Why was the IO-720 a failure?

[N201MKTurbo]

15 minutes ago, Tim Jodice said:

Depleted Uranium 

I used to work with osmium, that stuff is crazy toxic.

[aviatoreb]

1 hour ago, Nick Pilotte said:

You and your 8 cylinders!!!!   It’s not a Firebird.  Just kidding. My wife’s late father flew a Brave 400.  He flew it fast and low.  
 

if you were to fit a 720 in the O, you’d need to add STC’d Charlie weights made out of iridium or osmium. Safer than lead, but heavier for the same volume. 

I am not sure volume is an issue for the lead charlie weights.  While not as dense as depleted uranium - its cheaper!  I bet if more weight were needed and allowed aerodynamically and regulatory wise, then the volume is the least of the issues and double or triple the weight in lead could be conjured up.  Is that lead in the tail leaching?  I bet not.  But if it were, I bet coating it in something cheap like teflon paint or something would do the trick.

[thinwing]

1 hour ago, Nick Pilotte said:

You and your 8 cylinders!!!!   It’s not a Firebird.  Just kidding. My wife’s late father flew a Brave 400.  He flew it fast and low.  
 

if you were to fit a 720 in the O, you’d need to add STC’d Charlie weights made out of iridium or osmium. Safer than lead, but heavier for the same volume. 

lets see Iridium is 6400 per oz!.....

[thinwing]

1 hour ago, Nick Pilotte said:

You and your 8 cylinders!!!!   It’s not a Firebird.  Just kidding. My wife’s late father flew a Brave 400.  He flew it fast and low.  
 

if you were to fit a 720 in the O, you’d need to add STC’d Charlie weights made out of iridium or osmium. Safer than lead, but heavier for the same volume. 

lets see Iridium is 6400 per oz!.....

 

52 minutes ago, Tim Jodice said:

Depleted Uranium 

too radioactive for me...straight u238 better

[Raptor05121]

I don't have any experience with them personally but a good friend of mine got hired to fly Excalibur-converted Queen Air's for the current STC holder at the same time I got hired to fly the Caravan. We spend hours comparing planes/training/etc and while I'm sure I am speaking more to the airframes rather than the engine, it doesn't quite strike me as efficient as compared to a single turbine. 32 spark plugs. 16 cylinders. Four magnetos. Airframe to airframe, they both have about the same weights and useful loads and the twin is a bit faster. But overhauling two 720s at 1800hrs when a single PT-6 can stretch to 6,000. I know what my wallet would rather support if I had that cash.

Its time for Mooney to slap a small turboprop and make a 6 seater (I know, I know...301 and TBM...)

[Nick Pilotte]

I said that in jest, I should have said Mercury capsules instead.  Just have to make sure Weepnomore is able to reseal them. 

[Hank]

23 minutes ago, Raptor05121 said:

But overhauling two 720s at 1800hrs when a single PT-6 can stretch to 6,000. I know what my wallet would rather support if I had that cash.

What's the cost of two IO-720 OHs versus a PT-6 Hot Section? Even allowing for three pair of OH per Hot Section, aren't the piston OHs less costly?

[aviatoreb]

10 minutes ago, Hank said:

What's the cost of two IO-720 OHs versus a PT-6 Hot Section? Even allowing for three pair of OH per Hot Section, aren't the piston OHs less costly?

Besides that - the fuel difference is substantial.  Jet A is cheaper per gallon but a PT-6 uses lots more of it.  Im thinking of like that rocket engineering PT6 Bonanza - does it burn 35gph in cruise?  Its not THAT fast that it makes up the difference so its not really a long range airplane.  I don't know if an IO720 could be fitted to a A36 balance wise, but supposing it could - it would be a lot faster than standard A36 and anyway even the PT6 A36 is red-line speed limited so it might be almost as fast to just have the IO720?  But the fuel efficiency would be like half the number of gallons per hour.

The Io720 preferring not to fly as high as a Pt6 but in an unpressurized airplane, where the engine wants to fly at 25,000 and is a major hog at 12,000 or 15,000, I consider this an advantage.

The biggest reason for the PT6 and this is a big one, is the order of magnitude greater reliability for flying over harsh terrain.

I bet a io720 A36 would be pretty neat if they could balance it.

[Guest]

5 hours ago, Hank said:

I can only think of two reasons that the -720 wasn't widely adopted:

1. It's too freaking large and heavy to fit onto many airframes without destroying the W&B.
2. It's too thirsty, and many airframes don't have room or lift reserves for 100-gal tanks.

But it's sure pretty to look at . . . . .

Perhaps you’ve not heard of the Piper Comanche 400, err Mooney 200X2.  No weight and balance issues, carries 130 gallons of fuel and still has room for 700 pound of other stuff.

I’m so glad Piper copied the Mooney design and fixed it up so well!

Clarence

[Hank]

35 minutes ago, M20Doc said:

Perhaps you’ve not heard of the Piper Comanche 400, err Mooney 200X2.  No weight and balance issues, carries 130 gallons of fuel and still has room for 700 pound of other stuff.

I’m so glad Piper copied the Mooney design and fixed it up so well!

Clarence

I've seen your pictures, Clarence. But surely one model isn't your definition of "many airframes"???

[Raptor05121]

19 hours ago, Hank said:

What's the cost of two IO-720 OHs versus a PT-6 Hot Section? Even allowing for three pair of OH per Hot Section, aren't the piston OHs less costly?

FWIW I found an article on the PT-6 converted Bonanza and found this excerpt:

"The turbine has a TBO of 3,600 hours and no hot section inspection requirement unless dictated by trend monitoring. But at a $125,000 overhaul cost, the turbine will still require about $15 per hour more in engine reserves than the Baron’s two Continental IO-550s."

the -114A has a higher TBO and the -720 is undoubtedly going to cost more than the 550s so it seems a wash. As Erik pointed out above- turbine conversions on piston airframes generally don't go well because the speed limitations the FAA places on conversions.

http://blog.covingtonaircraft.com/2020/08/28/turbineair-bonanza/

Again, I think Mooney should find some capital and start an all-new 301-like turbine design (with a Mooney tail) and compete with the TBM. The Acclaim is almost a million dollars. A brand-new TBM is a shade over $3m. Bridge the gap?

 

Edited April 27, 2021 by Raptor05121

[aviatoreb]

47 minutes ago, Raptor05121 said:

FWIW I found an article on the PT-6 converted Bonanza and found this excerpt:

"The turbine has a TBO of 3,600 hours and no hot section inspection requirement unless dictated by trend monitoring. But at a $125,000 overhaul cost, the turbine will still require about $15 per hour more in engine reserves than the Baron’s two Continental IO-550s."

the -114A has a higher TBO and the -720 is undoubtedly going to cost more than the 550s so it seems a wash. As Erik pointed out above- turbine conversions on piston airframes generally don't go well because the speed limitations the FAA places on conversions.

http://blog.covingtonaircraft.com/2020/08/28/turbineair-bonanza/

Again, I think Mooney should find some capital and start an all-new 301-like turbine design (with a Mooney tail) and compete with the TBM. The Acclaim is almost a million dollars. A brand-new TBM is a shade over $3m. Bridge the gap?

 

Right - I agree completely - a turbine 301 clean sheet airplane would be very cool. I bet it would sell if it were a lot less than a tbm, say anything less than 2m.  1.8?  I don't know anything about realities of producing a new airplane so I do not know if that is possible.

We were spit balling a mod i think and a mod to an M20 would be fun.  Would a IO720 mod be possible?  Likely not for reasons said - too heavy requiring too much intervention to make the balance work, e.g. lengthen the rear end is not something you do as a mod but at the factory upon first build.  And at that point, I agree with you, better to put the money behind clean sheet turbine.

Actually, I really like the M20 acclaim.  If I had money in the 800-900k range I would consider it very highly.  Having 900k doesn't mean I have 3M or even 2M so that doesn't necessarily make me a buy for a tbm (but I would love one!) or a M30 if that existed for 2M (but i would love one!) but maybe someone.

[Raptor05121]

$800k is a hefty down payment on a $2m used TBM...just saying!

[A64Pilot]

Turbines while most will go high, they work well down low too. For an example try to find a piston powered crop duster anymore and a great many of them work the Mississippi river delta at maybe 100 MSL?

The PT-6 though is an ancient not very efficient design, if the money were there, someone could do a lot better, that’s what GE is doing, but again money is the driver, according to them they could easily build a turboprop that would never come off the wing for maintenance as they call it, they have been doing so for Commercial engines for years, but not many could afford it, they have to compete cost wise with the Pratt PT-6.

‘The T-800 engine was developed for the RAH-66 Comanche which of course was cancelled, but we put one in a Huey at the test activity, we couldn’t use the HP of course as it was way beyond airframe limits, but what us dumb pilots didn’t realize was that it was so fuel efficient compared to the Lycoming the Huey came with that we had over four hours of fuel as opposed to maybe two and a half?

 I don’t know if that engine is being produced or not, but even though it was very efficient, I think it’s cost was so high that it wouldn’t be used in the Commercial market, sometimes fuel is cheaper.

[N201MKTurbo]

Joe Henderson (RIP) used to fly turbine Air Tractors. Joe said he gets nose bleeds if he went higher than 100 feet. Before CHD had a tower, he would fly traffic patterns at 100 ft. 
 

The 100 ft thing was bs. He had a King Air he flew to Vegas every weekend. It had two spare Air Tractor engines on it.

[aviatoreb]

11 hours ago, Raptor05121 said:

$800k is a hefty down payment on a $2m used TBM...just saying!

Yeah - well if we are talking used then great - I have a used Mooney.  I can't afford a new Mooney.  Its an age old discussion.  800k for a new Mooney is an 800k very very used TBM.  Apples and oranges.  Well I have a used Mooney so you know how I spend my money.

[Tim Jodice]

This is what I think about when I am not doing anything.

Imagine this, working with what already exists starting with a M22 and a IO-720.

Do 201 like upgrades to the M22, bring it up to todays standards, raise the pressure differential to 5.5-6PSI, increase fuel capacity to 130 gallons and up the gross weight to 4300 pounds. 

Turbo normalize the engine Keeping it at its regular 400HP with high compression pistons.

Why you ask.

Regardless if you are Boeing or Mooney a clean sheet aircraft is extremely expensive. As every manufacturer has shown it is WAY less expensive to modify what you have.

Starting with a M22 that has never been updated from its original design likely has a lot low hanging fruit that would improve the airplane, aerodynamic clean up etc. Increasing the pressure differential would add weight but would make it more comfortable at 25,000 feet. 

If they can take original short body C/E with a gross weight of 2575 to 3368 (30% increase) with structural modifications I think that they could take a M22 with a 3680 to 4300. (16% increase) Adding a bigger engine higher pressure differential and all the wonderful (heavy) things like A/C and TKS that brand new aircraft have you would add say 450 pounds to the original 2440 then you would have a useful load of about 1400 pounds or 620 full fuel. 

Increasing fuel capacity simply (I think) requires sealing off more bays in the wing.

Now the engine. using the successful Bonanza TAT turbo normalized mod as a reference. they typically run 17GPH LOP or 85% (255HP) power running cooler than a factory turbo Bonanza making 65% power. According to people on Beechtalk they have good reports on engine life.

Apply a similar well made turbo system to a 720 and you have 340HP burning about 22-23 GPH in cruise. Maybe 250TAS@ 25000 feet?

With 130 gallons of fuel you would have about 5.5 hours of gas or 4 with a nice reserve. 4 hours being the average time most people are willing to sit in an airplane gives you a 1000 mile rang

This is what I think about when I am not doing anything.

Imagine this, working with what already exists starting with a M22 and a IO-720.

Do 201 like upgrades to the M22, bring it up to todays standards, raise the pressure differential to 5.5-6PSI, increase fuel capacity to 130 gallons and up the gross weight to 4300 pounds. 

Turbo normalize the engine Keeping it at its regular 400HP with high compression pistons.

Why you ask.

Regardless if you are Boeing or Mooney a clean sheet aircraft is extremely expensive. As every manufacturer has shown it is WAY less expensive to modify what you have.

Starting with a M22 that has never been updated from its original design likely has a lot low hanging fruit that would improve the airplane, aerodynamic clean up etc. Increasing the pressure differential would add weight but would make it more comfortable at 25,000 feet. 

If they can take original short body C/E with a gross weight of 2575 to 3368 (30% increase) with structural modifications I think that they could take a M22 with a 3680 to 4300. (16% increase) Adding a bigger engine higher pressure differential and all the wonderful (heavy) things like A/C and TKS that brand new aircraft have you would add say 450 pounds to the original 2440 then you would have a useful load of about 1400 pounds or 620 full fuel. 

Increasing fuel capacity simply (I think) requires sealing off more bays in the wing.

Now the engine. using the successful Bonanza TAT turbo normalized mod as a reference. they typically run 17GPH LOP or 85% (255HP) power running cooler than a factory turbo Bonanza making 65% power. According to people on Beechtalk they have good reports on engine life.

Apply a similar well made turbo system to a 720 and you have 340HP burning about 22-23 GPH in cruise. Maybe 250TAS@ 25000 feet?

With 130 gallons of fuel you would have about 5.5 hours of gas or 4 with a nice reserve. 4 hours being the average time most people are willing to sit in an airplane gives you a 1000 mile range.

Would $1,500,000 be enough? about $200,000 More than a M350 but about $700,000 less than a M500 being the least expensive turboprop. 

I have read people would buy a M350 but they won't fit in their hangar.

I know I know pipe dream but it is fun to dream!

[carusoam]

Tim,

Have you watched Mike Patey’s videos about building one off plane designs..?   Draco, Scrappy, and some other wicked fast plane...

Every 10minutes or so...  he gets side tracked while describing what he is doing... and goes back into what he is doing with a simple phrase.... ‘get back to work...’. 

 

Have you seen the M22 for sale around here?

Unfortunately, there isn’t convenient way of building an experimental plane that is usable out of an existing Mooney...

 

But...if you want to get it done... It is only writing an STC and getting it through the system...

STCs are expensive if you have to make money with them...

If you have the money and the dream... spending the dough can be like renting manpower...  there is a team of people at Rocket engineering that do this type of work...

Best regards,

-a-

[Jerry 5TJ]

12 hours ago, Tim Jodice said:

Do 201 like upgrades to the M22, bring it up to todays standards, raise the pressure differential to 5.5-6PSI, increase fuel capacity to 130 gallons and up the gross weight to 4300 pounds. 

You are re-inventing the Piper Malibu / Mirage: 5.5 psi, 120 or 140 gallons, 4300 pounds.  In production continuously since 1984. 

[Hank]

5 hours ago, Jerry 5TJ said:

You are re-inventing the Piper Malibu / Mirage: 5.5 psi, 120 or 140 gallons, 4300 pounds.  In production continuously since 1984. 

But it would have a Mooney wing, the correct tail and a much lower Cd!

[aviatoreb]

5 minutes ago, Hank said:

But it would have a Mooney wing, the correct tail and a much lower Cd!

But this one goes to 11.

[Jerry 5TJ]

Well, my fantasy Mooney is faster than your fantasy Mooney:  Mine cruises at Mach 0.92 on 12 GPH and has an interior the size of a Jai-alai fronton. 

[Tim Jodice]

7 hours ago, Jerry 5TJ said:

You are re-inventing the Piper Malibu / Mirage: 5.5 psi, 120 or 140 gallons, 4300 pounds.  In production continuously since 1984. 

Pretty much but,

It is smaller with more power=speed/range

A larger engine making more power on the same gas through efficiency. while the engine is heavy it means the power density is lower and is likely to have a better a service life.

getting to the front seat of a PA-46 is a challenge for some impossible for others. I have never measured it but it looks like it is wider than it is tall. You step down in to a M22. 

Again pipe dream but it would be nice if there was another pressurized piston single available. 

[kerry]

On 4/25/2021 at 7:21 PM, Tim Jodice said:

What can I say? It arouses me. 

 

I thought the space between the engine and firewall was tight on a Mooney.  Not much wiggle room there.

[Ibra]

You can’t have an IO720 in a Mooney: first, huge loss of ASI*MPG efficiency (you can’t brag on fuel bills ), second, high frequency landing harmonics (such heavy engine on donuts, grandma said it’s not good )

Edited May 7, 2021 by Ibra