The car vs the airplane...

[I.P. Freley]

I've also seen articles about small auto engines, like Subaru opposed engines and Mazda rotaries, used in light airplane applications. Instead of using gearboxes, they use BELTS. I can't imagine this would ever catch on for large production runs, but the big pulley/small pulley with three or more belts connecting the two is a good idea and one that doesn't add much weight...

 

[hindsight2020]

The previous posts have been pretty dead center about the major contentions regarding the question. The biggest factor when comparing light airplane engines and car engines is weight. In general, car engines are heavier than airplane engines, compounded by factors such as liquid cooling assemblies and fluid weight. All this makes car engines have lower (engine) power loading. Additionally, light aircraft are lighter than cars, which compounds the problem against cars as it relates to power loading.

The operational RPM of these engines are also different. Aircraft engines (piston) are run at max continous settings almost exclusively. Propeller efficiency issues make most light aviation applications to run in the viscinity of 2300-2600RPM.... Car engines on the other hand, do not run at their max power settings for long, if at all, through the mission profiles they are designed for. All of this goes to the dump with the gearing in cars, which automatically drops the argument to apples-to-oranges comparison. Another note on power comparisons, because aircraft engines are run flat out, their TBO is what it is...I would love to see that one with our cars, go to the dealership telling you 'BTW the TBO is 2000hrs'. So to theoretically put a car engine of similar output in an aircraft, provided you can even lift the nose on takeoff before you hit Vno on the thing (slight exageration folks), you will have to go put a new one much much sooner than 2000 TBO.

Then there is the ignition systems issue. For the most part it's a safety and legal issue. No doubt aircraft engines are ready for car injection systems, but once again, a safety issue, that's why they still want you to quit the engine by exhausting the mixture and not by opening the circtuit (ignition off). In spite of all this, I still side with the sentiments that aircraft engines can and should be updated, it's getting to be ridiculous.

Happy flying folks

 

[crash-proof]

Here's a very good read on the ill-fated Porsche PFM engine, wrote back in the 80s when it was just introduced.

http://www.seqair.com/Other/PFM/PorschePFM.html

 

[Gatorman]

Top speed on most cars is drag-limited, not gearing-limited, as in topping out at redline in top gear....

I believe it is the same for aircraft too....terminal velocity

 

[I.P. Freley]

In spite of all this, I still side with the sentiments that aircraft engines can and should be updated, it's getting to be ridiculous.

Indeed. If fuel injection was good enough for cars in the 50's, it should be standard-issue on all new aircraft engines.

Even if it weighs more and is more complex, I think the benefits of liquid-cooling on light airplane engines would by now outweigh the detriments. More even engine temperatures, longer life, and greater efficiency. Again, if it was okay for 30's and 40's-era combat aircraft, we should be able to make it safe and reliable in the present day. Imagine not needing to run the mixture rich enough to use the unburned fuel for engine cooling! A 320cid engine with even rudimentary fuel injection and liquid cooling... Wow. I'm getting goosebumps.

 

[Some guy]

I vaguely recall an article I read several years ago about light aircraft and FADEC / fuel injection systems. (I am thinking that the article may have been in Popular Mechanics) Does anyone know anything about this or have any decent links?

 

[The_Russian]

Buy a Camaro SS or a 05 GTO. Then you can go faster than a Cessna all day long and not worry about drag!!!

Har Har Har!

In all seriousness it is not about the horsepower, its about the torque the motor creates. A similarly rated aircraft engine (HP) has almost twice as much torque due to CID and low RPM operation. But, when it comes down to it, it's all about surface friction and fluid dynamics.

 

[hindsight2020]

aircraft speed limitations

post deleted

 

[VNugget]

In all seriousness it is not about the horsepower, its about the torque the motor creates.

Um, power = torque * RPM

A similarly rated aircraft engine (HP) has almost twice as much torque due to CID and low RPM operation.

Torque isn't some other magical force that acts indepenent of power. How you got the power value in question (high torque and low RPM, or low RPM and high torque) makes no difference, power is power.

Keep in mind I'm talking about the RPM of the engine, not the prop, so you don't have to say anything about varying efficiency.

 

[Immelman]

My 140hp/1.8L car makes approximately 90-95hp at the wheels, measured on a dynomometer. Well, not my personal car but friends' with the same model. It will go right up to the max speed, rev limited, in 5th gear, of 139mph. Don't ask how I know!