Gas turbine

Dave,

Small simple cycle gas tubines (think of a big turbocharger with a combustor on it) are pretty inefficient. You would likely see specific fuel consumption of about .8 pounds per horsepower hour in a machine like that. With a direct drive generator on it, it will weigh about 30 pounds and imagine that turbocharger with a starter motor for a typical v8 sticking out the end of it and the whole thing spinning at 90,000 rpm. The exhaust is going to be hot (probably about 1100 degrees F) too. If making 30kw and burning somewhere around 6 gal per hour is acceptable then it can be done, but it won't be cheap, probably around $20k for a machine like that.

Small gas tubines can be pretty efficient if you use heat recovery (regenerators or recuperators) to caputre the waste heat. These tend to be bigger and more expensive so that does tend to negate the advantages of the small turbomachinery. If you look at something in the 30kw range, the turbomachinery is very small (again think like the size of a truck turbocharger) and the heat recovery package will fit in a two drawer file cabinet and the whole thing could weigh about 200 pounds. The fuel efficienty would be about 3 to 3.5 gph for 30kw (which is better than a spark ignition engine and close to that of a diesel) and expect it to cost around $30k. In terms of weight and volume, probably a lot better than you can do with a diesel of that size and if you wanted to run propane, gasoline, fuel oil, diesel, or good booze (although that would be a waste of good booze) you could do it.

Just remember that running off of propane is going to result in a pretty big tank if you are sucking 3 gph out of it. If you want less power (like 10kw) then you could get the fuel burn down to about 1 gph, but still, at 1gph and if you want to run for 10 hrs that's a pretty good size propane tank.

 

If it's accurate it will be worth to put the whole generator/turbine not down below but on deck protected by a superstructure. It will make the vents and salt filtering easier, as also the maintenance.
The noise can still quite high in this configuration.
As I said before, I don't know nothing about turbine.
I just try to check several solution for genset. Just pocking
But a lot of you knows al lot about it, thank you for all the infos.
The salt filtering, mentioned by AdHoc, can be in fact the most difficult factor since filtering will restric the air intake.
For the exaust, up in the air like a gigantic smoke stack can be the solution for the safety of the crew.
The gear box is the biggest problem I think. It is what fail the most in chopper.
Cheers
Daniel

 

A machine like this won't have a gearbox.

The alternator is on the shaft and runs at shaft speed (90k rpm). All the power comes out of the alternator. The alternator would be a permenant magnet alternator, so there are no windings rotating at that speed. The power output electronics to chop the output are pretty big and clunky, but they are pretty much state of the art. If you want DC to drive a motor or charge a battery, then they are a lot more simple. Look up Capstone turbines to get an idea of what we are talking about here. With a heat recovery system the output temperature is 600 F, hot, but not horrible, and certainly not as hot as diesel exhaust when running at full bore.

 

Speaking of large fuel tanks...
LNG carriers have been turbine powered in the past, just burning off the boil off.
Now that gas costs lots more they are putting reliquidation plants on board and putting old slow speed engines back

 

Thanks for the Capstone link. I didn't know that kind of turbine and utilisation existed. they don't say realy much, but I will investigate for sure by calling them.
Cheers
Daniel

 

Yes, thanks for the Capstone link!

 

Be careful with the Capstone unit with regards to marine usage. I only pointed it out to show what a unit of this size class would look like.

It has air film bearings in it that are ill suited to the marine environment (salt would kill them) and they are really best suited for stationary usage because they cannot withstand any severe impacts....

 

Here you go, a helicopter turbine propelled vessel:

http://www.rib-kali.com/kali-engine.php

-Tom

 

Update

Evidently, the turbine has already been replaced by an outboard...

-Tom

 

Not at all surprised that they would do that, trying to run around England isn't a good fit for that particular turbine when you consider the higher fuel burn. It all comes down to fuel burn versus time versus installed weight.

If you look at the power to weight ratio, that particular turbine weighs about 158 pounds and provides about 300 hp at a cruise power setting, but has a specific fuel consumption of .7 pounds per horsepower hour. A 4 stroke outboard weighs 500 pounds, has 250 hp and has an sfc of aout .52 lbs/hp-hr. If you replace the turbine with an outboard, you will be burning 132 lbs/hr of fuel for 250 hp where the turbine is burning about 175. So for every hour you are running at high power the turbine is burning 42 pounds more fuel. The outboards will weigh 600 pounds, so the weight difference is on the order of 370 pounds (figuring 50 or so pounds for a prop and prop shaft and another 20 pounds for the increased tankage). If you are going to be running for more than 9 hours between fuel stops the outboards will have a lower overall propulsion system weight (engines + drives + fuel and tankage) and that is what is important here.

You might be able to make the case that the average propusion system weight will be lower with the turbine since once you start to burn off fuel the overall propusion system weight will actually be lower, and you can gain speed from that point on, but that probably isn't the biggest driver here.

As I said in an earlier post, turbines really don't make sense until you start looking at larger sizes (bigger turbines have better specific fuel consumption so the fuel burn isn't as big an issue) and you aren't trying to go all the way around England (30 hours of running). The bigger the engine, the shorter the mission and the faster you want to go the more turbines make sense.

 

Well that's certainly confusing Yellowjacket.

Can't say I really get your point.

I do wonder why they designed it with a turbine in the first place.

Here's a question you may be able to answer more clearly though:

What lead to the demise of the Bell-47? That was the name of the piston

workhorse wasn't it?

-Tom

 

There was nothing 'wrong' with a Bell 47; it was a great helicopter in its day. But many different technologies incorporated into helicopters have 'moved on', making the Bell 47 simply obsolete. One of these is engine technology. The 47's all came with piston engines from Franklin and later Lycoming. The latest Lycomings were the best, but none were very reliable or durable in a helicopter. One of the best 'service life extenders' for the Bell 47 has been the Soloy Turbine Conversion:

which adapted the ubiquitous Rolls/Allison 250 series engine to the Bell 47 airframe.

The other major obsolete component of the 47 was the rotor hub, which used the 'old school' type of greased ball joint bearings and passive servo type controls. The French in particular were at the forefront of replacing these with elastomeric mounting of the blades. Except with the heaviest helicopters, the entire industry has adopted this technology, making older designs less attractive due to their higher maintenance costs.

The basic form of the 47 lives on in the Aerospatiale (Eurocopter) Alouette:


and Llama:

,

both of which look superficially like Bell 47's with turbines, but in reality are much more advanced designs WRT main rotor hub and blades.

Bell wants NOTHING to do with the model 47, BTW and wishes all the remaining ones would just disappear

Jimbo

 

So, power to weight was the biggest issue?

 

Tom,

What I was trying to say is that a turbine, although it is a very light engine, doesn't always make sense. You have to look at the weight of the engine and fuel as a total propulsion system weight, and then see if it works for your mission. I did the quick look in about 5 minutes, and it didn't look to me at first cut that there was a pony in that pile if they are trying to run around the UK. If the mission is three hours, then a turbine would save a bunch of weight and might be a good idea. The smaller the power requirement the less turbines make sense. That's all.

As to the demise of the Bell 47, that happened directly as a result of the development of small turbine engines, specifically the Model 250 Allison engine that was developed for the Army LOH program which, although the Bell 206 lost that competition, it got the Jet Ranger program off the ground. When you look at what the payload of the 206 is (1487 pounds) compared to a 47 (482 pounds), it is obvious that the 206 is another whole world of capability compared to a 47. The 47 was really a post-WWII aircraft based on the power available at the time (150 hp recip) and they learned a lot between then and the early 60's when the 206 came along with the turbine. The fact that the 206 has been in production for over 40 years when the 47 was built for only 10 tells you something.

Bell outgrew the 47 and didn't see a future in small piston helicopters which is why Frank Robertson (who worked for Bell and saw the market for a small helo that he couldn't get Bell to build) went out and did the R22 on his own, and as they say the rest is history. There still is a helicopter that does what the 47 did, it is just called the R22 and Bell doesn't make it, although they probably wish they had listened to Frank in the first place.....

 

Very true, in fact I did read the other day that Bell has sold the type certificate for the 47 to Scott's Helicopter. They were one of the main support houses for the 47 and did a lot of spare parts business on that model.

They can finally wash their hands of it and to them that is a good thing. With the staute of repose in place in a few years it will be only a memory at Bell.