Jet Engines

[gmcjetpilot]

Originally Posted by mgomez

Note that you won't be going any faster, at least not if you take the Vne limitation seriously.

Thanks for the math. love math. Interesting.

That is why a micro jet needs to be designed from the ground up around the engine. It would still climb like a brick as you say if you did not oversize the engine, w/ a basic minimalist thrust engine.

The FJ33 Williams with 1000 lbs of thrust would be nice, but that engine and an airframe that could use it properly would cost in the millions. There are already many used turbo prop and jets you can buy for less than a million. I just saw a nice Lear 24D go for 1/4 mil! If I had some change I'd buy it.

There are laws of scale working here. At some point a turbine does not fit a small planes. If you're going to a turbine you almost have to talk about a larger plane to make use of it. Most practical turboprop engines are +600hp and small turbofans at least 900-1000 lbs, which is what is on the Eclipse. You may recall Williams Intl where dropped due to poor performance for the PW610. The PW610 core is rated up to 3000 lbs thrust, so you can see the laws of scale working. It cost almost as much to make a 900 lb thrust engine as a larger one. Most small business jets have more like 2000 lbs thrust. The new Citation Mustang has 2x1500 lb PW615, and is a larger plane than the eclipse. The rest of the Citations are 2000 lb thrust and up. It just shows the min economics of making a turbines.

Piston engines fit small GA planes for personal use very well, where high average yearly utilization is less than 200 hrs. You can buy a Lyc for $20k, burn 9 gal/hr, build and maintain it yourself if you want, and people still complain about that.

If you can afford a turbine plane you'd buy one. I guess the closest thing we have is the PropJet Lancair. My understanding is the build cost is about 1/2 mil, with a used Walter turboprop. If you have to ask about fuel cost than you can't afford one. There has to be a tax right off in there somewhere for individuals and companies to make it work.

Even the rich & famous are not owning their own jets anymore; they are going to the co-op's, like Flexjet for obvious reasons. You suck a bird into your engine, your plane is down for a significant amount of time and its going to cost you hundreds of thousands of dollars to fix it. With FlexJet you land and they call out another plane for you, no extra charge.

It remains to be seen if the VLJ's is a boom or bust. They are small 6,000 lb planes with small cabins and limited range. Older Citations and Lear's have more performance and cost less used than newer VLJ's. However the idea is with their modern technology, VLJ's operating cost are suppose to be much less. Plus the owner/pilot, single pilot, private license aspect saves on crew cost. Older turboprops and bizz jets cost in fuel and probably in maintenance. The price of the Eclipse today is around 1.6 mil and the wait is a few years. When you close the deal at delivery the price will be adjusted (up) for inflation.

People have tried to make and market tiny jets but they never caught on. There was the Paris Jet, 4-seater and a few others, but the MATH did not work out. There is just NO way to do a plane turbine right, cheaply. I have a new found respect for the Lycoming.

[john kelley]

Anybody remember the foxjet? Similar idea to today's VLJ even planned on williams engines like the initial eclipse. There are few truly new ideas in aviation it all comes down to execution and marketing. Seems like the ball is rolling pretty good now. I sure would like to be able to get a used VLJ some day for the price of a used barron.

http://www.machdiamonds.com/foxjet.html

Regards

[xl1200r]

I think the problem with small jets is not the making of them - any one of the big turbine manufacturers could come up with a 600lb thrust engine in a few hours if they had to. It's the fuel burn that kills them. They just aren't economical until they make huge power and carry a lot of people.

There's a company out there called Maverick that's gearing up to make some personal jets, but the cheapest one is a single-engined 5 seater at $1.2 million.

The problem is that there are two types of VERY good competitors out there - it's not big deal to get 6 or 8 people on a turbo-prop or even a twin that performs almost as well small jets.

[gmcjetpilot]

Originally Posted by xl1200r

I think the problem with small jets is not the making of them - any one of the big turbine manufacturers could come up with a 600lb thrust engine in a few hours if they had to. It's the fuel burn that kills them. They just aren't economical until they make huge power and carry a lot of people.

There's a company out there called Maverick that's gearing up to make some personal jets, but the cheapest one is a single-engined 5 seater at $1.2 million.

The problem is that there are two types of VERY good competitors out there - it's not big deal to get 6 or 8 people on a turbo-prop or even a twin that performs almost as well small jets.

The prototype twin engined Maverick Air jet crashed in 2003. I see they now have three planes on the drawing board, a single engine jet, a twin and a seaplane jet! Here is their site: http://www.maverickjets.com/index.php I wounder if they ever get anything flying again. The new designs look nothing like the Maverick I.

The other one, Excel-Jet, which was a single engine jet, showed promise but crashed in Colorado in the last year, killing two of the companies principles, possibly from wake turbulence. http://www.sport-jet.com/. Status, looks like they have another flying prototype, cool. About 0.98 mil "experimental" and 1.3 mil for a certified one in 2-3 years; A single engine jet has appeal, but most serious Bizz jets are twins for many reasons, not the least is redundancy and safety. However I do think the single engine excel-jet is cool design at a cost of 1 mil. It would be an option for the (rich) individual. If I was going to a jet I would by a used Citation I or II. You can get one tomorrow and they cost the same as one of these toy jets. Cessna of course has been around and service is available.

Turboprops are good for short trips and runways, jets longer trips and runways. in general. Turboprops are more efficient at lower altitudes and a jet needs longer trips to climb and have time at altitude, where it's more efficient to be optimal. There will always be room for turboprops, kingairs and C130's, however turbojets are smooth and props noisy and not as smooth. Both have economics and optimal missions. Thats why a jet is not a good choice for a little flying holes in the sky fun planes, they are made to get-up and go somewhere at least 500 nm away. A sport plane, $100 hamberger getting or going up to get away, going no where for any reason except for fun of flying, pistons -N- props do that nicely.

I think you missed my point. Yes manufactures can make a 600 lb turbine and do. The little 300-600 lb thrust missile engines are maxed out. To take the next leap in thrust for a jet engine, that's really safe, economic and reliable takes sophistication. Once you go past that plateau of 300-400 lbs, its a quantum leap in complexity and cost. Now that you have a bigger "core", making it either 1000 lbs thrust or 3000 lbs is not significant. Also the market just calls for engines that are at least 1000 lbs thrust. Now you could derate a 1000lb thrust engine, but its still a 1000-3000 lb core. The little missile engine are 200 lb thrust engine that are straining to put out 300 lbs. That may be part of the reason BD-5J's have such a bad safety history?

The Eclipse is a very very small jet and has two 900 lb thrust engines. Its cabin is smaller than many piston twins. The same PW610's can grow to 3,000 lbs thrust. The little engines at 900 lbs will probably last at that lower thrust.

Often a manufacture "core" has a range of power. The engine is really the same. Where the PW610 that makes 900 lbs on the Eclipse, it can make 3000 lb with a different fan, but the basic core design is similar. Having a jet that runs at the lower end of its temp and pressure limits will mean it last and be super reliable.

A single engine jet, like the the Excel or the Maverick "solo" concept with one the larger engine like a JT15 (3350 lb) would be cool. The Citation II had 2,200 lb thrust JT15A's. The later Citation V which had 3,000 lb JT15D's. I flew both. Nice planes and good engines. You can get a old Citation I for a little over a Mil. An old jet is still a jet.

As mgomez pointed out you need excess thrust to get off the ground, climb and lift usable payload. Yes you can fly a jet powered hang glider, but its not practical. The idea is climb high and save fuel. That is why total thrust of 1800-2000 lbs is about min. for any practical size personal jet that can carry at least 4 people. Remember you have to carry more fuel, which takes more structural weight and so on. Again scale.

The sad safety history of the 300lb-450lb thrust BD-5J microjets makes me think that its just too small. The engine is too small and the plane is too small. Again scale. At some point turbines, jet or prop are not practical for a small light plane.

If the LSJ makes it, they predict several thousand flying by year 2017. Next down is the single engine turboprops. Any way you cut it, a turbine is big bucks and out of reach of all but the very rich.

[fl-mike]

The little cruise missle engine that was in the Fly-market at Sun 'n Fun about six years ago was just about the coolest thing I ever saw. As I recall, it was from a Boeing AGM-86 air-launched cruise missle, was a Williams engine, and I think it is a 600 lb thrust engine. That inspired a lot of daydreaming.

http://www.hill.af.mil/museum/photos...r/williams.htm