P

prkaye

Well Known Member
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?
 
Cost, fuel burn, and inspection criteria;

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.
 
Good question

....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,
 
Possible

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.
 
ahhh

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

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

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 said:
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
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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.
 
Steve said:
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
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Steve, tomorrow is January 1st., not April 1st.:D Check your information. Good try, though!
 
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
 
fehdxl said:
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
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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.
 
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there are a couple of "homebuilt" they only one i can think of is epic aircraft but there are at least three others.

they all require you to use their builder assistance center though.
 
JETS

the guy that owns blue mountian avioncs put a small GE in a cozey there was a nice write up in eaa a year or so ago i think it was a engine called a J5 burned 30 gal hour
 
I bet we'll see more turbines in the future of GA and EAA'ers but I believe they will be in purpose built airframes, probably resembling Long EZ or wing and boom type shapes with the jet exhaust in the rear.

The 'next generation' very light turbofans will have much better efficiencies. However, my best guess is that turbofans will always be pricey due to the exotic materials and engineering tolerances required, to spite the fact that they are simpler in 'theory' than a piston engine.

Agreed, turbofans will also always perform most efficiently up higher in thin air where fuel burn is relatively low and airframe drag is equally low for relatively high true airspeeds. I would not be suprised to see efficiently low fuel burns for optimim economy cruise flight profiles for tomorrows turbofan GA planes that approach the more inefficient 100LL burners of yesterday.

But... Jets are lousy at pattern work if you are paying the bills, and equally wonderful at pattern work if you are not paying the bills and just flying them :)

It's still a ways out though. I'd 'settle' for a nice RV for now :D
 
fuel payload

On my earlier Mustang post, the 600 pound figure was the full fuel payload not the weight of fuel on-board. I misread the spec sheet. It's a small aircraft but not that small.

Oops,
Steve
 
BD-10

Google and youtube the BD-10. There are some videos of it on youtube. Pretty cool airplane that maybe someone with money could take to the next step.
 
Smaller Diameter= Lower Efficiency

Another factor is that the efficiency does down as a cubic function of the diameter, so you loose a lot of efficiency really fast. If you look at the new more efficient turbofans on the new Boeings for example, you can see that they are a lot bigger around than than the turbofans on an older plane.

Hans
 
nucleus said:
Another factor is that the efficiency does down as a cubic function of the diameter, so you loose a lot of efficiency really fast. If you look at the new more efficient turbofans on the new Boeings for example, you can see that they are a lot bigger around than than the turbofans on an older plane.

Hans
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Then the next step is the unducted fan.........

Sonn after that a student of aerodynamics will point out less blades are more efficient.

Then after we reduce the unducted fan blades down to 2 someone will point out the bsfc is better on an intermittent basis over a continuous burn.....

Someday we will put it all together with a direct drive piston engine and a constant speed 2 blade prop....... :rolleyes:
 
diameter of jet engines

nucleus said:
Another factor is that the efficiency does down as a cubic function of the diameter, so you loose a lot of efficiency really fast. If you look at the new more efficient turbofans on the new Boeings for example, you can see that they are a lot bigger around than than the turbofans on an older plane.

Hans
Click to expand...

The large diameter you see is the N1 section. The actual turbine engine is quite a bit smaller. The modern HIGH Bypass Ratio t-fan derives most of its thrust not from the jet exhaust but from the N1 fan section and bypass air.
It is essentially a ducted fan. Modern jet engines are amazing ( the F-22 can only do the things its does because of advancements in engine fuel and air management abilities.)
 
My .02

All,
Greetings from KIDP.

The Citation Mustang is really an efficient bird, as far as jets go. Actual fuel capacity is around 1350 lbs a side, when topped off. Just FYI> ;) It is a really cool airplane. I am an Avionics Tech for Cessna, on the Mustang here in Independence, KS.

Does anyone else have their horizontal stab stashed safely on the bed in their guest bedroom? :D
GJB


Have a great day!
Gregg J. Brightwell
RV-4 emp.
 
prkaye said:
..
What is it about jet engines that keeps them from being found in homebuilt and GA airplanes? Just cost?
Click to expand...
The price of nickel steel. Until this can be produced less expensively or an alternative less expensive material that remains strong at high temperature becomes available, jet (turbine) engines will remain very expensive.
 
But this is my personal favorite personal jet.



Max Takeoff Weight 4,480 lb
Empty Weight 2,480 lb
Useful Load 2,000 lb
Fuel Capacity 1,261 lb (186 gal)
Occupants 1 + 3
External Dimensions
Length 29 ft
Height 8.8 ft
Wingspan 36 ft
Baggage Capacity
Interior 18 ft3
Exterior 18 ft3


Performance
Max Cruise Speed (FL 350) 345 KTAS
Service Ceiling 41,000 ft
Range (FAA IFR +45 minute reserve) (4 occupants) 1,250 nm
Stall Speed (Vso) 61 kt
Takeoff Distance
sea level, ISA to 50 ft at MGTOW) 2,200 ft
Landing Distance sea level, ISA, max landing weight) 1,800 ft
Time to Climb to FL250 12 min
Time to Climb to FL410 27 min

Engine
Pratt & Whitney Canada PW615F Turbofan
Thrust 1,100 lb
 
FWIW...

......a new PT-6 -15, 680 SHP is around $280,000. How many would you like?
My fuel burn with one is a consistent 47 GPH @ $3.00/gal or $141/GPH. Any questions?

Regards,
 
gotta go high

Please keep in mind that in order to get the fuel effiency that is required to make a turbine engine practical you need to go high. That means for practicality sake you need to be pressurized. Lots of weight and lots of engineering. Even the BD-10 was pressurized. If it wasn't, it would run out of fuel very quickly. The engine that it used is an old lear turbojet. Any turbojet engine is a gas hog at low altitudes. Those little model jet engines are turbojets. They don't do much better. My vote is for a diesel or a small turboprop. The innodyn looked promising until things came to a halt with them.
 
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Even a turboprop works best at altitude. A friend who just got his first flight in his Lancair Propjet last summer is desperately tracking down his pressurization problems because it's expensive flying but even more so when you can't go over FL17 w/o O2.
 
And the gearboxes on turboprops make them harder and more costly to maintain than a jet. Not only do you have the turbine to deal with, but an expensive prop and gearbox, too.

There is really no free $100 burger with this one. Everything has it's price. Those Lycomings always look better after considering the bucks and Buck Rogers of owning a jet.
 
hughfi said:
I was always impressed with the RV4 videos on this site. Very cool indeed.

http://www.innodyn.com/aviation/action.html
Click to expand...

The Innodyn turbines are for a turbo-prop application, right? Isn't the original post about a jet engine?

w1curtis is right - the cost to produce the components which are made of very exotic alloys (Hastelloy, Waspalloy, Thermo-Span, Titanium, etc) makes the cost of the parts very high. I work in the jet engine repair industry and when I first started, the sticker shock of parts blew me away.
 
pierre smith said:
Fuel mileage with jets and turbines is horrible below 10,000', plus jet fuel weighs a pound more per gallon than gasoline.

Regards,
Click to expand...

Hey Pierre, here's a dumb question then -- why are you running a turbine in your Air Tractor then? Your average altitude is probably 100' AGL for the life of the aircraft. Need the extra power, maybe?

Hope you're doing well!
Paul
 
In 1974 I checked out in the F-15A and flew it for five years before retiring. It had 50,000 pounds of thrust and only weighed 39,000 pounds at takeoff. At that time it held all eight time-to-climb records and some may even stand today. Think of this: 9,843' in 27.57 seconds, 19,685' in 39.33 seconds, 29,528' in 48.86 seconds, 39,370' in 59.38 seconds, 49,212' in 77.04 seconds, 65,617' in 122.94 seconds, 82.021' in 161.02 seconds and 98,425' in 207.8 seconds. With a 600 gallon centerline tank the bird would climb to 42,000' in twelve minutes and only be 40 miles from the field and do it with military power only (no afterburner). I very often cruised at 50,000' on cross countries at .98 Mach. That is about 10 miles/minute. I don't go quite as fast now, but I want you to know that the RV you are flying right now has the light, responsive feel of a fighter and you built the aircraft! If you are still pounding rivets keep at it. These RVs are sweet, even if they don't have a jet engine!

Jim
 
JAT said:
In 1974 I checked out in the F-15A and flew it for five years before retiring. It had 50,000 pounds of thrust and only weighed 39,000 pounds at takeoff. At that time it held all eight time-to-climb records and some may even stand today. Think of this: 9,843' in 27.57 seconds, 19,685' in 39.33 seconds, 29,528' in 48.86 seconds, 39,370' in 59.38 seconds, 49,212' in 77.04 seconds, 65,617' in 122.94 seconds, 82.021' in 161.02 seconds and 98,425' in 207.8 seconds
Click to expand...
Most of those records were later taken by Soviet aircraft, but the one for 20,000 m (65,616 ft) is still held by the F-15. The records up to 15,000 m (49,213 ft) are held by one of the prototype Su-27s, and the records from 25,000 m (82,021 ft) to 35,000 m (114,829 ft) are held by prototype MiG-25s.

The lower altitude time to climb records are even more impressive if you consider that the clock starts during the take-off roll when the aircraft first moves down the runway. The current record for 3,000 m (9,843 ft) is 25.37 seconds.
 
Too old for risks.

Paul Eastham said:
Hey Pierre, here's a dumb question then -- why are you running a turbine in your Air Tractor then? Your average altitude is probably 100' AGL for the life of the aircraft. Need the extra power, maybe?Paul
Click to expand...

Hope you're doing well!

Hi Paul,
The old 1340 cu. in. Pratts are so old and crack cylinders so often that it's become less expensive in the long run to run a PT-6. My old 1340 powered Air Tractor wouldn't hardly go 1000 hours without needing a $25,000 overhaul. My PT-6 has over 8000 hours and hasn't had an overhaul, just the CT wheel (compressor turbine) replaced...that and $1500 hot section inspections at 1000-1200 hours. I would have already spent $200,000 on overhauls on a 1340 in the same time frame. I also use 1 quart of Exxon 2380 synthetic every 30 hours ($9.00) compared to 2 gallons a day of Aeroshell 120 (60W) at $80 a day in the 1340. I sat down and did some serious math and the big winner, all things considered, the PT-6 won hands down.

I also had to park the old Air Tractor in a cornfield when the master-rod cylinder started shucking the lower cylinder skirt and the pieces internally beating the $$it out of the other reciprocating pieces....I'm too old for that:)

FWIW, the PT-6 is one of the few engines I don't mind riding behind at night!

Regards,
 
No night ag..

......for me, Paul.......too many powerlines. California and Az are big on night ag, mainly because of high daytime temps and the associated chemical drift/evaporation problems during daytime ops. I do, however have a night-equipped Air Tractor...over 1 million candlepower with huge retractable lights...BTW, when one doesn't retract, it yaws the airplane 'cause it's out near the tip on a 50' wingspan.

Regards,
 
Hi Pierre, I share your sentiments about the PT-6 :D

The PT-6 engine was originally designed to run oil field pumps in Texas and Oklahoma, unsupervised, for days on end with no maintenance.

The best thing that ever happened to turboprop airplanes was the introduction of this "pump" to an engine mount. I've got many an hour with my life in the balance based on how well that engine performed. In over 4000 hours of PT-6 time I've got (8000 if you count 4000 with two engines)... I've never, ever had so much as a hint of quitting from that engine. I did see a very brief compressor stall one time, a momentary "BANG" in heavy ice (with ice protection in used BTW) followed by no more hint of complaints. I think she was just clearing her throat :p
 
Nothing's Perfect

The PT6 is a wonderful engine and a huge step forward over the old radials as Pierre points out. Night Ag ops? You ag guys have my total respect!

Like any engine however, PT6s do fail:

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070919X01414&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070920X01419&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20071106X01738&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070919X01415&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070904X01307&key=1

These are some single engine incidents just in the last year on C 208s.

I have a friend who suffered a power loss in a 208 as well with a sheared fuel pump drive. He just put it back down on the lake.

On the other hand, my dad has over 9000 hours in King Airs (18,000 engine hours) and only had to do one precautionary shutdown.

Very good engine but when you only have one...:(
 
3 shutdowns in 5000 hours with PT-6. But they were in BE-1900s that were used pretty hard. Still, enough reserve power in the good motor to make RTB a non event. Great motor. Would love to fly Pierres' ag plane when it's empty... ;-)
 
Kevin Horton said:
I'd love to see a reference for that "fact". All the info I have ever read says that the PT-6 was designed for aircraft turbo-prop applications first, and that other applications came later.
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I never really gave much pause for thought to the well told Oil Rig story that a Beech Engineer told me several years ago concerning the PT-6 engine. The same story was also told to me by another guy a few years later - stuff gets around in folk lore I suppose.

But I wouldn't be much of a pilot if I didn't share in the skepticism when a fellow pilot raises the BS flag! The internet is an amazing place to research, but some of what you find can be an equally loaded mess. I did find a very good source on the PT-6 engine in the form of a published aviation history book though:

http://books.google.com/books?id=V0...RwF&sig=ihcC7oTCw4CgvW59lFrkbT5ay-w#PPA433,M1

Check out chapter 8 starting on page 443 - they later get into the talking about the DS-10, the fore runner to the PT-6, and then the PT-6 itself. I have not found any reference to an oil rig pump, but who knows. I'll consider the story as a likely folk lore "busted" myth unless I see otherwise now!

As far as the Wikki reference on the PT-6 engine, well, it's not quite all there, but close.
 
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Yes, turbines do fail. I've found that not only does the engine design itself matter, but who has been working on that engine, and just as importantly, who has been operating said engine before you. ;)

My only in flight engine shutdown to date has been a TFE-731 (Garret/Honeywell Turbofan). Though an extensively used and very good engine all things considered, it has some history among operators for in flight shutdowns. It stood to reason it happened to me on a test flight following a complete engine overhaul and return to service. As we went up, oil pressure went down, sick engine was put to bed before metal fireworks display commencement, and an increased appreciation for the remaining engine ensued :D Returned for a landing and memory items on the checklist called for an immediate return to hotel followed by a nice dinner and drinks for the crew :D

Of course in this case it was an impending oil pump component failure that decided to call in for real and quit. At least further diagnosis and maintenance was not far away and we were flying again a day later.

Anything can happen... oil seals, pumps, bearings, turbine blades, FOD, birds, compressor stalls, fuel pumps, and on and on and on... When they design the perfect airplane that does away with the pilots maybe they'll also design the perfect airplane that does away with the mechanics, and engineers too! A self designing, self repairing, self flying airplane!
 
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Eddie P said:
When they design the perfect airplane that does away with the pilots maybe they'll also design the perfect airplane that does away with the mechanics, and engineers too! A self designing, self repairing, self flying airplane!
Click to expand...

Like the old joke about the pilot and the dog in the automated cockpit - the pilots job was to feed the dog, the dog's job was to bite the pilot if he tried to touch anything...
 
Eddie P said:
I did find a very good source on the PT-6 engine in the form of a published aviation history book though:

http://books.google.com/books?id=V0...RwF&sig=ihcC7oTCw4CgvW59lFrkbT5ay-w#PPA433,M1

Check out chapter 8 starting on page 443 - they later get into the talking about the DS-10, the fore runner to the PT-6, and then the PT-6 itself.
Click to expand...
That's a great reference. Thanks for pointing it out. It is interesting that by the time the PT-6 achieved certification, they had 11,000 hours of development running time, and almost 800 hours of flight test running time (page 448). They had a lot of problems at first, and had to make many significant design changes, but they did enough testing to have arrived at a reasonably reliable engine by the time it achieved certification. Unfortunately, it is too expensive for new amateur-built aircraft engine suppliers to do that much testing, so they have to rely on the early customers to find many of the problems. This is OK, as long as the customers understand that they are effectively paying for the privilege to do engine development testing.
 
Lousy or no maintenance..

rv6ejguy said:
The PT6 is a wonderful engine and a huge step forward over the old radials as Pierre points out. Night Ag ops? You ag guys have my total respect!

Like any engine however, PT6s do fail:

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070919X01414&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070920X01419&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20071106X01738&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070919X01415&key=1
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070904X01307&key=1

These are some single engine incidents just in the last year on C 208s.

I have a friend who suffered a power loss in a 208 as well with a sheared fuel pump drive. He just put it back down on the lake.

On the other hand, my dad has over 9000 hours in King Airs (18,000 engine hours) and only had to do one precautionary shutdown.

Very good engine but when you only have one...:(
Click to expand...

.......causes most of this stuff! With one exception, they were all South American failures. I have personally seen the absence of maintenance and or the inability of those mechanics to do Pratt approved work. High ITT temps are often neglected because the engine still runs and they fall into a misguided tranquility because it's run faultlessly for so long. In the end, the engine has an indelible memory...it records every overtorque, every overtemp and every overspeed. It will either reward your kindly efforts with a long faithful service life or come back to bite you hard for your tyrannic use of it. The same thing applies to our beloved Lycs.

My .02,
 
Oh turbine engines surely fail - we see some pretty nasty stuff come through my work from time to time. :)
 
Yes, maintenance quality has a lot to do with turbine engine reliability but I know other pilots who have had turbines fail even with good maintenance. One had two 731 failures in less than 3 years. Causes include oil and fuel pumps but also meltdowns and cracking parts. We don't know what the maintenance was like in these SA cases but hard use on turbines- gross weight, hot and high and high cycles takes its toll as does ham fisted pilots who ignore TIT and torque limits.

Point being, for risky ops or over bad terrain, it's nice to have two. No matter what's stamped on the side, you are in for a bad time when it quits and you only have one.
 
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