A multi engine jet somewhere in the world shuts down an engine nearly every day.

And you never hear about it because having a second engine provides safety.

Nobody else builds a single engine jet for this reason.

If you doubt a second jet engine adds safety, ask yourself if you would board a Boeing or Airbus if it had only one engine.

In the jet world, a second engine increases safety, speed, altitude, range, and efficiency. Cirrus doesn't know that, or at least they didn't when they started the SF-50 project.

Mike C.

Because such an ELOS or waiver is not listed in the TCDS for the SF-50.

Mike C.

Props don't work well with high true airspeeds and thin air. The blade angle gets pretty severe such that the lift vector is sideways to the direction of travel.

Turbo fan solves this by operating faster. Can't do that to a prop because the tips go supersonic. Turbo fan solves this by being smaller diameter and putting a shroud around the fan.

There are a few turboprops certified to FL410. Piaggio and Cheyenne 400LS. They have big engines and complex props. I think it is cheaper to fly a Citation than either a Piaggio or 400LS.

Mike C.

That was the reason you gave for your claim that the SF50 would never be certified above FL 250. Yet here it is at 280. How did they do that? And can that method be extended higher? Until we know what method they used to satisfy that certification requirement we don't know how high that method can take them.

Cessna 441 is certified to FL 350 and it's a lot cheaper to fly than a Citation.

Yes, it is, due to small block economical TPE331 engines. I think the 441 is the pinnacle of privately flown turboprops offering good speed, awesome range, and reasonable costs.

The TPE331-14s in the 400LS cost a lot. The Dowty Rotol props cost a LOT, too. Per mile, I think a Citation would be cheaper and obviously better in other aspects as well.

Mike C.

That sounds strange to me. Do you have a photo of the actual placard or the actual text from the POH?

That sounds strange to me. Do you have a photo of the actual placard or the actual text from the POH?

Thanks, Abram. I guess when I read that I would have interpreted it differently. KIAS max allowed for parachute deployment of 135 kts…..

Hmmm, I guess I'm confused about what aerodynamic effects and limitations when at FL280 would require that the plane be slowed to 92 KIAS.. I wonder if that's what Cirrus really meant by this placard.

Nobody is going to pull a chute at FL280. You’d have no pressurization or heat and who knows where you’d end up. Emer descent then pull.

Up high, although air molecules are further apart they are not moving slower when you see a lower IAS. Flutter, for example, is a function of TAS no IAS. Our ASIs use pressure to represent a speed but they don’t account for the spreading of molecules.

I’m assuming the limitation on the chute has to do with the high speed molecules suddenly impacting an open canopy.

Are supersonic prop tips operationally or just noisy? Curious about the TU95

I see your point, but if iced up and tumbling down thru cumulus... pull or try to salvage first?

Noise is only one problem, and generally not the biggest.
Drag and vibration are the two major issues. With part of the prop above and below supersonic speeds you get weird vibrations (I could not follow the explanation no matter how many times I tried to read it), and extremely high drag.

Basically, it is super inefficient.

Tim

Because such an ELOS or waiver is not listed in the TCDS for the SF-50.

Mike C.

I suspect the answer is that when flying at FL280, and the engine fails, Cirrus showed that a factory new tight cabin won't go above 15,000 ft cabin altitude before the plane glides down to 15,000 true altitude.

The glide can't be an emergency descent, as using an emergency descent to show compliance with FAR 23.841 is not allowed (per AC23-17C).

Basically, I think they nibbled at the edges of the rule in a way that got them a little more altitude, but I doubt it is extensible to high altitudes. As you go up, the leak rate and time of exposure increase making it increasingly difficult to meet the 15,000 ft cabin limit.

Mike C.