Looking at the latest announcements from TurbAero I was wondering why one would ever put a turboprop on an RV (There are airframes where a turbine obviously makes sense but I am asking about RVs in particular.). Now I get the 'cool' factor. Who doesn't like the smell of burned kerosine? I also don't want to start a debate here about the merits of experimentation. If you like experminenting please do. What I am trying to understand are some of the underlying physics/costs and not being an aeronautical engineer or engine expert I am having a hard time working this out by myself.

I see 4 different areas of comparison here:

1. Takeoff roll

2. Climb to altitude

3. Cruise at altitude

4. Cost

So let's be concrete.

Let's assume we have an RV-8 with an IO-360 M1B and compare that to an RV-8 with a TurbAero Talon turbine.

Anticipated performance and cost of the Talon engine can be found here:

https://turb.aero/community/resource...sked-questions
Performance numbers for one configuration of an IO-360 M1B on an RV-8 can be found here:

https://www.vansaircraft.com/rv-8/#aircraft-details-2
Van's claims 203 mph TAS at gross with 75% power (which is typically around 9gal/hr lean of peak for me at that altitude) and 575 feet take off distance which I assume was done on a paved runway.

So coming back to my 4. areas. How can I compare:

**1. Takeoff roll**

Now the Talon engine sates it has 200hp at sea level which according to Van's would save me 75 feet on take off distance. That assumes that it develops power as quickly as a piston engine. Do turbo props do that?

**2. Climb to altitude**

I am actually not sure how to make a good comparison here. Van's claims a 15% inmprovement in climb rate at see level for another 20hp but I rarely climb at max climb rate. I typically climb at 500 feet a minute or so which already gives me a pretty decent ground speed while climbing. So how do you compare that?

**3. Cruise at altitude**

Van's shows his numbers at 8000 feet which is roughly the altitude I cruise at and feels quite comfortable. At 75% power that would be 135HP at 9gal/h. Now I don't fully understand how you measure power on a turbine but assume that shaft power would be the equivalent to the power spec of a piston engine. Using that assumption the Taleon engine should be able to make 180HP at 15-17gal/h at that altitude.

So that gives me 1.33 times the power. Now I was told that power and speed on airplanes is related roughly by the power of three (is that correct?). So that would provide a speed increase of approximately 10% taking the cruise TAS to 223mph. Flying higher will be somewhat better in fuel efficiency but I really don't want to have to always cruise with oxygen which limits me to 12500 feet. Also TAS is limited to 230mph per vans.

I don't know how to compare this at 12500 feet which would be the highest altitude I am willing to fly permanently and should be more favorable to the turbo prop.

**4. Cost**
The Taleon engine will cost 80-85k$ . Lycoming will cost 43k$ with dual EMAG.

At my typical altitude I would get 10% more speed put use more then 50% more fuel. Now I know AVGAS is more expensive then Jet A but looking around its usually cheaper by 1 dollar or so which is about 25%. Also the IO360-M1B can be operated on unleaded fuel so AVGAS is not stricly required. It's just the convenient choice in the US.

So from all I can see the turbine is strictly more expensive for a 10% speed increase. Is that the correct way to look at it?

Again I understand very little about all of this and probably made many mistakes above. The reason for posting this is to learn something.

Thx

Oliver