Range and Endurance lesson

[Skymark]

I'm working on my Instructor rating. I'm wondering how the Range and Endurance lesson is generally taught. I didn't have this lesson when doing my licences 20 years ago. This lesson can be quite involved, determining the correct cruise performance values from the POH charts (ex extrapolating for current temperature, and power setting, and converting TAS to IAS). When doing the PGI my instructor said to use the current conditions of the day when using the charts so the calculated values will be real when you fly the lesson. I have not covered the lesson in flight yet. I'm curious to know how others teach this. So for new students, what did your instructor teach for this lesson and for current instructors, how do you teach this?

[pepsi]

Go to this website that can help you: http://www.studyflight.com/range-and-endurance

[Big Pistons Forever]

Range and Endurance for me exists at two levels, practical and theoretical.

The R & E theoretical Part is the PGI which will explain the concepts with a review of the power required chart to show where Range and Endurance points are and with a review of the POH charts to show how to find the data. In the air the lesson concentrates on finding the actual endurance speed as a way to find it if you needed it but mostly as an introduction to slow flight which is the next lesson

The second part was practical R & E. The concept of Endurance was introduced on the very first lesson when I talked about the importance of knowing the “time in your tanks “. On every flight I do I expect the student to tell me the Endurance we have with the fuel on board based on a training block fuel flow.

Practical range instruction is covered in the navigation lessons.

FWIW I have never flown a light aircraft at the best range speed or at the true maximum endurance speed for real in the 41 years since I got my first license. The only time I have flown those speeds was during flight training exercises.

[NotDirty!]

Do they still teach the experimental method? figure out the minimum power required to maintain alititude - there's your max endurance; note the speed at different power settings to figure out best range?

[Schooner69A]

I'm with BPF: started flying in '57; never flew an aircraft for endurance or range yet...

[lhalliday]

Do they still teach the experimental method? figure out the minimum power required to maintain alititude - there's your max endurance; note the speed at different power settings to figure out best range?

The folks who taught me to fly (Langley Flying School) do. It's not a flight test item, but I found it helpful to understand the airplane's performance and start exploring the flight envelope. When I bought my own plane I did this exercise in one of my "let's get acquainted" flights.

...laura

[NewCommercialPilot]

I'm with BPF: started flying in '57; never flew an aircraft for endurance or range yet...

Not even when the engine tossed a blade on the F-86 at 200 feet in West Germany (1963?)? You didn't try to extend your glide??

[AOW]

I'm with BPF: started flying in '57; never flew an aircraft for endurance or range yet...

Not even when the engine tossed a blade on the F-86 at 200 feet in West Germany (1963?)? You didn't try to extend your glide??

I would assume that with engine trouble at 200 feet in a single, you would want to fly for minimum range to get back onto the ground as close as possible to the runway!

[Skymark]

Thanks all for the feed back. R&E is one of the lessons in the instructor guide, so yes it's still being taught. I know it's one of the things you learn that you'll probably never really use.

Thanks pepsi for the website link, it's nice to see how other's present lessons.

Yes, NotDirty, the experimental method is covered as well as the POH charts. That method seems more straight forward then a lot of charts, math and theory.

[Schooner69A]

"You didn't try to extend the glide...when the engine calved at 200 feet?"

Of course, I did. I immediately relieved the aircraft of several hundred pounds of dead weight thereby allowing it to gain a few more feet in altitude which permitted a slight extension of the impact point. (;>0)

[photofly]

To my mind there's one inportant take-away from the lesson on range and endurance. That is, if you ever find yourself in the air and uncomfortable about your fuel situation, slow down. Best range and best endurance speeds are slower than the range of typical cruising speeds. If that's the only thing a student remembers about that range and endurance lesson ten years after, it has still been a valuable lesson.

[Bede]

What I emphasize during training is to be familiar with the POH. The big difference is between lots of power, and less power. For most cases in the C150.C172, your best range AND endurance, according to the book will be at around 2100 RPM. You're not going to get much more endurance or range trying to reduce the power even more.

The purpose of the demonstration whereby you reduce power until you can't maintain level and add pwr to see the difference in speed is just to reinforce the theory- knowing that best endurance is at min drag.

I also want to second BPF's comment about knowing the endurance for every flight given the fuel load. I do this as well and ask every flight following the walkaround.

[Skymark]

Thanks Bede

[trey kule]

To my mind there's one inportant take-away from the lesson on range and endurance. That is, if you ever find yourself in the air and uncomfortable about your fuel situation, slow down. Best range and best endurance speeds are slower than the range of typical cruising speeds. If that's the only thing a student remembers about that range and endurance lesson ten years after, it has still been a valuable lesson.


Hmmmmmm. So I am cruising along in a 172, and find that I have an unexpected 15 kt headwind, which is making a bit edgy about my fuel...and the solution is to slow down?
Unless you were hammering along at max power,not sure that slowing down is what you want to do.

[ahramin]

Well, let's take a C172S on a 400 nm flight at 74% power giving 118 kts at 6000'. Headwinds of 20 kts forecast so we load 52 USG (42 for the trip plus 10 for a one hour reserve). One hour into the flight we have 41 USG left and we notice the headwind is 35 kts, and we've only covered 80 nm instead of 95 nm as planned. We now have 320 nm to go, and if we keep our present high power cruise, we will have under 2 USG left at destination. At that point you can press on and land with less than 15 minutes fuel (legal but not a good idea), divert or turn back (safe but not what you want), or reduce power and continue. Reducing power to 62% for 109 kts leaves us with just under 4 USG at destination, not great but better. A further power reduction to 54% power giving 103 kts gets us overhead with 4.2 USG which is around 30 minutes of fuel. It adds 50 minutes to the trip, but is probably still faster than a divert and much better than running out of fuel as we get to destination.

Unless you are already flying around under 60% power, speeding up is not going to help you unless the headwind component is over 40 kts.

[photofly]

So I am cruising along in a 172, and find that I have an unexpected 15 kt headwind, which is making a bit edgy about my fuel...and the solution is to slow down?

Yes. It’s unintuitive, which is why it’s an important point to emphasize during the lesson.

There is a rule of thumb that says add half the headwind to the still-air best range airspeed. So in the case of a 15k headwind best range speed might be 7kts faster than the usual 70-whatever knots. That’s still slower than a typical cruise speed. I haven’t any theoretical analysis or justification for that rule to offer.

Regardless, the rule is gravy. The meat is, if you’re tight on fuel, slow down.

The purpose of the demonstration whereby you reduce power until you can't maintain level and add pwr to see the difference in speed is just to reinforce the theory- knowing that best endurance is at min drag.

Oh dear. Best endurance isn’t at minimum drag. Best range is at minimum drag.

In noddy-PPL-land, where propeller efficiency is constant, and thrust power is proportional to fuel flow, it is, anyway.

And, not that it’s in syllabus, but best endurance is found at (Cl^3/2)/Cd |max

[Skymark]

...but best endurance is found at (Cl^3/2)/Cd |max

Can you explain that? What's Cl Cd max ??

[7ECA]

Coefficient of Lift. Coefficient of Drag.

Crack open the FTM and see fig. 2-18 Power/Drag Curves.

[AuxBatOn]

Oh dear. Best endurance isn’t at minimum drag. Best range is at minimum drag.

In noddy-PPL-land, where propeller efficiency is constant, and thrust power is proportional to fuel flow, it is, anyway.

For a propeller aircraft. For a jet aircraft, it's a different story... (min drag = max E)

[photofly]

Because in a simple model of a turbojet, it is thrust, not power, that is proportional to fuel flow.

In both propeller and turbojet, level flight at minimum drag means the minimum amount of thrust is required. For the jet only, that means minimum fuel flow, which means maximum endurance.