# Would you be interested in a 200 hp turboprop?

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#### BBerson

##### Light Plane Philosopher
HBA Supporter
I think the small turbine market is military. They want jet fuel power plants.
The turbine is lighter than jet fueled Diesel engine.

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#### Marc Zeitlin

##### Exalted Grand Poobah
... IF they can hit the target, at an affordable price (meaning new Lyc prices), then .52 is easily tolerated; fuel price would make up the spread and the only thing lost is payload/range.
That's a good point that I had forgotten to consider - Jet-A is about $0.90 cheaper than 100LL at this point, which is pretty close to 20%, so the difference in operating costs is small. So, yeah, if they can prove 3K hr TBO at the same price as an 0-360, maybe I would be interested... My engine (1650 hrs) will probably need an OH in 3 - 6 years - that gives them some time to prove it. I was hoping to go to an electric motor and batteries, but that's clearly a pipe dream in that time period. Hmmm. #### TurbAero ##### Well-Known Member Lifetime Supporter It is possible to make a 200hp turboprop with a 15gph sfc but it would require multiple compressor and turbine stages, the use of exotic materials and ceramic coating to sustain the heat. As has been raised in subsequent posts, we are not achieving better SFC through these means. We are using recuperator technology which by necessity requires modest pressure ratios and temperatures. The trick is making that efficient, light and compact enough for aero applications. Ross has elocuted this nicely and indeed, this is the crux of the technical challenge for our program. If size/weight was not an issue, because the technology has been proven and is in use in ground applications, it would have been done before for aero applications. However, packaging an effective heat exchanger within the envelope of an acceptable sized aero engine and making it cost-effective are the challenges we face with our program. These challenges are not insignificant. The design of the rest of the turbomachinery and mechanical components is fairly straight forward. Not simple because every single component is a complex and highly precise piece of equipment, but at least the development processes for the turbomachinery is well known and is a path well trodden. The TurbAero webpage indicates that this engine weighs about 270 lb. This is 20 lb. less than a 180 HP Lycoming O-360. It also indicates a BSFC of 0.52, which compares particularly unfavorably with the approximate 0.4 - 0.42 that the 180 HP Lycoming can achieve when using EFII/EI and aggressive leaning. They indicate a TARGET TBO of >3K hours (obviously unproven at this point) vs. a proven TBO (granted, with a large standard deviation) of 2K - 2.4K for the Lycoming engine. With no price indicated and no proof of performance and or TBO, everything is speculation. But given the large increase (~25%) in BSFC between the two engines, very small difference in weight, and unproven TBO difference, I'm having a hard time seeing any advantage in performance or TOTAL cost in this turbine engine. Possibly, for aircraft that fly 500 - 1000 hours/year and need minimal maintenance attention, the additional fuel cost might be acceptable. For someone that flies 50 - 100 hours/year and doesn't pay for maintenance, I cannot for the life of me see the appeal - I'll be paying 25% more for gas for the foreseeable future, and for what? Magically get the BSFC down to the 0.4 - 0.42 level, and I'm in. Mark, all your points are valid. It is horses for courses when it comes to what powerplant a builder will select. We intend to provide an option for those who may wish to go the turbine route. Whether we can achieve our targets is speculation at the moment. Given time, we will either validate or disprove whether our targets are achievable. I hope it is the former. When it comes to the weight of our engine, we expect to be able to revise that downwards. Our latest recuperator design will facilitate a weight saving and our gearbox for the prototype is built like the proverbial outhouse with significant margins built in (for both stresses and lifing) which should be able to be reduced over time, resulting in weight savings etc. I'd just like to make a point in relation to the SFC figures. Please bear in mind that the Lycoming uses fuel that has a specific gravity of 6.2 lbs/usg whereas our turbine will use fuel with a specific gravity of 6.8 lbs/usg, almost a 10% difference in SG. It is fuel flows that need to be compared, rather than SFC's when it comes to different fueled engines. Since fuel and fuel flow is generally measured by capacity i.e.$/usg or USG put into the tanks, fuel flows measured in volume rather than SFC is a more appropriate comparison.

In relation to fuel, there is also a cost differential between Avgas and JetA, generally in favour of JetA. Using todays fuel rates from globalair.com for Oshkosh as an example, 100LL is $4.89 and JetA is$4.19 per gallon which is around a 14% difference.

Doing a quick and dirty (I don't have accurate lean of peak figures that I can find for an IO360) comparison between an IO360 and our TA200 at 10,000' and 150hp, from Lycoming's manual for the IO360-B1C model (and even for the new YIO390), a 150hp cruise at 10,000' cannot be achieved by the IO360. Lets assume however that it could and that a SFC of say 0.45 lbs/hp/hr is achieved. Let's also assume a conservative SFC for the TA200 of 0.60 lbs/hp/hr (assuming we do not hit our target of 0.52), then we get the following fuel cost results:

IO360: 0.45 lbs/hp/hr x 150hp = 67.5 lbs of 100LL @ 6.2 lbs/gal = 10.9 gallons @ $4.89 per gallon =$53.20 per hour fuel cost

TA200: 0.60 lbs/hp/hr x 150hp = 90 lbs of JetA @ 6.8 lbs/gal = 13.2 gallons @ $4.19 per gallon =$55.30 per hour fuel cost

If we hit our target SFC at design point, then the fuel costs should be less for these higher powered cruise settings. We acknowledge that at low power settings where our turbines would be operating off design, that SFC takes a hit and the reciprocating engines are more efficient at the lower power settings, but at the lower power settings, neither engine is burning a lot of fuel so the fuel cost saving is marginal.

Now if an owner wants to operate higher than 10,000' our TA200 will still offer reasonable power into the Flight Levels, where the SFC will also improve.

However, the aircraft owner now looks at those fuel burns and notes that he now needs to carry more fuel to fly the same distance, even though the fuel cost may be similar. He needs to have bigger tanks if he's going to fly the same distance. Offset against that is that with a turbine, a more aerodynamically efficient cowling and intake system is likely possible. This will reduce the power requirements for the same speed cruise or alternatively, set the same power and cruise faster. Also, realistically, the installed weight of our turbine is likely to be at around 100lbs or more better than the reciprocating engine. That equates to better performance/increased payload capability which is a bonus to the owner. With our TA200 essentially being flat-rated at 200hp to almost 10,000', there is an advantage for high altitude take-off and climb performance against a normally aspirated piston.

If we can get a 3,000hr TBO, then that will also be a benefit. As has been said, these are targets. We still need to test and be able to demonstrate the performance. We are working towards that aim and believe me, it's not an easy path but it is one that we are conscientiously pursuing and for my team, the light is at the end of the tunnel.

With the PBS TP100 offering a SFC of around 0.9 lbs/hp/hr and the best of the majors (P&W, GE etc.) with their higher powered engines offering SFCs to around 0.6 lbs/hp/hr, for us to achieve a SFC of better than 0.60 in a small hp engine will be quite an achievement.

As I have said, a turbine will not be for everyone. There is no doubt now that there will be a sticker price that is definitely in favour of a piston engine but through life costs are more important to some and features and characteristics will also be important to others. We shall at least, offer builders and owners an alternative.

#### rv6ejguy

##### Well-Known Member
It's easiest to compare cost per pound of fuel when using BSFC and 100LL vs. Jet A. That's .63/ lb for Jet A and .82 for 100LL. Quite a difference there. So, as pointed out, the turbine BSFC can be a fair amount worse and still deliver comparable costs per hour with regards to fuel burn to a piston engine.

The PW120A has a SFC (disregarding exhaust thrust) of under .5 with a 12 to 1 PR at altitude. ESFC around .47.

For comparison, standard Lycomings can achieve .42 BSFC running LOP. Modified higher compression models with EI and EFI can achieve .36 to .38.

#### Merlin

##### Active Member
As has been raised in subsequent posts, we are not achieving better SFC through these means. We are using recuperator technology which by necessity requires modest pressure ratios and temperatures.

Ross has elocuted this nicely and indeed, this is the crux of the technical challenge for our program. If size/weight was not an issue, because the technology has been proven and is in use in ground applications, it would have been done before for aero applications. However, packaging an effective heat exchanger within the envelope of an acceptable sized aero engine and making it cost-effective are the challenges we face with our program. These challenges are not insignificant. The design of the rest of the turbomachinery and mechanical components is fairly straight forward. Not simple because every single component is a complex and highly precise piece of equipment, but at least the development processes for the turbomachinery is well known and is a path well trodden.

Mark, all your points are valid. It is horses for courses when it comes to what powerplant a builder will select. We intend to provide an option for those who may wish to go the turbine route. Whether we can achieve our targets is speculation at the moment. Given time, we will either validate or disprove whether our targets are achievable. I hope it is the former.

When it comes to the weight of our engine, we expect to be able to revise that downwards. Our latest recuperator design will facilitate a weight saving and our gearbox for the prototype is built like the proverbial outhouse with significant margins built in (for both stresses and lifing) which should be able to be reduced over time, resulting in weight savings etc.