WSH wrote:
I'm reviving this thread because there seems to be a common misconception that "speeding up" into a headwind will increase your range.

Increasing your speed into a headwind to maximize range will ONLY work if your already starting from your best range speed, I.E. L/D max or "Best Glide". For example: that's 80 MPH (IAS) at max Gross in my 182. I don't know many who plan a XC going 80 MPH in a 182.

So, you must SLOW down in a headwind, from "normal" cruising speeds, to extend your range. If you must continue to slow even further to make your destination, you need to re-dispatch as you approach your new "best range" speed or if you will be going so slow that making an extra fuel stop(if possible) and losing an hour+/- makes sense and would be the better(faster) option in the long run.

We know that slowing down to Vbr (or even Vbe) will give us better range in still air than in our "normal" cruise profile. But we are discussing advantages and disadvantages between relative airspeeds in the typical cruise range, not the perfect target airspeed or horsepower settings off near one end or the other of the curve. Given the non-linear relationship between aircraft performance and fuel burn, better range/more miles can be achieved at a higher TAS relative to some other TAS which might be better for fuel endurance/time at many places in the tangle of computed and plotted compound graph curves.

A perfect example: Why is Vbr faster than Vbe in most (if not all) fixed wing GA aircraft? Think about it.

Look, if there is any doubt, do this: calculate the range of your aircraft flying at Vbr or Vbe in a headwind component that exceeds either of those speeds

It is not an inconsequential point to consider that if your trip is of fixed distance and you have enough fuel to reach it at any speed then this is strictly academic. Dealer's choice as to whether you want to save money or time

WSH wrote:ROT for headwind, add half of the wind velocity to Vbg.

By the way, if that is true, why wouldn't it also be true at any speed?

kevbert wrote:If you've got zero thrust, then headwind or tailwind doesn't mean a thing. Headwind or tailwind is relative to the ground. Your plane doesn't interact with the ground if your wheels aren't touching it. The plane's indicated airspeed is all that will matter, and the plane's Vbg is your best glide speed, whether the wind is blowing or not.

If best glide is 90 mph and you are in a 90 mph headwind, then it seams prudent to at least glide at better than 90 mph to make forward progress.

Tim

Deleted

qmdv wrote:If best glide is 90 mph and you are in a 90 mph headwind, then it seams prudent to at least glide at better than 90 mph to make forward progress.

Tim

Yeah, but it will look a lot cooler on the youtube video when you slowly descend straight down like a hellachopper in the 90 mph wind and gently set it on the ground with no forward motion!

Seems like a who's on first and what's on second thread....With proper planning, you shouldn't run out of gas.

Bonaza man, your 182 comments caught my eye...were you running a 470 or 520 in the 182's that went 150-160 plus knots? Just seems fast...150-160 cruise seems more like a 206. Cruise with the 260SE in the 182 Katmai conversion only gets you 153 knots and the standard with the 470 gets you 130 knts. Granted, my POH says 130 but thats in a zero wind environment. It also states I need just over a 1000 feet to get over a 50ft obstacle....honestly with the mods I am getting off and over in around 600 feet. Low Rider (180) and I (182) challenge each other daily and the 182 is getting the same spec. He just turns around better.

I have been flying a 182 for over a decade. Never have I seen a 182 go that fast unless your full power-on going downhill with the small tires and mexican hub caps.

This is a backcountry forum. Isn't everyone trying to go slower anyway? No need to be in a hurry. Thats over on the Citation forum. If I am going CX with my 29's I can get 110-115 on a calm day.

[/b]Richard,

once&futr_alaskaflyer wrote:

tcj wrote:

And that leads to my question: How *much* should you increase your fuel burn in a headwind to achieve maximum miles per gallon?

kevbert

Thats a very interesting question. I'd like to know more about this so I'll bite and all youall can correct me.

Increase the throttle a lot in a head wind for maximum miles per gallon. My reasoning is it's like the trick question "How much fuel is needed to make a round trip when there is a constant speed wind giving you a tail wind going and head wind coming back?" You can't just use the no wind fuel required answer because you are in the head wind longer than you are in the tail wind. So, seems logical like you found out to spend as little time as possible in the head wind. There's probably a point near full throttle where you run in to diminishing returns though. How's that?

The fuel burn vs airspeed curve is a parabolic curve. As long as the airplane is flown over the relatively flat portion of the curve fuel consumption is not greatly affected by flying faster than the max range airspeed. But as you say, as you increase horsepower there is a point where there are increasingly diminishing returns and then probably negative returns. On the other hand decreasing your speed allows for the wind to have a longer effect on your airplane's ground speed because your trip is longer.

Mathematically, I would think that marginally increasing your speed over what your "normal" cruise speed would be is the most efficient operation in a headwind. What is "marginal"? Well, you would have to calculate where the flat portion of the curve exists for your conditions and then set your speed to the fast end of the flat portion Could there ever be a rule of thumb? Don't know. I would think that if you normally putter along at 45-65% power in cruise like I do, increasing your TAS in a headwind by a few knots is more efficient than doing nothing or pulling power back even more. But increase power too much and you will fall down the backside of the curve. Need more slide rules and better instrumentation in the panel than I currently possess to get any better than that.

Your mistaken, your "thinking" is just not true. Anytime you increase your airspeed in a headwind from "normal" cruise speeds, even just a little, efficiency/range goes DOWN.

Of course you can create some unrealistic headwind component that will flip the equation around for a mathematical "gatch'ya". However, as a practical matter, in the real world, you would slow down from normal cruise speeds in a headwind to increase efficiency and reserves available to make your destination.

Anyone who has a GPS integrated with a Fuel Flow gauge can see the results. Speeding up into a headwind, from anywhere reasonably above Vbg, hurts range and efficiency. It's that simple.

It seems simple when you continue to insist on speaking about endurance and range and the associated best speeds for each as if they are the same thing. Of course, they aren't and it ain't simple.

Can you calculate exactly where the equation flips in my tongue in cheek example? Is it at HW=TAS? 0.5 x HW=TAS? Where?

I'm not an engineer nor did I play one on TV but I know that if you disregard the time spent in a headwind condition as a variable when calculating range, along with your other variables, your output will be off.

Good discusssion btw

once&futr_alaskaflyer wrote:It seems simple when you continue to insist on speaking about endurance and range and the associated best speeds for each as if they are the same thing. Of course, they aren't and it ain't simple.

I don't know why you think I am "insisting" on associating the two as if they are one, that is not my intent? I guess I need to work on my delivery. When I speak of "efficiency" in this context, I mean more MPG, not endurance. Is that "simple" enough?

For "Best Endurance" one needs to be as near to sea level as possible, to optimize engine performance, and the lowest BSFC to maintain level flight. As we slow from Vbr to Vbe and the minimum speed required for level flight, to somewhere just above stall, induced drag goes up and range goes down.

We'll save the "behind the power curve, increased drag" debate for another thread!

Can you calculate exactly where the equation flips in my tongue in cheek example? Is it at HW=TAS? 0.5 x HW=TAS? Where?

I'm not an engineer nor did I play one on TV but I know that if you disregard the time spent in a headwind condition as a variable when calculating range, along with your other variables, your output will be off

Here is what I think I know.

For "Best Range" with NO wind we need two things to occur. We need the lowest drag for the airframe and the best BSFC for the engine. For the lowest drag, we use L/D Max. The best BSFC is found somewhere around 10-20 df Lean of Peak along with the most efficient propeller RPM. In reality, Mp and RPM's don't matter when LOP, it's only the fuel flow that is needed to calculate the % of power but many who are not familiar with LOP ops find it useful to think in terms of MP and RPM's.

So, starting from Vbr, when we encounter a HW, we increase speed to reduce the time spent fighting against it. OK, that makes sense and is in complete agreement with the conventional wisdom "that you should increase your speed into a HW to increase the range". I think most of us were taught that and it's true, some of the time. Now where things go south, at some point the increasingly higher BSFC needed to overcome the increasing HW's and rising total drag from increased speed, reaches a tipping point. And, the advantage realized from reducing the time spent in increasing HW, is lost and/or is offset by the higher BSFC required to combat the HW's and increasing total drag. And, predictably, range begins to suffer.

Exactly where that "tipping" point is and range begins to decline? I'm not sure, I just know from personal experience it's well below normal cruise. I've never actually found it because I've always reached the point where it just makes more sense to stop and get fuel than continuing to slow any further to increase my landing reserves. My very uneducated WAG is possibly somewhere around the "Carson Cruise" (1.316* L/D Max) and maybe combined with some % of the HW component. Carson Cruise for my 182 is 105 MPH, which is only 25 MPH over Vbr, with my normal cruise being @155 MPH. So rarely, in fact I think never, have I slowed down 50 MPH to make my destination. For those who don't know Carson, he was a Naval Aviator/Professor who crunched the numbers and came up with what is, at least in his opinion, the most efficient speed to fly. Here are some links,

From Carson, his ownself.

http://cafefoundation.org/v2/pdf_tech/M ... Carson.pdf

An addendum from a colleague:

http://www.nar-associates.com/technical ... screen.pdf


The "Readers Digest" version:

http://www.eaa1000.av.org/technicl/perf ... rfspds.htm


And lastly, Peter Garrisons opinion:

http://www.flyingmag.com/very-best-speed-fly


Hope this helps explain my position and clears up at least some of the confusion.

BTW: There will be a pop quiz in the morning!

There are lots of views about headwinds and tailwinds, but whatever your preferences are, going faster (airspeed) into a headwind and slower (airspeed) with a tailwind makes sense. Simplest case is best glide if an engine quits--add about 1/3 of the wind speed and you'll go further. Try it sometime on final on a (head)windy day--you'll see better penetration if you add some airspeed over still-air best glide. Glider pilots are intimately aware of this. I now have a fuel flow meter and I saw my "remaining gallons" go up as I went from 8.5 gallons per hour to 10.0 gallons per hour because I "penetrated" the wind. Less time aloft is less time the wind is carrying you the wrong way.