Tandem Rotax 916 concept

[Reynard]

This might be a fantasy, but what other options are there for a drop in IO540/550 ‘modern’ replacement ?
 

Copied from PabloSniper Mundo & Tecnologia Facebook page

 

Twin Rotax 916 Power Package Concept
A Modern Replacement for Legacy IO-540 / IO-550 Engines
Summary

We would like to develop a dual-engine Rotax 916 power package designed to replace traditional IO-540 and IO-550 installations. The goal is to deliver equivalent or superior power, built-in redundancy, and excellent high-altitude performance — all while keeping weight and required airframe changes to a minimum.
A key requirement of the project is that the entire assembly must fit the same engine mount footprint used by IO-540 and IO-550 engines.
Additionally, the overall length of the two Rotax engines installed in tandem is very close to that of an IO-540 or IO-550, making this concept physically compatible with existing cowlings and firewall spacing.

Why This Concept Makes Sense
Modern Performance With Redundancy

Two Rotax 916 iS engines produce 320 hp, allowing this package to directly replace the 310 hp IO-550 found in aircraft such as the Cirrus SR22 — with the added benefit of turbo-normalized power maintained at altitude.

Similarly, a pair of Rotax 915 iS engines deliver 282 hp, making them a modern replacement for the 260 hp IO-540 commonly used in aircraft such as the RV-10.

Comparable Installed Weight

Although each Rotax engine is lighter, the full assembly — engines plus the shared shaft system — should be considered practically equivalent in installed weight to an IO-540/550. This keeps CG and structural considerations close to existing standards.

Efficiency, Fuel Flexibility & Lower Operating Costs

Rotax engines offer exceptional fuel efficiency, smooth operation, fully electronic engine management, and — importantly — the ability to run on automotive gasoline (MOGAS).
This means the kit could be applied to any aircraft currently using an IO-540 or IO-550, providing a modern, fuel-flexible alternative with significantly lower operating costs and easier global fuel availability.

Few Additional Modifications Required

The design goal is a clean installation requiring few additional changes, making it practical for OEMs and retrofit applications.
Matching both the engine mount geometry and the overall length envelope of the IO-540/550 is central to this concept.

What We Are Looking For

We are seeking a strategic partnership to co-develop a complete, modern engine package capable of replacing the aging IO-540 and IO-550 families with efficient, redundant, altitude-capable powerplants that fit existing engine mounts and appeal to both new aircraft manufacturers and the retrofit market.

 

[Thruster88]

Don't think this twin rotax will fly for many reasons. There is nothing wrong with basic LyCons, 2 valves per cylinder, push rod engine just like the rotax. Electronic fuel and ignition single lever control has been done by lycoming, the TEO-540. The TEO-540 could be an option on a Cirrus if the demand was there.

[BurnieM]

Not sure how you would couple them without a major redesign. Probably simpler to design a brand new engine.

[FlyBoy1960]

the flywheels would be going in different directions ?

[facthunter]

That's how it's shown.. One shaft inside a tube'.  BOTH turning in opposite directions. All a bit uncompact, untidy and "Heath Robinson" For My liking. How would you Keep alignment? Nev

[Marty_d]

Contra rotating props?

Seems like a difficult solution.

[KRviator]

You'd be far, far, better off trying to put a 916 into a run-out O-320 airframe.

A pair of 916's in something like a Twin Comanche would turn it into a rocketship. And an affordable (to operate, not install...) one at that.

[Reynard]

It’s a pity Rotax dropped their 6 cylinder 936 engine prototype before commercialisation. From memory it was around the 300hp mark.

[BrendAn]

On 26/11/2025 at 10:38 PM, Reynard said:

This might be a fantasy, but what other options are there for a drop in IO540/550 ‘modern’ replacement ?
 

Copied from PabloSniper Mundo & Tecnologia Facebook page

 

Twin Rotax 916 Power Package Concept
A Modern Replacement for Legacy IO-540 / IO-550 Engines
Summary

We would like to develop a dual-engine Rotax 916 power package designed to replace traditional IO-540 and IO-550 installations. The goal is to deliver equivalent or superior power, built-in redundancy, and excellent high-altitude performance — all while keeping weight and required airframe changes to a minimum.
A key requirement of the project is that the entire assembly must fit the same engine mount footprint used by IO-540 and IO-550 engines.
Additionally, the overall length of the two Rotax engines installed in tandem is very close to that of an IO-540 or IO-550, making this concept physically compatible with existing cowlings and firewall spacing.

Why This Concept Makes Sense
Modern Performance With Redundancy

Two Rotax 916 iS engines produce 320 hp, allowing this package to directly replace the 310 hp IO-550 found in aircraft such as the Cirrus SR22 — with the added benefit of turbo-normalized power maintained at altitude.

Similarly, a pair of Rotax 915 iS engines deliver 282 hp, making them a modern replacement for the 260 hp IO-540 commonly used in aircraft such as the RV-10.

Comparable Installed Weight

Although each Rotax engine is lighter, the full assembly — engines plus the shared shaft system — should be considered practically equivalent in installed weight to an IO-540/550. This keeps CG and structural considerations close to existing standards.

Efficiency, Fuel Flexibility & Lower Operating Costs

Rotax engines offer exceptional fuel efficiency, smooth operation, fully electronic engine management, and — importantly — the ability to run on automotive gasoline (MOGAS).
This means the kit could be applied to any aircraft currently using an IO-540 or IO-550, providing a modern, fuel-flexible alternative with significantly lower operating costs and easier global fuel availability.

Few Additional Modifications Required

The design goal is a clean installation requiring few additional changes, making it practical for OEMs and retrofit applications.
Matching both the engine mount geometry and the overall length envelope of the IO-540/550 is central to this concept.

What We Are Looking For

We are seeking a strategic partnership to co-develop a complete, modern engine package capable of replacing the aging IO-540 and IO-550 families with efficient, redundant, altitude-capable powerplants that fit existing engine mounts and appeal to both new aircraft manufacturers and the retrofit market.

 

It's not April fools day is it

[Marty_d]

4 hours ago, BrendAn said:

It's not April fools day is it

That's what I first thought too when I saw the drawing.

[bexrbetter]

On 28/11/2025 at 4:51 AM, Reynard said:

It’s a pity Rotax dropped their 6 cylinder 936 engine prototype before commercialisation. From memory it was around the 300hp mark.

 

[Reynard]

Those old enough to remember the tandem engine ‘Super70’ Chamberlain tractors may recall their oddity. Contemplating a tandem engine concept in a modern aircraft is certainly odd.

[Thruster88]

The Continental CD-300 jet A piston diesel engine is the only new certified engine in the 300hp class to challenge the existing Lycoming 540/580 and Continental 520/550 avgas burning engines. The CD-300 diesel powers the Diamond DA50-RG, a luxurious 5 seat retractable with Impressive performance at altitude due the turbocharger. At the altitude most pilots of this class of aircraft fly the Cirrus has it covered. Ultimately the market will decide. One thing is certain, the buyers of this class of aircraft will never be intersted in a twin Rotax.