BeechTalk - BT

Username Protected · **Posted:** 11 Jan 2019, 09:50

Username Protected wrote:

Engineering question.

Go back a few pages and look at the Globalhawk. They went with a single turbofan with effectively a V Tail. I am fairly sure that efficiency (loiter time) matters more than price, yet DoD went with a larger and much more complex control system to have the single engine.
Boeing and Airbus have gone from four engines down to two.

The point being; what aspect of turbofans has such a huge drag or efficiency cost that everyone wants larger and fewer engines? Are there any rules of thumb or is this all guesswork and proprietary knowledge?

The Eclipse climbs/performs much better on roughly the same thrust and weight; therefore the V/X tail of the SF50 and airflow inlet must have some significant penalties (which is the main point of comparison why the single engine turbofan does not make sense). Based on the point above, what aspect about this comparison is invalid?

Tim

The GlobalHawk is not made to take people from point A to B with as little hassle as possible.

Username Protected · **Posted:** 11 Jan 2019, 10:04

Username Protected wrote:

Engineering question.

Go back a few pages and look at the Globalhawk. They went with a single turbofan with effectively a V Tail. I am fairly sure that efficiency (loiter time) matters more than price, yet DoD went with a larger and much more complex control system to have the single engine.
Boeing and Airbus have gone from four engines down to two.

The point being; what aspect of turbofans has such a huge drag or efficiency cost that everyone wants larger and fewer engines? Are there any rules of thumb or is this all guesswork and proprietary knowledge?

The Eclipse climbs/performs much better on roughly the same thrust and weight; therefore the V/X tail of the SF50 and airflow inlet must have some significant penalties (which is the main point of comparison why the single engine turbofan does not make sense). Based on the point above, what aspect about this comparison is invalid?

Tim

Because it's a turbofan. Larger engines allow for higher bypass ratios as long as you can keep the weight of the blades down. Next goose chase seems to be pressure ratios, but that's all material science.

Username Protected · **Posted:** 11 Jan 2019, 10:08

Username Protected wrote:

If they ever get it to the point where you just push a button and it does the rest, they will sell a million of them.

Fantasy: push button teleporter.

Reality: 4 weeks to get trained to fly it, yearly retraining.

Quote:

They never thought they wanted to be pilots... until now.

First day of ground school will fix that.

Mike C.

Username Protected · **Posted:** 11 Jan 2019, 10:10

Username Protected wrote:

Fantasy: push button teleporter.

Reality: 4 weeks to get trained to fly it, yearly retraining.

Mike C.

This thread has already proven that the rules do get changed.

FAR/AIM is ripe for disruption.

Username Protected · **Posted:** 11 Jan 2019, 10:10

You’re funny, Mike.

Username Protected · **Posted:** 11 Jan 2019, 10:14

Username Protected wrote:

The goal of private aviation is to get from point A to B with as little hassle as possible.

Getting and maintaining a type rating is hassle.

You yourself said doing so would never make up the speed difference between you PC-12 and a jet.

Minimum hassle is frax or charter. SF50 doesn't change that. The minimum hassle option has existed for decades.

A large number of you have forgotten the SF50 is an airplane that needs a real pilot.

Mike C.

Username Protected · **Posted:** 11 Jan 2019, 10:19

Username Protected wrote:

A large number of you have forgotten the SF50 is an airplane that needs a real pilot.

Mike C.

For now, hire one. Soon you won’t need to

I enjoy flying airplanes. Most folks don’t. You and I aren’t SF50 buyers. “Flying it” is t the motivation.

Username Protected · **Posted:** 11 Jan 2019, 10:27

Username Protected wrote:

Go back a few pages and look at the Globalhawk. They went with a single turbofan with effectively a V Tail. I am fairly sure that efficiency (loiter time) matters more than price, yet DoD went with a larger and much more complex control system to have the single engine.

Drones don't care about cabin noise.

Drones don't care about limited CG ranges, they can be loaded in a very small CG range that is efficient to avoid the trim drag of the V tail.

Drones don't care about redundant pressurization.

Drones don't care, as much, about redundant propulsion.

Drones don't care about certification.

As for control system, the Global Hawk has what would be fly-by-wire with no pilot input on board. Thus the V tail requires no mechanical mixers, all done in software.

Mike C.

Username Protected · **Posted:** 11 Jan 2019, 10:32

Username Protected wrote:

Additional engines, even smaller ones, burn more than a single one in most cases.

That's true. The larger the turbine engine, the better the fuel specifics can be.

But the catch is that a single engine jet can't operate at efficient altitudes, and the installation of the single jet engine isn't as efficient as two on traditional pylons.

So when looking at the entire system, the single is less efficient.

Quote:

Adding engines provides redundancy, performance, or both at the expense of dollars per hour. Cirrus opted for the less expensive route because that's where their market is.

Your analogy fails for jets due to the increased ceiling a twin gets to enjoy over a single.

An Eclipse EA500 goes faster, higher, further, on LESS fuel than an SF50. Two engines are required to fly in the high flight levels where jets are efficient.

Mike C.

Username Protected · **Posted:** 11 Jan 2019, 10:34

Username Protected wrote:

I enjoy flying airplanes. Most folks don’t.

So Cirrus market is a number of SR pilots who hate flying their airplanes?

Not a big market...

Mike C.

Username Protected · **Posted:** 11 Jan 2019, 10:34

Username Protected wrote:

Your analogy fails for jets due to the increased ceiling a twin gets to enjoy over a single.

An Eclipse EA500 goes faster, higher, further, on LESS fuel than an SF50. Two engines are required to fly in the high flight levels where jets are efficient.

Mike C.

Yawning.... nobody cares about "higher in the flight levels". I wanna go to Miami.

Username Protected · **Posted:** 11 Jan 2019, 10:34

Username Protected wrote:

The GlobalHawk is not made to take people from point A to B with as little hassle as possible.

but it almost certainly was designed to have the engine be easily swappable in the field, and to not have the engine occupying space where ground-peering sensors could go. that means put the engine on top rather that inside paris-jet style. Engine on top means a v-tail, whether it's a $100M global hawk or a sonex jet.

Username Protected · **Posted:** 11 Jan 2019, 10:35

Username Protected wrote:

An Eclipse EA500 goes faster, higher, further, on LESS fuel than an SF50. Two engines are required to fly in the high flight levels where jets are efficient.

so that's why eclipse has a multi-year order backlog and cirrus is defunct ?

Username Protected · **Posted:** 11 Jan 2019, 10:39

Username Protected wrote:

An Eclipse EA500 goes faster, higher, further, on LESS fuel than an SF50. Two engines are required to fly in the high flight levels where jets are efficient.

so that's why eclipse has a multi-year order backlog and cirrus is defunct ?

Username Protected · **Posted:** 11 Jan 2019, 10:43

Username Protected wrote:

so that's why eclipse has a multi-year order backlog and cirrus is defunct ?

At this stage in the product cycle, Eclipse had a far larger backlog than Cirrus.

Without the Chinese purchase of Cirrus, they would be defunct. Eclipse failed at a time when the Chinese were not buying every aviation company they could. In fact, the Chinese are currently propping up Eclipse #2, One Aviation, during their bankruptcy, and seem poised to own that, too.

Mike C.

Cirrus SF50