Turbine question for a newbie

[av8innz]

Has anyone ever looked into fitting a Rolls Royce Alison C18 turbine
These are pretty bomb proof engines and they do not require the case half inspections like the larger C20 engines.
Now most Hughes/MD 500 helicopters have changed to C20 versions there are quite a few C18 's up for grabs.

Parts are available pretty much everywhere around the world
Very compact units and only weigh 136lb!!!

317hp (flight idle)
Fuel cosumption approx 130lbs/hr

no carb ice
Warm air to cabin/screens via bleed air
Runs on diesel or JetA1
no mixture control
Proven track record
(power/weight 136 Ib; 2.33 shp/Ib )

Output is 6,000rpm so need a 3:1 reduction gear box of some sorts.
Comments please.

[RV6_flyer]

What I know about Turbine engines in Amateur Built Aircraft in one sentence.

All turbine engine powered amateur built aircraft must have an approved FSDO maintenance program before you can get an airworthiness inspection.

[av8innz]

That was fast!!
I assume the Manufacturers maintenance intervals /requirements would be adopted.
It was more a question of has anyone done this or looked into it yet.

[John Clark]

Originally Posted by av8innz

Very compact units and only weigh 136lb!!!

317hp (flight idle)
Fuel cosumption approx 130lbs/hr

no carb ice
Warm air to cabin/screens via bleed air
Runs on diesel or JetA1
no mixture control
Proven track record
(power/weight 136 Ib; 2.33 shp/Ib )

Output is 6,000rpm so need a 3:1 reduction gear box of some sorts.
Comments please.

Turbine power would be wonderful in an RV. As a 12000+ hour turboprop pilot I would love to have turbine power in my RV8. But there are some very real reasons that there are no viable turbine powered RVs around. Let's go through your list:

136 pounds Basic engine yes, but what does the finished installation and extra fuel weigh?

317 HP Max output, not flight idle.

Fuel consumption approx 130lbs/hour 19 gallons per hour.

No carb ice. True, no carb! But the problems of inlet ice make carb ice look simple. For example, the CT7 GE engines have electrically heated inlet ducting powered by a dedicated alternator.

Warm air to cabin/screens via bleed air True again. but the bleed air coming out of the engine is something over 700 degrees F. Mixing valves needed to make it useable. You can also run a "pack" or air-cycle machine to make cool air but it is complex.

Runs on diesel or Jet-A True, a lot of Diesel or Jet-A. The burn number your quote is a little under 3 times the burn of a Lycoming. Oh, yeah the fuel is heavier too, 6.84 lbs per gallon vs 6.0 for gasoline.

No mixture control True again! But it does have a very complex fuel metering system and various governors.

Proven track record True. Well developed turbine engines are very reliable. The downside is cost. These engines were developed for military and commercial operations where they were to flown a lot and the cost could be amortized.

Reduction gear This can be a very complex engineering issue when you have to combine it with a way to control the prop. In the case of a single shaft turbine you will need to have a way to move the prop to "flat pitch" for starting. You might want to do a search on this site, lots of discussion of reduction gear systems.

Again, I'd love to see it work, but I'm not going to wait for it to happen.

John Clark
ATP, CFI, SA-227, BA-3100, SF-340
RV8 N18U "Sunshine"
KSBA

[gmcjetpilot]

Originally Posted by av8innz

Has anyone ever looked into fitting a Rolls Royce Alison C18 turbine. Now most Hughes/MD 500 helicopters have changed to C20 versions there are quite a few C18 's up for grabs.

Parts are available pretty much everywhere around the world
Very compact units and only weigh 136lb!!! (VERY expensive parts)


Output is 6,000rpm so need a 3:1 reduction gear box of some sorts.
Comments please.

How much money for one of these?

Have you priced an impeller? More than may be a whole Lycoming new. May be not that much but probably $9,000 to $12,000?

Helicopter engine aren't going to have a gear box for a prop, or prop control. To work that little piece of engineering out might be a challenge and expensive. You may get the engine but not the fuel controllers and all the pumps and stuff to make it run. COST? BIG TIME.

There has been MUCH debate about turbines on these forums. See the search drop down in the tool bar? Type in "turbine" or "Innodyn". You will get all the Pros and Cons for putting a turbine engine in a RV.

Personally I don't think a turbine is a good match for RV airframes. RV's are made for 160-200 HP, 260HP for the RV-10. The airframes are made for 320-400 lb engines. RV have a Vne that would restrict speed. Fuel burn? Most RV's have small tanks.

The biggest draw back of turbines is the FF. Yes they are light and powerful but fuel burn per unit HP is much higher than a piston engine. Innodyne makes some unbelievable claims so ignore that.

I fly turbine aircraft and understand the allure, mystery and attraction to burn Jet A. However for a personal plane that will fly 100-150 hours a year, its kind of a waste, in my opinion. If you are rich and want to be the only one on the block with a turbine, there are better choices. It's probably going to be cheaper and better to buy a plane that was designed for a turbine, even certified factory plane. Frankly the new VLJ are looking interesting for the rich.

The Lancair IVP with a Walter (PT6 euro clone) is a better airframe to engine match. It's pressurized for one and it can hall four people. One of these IVP's are 1/2 mil at least, closer to 3/4 mil.

The Lancair IVP or a high gross utilitarian bush plane make more sense for a little turbine, the RV not so much.

[av8innz]

Hi John.
Please see my notes relating to each point.

Originally Posted by John Clark

Turbine power would be wonderful in an RV. As a 12000+ hour turboprop pilot I would love to have turbine power in my RV8. But there are some very real reasons that there are no viable turbine powered RVs around. Let's go through your list:

136 pounds Basic engine yes, but what does the finished installation and extra fuel weigh?

I imagine the engine mount would be same if not lighter than std Lycoming,
Not sure what else would be needed, battery weighs same as std lead acid (or less even) fuel would be more but of course you would not be in the air for as long for any given A to B flight. I would be guessing but this HP should be able to generate a TAS of 220kts
317 HP Max output, not flight idle.
Correct

Fuel consumption approx 130lbs/hour 19 gallons per hour.
At 220kts that would be 1.7lbs/NM, not bad really!!

No carb ice. True, no carb! But the problems of inlet ice make carb ice look simple. For example, the CT7 GE engines have electrically heated inlet ducting powered by a dedicated alternator.
C18 has antice bleed (pilot selectable if visible moisture and OAT+<5 deg C)
so already catered for.
Warm air to cabin/screens via bleed air True again. but the bleed air coming out of the engine is something over 700 degrees F. Mixing valves needed to make it useable. You can also run a "pack" or air-cycle machine to make cool air but it is complex.
Can be sourced from any MD500 wreck or purchased new. all very 'manual' to operate, Just a duct with a mixer valve -straightforward to incorporate!!
Runs on diesel or Jet-A True, a lot of Diesel or Jet-A. The burn number your quote is a little under 3 times the burn of a Lycoming. Oh, yeah the fuel is heavier too, 6.84 lbs per gallon vs 6.0 for gasoline.

Not sure what normal endurance is for a RVx with a 300hp engine!! . However a 300hp lycoming does not exactly sip the avgas either, I would guess something like 15gal/hr so that would be 90lbs/hr versus the 130lbs/hr for the C18 so approx 44% higher burn rate for the turbine. In NZ Jet A1 is 30cent/litre (about $1.00/gallon) cheaper than avgas (25%) thats so difference is now down to only 20%, so this plus the much longer tbo for the turbine makes the case very strong for this C18 model, especially when Im flying over mountains or the Ocean (which is most the time in New Zealand)

No mixture control True again! But it does have a very complex fuel metering system and various governors.
This comes with the engine. once setup very rarely needs adjustment.
Proven track record True. Well developed turbine engines are very reliable. The downside is cost. These engines were developed for military and commercial operations where they were to flown a lot and the cost could be amortized.

Can pickup C18 with mid life components for about US$25k

Reduction gear This can be a very complex engineering issue when you have to combine it with a way to control the prop. In the case of a single shaft turbine you will need to have a way to move the prop to "flat pitch" for starting. You might want to do a search on this site, lots of discussion of reduction gear systems.

em good point, I will chew this over

Again, I'd love to see it work, but I'm not going to wait for it to happen.

John Clark
ATP, CFI, SA-227, BA-3100, SF-340
RV8 N18U "Sunshine"
KSBA

interesting points, thanks for the feedback. what do you think can be done re the prop issue.

cheers

Mark

[av8innz]

Originally Posted by gmcjetpilot

How much money for one of these?

Have you priced an impeller? More than may be a whole Lycoming new. May be not that much but probably $9,000 to $12,000?

Helicopter engine aren't going to have a gear box for a prop, or prop control. To work that little piece of engineering out might be a challenge and expensive. You may get the engine but not the fuel controllers and all the pumps and stuff to make it run. COST? BIG TIME.

There has been MUCH debate about turbines on these forums. See the search drop down in the tool bar? Type in "turbine" or "Innodyn". You will get all the Pros and Cons for putting a turbine engine in a RV.

Personally I don't think a turbine is a good match for RV airframes. RV's are made for 160-200 HP, 260HP for the RV-10. The airframes are made for 320-400 lb engines. RV have a Vne that would restrict speed. Fuel burn? Most RV's have small tanks.

The biggest draw back of turbines is the FF. Yes they are light and powerful but fuel burn per unit HP is much higher than a piston engine. Innodyne makes some unbelievable claims so ignore that.

I fly turbine aircraft and understand the allure, mystery and attraction to burn Jet A. However for a personal plane that will fly 100-150 hours a year, its kind of a waste, in my opinion. If you are rich and want to be the only one on the block with a turbine, there are better choices. It's probably going to be cheaper and better to buy a plane that was designed for a turbine, even certified factory plane. Frankly the new VLJ are looking interesting for the rich.

The Lancair IVP with a Walter (PT6 euro clone) is a better airframe to engine match. It's pressurized for one and it can hall four people. One of these IVP's are 1/2 mil at least, closer to 3/4 mil.

The Lancair IVP or a high gross utilitarian bush plane make more sense for a little turbine, the RV not so much.

Hi George,
Flying helicopters, the idea of being able to Zip along at 210kts plus for 130lbs / hr consumption seems really good value.
Props seem to be the problem, and the airframe constraints are interesting.

I have just viewed the Innodyne site - not sure, all new and unproven Nothing like a RR badge for the confidence.

[pierre smith]

Good morning,
I own one of each......an RV-6A with a 180 Lyc and an Air Tractor with a PT-6-15/680 SHP and it burns 47 GPH working. Unless you can find an engine with a planetary gearbox/reduction unit like a PT 6 or Walter, the engineering alone would be a staggering cost to be done right. BTW, a new PT-6 costs around $275,000, used..$125,000. Walter can be bought for around 110,000. How many would you like?

I flew both these airplanes this weekend and a friends RV-4......just love the Lycs in them....well matched. That said, if you have the dollars and time, you are after all, in "Experimental" Aviation. It's just that most of us would rather fly a known product than experiment. Your call.

Regards,

[Andy_RR]

Do you really get 130lb/hr fuel consumption at RV-type altitudes?

A turbine's efficiency is very pressure ratio-sensitive, so most turbines rely on the reducing atmospheric pressure at altitude to dramatically increase the available pressure ratio (atmospheric pressure being the denominator of the equation).

A

[John Clark]

Originally Posted by av8innz

interesting points, thanks for the feedback. what do you think can be done re the prop issue.

cheers

Mark

Short answer, millions of dollars in engineering. You need a small version of the prop gearbox developed by GE for the CT7. The engine itself was developed for helicopter use. In order to convert it for aircraft use General Electric developed a stand-alone prop gearbox. The gearbox has it's own oil system allowing the use of a hydraulic prop govenor. It also has to be engineered to take the thrust loads from the propellor. A drawing and some specs at:

http://www.geae.com/engines/commercial/ct7/

Another, more practical problem is that you are proposing speeds that are beyond the limits of the existing RV airframes. I realize that we are talking experimental aircraft here but the FAA will not allow a turboprop aircraft to operate over Vno (Maximum Structural Cruising Speed) This eliminates the "yellow arc." In the case of my RV8, instead of having a "red line" of 200 knots it would be reduced to 168 knots, the "top of the green."

Instead of "reinventing the wheel" you might want to take a look at this:

http://www.legendaircraft.net

Regards,
John Clark
RV8 N18U "Sunshine"
KSBA