_TV91/

Cheers
John

[monty]

Thanks John..

I've sent them an inquiry. After looking at this thing and scratching my head for a while, I've settled on the deep groove ball at the pinion to eliminate the hydro-thrust bearing. In the place of the original thrust bearing, I will mount a scavenge pump/oil slinger. This should help oil return, and allow a smaller return tube. Speaking of oil.....what flow rate, and pressure pump do I need to look for?

I found a US supplier of bearings that makes deep groove and angular contact bearings.They might be of interest to the group. Probably where Turbonetics gets their super top secret bearings. I am going to use the 201T, which is good to 83Krpm, and around 500 lbs of thrust load. Nice thing is I can do all my prototyping with El Cheapo TM 6201 bearings. On the flip side the Barden bearings are not cheap!

Barden Bearings

I've also ordered one of these.

Hopefully it will work for kero-start.

I've contacted KTS and found a US supplier, but haven't heard from them yet....have my order confirmation on the turbine but no tracking # yet...and waiting to hear from turbomaster...I hate waiting!

I'm going to shamelessly copy what you guys did on the can and evap. tubes!

Monty