How is range increased when flying into a headwind?

[AlwaysReady]

Hi, I got this question and answer from a book but I can't seems to relate into it. Can someone kind enough to explain it in a different word?

How is range increased when flying into a headwind?

Range is increased when flying into a headwind because the best range speed will be a little faster, and the airspeed represents the rate of distance covered. Therefore, range will be increased with a headwind. The increased fuel flow is compensated for by a higher speed, allowing less time en route for the headwind to act.

Thanks a lot..

[Lightning Mate]

After nearly thirty years of flying this is a new one on me!

You learn something every day.

[Mohit_C]

A thread which might be of interest:
http://www.pprune.org/tech-log/69139-technical-questions.html
:ok:

[bingofuel]

I think what the question is asking is why we generally speed up when flying into a headwind and slow down with a tailwind for best range.

[AlwaysReady]

Well, everyday is a learning day for aviators. ;)

Just need affirmative support for what I've been thinking.

Thanks for all the help.

[Heli-Ice]

I think bingofuel hits it on the head.

In my S300C helicopter and some FW I have flown, my range has usually decreased in headwind. If I try and speed these machines up, the fuel burn also goes up and voila, less range.

To me it seems that you are looking at JAA exam questions and IMO they very easily get misunderstood, even by English native speakers.

[Lightning Mate]

To me it seems that you are looking at JAA exam questions and IMO they very easily get misunderstood, even by English native speakers.

Borderdash.........:mad:

Ex-JAA exam question consultant. Bye................

Bye the way,

If you are contemplating a professional licence, then I suggest you speak to professionals. :mad:

Bye again.

[ab33t]

my plane does not seem to do this , maybe Im doing something wrong

[Obs cop]

This question is always a little ambiguous.

In essence it's looking at an understanding of the difference between best endurance speed, best range speed, long range cruise speed and the effects of wind.

Best range speed is generally higher than best endurance speed, and generally with a jet best endurance speed is at minimum drag speed (on the JAA assumption that a jet has constant thrust regardless of airspeed), best range speed is generally faster at 1.32 x min drag speed and then Long Range Cruise speed is generally about 4% faster than best range speed but has about 99% of the range for a given fuel.

If we had a flight of 2 hours with nil headwind at altitude and a speed of 450 kts Tas we would obviously cover 900 miles. Assume also the aircraft burns 1000kg of fuel per hour and so uses 2000kg of fuel.

Add a 100 kt headwind and we suddenly need 2 hours 34 to cover the same distance due to the wind due a groundspeed of only 350 knots. We now need 2566kg of fuel.

If we add 18 knots airspeed (just 4% as JAA exams would indicate is the variation for LRC) then we now cover the ground at 368 knots. This gives us 99% of our range fuel burn wise, however it now only takes 2 hours 26 minutes. Our fuel burn over the journey is now 1010kg per hour due to a 1% penalty for fuel consumption, but we only burn fuel at that rate for 2 hours 26 mins. The fuel burn is thus 2457kg for the same route a saving of 4.25% or 109kg which is a further 6 minutes of flying time of available fuel hence more range if you are fuel limited.

This 8 minute reduction in the time you are exposed to the headwind, actually means that it offsets the 1% increase in fuel burn with a 5% reduction in the amount of time in the air.

The key is that a headwind is a penalty that gets worse the longer you spend in it, however most jet aircraft in particular can fly 4% or 5% faster for only a minimal fuel penalty.

The same basic principle applies to propeller aircraft, in that you get the most benefit range wise by using the faster best range speed flying into a headwind, whereas you get more range by using best endurance speed when flying with a tailwind as you want to get the most time in this "free" groundspeed benefit.

IF I recall correctly,

Obs

[Dick Whittingham]

First, your absolute range available will be less in a headwind

Second, your range loss will not be quite so bad if you increase IAS a touch

Third, this depends on the shape of the drag curve. If you are high and flying at Mcdr then increasing speed will give too sharp a drag rise and screw things up

Fourth, long range cruise, explained above, is a separate but related subject.

Fifth, the same principle applies if gliding for range. Increase speed a touch if gliding into a headwind

Dick

[Heli-Ice]

Lightning Mate

Was it something I said or you just don't love me? :cool:

[fly_antonov]

First, your absolute range available will be less in a headwind

Second, your range loss will not be quite so bad if you increase IAS a touch

Third, this depends on the shape of the drag curve. If you are high and flying at Mcdr then increasing speed will give too sharp a drag rise and screw things up

Fourth, long range cruise, explained above, is a separate but related subject.

Fifth, the same principle applies if gliding for range. Increase speed a touch if gliding into a headwind

Dick


Dick is 100% right.

Headwind never increases your ground nor air range over no wind, in any way.
If that were true, aircraft would try to fly into jetstreams in opposite directions.
Poor wording I shall say.

How is range increased when flying into a headwind? shall be replaced by:
When flying with headwind, how can range be increased?
Answer: by flying slightly faster ...

Ex-JAA exam question consultant. Bye................


You kind of proved the point. If the JAA had not consulted incompetent people like yourself, people would not have had these problems. :ugh:
"Bye the way", did I miss the part where you said that Heli-Ice r*ped you?
Relax, drink some chamomile tea and enjoy life as it is.

[Heli-Ice]

fly antonov

This is excactly what I meant by my posting. I was not trying to slag anyone, just pointing out that in many cases, the JAA exam questions contain poor wording for some reason.

That happens even when people put their whole efforts into things in good faith.

Good point about the jet streams :ok:

[3 Point]

While I agree with the explanations above I like to keep things simple and have often found that this explanation is easy to understand ...

Imagine a light aeroplane with a best range speed of 60Kts, it can hold fuel to fly for one hour, what is it's range in still air? Answer 60Nm (not a triumph of modern design I know but, just imagine!)

Now, fly that aeroplane into a headwind of 30Kts, what is its groundspeed? 30Kts! it still has fuel for one hour but, at 30Kts it will only go 30 Nm ergo headwind reduces range.

Now imagine it finds a headwind of 60 Kts, its groundspeed becomes zero and so consequently it will burn up all its fuel and get nowhere, how can we make forward progress?

Lets say we speed up to 90Kts and lets imagine that at this higher airspeed we burn more fuel per minute such that the fuel tanks are empty in 40 minutes. At 90 Kts we are making 30Kts groundspeed into our 60Kt headwind so, even though our flight will only last 40 minutes instead of 1 hour we will make better progress into the wind because we have 30Kts of groundspeed. 30Kts for 40 minutes is 20 Nm; far less than in still air but far more than plugging away at 60Kts against the headwind.

So, with a headwind we have increased our range by flying faster even though the increased fuel consumption (per minute) means the flight will last less time. Same principle with different numbers applies to any aeroplane flying into a headwind.

Happy landings!

[Obs cop]

3 Point,

You have my congratulations on the most simple and straightforward answer to a question many struggle with.

I take my hat off to you,

Regards,
Obs

[Tinstaafl]

Before answering this question you need to know the starting speed. Is the aircraft flying at normal or high speed cruise airspeeds, or at best range speed? If at best range speed then the answer is to increase speed by a small amount. If at typical or high speed cruise then the answer would be to reduce speed (unless in some *very* fast headwind)

It all depends on the reference point.

[Nine_Inch__Wings]

And lightning, you come across as a real ****. hahaha. Learn a bit of netiquette.

And 3 point has a wonderful way of explaining. top-notch :ok:

[Dick Whittingham]

Tinstaafl

With respect, I think everyone on this thread has accepted that the question relates to 1) flying at best range speed and 2) encountering a headwind and 3) deciding on the best course of action to maintain optimum range performance.

Of course, if you are flying initially at speeds other than best range and your aim is to finish up in a headwind at some other speed than the optimum for range in those conditions this introduces a host of "ifs" and "buts" - all of which would need defining before an answer could be found. Even your own assertion is only partially true unless you state your starting assumptions more precisely.

If the thread wanders off into cruise management, cost indexes and aircraft operating rules then we will have opened up a can of worms worth a new thread on Tech Log. I think the original query has been adequately covered

Dick

[Pugilistic Animus]

how is range increased in a HW? simple! by turning it into a tail wind:ouch::}

[Tinstaafl]

G'day Dick,

I realise everyone commenting in this thread would assume the starting point is at or near best range speed but the way the discussion was going wasn't so clear for other readers not as familiar with the topic. 'Increasing speed' as a simple answer is wrong if the aircraft is already at typical cruise speeds ie significantly above best range speed.

[potatowings]

Guys, this is a very simple question and if you follow this principle it works for all machines from Gliders to 747's.

follow the stops below

1. draw your typical drag curve graph
2. draw a tangent to that drag curve that starts at the origin (ie where the x and y axis cross)
That's your STILL AIR best range speed.

now...

3. move the tangent line "forward" by 20 knots (ie. to the right of the x axis) to represent a 20 knot headwind. Notice how the best range speed now touches the drag curve at a higher speed, therefore best range speed is a little higher.

4. Now do the reverse to represent a tailwind. Notice how the best range speed is less.

Simple rule of thumb... fly a little faster to get out of the headwind quicker, it aint helping you!

Fly a tiny bit slower to stay in the tailwind longer, it is helping you!

In theory this is practical and from my days on the straight winged props it did make a measurable difference.

In a swept wing jet where the drag curve is very shallow anyway and the fuel consumption is marginally different.... in my experience/opinion, the difference is very hard to measure unless you are on a 7 or 8 hour flight, but even then so many other factors come into play.

I like this question because it does have some practical application, even if it is limited, but it really tests you knowledge of the drag curve.

Remember though, if you are flying significantly above your best range speed, ie high speed, all this doesn't matter as you might be getting close to your Mmo and as such compressibility comes into play and the theory is shot. This is a max range theory question.

[demomonkey]

Lightning Mate wrote:
Borderdash.........http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/censored.gif

Ex-JAA exam question consultant. Bye................

Bye the way,

If you are contemplating a professional licence, then I suggest you speak to professionals. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/censored.gif

Bye again.

I think you mean 'by the way'. What was the point you were making about JAA not being able to construct questions in clear English? U r a level 1 spooker write? Have you thought about speaking to a professional? :E