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22 Jun 2021, 23:14 [ UTC - 5; DST ]


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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 13 Apr 2021, 15:01 
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Username Protected wrote:
Wow. Super cool. What’s the aoa at fl410 at mct?
And did you mean at 15 minutes out you started your descent?

My question too, along with what the distance was at ToD. IOW, what was your profile?

Idle descent is great for making fuel. We always did it in the little Lears, but our ToD was at 2:1 with power to idle. From 410 that equated to 82 NM (I usually cheated and started pulling the handles back at 90), and about 15 minutes to touchdown.

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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 13 Apr 2021, 20:55 
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Nice! One question, in the the Citation LR Planning Guide you provided, they mention that an AOA of 0.35 is the aircraft’s best L/D or lift to drag ratio.

However, in the Citation 500/501 manual I have, 0.35 is the AOA for best velocity to drag, i.e. best range in still air. Best L/D is achieved with an AOA of 0.6.

Sierra notes that they modify the AOA gauge with new software to account for their wing mod, but I still think they mean that an AOA of 0.35 corresponds to the best velocity to drag ratio.

Of course in prop planes, best range is achieved by flying at best L/D.

But do you also have a direct readout of groundspeed to fuel flow?


A velocity to drag ratio doesn’t make sense. [edit: having thought about it, I can see that it does make sense. But the remainder of my post should clear up the aoa discrepancy...which might be found interesting.] For jets the trick is to minimize the ratio of thrust to velocity. This corresponds to maximizing the square root of lift over drag. You don’t target max L/D, but rather L^(1/2)/D.

What max L/D gives you is max endurance (again, for a jet).

There’s a bit more to it, but that’s the gist of it.


Why distinguish between props and jets? Why would the formulas for max endurance max range be different between jets vs. props?

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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 13 Apr 2021, 21:04 
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For no other reason than jets us TSFC (thrust specific fuel consumption). Props by convention use SFC (fuel consumption per brake horsepower). That engine power then gets to thrust via propeller efficiency.

So it just changes the math. The aerodynamics of course don’t care (or in other words, gliding range would see no difference between the two)

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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 13 Apr 2021, 22:03 
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Why distinguish between props and jets? Why would the formulas for max endurance max range be different between jets vs. props?


If you want to read more about the “why”, download yourself the PDF of Aerodynamics For Naval Aviators. It covers this in glorious fashion.


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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 15 Apr 2021, 00:50 
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Why distinguish between props and jets? Why would the formulas for max endurance max range be different between jets vs. props?


If you want to read more about the “why”, download yourself the PDF of Aerodynamics For Naval Aviators. It covers this in glorious fashion.



Yes, very detailed, just like similar discussion of Energy Maneuverability, Specific Excess power (Ps) and the Rutowski climb profiles for jets taught in the USAF. Best climb rate speed, maximum range, are not the same as L/D Max. I kind of cringe when I hear people say L/D max gives you best range in cruise.

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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 15 Apr 2021, 02:26 
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Username Protected wrote:

Why distinguish between props and jets? Why would the formulas for max endurance max range be different between jets vs. props?


If you want to read more about the “why”, download yourself the PDF of Aerodynamics For Naval Aviators. It covers this in glorious fashion.

It's interesting that neither this book nor the Citation 500/501 manual mention minimum sink speed. It was of great importance when I learned to fly gliders. I recall it was a few knots less than best L/D speed.

In a jet, would probably only be useful if you lost all power over water and needed maximum time to prepare for ditching.

According to the Citation 500/501 manual, AOA of 0.6 not only represents best L/D (which should give max power-off glide range), but also optimum approach speed (1.3 times Vso), maximum angle of climb, and max endurance (for those three letter agencies...er, I mean when you are flying a holding pattern).
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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 15 Apr 2021, 09:55 
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Username Protected wrote:
Why distinguish between props and jets? Why would the formulas for max endurance max range be different between jets vs. props?


Please login or Register for a free account via the link in the red bar above to download files.

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 Post subject: Re: Hypermiling a Citation 501
PostPosted: 18 May 2021, 01:48 
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Mike,

If you want Mark's article PM me and ill e/m it to you, it works!

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