The car vs the airplane...

[coolyokeluke]

The problem I see with the above is that modern auto engines are far more powerful than their more ancient brethren in cars, to the extent that a 3-liter auto engine in something as mundane as a Honda or Mazda sedan makes as much power as an engine of twice the displacement from thirty years ago, with lower-octane fuel and no commensurate bump in compression ratio. Of course they achieve it at a higher RPM... But not something as crazy as TWICE the RPM.

Obviously I've forgotten a lot about the basics of engines, at least as far as the math is concerned.

Those smaller engines with higher operating RPM's would require reduction gears if affixed to a propeller. They don't make much torque at low RPM like the older, larger displacement car and airplane engines. So not having a gearbox is a weight saving issue as well as something else that could break in an airplane. I'm speculating here, but I think the idea of air/vs liquid cooling comes down to the same issues; weight and complexity. As far as sticking a 350 V8 on an airplane, lots of homebuilders have done it. One of the issues I always hear about with car engines in aircraft is that our large displacement low horsepower aircraft engines are designed to run flat-out, where car engines rarely and only briefly make maximum power. I'm all for advancing the state of aircraft engine technology, but there are reasons (one of which has sadly been liablity issues) that our engines have changed little in the last 50 years: relaiblity and weight.

 

[avbug]

As far as sticking a 350 V8 on an airplane,

ORENDA!

Making a comparison between automotive applications and aircraft applications is nonsensical.

Aircraft powerplants are limited in RPM by propeller constraints.

I've run piston engines in aircraft at much higher RPM's, especially automotive engines such as the Subary Stratus) in aircraft installations...but with very little gain in performance at higher revs.

 

[UnAnswerd]

lol...who wants to pull out a 350, bolt on a prop and see if it will fly?

I have a welding book that shows a finished engine mount used for the installation of a 4.3L V6 engine into an airplane. The 4.3 is essentially a 350 minus 2 cylinders.

I also remember seeing some kitplane with a Chevy 502 installed........

 

[TrafficInSight]

There was an article in a mid 80's issue of AOPA Pilot about a Globe Swift with a Buick 255 V-8 in it. It never caught on.

 

[I.P. Freley]

The top speed in a car is limited by the gearing in the drive-train. That engine can only turn so fast before it becomes a pile of parts.

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

Many cars don't achieve top speed in their top gear, though. In Corvettes, at least the more modern ones with a 6spd, top speed can't be achieved in 6th because the gearing is too tall, but it can redline in 5th gear, which would be an example of what you said.

 

[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!