Friday Mooney Turboprop Musings

[Geoff]

The potential 300lb GW increase from the factory got me thinking...

Could it be a stepping stone to a RR250 500 SHP conversion sans pressurization? 

Imagine a fowler flap, oleo strut, 130 gal, RR250 powered M20TP with a gross weight of 3750 and an empty weight of ~2350 (since the RR is lighter than the Continental).  UL of 1400 and a full fuel payload of 529 lbs.

The RR250 burns ~25 gph so full fuel would give ~5 hours of range at a speed of who knows (225 knots?  at 17000).  4 hours might get you 1,000 NM down range.

Acclaims gets ~205 knots at that altitude on 20 gph on only 270 hp so its not unthinkable.

There is a market of the Matrix, perhaps there is a market for folks who can't get/don't like avgas.  

Once the certification is done on the flaps and landing gear would an engine change be that much more work?  I don't know.

Its a $1 MM plane at least but so is an SR22T.

Happy Friday!

[carusoam]

Way to go Geoff!

I like the way you think.

When discussing turbine Mooneys... I have to at least invite Erik... @aviatoreb

Best regards,

-a-

[N201MKTurbo]

A friend of mine was flying a turboprop A36 recently. He said it didn’t go all that much faster or higher. He said the biggest thing was the smoothness of the engine. It was for sale and nobody wanted to buy it. He said he wouldn’t spend the money on it.

[Davidv]

11 hours ago, Geoff said:

The potential 300lb GW increase from the factory got me thinking...

Could it be a stepping stone to a RR250 500 SHP conversion sans pressurization? 

Imagine a fowler flap, oleo strut, 130 gal, RR250 powered M20TP with a gross weight of 3750 and an empty weight of ~2350 (since the RR is lighter than the Continental).  UL of 1400 and a full fuel payload of 529 lbs.

The RR250 burns ~25 gph so full fuel would give ~5 hours of range at a speed of who knows (225 knots?  at 17000).  4 hours might get you 1,000 NM down range.

Acclaims gets ~205 knots at that altitude on 20 gph on only 270 hp so its not unthinkable.

There is a market of the Matrix, perhaps there is a market for folks who can't get/don't like avgas.  

Once the certification is done on the flaps and landing gear would an engine change be that much more work?  I don't know.

Its a $1 MM plane at least but so is an SR22T.

Happy Friday!

It’s an interesting idea but there is actually not a market for the Matrix.  Piper stopped producing it a few years ago because of lack of demand. Turboprops become more efficient up high so your best fuel economy (and TAS) is going to exist at higher altitudes where you want the pressurization.  Even at 17k, it’s great to have room for 4 adults but making them all wear cannulas isn’t fun. The Vne of Mooney’s at 195 is also a big limiting factor to maximizing the power of the RR engine down low. 
 

As @N201MKTurbo points out the benefits are smoother and reliability.  Burning Jet-A is also a plus but diesels do that too.  Unfortunately there isn’t a huge market for people who want to spend the extra $ for these things alone.

[Awful_Charlie]

Remember when you bolt a turbine on, the Vne redline reduces to Vno (what used to be the beginning of the yellow ASI segment, which then disappears) so you lose a bunch of potential speed options there.

If you absolutely must have a turbine Mooney then it sort of exists in the from of a TBM

Edited December 5, 2020 by Awful_Charlie

[G-SLOT]

I'd be interested in this or a diesel engine to replace the IO550 though suspect it will be many years in the making.

[aviatoreb]

47 minutes ago, Awful_Charlie said:

Remember when you bolt a turbine on, the Vne redline reduces to Vno (what used to be the beginning of the yellow ASI segment, which then disappears) so you lose a bunch of potential speed options there.

If you absolutely must have a turbine Mooney then it sort of exists in the from of a TBM

Exactly.  Without doing something about the airframe Vno speed, the Acclaim is already so fast that a more powerful Mooney wouldn't be permitted to go much faster  for airfare reasons.

The only way would be to strengthen the airframe to increase the Vno.  I bet that could be done and reputation is that the liquid rocket has gussets added at certain places to strengthen the airframe.

If the acclaim can go 242kts at 25,000 ft on full power - burn up the engine speed - but 270hp, then a 500hp turbine mooney clearly could go faster and actually do that faster speed in cruise. I will guess - make up a number (with a little computation on a piece of envelope), 265 or 270TAS in cruise.  IF the airframe can be strengthened. Since that is 184IAS which is too high.

That's what I have read about the Bonanza turbine. That it is airspeed limits limited, not power limited.

I disagree that a TBM is a turbine Mooney of sorts.  A TBM is fantastic, and we all know the M is for Moooney, but it is dramatically different from an M20.  An M20 is like a cool little sportster.  Usually a 2 seater.

The main argument for a turbine in my book is not the speed but the reliability and the availability of the fuel.  If just the second then diesel makes more sense.  So then we are down to reliability.  Speed - the acclaim has already squeezed most of the speed out of the airframe without strengthening the airframe.

Is the tail even big enough to oppose the p-factor forces in a 500hp take off run?

[N231BN]

The issue here is turbine engines are normally aspirated. The PT6A-11 in a Cheyenne I is rated at 500hp but is capable of producing about 700hp max. At 25,000ft it can only make a little over 300hp. An additional 30hp at max cruise isn't going to make enough of a difference to justify the cost and increased fuel burn, especially if you have to reduce VNE to VNO. The climb rate would be phenomenal however.

The PT6A-42 in a Meridian is really a ~1000hp engine, flat rated to 500. That's how they can get the performance out of it at altitude.

It would take a very interesting-looking propeller to harvest 500hp while providing ground clearance on a Mooney.

[carusoam]

Interesting discussion... I should invite @Jerry 5TJ to join.

Interesting thoughts on tail size vs. T/O run, Vne vs. Vso, and airframe strength modifications...

Best regards,

-a-

[exM20K]

28 minutes ago, N231BN said:

It would take a very interesting-looking propeller to harvest 500hp while providing ground clearance on a Mooney.

That plane would have the pitch angle of a DC3 sitting on the ground.  Acclaim sits something like 5* nose up, which makes rear seat access a lot harder than in the 231: front seat back won’t stay forward.  It wants to flop back...

[Vance Harral]

3 hours ago, N231BN said:

The issue here is turbine engines are normally aspirated.

I've been told this many times, and I get the point that the power the engine can produce decreases with increasing altitude.  That said, the first-stage of the induction system on a turbine immediately compresses the incoming air to much higher than ambient pressure.  The engineer in me just can't call that "normally aspirated". 

[carusoam]

Hmmmmm.

Is that you’re compressor section showing, sir?

• turbo charged
• turbo normalized
• turbine

Best regards,

-a-

[N231BN]

I've been told this many times, and I get the point that the power the engine can produce decreases with increasing altitude.  That said, the first-stage of the induction system on a turbine immediately compresses the incoming air to much higher than ambient pressure.  The engineer in me just can't call that "normally aspirated". 

So does a piston in a cylinder, same principal. Suck squeeze bang blow

[jaylw314]

28 minutes ago, Vance Harral said:

I've been told this many times, and I get the point that the power the engine can produce decreases with increasing altitude.  That said, the first-stage of the induction system on a turbine immediately compresses the incoming air to much higher than ambient pressure.  The engineer in me just can't call that "normally aspirated". 

You're thinking too hard about it--it's that well-developed engineering part of your brain 

Technically, our IO-360's have a compression ratio of what, about 9:1?  I'm guessing there aren't many jets with CPR's that high, so if anything, internal combustion engines are more "abnormally aspirated" than turbines.

Edited December 5, 2020 by jaylw314

[N231BN]

There are some multi-spool turbine engines that would be considered turbocharged. The PW100 series is one example.

Terminology aside, my point was it would take a large turbine engine to exceed the Acclaim's 270hp at FL250.

[aviatoreb]

23 minutes ago, N231BN said:

There are some multi-spool turbine engines that would be considered turbocharged. The PW100 series is one example.

Terminology aside, my point was it would take a large turbine engine to exceed the Acclaim's 270hp at FL250.

How big?

[N231BN]

How big?

500+AMU big

[ToddCC22]

What are the thoughts if putting a Continental CD-265 on the current airframe became a factory option?

[aviatoreb]

2 minutes ago, ToddCC22 said:

What are the thoughts if putting a Continental CD-265 on the current airframe became a factory option?

Fantastic.

[carusoam]

Looks like it’s going to be a little more challenging to select a proper turbine than we thought... 

1) Down low... fuel efficiency seems to be the challenge...

2) Up high... air availability seems to be the challenge...

The turbine in Tom’s plane seems to be properly sized for speed, for our typical operating altitudes...  even though Tom’s Lanceair IVPT is comfortably pressurized... ( @Yooper Rocketman )

Is Jerry’s Rocket Engineering / Piper propjet... pressurized?  ( @Jerry 5TJ )

PP thoughts only, no turbine experience...

Best regards,

-a-

[carusoam]

Continental CD-265...

Only uses 2500RPM to produce 265hp...

Back to My favorite STC writer to see if that can be boosted up to 2700 rpm...  

http://www.continental.aero/diesel/engines/cd200.aspx

Best regards,

-a-

[AerostarDriver]

An option for a turboprop Mooney would be the PBS TP100 which has been flying around on an RV-10 for a while now.

PBS TP100 Turboprop Engine - PBS Aerospace

[aviatoreb]

30 minutes ago, AerostarDriver said:

An option for a turboprop Mooney would be the PBS TP100 which has been flying around on an RV-10 for a while now.

PBS TP100 Turboprop Engine - PBS Aerospace

Interesting little engine.  It says 241hp max  for 5 min. 214hp max continuous but 188hp “normal”.  That’s a step back in power but anyway reliability is an important part of turbo prop.  I don’t see anything about fuel specifics.

[Geoff]

20 hours ago, exM20K said:

That plane would have the pitch angle of a DC3 sitting on the ground.  Acclaim sits something like 5* nose up, which makes rear seat access a lot harder than in the 231: front seat back won’t stay forward.  It wants to flop back...

I understand the new gear for the GW increase will be taller than the existing gear so there may be a few more inches to work with before resorting to S turns on the taxiway!

[Geoff]

22 hours ago, aviatoreb said:

The main argument for a turbine in my book is not the speed but the reliability and the availability of the fuel.  If just the second then diesel makes more sense.  So then we are down to reliability.

This is exactly why I like this idea.  The current Acclaim/ovation with Fiki is ALMOST a no excuses air plane. As everyone said, it has all the speed and capability for 2-3 people but with the piston up front but I hesitate to do long night/water/mountain crossings.  Plus if you live anywhere but the US fuel is and will become a bigger issue.  Dispatch rate would be higher with fewer oil change maintenance events during the year.

I started thinking this way after a good friend had to land on a highway at night after an engine failure. I would rather have a turbine than BRS personally. 

I guess I could always go buy an almost used up meridian for that $1 MM, but at 6 ft I don’t really like the cockpit (too cramped). Which is pretty rich for a Mooney driver to say.  Plus I would need another $200k for an upcoming engine OH. 

Anyway, I just wish (and think others do too) there was a capable new or near new TP in the $1mm-$1.5mm range instead of $2+mm.  Maybe I’m just old and think everything is too expensive.