Look up the speeds for small jets. If anything, I was slow.

FJ33-4A (the -5A slated for the SF50 not yet certified BTW): 22,875 RPM

PW610F (Eclipse EA550): 22,542 RPM

FJ44-3A (525 series): 18,500 RPM

JT15D-5A (560 series): 16,540 RPM

TFE731-3A: 21,000 RPM

Mike C.

I stand corrected for small jets.

About 100 knots and 15,000 ft.

The prop begins to lose performance at high true airspeeds and in thin air. The turbofan does not. This is because the prop turns slowly, the fan does not. The slow prop has a high advance angle and the blade thrust is not aligned in the direction of flight.

Example of high advance angle ~300 knots and ~FL250, 1600 RPM:

https://www.youtube.com/watch?v=ugvWNAXgswE

Put that at 400 knots and FL410 and the prop simply can't produce good forward thrust.

Meanwhile, fans are running 15,000 to 20,000 RPM. They don't suffer the issue of high advance angle.

You can't speed up the prop to 15,000 RPM, it would go supersonic and fly apart as well.

Mike C.

It's not like Cirrus is the only one that decided to build single-engine jets. At one point, there were nearly 1/2 dozen entries in this field. Most fell victim to Great Recession, and Cirrus is the only one who got the money to complete the project so far, but obviously a lot of smart folks think that single engine jets make sense for their market.

And a lot of really SMART folks WHO KNOW HOW TO BUILD JETS have decided to NOT build an SEJ, even BEFORE there was a recession.

Diamond and Piper are still here, Eclipse sort of as well. Not a peep out of them to restart their SEJ projects.

Guess they got smarter.

Mike C.

You can also interpret that as a lot of smart folks stuck their toe into the market, took a look and realized it was not as lucrative as they though and smartly bailed. Cirrus sold their Chinese owners a dream that may be hard to realize. Others are not willing to risk their money on a SEJ, but risking Chinese money will not hurt anyone in Minnesota.

We shall see.

I'd love to see you try, but from a VERY safe distance. On second thought, just send me the video, if the camera survives the shrapnel.

Just for grins, assume prop blade is only 1 lb, has CG at 1 ft radius, turns 25,000 RPM.

Centripetal force is 210,000 lbs per blade, > 100 tons. Good luck on designing that hub.

Takeoff thrust would be anemic, too.

Mike C.

Who are those real smart folks who decided not to build one? There are only 4 significant light GA manufacturers out there - Cirrus, Textron, Piper and Diamond. 3 out of 4 of these decided to build single engine jets, with Eclipse thrown in for good measure. Guess they knew something you don't.

Companies over the years who have built GA jets and not an SEJ:

Astra
Beechcraft
Bombadier
Cessna
Challenger
Dassault
Embraer
Gulfstream
Hawker
Honda
LearJet
Mitsubishi
Sabre
Textron
Westwind

Gulfstream investigated this back in the early 1980s with the Peregrine. Abandoned the project very early. It was an outgrowth of the Hustler concept (combo turboprop and jet, seriously muddled thinking there).


For PISTONS.

Not surprising that the PISTON makers used PISTON THINK to decide an SEJ was worthwhile. Note that the only company in both categories (Textron) never even hinted they would build an SEJ.

Mike C.

Right. That's the part you don't get. SF50 is a jet for a piston pilot. Their CUSTOMERS have "piston think", so they are building what the customer wants.

They are building what the customer THINKS they want. They want a jet with the proportionate advantages a single engine piston has over a twin piston.

But that isn't what they are going to get.

Mike C.

Their CUSTOMERS have "piston ignorance". Exploiting a markets ignorance has never been a good strategy.

I posted quite some time ago that the twin VLJ manufacturers are just waiting for the SF50 buyers to get some experience and education and realize how much more they can get for their $2MM. The SF50 may not help Cirrus but it will help the low end of the used VLJ market. If they can afford a SF50 they can afford a used Mustang or Phenom 100 or Eclipse and get much more capability.

Once the early SF50 buyers get educated and word gets out among SF50 potential buyers I think new SF50 sales will dry up. They will have a good run for 2 - 3 years and maybe 100 aircraft.

Used aircraft brokers are going to make a ton of money selling SF50s over and over again. Each new buyer brings the dream, each learns the reality, plane back on the market, rinse and repeat.

If you really want an SF50, there will be PLENTY of opportunity to buy one. Between the type rating wash outs and the busted dreamers, there will be very lightly used planes on the open market in short order.

Mike C.

Used aircraft brokers are going to make a ton of money selling SF50s over and over again. Each new buyer brings the dream, each learns the reality, plane back on the market, rinse and repeat.

If you really want an SF50, there will be PLENTY of opportunity to buy one. Between the type rating wash outs and the busted dreamers, there will be very lightly used planes on the open market in short order.

Mike C.

And Cirrus has done so in the Piston space, why do you think their business model has changed?

Tim