Large Radial Engines Were About As Good As Can Be? (3 Viewers)

[z42]

Interesting "entry" into the GA market.

Small Aircraft Jet Fueled Engine - DeltaHawk Engines

Powerful Technology Through Time-Proven Innovation. The first clean sheet piston engine design FAA certified in over 60 years.

www.deltahawk.com

I think they've been at it for a couple decades at this point. They might have seen some sales for drones and such already though.

But yes, if I were to design a new engine for the GA market, it would look something like that. Diesel, so it can run on Jet A available at every larger airport on the planet. And a piston ported two stroke to give better power/weight, and also gets rid of the weight and complexity of the valvetrain.

 

[pinehilljoe]

Once the jet engine became reliable, why continue piston engine refinement? The jet allows an order of magnitude more air into the engine; the IC engine air intake and therefore power, is limited by the size of the cylinders and stroke volume; and the jet produces power with essentially one moving part.

 

[GregP]

Once the jet engine became reliable, why continue piston engine refinement? The jet allows an order of magnitude more air into the engine; the IC engine air intake and therefore power, is limited by the size of the cylinders and stroke volume; and the jet produces power with essentially one moving part.

One REALLY good reason is the cost of a turbine.

With CNC machinery, they SHOULD be cheap, but they aren't. So, pistons soldier on in lower-horsepower form, using designs from the WWII timeframe. There is NOTHING overly complicated about an IO-360, but they charge an arm and leg for it. We need to overhaul the legal system to make it VERY hard to sue anyone for an airplane crash unrelated to the engine.

Jimmy Leeward's crash at Reno in 2011 is still ongoing including suing the engine builder, and the engine was running quite well until impact. There is no way the engine caused anything to happen that affected the aircraft. We all know it was a maintenance issue, They reused the nylock nuts on the trim tab too many times and they came loose.

But, the cost liability insurance is in the purchase price of every aircraft, aircraft engine, and propeller, passed along to the consumer. What we really need is a legal overhaul, not another lawsuit.

 

[Shortround6]

As a not very good comparison a 200hp aircraft engine that has a 2000hr overhaul life (max life, not a 2000 hour guarantee) and flies at 150mph is a 300,000 mile engine
And that 200hp engine weighs around 130kg. "dry" or a bit heavier than a Honda K series car engine of the early 2000nds.
Good luck trying to fly a Cessna 172 with 2 liter Honda engine without a reduction gear.

Yes a modern engine will be both a bit lighter and more powerful but under 400hp aircraft engines are very constrained by weight. What is the power to weight ratio, not the power per cubic inch?
Yes some modern light aircraft engines used reduction gears (or even belts) but the propellers are a problem. With an ungeared engine the rpm of the engine is somewhat governed by the diameter of propeller and you also need a certain propeller diameter to get performance. The Prop turns power into thrust. A small high rpm propeller may give good speed. It does not get the plane out of a high and hot airfield, not enough thrust. A few modern light planes have used variable pitch propellers. The more "stuff" that gets hung on an aircraft engine the more expensive it becomes, the more maintenance it needs and there is more "stuff" to go wrong and get sued over.

 

[z42]

Once the jet engine became reliable, why continue piston engine refinement?

For large engines, sure. Turbines, however, don't scale down very well and they tend to be expensive to buy. So for GA there's still a place for piston engines. Though as mentioned the small size of the market and the lawsuit-happy culture means developing a new engine is an iffy prospect.

The jet allows an order of magnitude more air into the engine; the IC engine air intake and therefore power, is limited by the size of the cylinders and stroke volume; and the jet produces power with essentially one moving part.

In piston engine terms, turbines run very lean as they need a lot of extra air so they don't melt. So just blowing a lot of air through the engine isn't really the reason for the superior power/weight.

 

[z42]

One REALLY good reason is the cost of a turbine.

With CNC machinery, they SHOULD be cheap, but they aren't.

I suspect part of the reason is that turbines have been aimed at the commercial and military markets, where power/weight and fuel efficiency are a lot more important than price. Airline customers would happily pay 5x for an engine if it means a 10% reduction in fuel burn (like 99% of statistics, this one is also completely made up). For GA, not so much.

There are a couple of companies developing turbines for GA, see e.g TurbAero | Turboprop Engines | Light Aircraft and UAV | General Aviation and About Us | TURBOTECH | Innovative turbines, Turboprops, Turbogenerators & Range-Extenders

Will be interesting to see if any of these succeed.

AFAIK both of the above are recuperated, to get back some of the efficiency loss of small turbines.