Yep. I just learned 4 MORE bad things about the SF50. It has absolutely no chance of success.

Me to.

Tim

"Must use the same technology as peril sensitive sunglasses worn by Zaphod Beeblebrox."

Hilarious.

Tail volume is surface area of tail times distance from CG. More tail volume is more stable, less is less as one might expect. If you have a short arm to the CG you get a large tail. Look at the fin on a 747SP for example, which I think is the biggest fin ever put on any airplane due to the short tail. The SF50 has a similarly outsized tail caused partially by the short arm and partially by being a V/X tail with lesser natural stability.

The total tail volume is made up of the fixed part and the variable part, the control surface. The area of the control surface is defined by the amount of change in force the surface needs to produce. If the ratio of control to fixed surface area is small, then the tail is not being asked to provide much change in lift one way or the other. If the ratio is large, then the tail is being asked to provide a big change in lift and this would only happen if you need it. Lift induces drag. So, all others things being equal, a tail with large control surfaces implies one that causes more drag.

Why does the SF50 needs such large control surfaces? One reason is that each surface is the combined result of both pitch and yaw controls. So the control surface has to not stall or become ineffective even when the pitch and yaw control inputs are maxed out. For example, maximum right rudder and up elevator means the left ruddervator is maximally deflected up. If you don't give the control surface the authority to work under those conditions, you can enter weird control zones of reverse command, more right rudder pedal results in less yaw, for example, because the control surface is stalled on the left ruddervator.

In a conventional tail, no surface has to do more than that axis requires. There is no need for headroom for mixing control inputs.

Mike C.

Tail volume is surface area of tail times distance from CG. More tail volume is more stable, less is less as one might expect. If you have a short arm to the CG you get a large tail. Look at the fin on a 747SP for example, which I think is the biggest fin ever put on any airplane due to the short tail. The SF50 has a similarly outsized tail caused partially by the short arm and partially by being a V/X tail with lesser natural stability.

The total tail volume is made up of the fixed part and the variable part, the control surface. The area of the control surface is defined by the amount of change in force the surface needs to produce. If the ratio of control to fixed surface area is small, then the tail is not being asked to provide much change in lift one way or the other. If the ratio is large, then the tail is being asked to provide a big change in lift and this would only happen if you need it. Lift induces drag. So, all others things being equal, a tail with large control surfaces implies one that causes more drag.

Why does the SF50 needs such large control surfaces? One reason is that each surface is the combined result of both pitch and yaw controls. So the control surface has to not stall or become ineffective even when the pitch and yaw control inputs are maxed out. For example, maximum right rudder and up elevator means the left ruddervator is maximally deflected up. If you don't give the control surface the authority to work under those conditions, you can enter weird control zones of reverse command, more right rudder pedal results in less yaw, for example, because the control surface is stalled on the left ruddervator.

In a conventional tail, no surface has to do more than that axis requires. There is no need for headroom for mixing control inputs.

Mike C.

Mike's Zaphod Beeblebrox reference just won the thread.

I think you are right. I found this in a Q&A session with a Cirrus test pilot:

Q: Is the Vision jet complicated to start or to handle on the ground?

A: Not at all. Starting—there's nothing to it since it's all FADEC controlled. You turn the key—not many jets have that—you count to about 10, and it's up and running! You bring your generator online when your engine is spooled up, and start taxiing. We use a castering nosewheel like on the SR20 and 22, but this one has a centering mechanism so it's easier to go straight. The trailing-link gear is smooth, solid, and it feels more substantial.

http://www.planeandpilotmag.com/aircraf ... KzIkHtEzaw

Mike C.

Wow taxiing with the brakes. That will get expensive after a while.
What do you do with all the trust on a jet will taxiing?
I never use the brakes on the TBM. On a turboprop we can taxi in beta and save the brakes. A beta block is cheap compared to brakes.




I think you are right. I found this in a Q&A session with a Cirrus test pilot:

Q: Is the Vision jet complicated to start or to handle on the ground?

A: Not at all. Starting—there's nothing to it since it's all FADEC controlled. You turn the key—not many jets have that—you count to about 10, and it's up and running! You bring your generator online when your engine is spooled up, and start taxiing. We use a castering nosewheel like on the SR20 and 22, but this one has a centering mechanism so it's easier to go straight. The trailing-link gear is smooth, solid, and it feels more substantial.

http://www.planeandpilotmag.com/aircraf ... KzIkHtEzaw

Mike C.

A key?
Who wants a key in a jet? That is so piston thinking mentality.



I think you are right. I found this in a Q&A session with a Cirrus test pilot:

Q: Is the Vision jet complicated to start or to handle on the ground?

A: Not at all. Starting—there's nothing to it since it's all FADEC controlled. You turn the key—not many jets have that—you count to about 10, and it's up and running! You bring your generator online when your engine is spooled up, and start taxiing. We use a castering nosewheel like on the SR20 and 22, but this one has a centering mechanism so it's easier to go straight. The trailing-link gear is smooth, solid, and it feels more substantial.

http://www.planeandpilotmag.com/aircraf ... KzIkHtEzaw

Mike C.

That is knowing your customer. What is so special about having to push a button/toggle versus turn a key?

Tim

Its "car think". The idea is to make the airplane seems as simple as driving a car and the use of a key is a subtle element of that deception.

I'm always amused when I see a car commercial advertise "cockpit inspired interior". They obviously have never looked at a cockpit.

Then, more amusingly, I see airplanes advertised with "automotive inspired cockpits". Indeed, Cirrus says (of the SR series) "Inspired by the unmistakable style of the most legendary sports cars...".

Seems we have a circular inspiration loop going on here.

Mike C.

That is knowing your customer. What is so special about having to push a button/toggle versus turn a key?

Tim

Sounds like a business opportunity for a start button STC…

"That's right SF50 pilots you can have a big boy start button just like the real jet pilots!"

For you social climber pilots you can get our "Global Player" model that features TWO start buttons designed to look exactly like those on a G-V engine panel (either will start your single engine).

Keys are for piston pansies![/quote]


Hilarious

You're still forgetting about the vertical stab that isn't there. Yes, a V-tail does induce more drag than an elevator for a given amount of down/up force. But, it doesn't induce more drag than an elevator AND a vertical stab.

There are nits to pick with the SF50, but I don't think that the V-tail is one of them.

Making a surface that can deflect 12" doesn't add any more drag than a surface that can deflect 6". The drag comes from actually deflecting them, which won't be done at speed. Nobody is going to be full deflecting anything at 300kts and FL280.