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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 03:06 
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I feel like all of the SF50 problems boil down to lack of redundancy ... and lack of efficiency (due to being held down to FL280).... But I imagine if they could squeak a few more thousand in certified altitude... they'd have a home run, neh?
I haven't done the math but I expect it would take more than a few thousand. As a single, the SF50 is required by FARs to have a lower stalling speed than a twin, hence more wing, so the most efficient IAS for the airframe is lower than a twin. Jet engines are most efficient at max power setting which, at low altitudes, pushes the airframe way faster than its most efficient IAS. So the key to efficiency for a jet is to climb high enough that the thrust from the most efficient power setting pushes the plane not too much faster than the efficient IAS for the airframe. A bigger wing moves that best altitude higher.


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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 10:21 
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A wise man once said don't buy the A model of anything!

This may have been true in cars, but we had few opportunities...

It is a regular and avoidable mistake in aviation!

Let those "early adopters" be the Guinea pigs, but I'm betting the B model is going to be a much better airplane that flies higher, farther and has more aesthetic appeal, with another foot or so from it's tip to it's tail.

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 14:13 
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Username Protected wrote:
I feel like all of the SF50 problems boil down to lack of redundancy ... and lack of efficiency (due to being held down to FL280).... But I imagine if they could squeak a few more thousand in certified altitude... they'd have a home run, neh?
I haven't done the math but I expect it would take more than a few thousand. As a single, the SF50 is required by FARs to have a lower stalling speed than a twin, hence more wing, so the most efficient IAS for the airframe is lower than a twin. Jet engines are most efficient at max power setting which, at low altitudes, pushes the airframe way faster than its most efficient IAS. So the key to efficiency for a jet is to climb high enough that the thrust from the most efficient power setting pushes the plane not too much faster than the efficient IAS for the airframe. A bigger wing moves that best altitude higher.


Thanks. I didn't think of the stall speed requirement and it's knock-on effects.

See, I learned something in here. Only took 318 pages. :D :woot:

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 14:22 
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Username Protected wrote:

See, I learned something in here. Only took 318 pages. :D :woot:


I gave Mike a like... had to contribute to his post to like ratio... :)

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 14:39 
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Username Protected wrote:
A wise man once said don't buy the A model of anything!

This may have been true in cars, but we had few opportunities...

It is a regular and avoidable mistake in aviation!

Let those "early adopters" be the Guinea pigs, but I'm betting the B model is going to be a much better airplane that flies higher, farther and has more aesthetic appeal, with another foot or so from it's tip to it's tail.


I have been advised not to buy the first 100 sn of a new type.

It can take that long to figure out the problems and slip stream into the assembly line.

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 19:38 
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Cirrus Jet on the ramp at Frederick, Maryland airport on Friday.


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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 19:52 
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I wonder how much ramp fees Signature is charging on that clown jet.

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 19:59 
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Mike, if the folks in recent n loving 'Yurp can see there way to allowing a PC12 to carry pax for hire, I don't see why the 'Murcans could not increase the permitted altitude of the SF50 after it has been flying a while...

At least it seems that way to me....

Maybe require the pilot wear an O2 mask?

RVSM airspace will require back up systems. I'd have to review requirements again but if you're trying to stay below a weight limit, higher pressure differential, RVSM, quick don mask with bigger oxy system and some other issues may be difficult to address.

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 Post subject: Re: Cirrus SF50
PostPosted: 22 Apr 2017, 20:37 
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Just thinking outta the box... what would Cirrus need to prove to the FAA that a single jet + chute is an ELOS to a twin jet, and allow it up to, say, FL310 or so?

Maybe a certain number of saves or hours of operation?

I feel like all of the SF50 problems boil down to lack of redundancy (thus, "unsafe in a failure" -- possibly mitigated by the chute or maybe clever autopilot auto-descent in depressurization cases?) and lack of efficiency (due to being held down to FL280)

There is no certification cure for pregnant guppy looks. :D

But I imagine if they could squeak a few more thousand in certified altitude... they'd have a home run, neh?

Not a jet pilot. Assume the above is pure rubbish and jeer at me accordingly. :popcorn:

Satisfying the FAA, especially with a new category, is without a doubt challenging. The check boxes for a turbine are extensive. Creating adequate safeguards and redundancies required for turbines get tough when you're only starting out with one engine. Things like pressurization, electrical, and hydraulics all start to die with total power loss. Convincing the FAA of adequate redundancy could prove to be more challenging than adding a second engine.

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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 07:27 
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PC12 and TBM are RVSM.


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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 09:19 
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PC12 and TBM are RVSM.


I believe RVSM is mostly about a assured performance of the autopilot system.


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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 11:56 
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Well, it also requires checking one altimeter against the other and a back up to be sure altitude is confirmed and to be able to fly accurately if one fails.
My point was, staying at FL280 and below eliminates more complexity and systems. RVSM is just one.
To Jason's point, yep, them foreigners beat us to the punch with those; they weren't initially certified by FAA domestically were they? Gross weight on those is much higher.
Aren't they trying to stay around 6,000 pounds max gross and keep it affordable?
Between high, fast and cheap, you usually get to pick two :)

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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 13:24 
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RVSM requires two independent altimetry systems including:
Cross-coupled static source/system with ice protection
Equipment for measuring static pressure sensed by the static source, converting to pressure altitude and displaying the pressure altitude to the flight crew (DADC Digital Air Data Computer and altimeter.
Also, the static sources are checked and calibrated or moved if not getting accurate measurements. (Static source error correction.)
Equipment for providing a digitally coded signal corresponding to the displayed pressure altitude.
Automatic altitude control devise (A/P altitude hold)
Altitude alerting system.
Auto pilot.
Stand by altimetery systems may not be required by regulation, but may be part of the certification certificate.
MEL: any of the following inoperative will affect:
Either of 2 independent altitude measuring systems.
Transponder or altitude reporting feature.
Altitude alerter system.
Automatic altitude control
Must have a periodic check and maintenance system.
Follow operational practices and procedures.

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Dave Siciliano, ATP


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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 15:56 
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Username Protected wrote:
Satisfying the FAA, especially with a new category, is without a doubt challenging. The check boxes for a turbine are extensive. Creating adequate safeguards and redundancies required for turbines get tough when you're only starting out with one engine. Things like pressurization, electrical, and hydraulics all start to die with total power loss. Convincing the FAA of adequate redundancy could prove to be more challenging than adding a second engine.


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 Post subject: Re: Cirrus SF50
PostPosted: 23 Apr 2017, 17:15 
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If i ever buy a low s/n airframe it will only be with the option of trading it in within 5 years for a very liberal credit.


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