Why no jets?

prkaye · #1 12-31-2007, 07:17 AM

Ok, before i ask this, the disclaimer - I realise this is a really naive question! Another disclaimer...NO I'm NOT thinking about putting a jet engine in my RV-9A! This is just curiosity

...
I don't really know much about jet engines, except that they look and sound really cool. I've often wondered why you don't see more kit planes with a small jet engine (say the equivalent of about 200 hp). The only think I have seen really is the BD5-J, but only a few of these have actually been flown (one crashed here near Ottawa a couple of years ago preparing for the airshow, killed the pilot). There's also the Viper II, but then we're taking about a high-performance aircraft that would probably cost close to a million bucks to get flying.
So, my basic question is - is there a fundamental reason why it is impossible/impractical to design a bird with roughly the performance of an RV-8, that runs on a small jet engine instead of using a pistone or turbine engine with a propellor? They make really small jet engines for radio control planes, so I don't see why not? Even if only for the "cool factor", I bet a plane that does as well as an RV-8 on a small jet engine would be popular... but would it be impossible from a weight or cost standpoint?
What is it about jet engines that keeps them from being found in homebuilt and GA airplanes? Just cost?

Mel · #2 12-31-2007, 07:28 AM

These are probably the most common reasons. Turbine engines cost more. The turbines for models you speak of cost more than a Lycoming. To get any kind of range, you would have to have much larger fuel tanks. Turbine engines require much more stringent traceability, and inspection programs.

pierre smith · #3 12-31-2007, 07:28 AM

....but there is a jet-powered aerobatic glider doing airshows. Here:

http://www.silentwingsairshows.com/jet.html

A friend and I have discussed putting two of these under the wings of an RV. FOD (foreign object damage) would be a problem, though. Fuel mileage with jets and turbines is horrible below 10,000', plus jet fuel weighs a pound more per gallon than gasoline.

Regards,

RV7Guy · #4 12-31-2007, 08:03 AM

I can't find it but a builder in France put to RC Turbines on the popular CriCri. It flies great. But the CriCri airframe is somewhere in 300lb range.

The largest RC Turbine engine runs about 45lbs of thrust and will burn a gallon of fuel in 10 minutes or so.

I guess you could power a light RV 3 with a bunch but of model turbines. You'd have to add engine weight equivalent to the nose but I think it would be a possibility.

BTW, the RC turbine will run you about $5K each ready to go.

prkaye · #5 12-31-2007, 08:11 AM

Quote:

Fuel mileage with jets and turbines is horrible below 10,000', plus jet fuel weighs a pound more per gallon than gasoline.

Ah, that explains a lot. I didn't know that.

Steve · #6 12-31-2007, 08:44 AM

The new Cessna Mustang jet holds 600 pounds of fuel or 85.7 gallons. It will cruise at 340 ktas with an IFR range of 1167 nm. The numbers work out to a fuel burn of 174 lbs/hr or 24.9 gph. Thats about the same mileage as a small piston twin and much better than a Cessna 310 twin but you'll arrive much sooner than any prop plane.
To get those numbers, you and the applicable pilot and aircraft ratings will cruise at FL410 where turbine engines perform best.

Steve

rv6ejguy · #7 12-31-2007, 09:01 AM

Quote:

Originally Posted by Steve

The new Cessna Mustang jet holds 600 pounds of fuel or 85.7 gallons. It will cruise at 340 ktas with an IFR range of 1167 nm. The numbers work out to a fuel burn of 174 lbs/hr or 24.9 gph. Thats about the same mileage as a small piston twin and much better than a Cessna 310 twin but you'll arrive much sooner than any prop plane.
To get those numbers, you and the applicable pilot and aircraft ratings will cruise at FL410 where turbine engines perform best.

Steve

Me don't think so. That's EACH engine maybe. The tests I read were showing 570 lbs./ hr. total at 336 knots TAS and 35,000 feet. No way any comparable jet will get better mileage than a piston aircraft. The fuel capacity is around 2500 lbs., not 600.

captainron · #8 12-31-2007, 09:55 AM

Quote:

Originally Posted by Steve

The new Cessna Mustang jet holds 600 pounds of fuel or 85.7 gallons. It will cruise at 340 ktas with an IFR range of 1167 nm. The numbers work out to a fuel burn of 174 lbs/hr or 24.9 gph. Thats about the same mileage as a small piston twin and much better than a Cessna 310 twin but you'll arrive much sooner than any prop plane.
To get those numbers, you and the applicable pilot and aircraft ratings will cruise at FL410 where turbine engines perform best.

Steve

Steve, tomorrow is January 1st., not April 1st.

Check your information. Good try, though!

fehdxl · #9 12-31-2007, 10:05 AM

From the Mustang web-site. <http://mustang.cessna.com/specifications.chtml>, the 600 pounds comes from how much payload it can carry after loading it with full-fuel and one 200 pound pilot. At first, I mis-read what it really said too. -Jim

captainron · #10 12-31-2007, 11:04 AM

Quote:

Originally Posted by fehdxl

From the Mustang web-site. <http://mustang.cessna.com/specifications.chtml>, the 600 pounds comes from how much payload it can carry after loading it with full-fuel and one 200 pound pilot. At first, I mis-read what it really said too. -Jim

600 pounds sounds like around the minimum fuel I'd like to have aboard when landing, and it's probably about the point where the "Low Fuel" light, also known as the "Resume' Update" light comes on.