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 Post subject: Re: Cirrus SF50
PostPosted: 26 May 2017, 23:27 
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Throttle response time isn't irrelevant.

While blown lift isn't as apparent on a single, it's still there but to a lesser extent.

Also, while the wing is landing at the same speed, I doubt it's the same NACA airfoil.

E-2C, T-45 and 737 have the same landing speed give or take a couple knots.

WILDLY different stall characteristics and handling at the same speed. (the 45 was closest to the ragged edge of the three)

Just because a plane lands at a given speed, doesn't mean the rest of the wing is the same.

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 Post subject: Re: Cirrus SF50
PostPosted: 26 May 2017, 23:28 
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Username Protected wrote:
We're comparing the SR22 to the SF50...at similar landing speeds. Prop lift is irrelevant when landing.


Prop drag is very relevant.

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 Post subject: Re: Cirrus SF50
PostPosted: 26 May 2017, 23:46 
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Username Protected wrote:
That doesn't make runway overruns more prevalent in the SF50 than the SR22...I'm guessing that what matters to Cirrus.


We don't know yet, do we?

At this time I can only relate the experience of other light turbojets flown by GA pilots.

So far Cirrus has not released the SF50 to normal GA usage. Have any customers been typed in the SF50 and flying it SP?

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 Post subject: Re: Cirrus SF50
PostPosted: 26 May 2017, 23:49 
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Username Protected wrote:
We're comparing the SR22 to the SF50...at similar landing speeds. Prop lift is irrelevant when landing.


Prop drag is very relevant.

Good thing it requires a type rating! :cheers:
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 Post subject: Re: Cirrus SF50
PostPosted: 26 May 2017, 23:54 
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Username Protected wrote:
That doesn't make runway overruns more prevalent in the SF50 than the SR22...I'm guessing that what matters to Cirrus.


We don't know yet, do we?

At this time I can only relate the experience of other light turbojets flown by GA pilots.

So far Cirrus has not released the SF50 to normal GA usage. Have any customers been typed in the SF50 and flying it SP?

You're quick...I deleted that post due to lack of facts. :D
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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 00:15 
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Think about how much drag a windmilling prop generates when OEI in a 421 (similar weight). Having two when landing makes a big difference.

At Simcom we would practice a double flameout scenario from 25,000' simulating running out of fuel or iced intakes. After feathering both props, its unbelievable how well the plane will glad and how much runway you can float if you are hot.

Even with one feathered you use substantially more. I landed both the PBaron and the 421 OEI and the lack of drag was impressive.


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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 00:45 
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Username Protected wrote:

Just trying to learn - how are the SF50's aerodynamics that of a jet rather than, say, a 58 baron?


Do you understand the difference in the aerodynamics of a Cirrus vs. a Baron vs. a Turbojet?

Having props or not having props make a big difference in both the thrust and drag at various times in the flight profile. A Barons props on the wings and the immediate prop wash over the wings give the prop twin responsiveness to power changes that a turbojet does not have. Both in adding power and reducing power.

As I said earlier you have more tools to manage landing and stopping a prop plane then a light turbojet.


No, not really. That's why I was asking (not being sarcastic). I haven't flown a jet (pretty sure this a fanjet rather than a turbojet, but :shrug: ), have deadsticked a piston single, and played with a twin with an engine at idle, "zero thrust" and feathered. So I have some feel for the differences there. These aren't geared large diameter props like a 421 or a turbine, but I'll totally agree they produce drag and can also create lift.

When I say "aerodynamic differences" I didn't actually mean the thrust or drag from the engine (prop or jet). I meant the wing and it's flying characteristics. I mistakenly thought you were referring to "jet aerodynamics" as the stuff pertaining to going really fast at high altitude with a big spread between ias and tas, swept wings, aggressive increases in drag on the backside of the power curve and high aoa, heavy wing loadings, etc.

If you're saying the plane's hard to slow down, I get it. There's not prop disc and there's some residual thrust. Harder than a piston, got it. I would think it's noticeable and requires an adjustment in technique, similar to getting out of a Husky on floats and into a Cirrus.

Regarding runway overruns - I would imagine VLJ's overshoot because of a combination of higher landing speeds relative to what the pilot's used to and a preference for new pilots to come in fast rather than slow. If you're used to landing at 55kts and you're a bit long, you'd have an intuition for how long you can be and still be OK. If you step up to a faster plane and land at 90 or 100kts, that intuition will be very wrong and humans are bad at intuiting the amount of extra energy to dissipate /runway length needed with even a small increase in speed. The SF50 stalls 6kts faster than an SR22, it's Vref is 10kts faster. It won't be as big an adjustment. Of course, we'll have to see how many get bent (some certainly will).

Thank you for engaging with me, by the way.

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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 09:35 
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No, not really. That's why I was asking (not being sarcastic). I haven't flown a jet (pretty sure this a fanjet rather than a turbojet, but :shrug: ), have deadsticked a piston single, and played with a twin with an engine at idle, "zero thrust" and feathered. So I have some feel for the differences there. These aren't geared large diameter props like a 421 or a turbine, but I'll totally agree they produce drag and can also create lift.

When I say "aerodynamic differences" I didn't actually mean the thrust or drag from the engine (prop or jet). I meant the wing and it's flying characteristics. I mistakenly thought you were referring to "jet aerodynamics" as the stuff pertaining to going really fast at high altitude with a big spread between ias and tas, swept wings, aggressive increases in drag on the backside of the power curve and high aoa, heavy wing loadings, etc.

If you're saying the plane's hard to slow down, I get it. There's not prop disc and there's some residual thrust. Harder than a piston, got it. I would think it's noticeable and requires an adjustment in technique, similar to getting out of a Husky on floats and into a Cirrus.

Regarding runway overruns - I would imagine VLJ's overshoot because of a combination of higher landing speeds relative to what the pilot's used to and a preference for new pilots to come in fast rather than slow. If you're used to landing at 55kts and you're a bit long, you'd have an intuition for how long you can be and still be OK. If you step up to a faster plane and land at 90 or 100kts, that intuition will be very wrong and humans are bad at intuiting the amount of extra energy to dissipate /runway length needed with even a small increase in speed. The SF50 stalls 6kts faster than an SR22, it's Vref is 10kts faster. It won't be as big an adjustment. Of course, we'll have to see how many get bent (some certainly will).

Thank you for engaging with me, by the way.


https://www.faasafety.gov/gslac/alc/lib ... px?id=6577

Re: the "turbojet vs turbofan" thing. The FAA refers to all jets as "turbojets" in their terminology.

Whether it's a straight pipe Lear 24 or SF50 with a fan. That's why Allen keeps using the turbojet reference.


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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 09:40 
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For someone who has never flown a turboprop or piston twin, the absence of prop drag, beta, reverse and blown lift is going to be a non-issue.


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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 10:44 
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I would see the big difference in landing being how clean the jet is and how easy to land a bit fast and long. In pistons and turbines, one can still round out and land at or just above stall. In jets, it's more important to get wheels on the ground in the approach threshold to stop on runway; especially, when it's short. We have what is called a "working landing" where one plants wheels on ground by a point even if not as smooth. It will be interesting to see how that's handled. Of course, a set speed over the threashold (Vref) which is very important where the piston and turbine can be more forgiving.

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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 10:48 
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The Turbo Cirrus has that awesome composite Hartzell prop. That thing is one crazy speed brake. Pull it to idle and it almost feels like Beta. You can feel the seatbelts tighten. I always liked that about the composite prop. You can go down and slow down in a hurry. I have heard the metal props are much less draggy, but does seem like landing is aided with the type of prop a lot of Cirrus drivers are familiar with. The jet will certainly require more attention to Vref, but Cirrus has been grooming Cirrus pilots for several years now, on really paying attention to short final approach speeds. That in response to a rash of landing accidents. So attention to approach speeds won't be a huge concept for the average Cirrus driver stepping up.

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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 11:03 
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Thanks Chuck. I wasn't aware of that and it certainly will be of help. The second part will be to get wheels safely on the ground to start braking; especially, on short or wet runways. I'm sure it will all be addressed in training, but it's still an issue we'll hear more about just as in some existing jets.

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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 11:49 
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Don't think the jet was designed to fly like the SR22 except for the approach speed. Has a much better, harmonized feel( Bonanza like). No springs in the flight control system that I could detect. Don't expect overruns to be much of an issue because the jet is considerably easier to fly than SR 22, 85 knot approach speed, Cirrus pilots have been taught the importance of proper approach speed, and the resulting competence from a type rating. My first landing was in a rain shower and 7 or 8 knot tailwind. Was able to turn off midfield with little braking. Only glitch I observed was a less experienced pilot landed on a wet runway and was off centerline enough to put the right main on centerline and the right tired was skidding on the paint then grabbing on the concrete. Again, was turning off midfield. If there ever was a jet that could be operated safely without a type rating, it would be the SF-50.

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 Post subject: Re: Cirrus SF50
PostPosted: 27 May 2017, 16:23 
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Username Protected wrote:
https://www.faasafety.gov/gslac/alc/lib ... px?id=6577

Re: the "turbojet vs turbofan" thing. The FAA refers to all jets as "turbojets" in their terminology.

Whether it's a straight pipe Lear 24 or SF50 with a fan. That's why Allen keeps using the turbojet reference.


Thanks Scott, that's helpful. I kinda figured there was a reason and I now vaguely remember reading that for one test or another a while back.


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 Post subject: Re: Cirrus SF50
PostPosted: 30 May 2017, 09:07 
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Username Protected wrote:
In jets, it's more important to get wheels on the ground in the approach threshold to stop on runway; especially, when it's short. We have what is called a "working landing" where one plants wheels on ground by a point even if not as smooth. It will be interesting to see how that's handled.

This is important, and is a big difference between jets and pistons. In the case of every production jet that I know of, the fully configured landing attitude is nose high, meaning that if you don't flare at all, you'll land on the mains first. You can't do that in a piston plane or you'll bounce off the nosewheel. If the SF50 is "conventional" in this regard, then planting the plane at a slightly high speed and then using the (hopefully very capable) brakes to stop will go a long way to preventing the "hot float" down the runway, or PIO from forcing it on that gets piston drivers into trouble.

Those who've seen the SF50 coming in to land, what's it's landing attitude look like?

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