Drag comparison only applies if engines are close enough in power that it is immaterial. Engine placement matters a lot, I highly doubt the static thrust for the Williams engine achieved on a test stand with optimal parameters is even close to what they actually get on the SF50. You lose efficiency and thrust on the long inlet, some on the thrust vectoring....
I believe you would need some complex CFD modeling to make the prediction you have made.

Tim

So the "sweet spot" for this jet is how far a piston airplane can go in less than 2 hours?

Mike C.

It doesn't take a slide rule to tell you the SF50 has more drag than an EA550. Just look at both airplanes with a discerning eye.

I find it kind of funny that people are saying the reason it doesn't climb so well is not because the drag sucks, but because the engine installation sucks, as if that excuses the issue.

In the end, it is both.

Mike C.

It doesn't take a slide rule to tell you the SF50 has more drag than an EA550. Just look at both airplanes with a discerning eye.

I find it kind of funny that people are saying the reason it doesn't climb so well is not because the drag sucks, but because the engine installation sucks, as if that excuses the issue.

In the end, it is both.

Mike C.

So the "sweet spot" for this jet is how far a piston airplane can go in less than 2 hours?

Mike C.

Definitely something wrong with you Tim. Anyone with a double digit IQ should be able to give the airplane a quick once over with the eyeball and give you a coefficient number accurate to within +5%/-10%. Just ask Mike.

it definitely won't be the eclipse, they could come out with a plane that cruises at FL510 and makes it's own fuel, and no one would buy it. You can't treat customers like an ATM for long. Cirrus has customer service figured out, they will sell plenty of these on that basis alone, even if some of the SETP's are a better airplane spec-wise.

it definitely won't be the eclipse, they could come out with a plane that cruises at FL510 and makes it's own fuel, and no one would buy it. You can't treat customers like an ATM for long. Cirrus has customer service figured out, they will sell plenty of these on that basis alone, even if some of the SETP's are a better airplane spec-wise.

My Bonanza can weigh 4000 lbs, 2/3 the weight of the SF50. The greater weight limit takes the stall speed from 61 to 64 kts. How do you calculate the SF50 will have 5 times the impact energy? My calculations require a stall speed of 117 knots for the SF50 to give a 5-fold increase energy over my airplane. Surely that's no so?

Ashley

My Bonanza can weigh 4000 lbs, 2/3 the weight of the SF50. The greater weight limit takes the stall speed from 61 to 64 kts. How do you calculate the SF50 will have 5 times the impact energy? My calculations require a stall speed of 117 knots for the SF50 to give a 5-fold increase energy over my airplane. Surely that's no so?

Ashley

Not your typical Bonanza.

I assumed a more common version, like a G35, gross 2775 lbs, stall speed 48 knots.

Data from here:

http://www.risingup.com/planespecs/info ... e110.shtml

The SF50 has a listed stall speed of 67 knots, but this is at max LANDING weight of 5,550 lbs and with FULL flaps. Assuming you have the time to put down the flaps, upping the weight to 6000 lbs raises the stall speed to 70 knots. If you leave the flaps at takeoff setting, then the stall speed is even higher.

Impact energy is proportional to weight * velocity ^ 2. The SF50 is 2.16 times heavier than the G35, and it stalls 1.46 times as fast. Do the math, this works out to 4.6 times as much energy. If you don't get the flaps down, then the ratio goes even higher.

Thus the SF50 has about 5 times the impact energy, and carries 4 times as much fuel, of a Bonanza if it has an engine failure in takeoff and has to put down off the end of the runway.

The extra speed greatly increases the odds of hitting something as you cover so much more ground in the same time.

The odds of surviving the Bonanza takeoff crash are pretty good. The odds of surviving the SF50 takeoff crash are FAR less. I would not take the risk or subject my passengers to it.

PS: Winds make the impact energy ratio even larger. At 15 knots down the runway, the SF50 has 6.4 times the impact energy of the G35.

Mike C.

Fair enough. What you said didn't ring true for my Bonanza. I shouldn't have been surprised the older Bonanzas were so much lighter and that, partly as a consequence, they stall much slower.

I can't help but point out that your own MU2 is roughly twice the weight of an SF50, and stalls even faster than it. (The faster stall speeds permitted in certifying twins always seems an overlooked safety consideration to me.) I'm told a lot more thought goes into designing a modern airframe, so it will absorb the kinetic energy and protect the humans inside. I believe the SF50 will have superior crash-worthiness to a any Bonanza, or to any MU2.

I admit to messing with you. I saw your point about the inherent problems of a single single jet. That was interesting, but many pages ago. You've made some other useful points on this thread, but you're more interesting elsewhere!

Ashley

Remind me again how that parachute works on all those other planes...

Peace,
Don

The MU2 has a second engine to overcome an engine failure on takeoff.

For a jet, being a twin is even easier to fly away on engine failure.


This will be tested someday.

Mike C.

Sometimes, they don't, particularly at low altitudes.

Mike C.