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.

[facthunter]

At High altitude, Diesel Fuel would have to be Heated. AVTUR is the More likely fuel.  Any Piston Operating above abut 8,000 feet would need supercharging really. Cruise is usually at 75% Power, OTA.   Mechanically driven superchargers often have 2 speeds  The Liberators has turbo'd  P&W R 1830's.  Nev

[BrendAn]

2 minutes ago, facthunter said:

At High altitude, Diesel Fuel would have to be Heated. AVTUR is the More likely fuel.  Any Piston Operating above abut 8,000 feet would need supercharging really. Cruise is usually at 75% Power, OTA.   Mechanically driven superchargers often have 2 speeds  The Liberators has turbo'd  P&W R 1830's.  Nev

The diesels would run on jet fuel I would imagine.

[turboplanner]

A single Rotax fits into the heaviest RA Applications.

A lot of the Rotax type engines like CanAm were developed from the harsh environment and constant-power demand Skidoos. They had to be better than the typical two strokes of the day. 

 

Running in parallel with this class of engine were the Outboards which moved from two stroke due to emission requirements and today include 300, 320 hp.

 

A double-in-line Rotax combination is not the future because it would fit into GA, where light mass, longer life and better reliability are the key requirements.

 

GA engine designers have fitted radials, V, Light twins, Tandem engines and evolved to relatively simple, light, reliable engines which handle long distance and multiple flights over years of activity.

 

There will always be one though, coming up with an invention and hoping to take over the industry.

[facthunter]

Plenty try But relatively FEW succeed. It's hard to make a buck out of producing an aeroplane engine. IF you made a good one the fiddlers would still wreck it fiddling and being Insensitive..Nev

[BrendAn]

The future might even be hybrid.

Like a small turbo prop running a prop and battery charging.

If they come up with a small fuel efficient turbine one day. And light weight batterys. 

[facthunter]

Some Peoples behaviour with pistons requires transition to electric as soon as Possible. It's ALMOST FOOLproof. Nev

[facthunter]

There's explosions going OFF inside them all the time you Know and they are trying to fling bits  out with great force and vibrate Like Blazes. ICE motors are awful things. High combustion temps Make Nitrous Oxides. Most fuels have some sulphur in them. They STINK & Have to be warmed up and get too cold on descent..  Can Leak fuel. Crash and Burn.  Nev

[BrendAn]

3 hours ago, facthunter said:

There's explosions going OFF inside them all the time you Know and they are trying to fling bits  out with great force and vibrate Like Blazes. ICE motors are awful things. High combustion temps Make Nitrous Oxides. Most fuels have some sulphur in them. They STINK & Have to be warmed up and get too cold on descent..  Can Leak fuel. Crash and Burn.  Nev

 the ice is still the most fuel efficient and reliable engine available. It will be a long time before electric takes over except for Hybrid, but If there I ever a major breakthrough in battery technology it may happen. Can't see it yet .

[BrendAn]

this might be interesting 

[onetrack]

The Mazda Vision X-Coupe is a gimmicky prototype, and it will never make it to the production stage. Car companies spend hundreds of millions on ideas like this, then throw it all in the bin, when it proves to not be practical.

[onetrack]

Let me know how you go, trying to find that "carbon-neutral fuel derived from microalgae", bowser! - anywhere!

 

The Japanese Govt has thrown about $3B into research into alternative fuels, trying to get away from fossil fuels, and become independent as regards their transportation fuels - but despite promising to deliver on large and reliable alternative sources, such as methane hydrate fuels, bio-fuels, hydrogen fuel, LPG-derived fuels, and a dozen other wild ideas - nothing they have done so far, has promise, as regards delivering large quantities of alternative IC fuels at modest cost.

 

Meantimes, the battery research and developments continue on at a sizzling pace - and most of it, is coming from China.

 

Edited 1 hour ago by onetrack

[BrendAn]

6 minutes ago, onetrack said:

Let me know how you go, trying to find that "carbon-neutral fuel derived from microalgae", bowser! - anywhere!

 

The Japanese Govt has thrown about $3B into research into alternative fuels, trying to get away from fossil fuels, and become independent as regards their transportation fuels - but despite promising to deliver on large and reliable alternative sources, such as methane hydrate fuels, bio-fuels, hydrogen fuel, LPG-derived fuels, and a dozen other wild ideas - nothing they have done so far, has promise, as regards delivering large quantities of alternative IC fuels at modest cost.

 

Meantimes, the battery research and developments continue on at a sizzling pace - and most of it, is coming from China.

 

I don't really care, just thought it was interesting. I laughed because I was just thinking how long is it going to take for o/t to jump on this. Didn't have to wait long.😁

Edited 1 hour ago by BrendAn