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ODwyerPW
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Joined: Thu Dec 09, 2004 6:30 am

Lycoming IO-720, Why not more popular?

Tue Oct 01, 2019 5:53 pm

The Lycoming 540 (flat 6 cyl) had enjoyed great popularity and continues to be advanced. (https://www.lycoming.com/engines/ie2)

The Lycoming 720 (flat 8cyl) was an evolution of that engine, featuring the same bore and stroke. It's rated at 400bhp, but has been applied in aircraft where it exceeded 550hp (NorthWest Ranger float equipped plane).

I can't find any record of it being used in twin engine configuration other than later Beechcraft 80 conversions.

Why wasn't it more popular? It enjoys a similar power to weight ratio to the 540. However, Lycoming never equipped it with a Turbo (though aftermarket examples exists).

Is it just that once you need 450+ hp, it's just more feasible to go PT6-A? Was the fuel consumption on the 720 that much worse than the 540? How did the engine perform/sound?
learning never stops.
 
IADCA
Posts: 1868
Joined: Mon Feb 26, 2007 12:24 am

Re: Lycoming IO-720, Why not more popular?

Tue Oct 01, 2019 5:58 pm

ODwyerPW wrote:
The Lycoming 540 (flat 6 cyl) had enjoyed great popularity and continues to be advanced. (https://www.lycoming.com/engines/ie2)

The Lycoming 720 (flat 8cyl) was an evolution of that engine, featuring the same bore and stroke. It's rated at 400bhp, but has been applied in aircraft where it exceeded 550hp (NorthWest Ranger float equipped plane).

I can't find any record of it being used in twin engine configuration other than later Beechcraft 80 conversions.

Why wasn't it more popular? It enjoys a similar power to weight ratio to the 540. However, Lycoming never equipped it with a Turbo (though aftermarket examples exists).

Is it just that once you need 450+ hp, it's just more feasible to go PT6-A? Was the fuel consumption on the 720 that much worse than the 540? How did the engine perform/sound?


That's pretty much what I would guess. Even some frames that use the 540 (BN-2, for example) were sometimes fitted with turbos, which is a clue.
 
pilotpip
Posts: 2839
Joined: Fri Sep 19, 2003 3:26 pm

Re: Lycoming IO-720, Why not more popular?

Tue Oct 01, 2019 6:07 pm

It's heavy, has cooling issues because of the length, and it burns a ton of gas. All reasons that it didn't survive.
DMI
 
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ODwyerPW
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Joined: Thu Dec 09, 2004 6:30 am

Re: Lycoming IO-720, Why not more popular?

Tue Oct 01, 2019 6:41 pm

Interesting article on the Piper PA-35 Pocono. It's prototype used a turboed Lycoming TI0-720 making 475hp. Lycoming was working to increase the power to 520 hp, but it never came to pass.

http://airpigz.com/blog/2010/11/5/1968- ... souls.html
learning never stops.
 
GalaxyFlyer
Posts: 3682
Joined: Fri Jan 01, 2016 4:44 am

Re: Lycoming IO-720, Why not more popular?

Tue Oct 01, 2019 7:05 pm

The aftmost cylinders had cooling problems, not enough cool airflow at the rear of the cowling. By the time it came out, the PT-6 was entering service on the King Air and Turbo Beaver, so the IO-720 didn’t fill a need anymore.

GF
 
FlyHossD
Posts: 1934
Joined: Mon Nov 02, 2009 3:45 pm

Re: Lycoming IO-720, Why not more popular?

Wed Oct 02, 2019 1:10 am

ODwyerPW wrote:
The Lycoming 540 (flat 6 cyl) had enjoyed great popularity and continues to be advanced. (https://www.lycoming.com/engines/ie2)

The Lycoming 720 (flat 8cyl) was an evolution of that engine, featuring the same bore and stroke. It's rated at 400bhp, but has been applied in aircraft where it exceeded 550hp (NorthWest Ranger float equipped plane).

I can't find any record of it being used in twin engine configuration other than later Beechcraft 80 conversions.

Why wasn't it more popular? It enjoys a similar power to weight ratio to the 540. However, Lycoming never equipped it with a Turbo (though aftermarket examples exists


For a short time, I flew AeroCommander 680s that had the "Mr. RPM" conversion with two IO-720s; they also had RayJay turbos.
My statements do not represent my former employer or my current employer and are my opinions only.
 
FlyHossD
Posts: 1934
Joined: Mon Nov 02, 2009 3:45 pm

Re: Lycoming IO-720, Why not more popular?

Wed Oct 02, 2019 2:08 am

Oh - and the Piper Comanche 400 also used the IO-720.
My statements do not represent my former employer or my current employer and are my opinions only.
 
Lpbri
Posts: 181
Joined: Tue Sep 27, 2016 7:18 pm

Re: Lycoming IO-720, Why not more popular?

Wed Oct 02, 2019 8:38 pm

Early Twin Bonanzas had them.
 
GalaxyFlyer
Posts: 3682
Joined: Fri Jan 01, 2016 4:44 am

Re: Lycoming IO-720, Why not more popular?

Wed Oct 02, 2019 9:08 pm

Lpbri wrote:
Early Twin Bonanzas had them.


No, that was the Swearingen Excalibur 800 mod; originally Lycoming GSO-480 engines

GF
 
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kitplane01
Posts: 1350
Joined: Thu Jun 16, 2016 5:58 am

Re: Lycoming IO-720, Why not more popular?

Fri Oct 04, 2019 2:23 am

Overhauling an IO-720 costs over $100,000. Buying a new one costs about $200,000.

Also, who knew you could buy a new IO-720.

http://www.airpowerinc.com/productcart/ ... odID=10174

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