Holy thread resurrection Batman!

Jager you are partially correct. At altitude we fly a MACH number, typically about .80 MACH in the B757. A typical cost index is 80 and that normally equates to about .80 MACH depending on the weight of the aircraft and the altitude and temp that you are flying. If the company wants us to fly faster they will assign a higher cost index (say 200) and we will fly faster and burn a bit more gas. Fly a bit slower, say with a cost index of 0 and you will take longer to get there but burn a bit less fuel. At a typical altitude of 35,000 feet (FL350) that will equate to an indicated (KIAS) airspeed of about 260-280 knots. The true airspeed will be about 450-470 knots.

The airplane has no idea what the winds are doing, it is just flying through the air. If the airmass (i.e. winds) are 100 knots on the tail and the true airspeed is 460 knots the aircraft will be doing 560 knots over the ground. If the wind is in the face it will be doing 360 knots over the ground. The groundspeed is the only thing that will change due to the wind.

You can only fly so fast (indicated), so although you may push up the thrust levers to increase your speed into the headwind, you can only go so fast before you hit the zipper or max allowable indicated airspeed. Once that happens you can no longer go any faster and you are at the mercy of the head wind. One thing often associated with the high speed core of the jet stream is turbulence, so you often have to slow down a bit avoid getting into a high speed buffet or overspeed because of the turbulence.

What you are referring to, and in this sense your are correct, is the concept of flying into a headwind you would normally fly a little faster than normal econ or long range cruise airspeed to offset the fact that your groundspeed is lower. Some aircraft have specific charts to adjust the long range cruise speed based on the headwind, another gouge is add 10% of the headwind component to your normal max range or long range cruise airspeed. You could also reduce your airspeed by 10% of a tailwind to maximize your range and minimize the fuel burn with the tailwind.

Most modern transport category aircraft have a flight management system to make all these calculations for us based on the cost index and actual winds.

Skins, the jet stream can absolutely drop down into a big U shape as it moves west to east and does so right in the middle of the country at times. It is usually stronger in the winter months. It moves around and can give you a headwind from FL to MI if the U shape dip moves far enough east.

Last week on my way from SLC to MEM I had 144 knots of wind at FL350 from 293 degrees, right on my tail as I was headed 111 degrees. True airspeed was 467, ground speed was 610, and the KIAS (indicated) was 275. MACH number was .811.

Sometimes we will take less than "direct" or great circle routing to avoid very strong winds, typically though it is easier to adjust the altitude. This morning there was a lot of turbulence over Texas above 30,000 feet so we flew from San Antonio to Phoenix at FL300 (30,000) feet instead of FL380 or FL400 to stay below it. Lots of traffic with people were flying even lower to stay out of the constant light to moderate chop and turbulence. We then flew from PHX to MEM at FL310 instead of FL390 until about OKC where the turbulence subsided and then we climbed to FL350 for the rest of the flight.

Aircraft is a B757, check it out on flight aware if you like, FDX 881. That was me

Anyway, sorry for the long post, guess I just felt like typing tonight. Hope I didn't goober up the explanation too much for folks to read.

quote:

Originally posted by Jager:

quote:

Originally posted by Jager:


That is not technically correct. If it is flying into the wind, it will increase throttles to maintain desired speed. If it is flying with the wind, they throttle back the engines.

There is no 'faster' to it. Commercial airlines are going to maintain a specific speed threshold.

quote:

Jager, to be technically correct, airplanes fly through air and maintain airspeed. They will often adjust their route and/or altitude to find favorable winds that give them better ground speed. They don’t just throttle up to increase speed.

Yes, they will.

Doing 500 KIAS, encounter 150 kt headwind, speed will reduce accordingly to 350 kts ground speed.

Pilot WILL increase throttles to overcome the reduction in speed - of course, observing aircraft design limitations - and more than likely will adjust altitude to avoid the headwind. But no pilot is going to crawl along at 350 kts ground speed unless they are forced to.

What you said - was exactly what I said...

Very few pilots are going to pull the throttles back just because they have a tail wind. Most of the time planes will be flown at a given % power or engine setting with an anticipated airspeed at that throttle setting. That is to say that ground speed is a result of the airspeed; pilots aren’t seeking a ground speed most of the time. It’s unlikely that the pilot will have reserve power that is only used if there’s a headwind. ATC may give time restrictions crossing a fix, or there could be an arrival window at an airport, but that’s not typical.

I fly a piston aircraft so I don’t have the excess power of a turbo jet, but in cruise flight I’m flying wide open throttle from takeoff to the initial segment of the approach. I don’t have any excess power. Power is controlled with the mixture setting- 50-100 degrees lean of peak for my fellow aviators- generally 16-16.5 GPH.

Turbo jets are a different animal, but typically the desired ground speed is faster- cruise settings aren’t going to leave much room to push up the throttles.

quote:

Originally posted by Skins2881:

I don't know the routes planes take but I assume it's generaly a straight line from point to point and it wouldn't say fly to Texas that take a right and heat to MI, or fly from FL to NY then take a left to get to MI. If that's the case I guess I could see a tail wind.

I don't think Hi and Low pressure systems create 150mph winds around the systems, but if that is the case than I guess you could have a storm system blow just about any direction at any given point.

Routing depends on a number of factors; wind is a consideration on long trips, but not so much on shorter trips. Most of my flights are 6+ hours long on each leg, and wind becomes significant over and extended period when range and fuel load are considered.

Short routes are usually dictated by airways, or set route structures that are defined by waypoints and ground based radio stations, as well as GPS naviation. They're seldom straight line. Long routes also use airway structures, but follow a "great circle" route.

If you've ever looked at the map projections that NASA uses when tracking space craft, they appear like big wavy lines, when in fact the craft is tracing a straight line in orbit. It's an example of a great circle route. The shortest distance between two points is a big arc on a map. We fly great circle routes.

Winds in the northern hemisphere, as noted, move from high to low pressure. Due to the earth's rotation, the winds are turned or altered 90 degrees, by coriolis force. Whether the air is rising or falling during that time affects the direction of turn; as viewed from above, high pressure turns clockwise, and low pressure counterclockwise. Pressure systems and air mass movement (parcels of air with the same moisture and temperature properties) determine the position of the jet stream, which typically varies between 100 and 200 knots.

A couple of days ago from 40,000' down to 24,000 over Algeria and the med, I had headwinds in excess of 100 knots. We couldn't climb above or descend below.

Generally turbine aircraft need to fly high for fuel efficiency, despite winds. Aircraft also fly a narrow speed range, so far as cruise airspeed. For oceanic routings normally a constant-mach technique is used, with each aircraft maintaining an assigned mach number and using time to separate the flights. Speed can vary a little, but not much. In the case of this last flight, turbulence made airspeed vary such that our mach number kept bumping close to the "red" range or the mach limits (too fast), and there wasn't a significant amount we could reduce because margins need to be maintained above the "foot" or lower limits (stall, or underspeed). I reduced speed to .81 Mach for a time, and then returned to holding .83. There wasn't a lot of room to work above or below that.

With a slower speed, it meant being exposed to the headwinds longer, with an creased fuel burn. though we didn't ave a lot of room to the buffet margin (overspeed), going much faster than our planned cruise would have meant an increased fuel burn, with a lower reserve on arrival.

You can look at a graphic of global wind movement here:

https://earth.nullschool.net

quote:

Originally posted by ECSquirrel:
mixture setting- 50-100 degrees lean of peak for my fellow aviators- generally 16-16.5 GPH.

I'm curious -- what are you flying? 16 to 16.5 gph running lean of peak, indicates a much thirstier engine than Bonanzas with IO-520 or IO-550. I burn about 15.5 gph, running 25 to 50 degrees rich of peak.

You can do better running lean of peak.

quote:

Originally posted by V-Tail:

quote:

Originally posted by ECSquirrel:
mixture setting- 50-100 degrees lean of peak for my fellow aviators- generally 16-16.5 GPH.

I'm curious -- what are you flying? 16 to 16.5 gph running lean of peak, indicates a much thirstier engine than Bonanzas with IO-520 or IO-550. I burn about 15.5 gph, running 25 to 50 degrees rich of peak.

quote:

Originally posted by sns3guppy:
You can do better running lean of peak.

Turbo Normalized A36. I can pull power back if I choose, but I"m able to maintain 29" of manifold pressure all the way up to class A airspace. The fuel flow is actually lean of peak, but it sounds high because I'm giving up efficiency for speed.

The engine setup is pretty crazy- I'm still learning it. A normal IO550 is setup with 28 GPH on take off and will cruise at peak EGT @ 10K ft at what- 13-14 GPH? At wide open throttle that engine is only making what- 22" of manifold pressure? The TN fuel system is setup well over rich @ 36 GPH on takeoff to maintain a large margin for engine detonation. The turbo system maintains sea level pressure, and the intercooler allows you to push more fuel through the engine (generating more HP) while maintaining comfortably cool CHTs. In cruise in the mid teens the plane is capable of 190 knots true with CHTs in the 360 degrees. I'm chasing an issue with the system right now so I'm little slower than that, but I'll get her dialed in.

quote:

Originally posted by ECSquirrel:

A normal IO550 is setup with 28 GPH on take off and will cruise at peak EGT @ 10K ft at what- 13-14 GPH? At wide open throttle that engine is only making what- 22" of manifold pressure? The TN fuel system is setup well over rich @ 36 GPH on takeoff to maintain a large margin for engine detonation. The turbo system maintains sea level pressure, and the intercooler allows you to push more fuel through the engine (generating more HP) while maintaining comfortably cool CHTs. In cruise in the mid teens the plane is capable of 190 knots true with CHTs in the 360 degrees. I'm chasing an issue with the system right now so I'm little slower than that, but I'll get her dialed in.

A normally aspirated airplane at 10,000' will pull just shy of 20" Hg. Figure 1" per 1000' pressure altitude, with standard pressure sea level at 29.92". Therefore, at 10,000', 19.92" Hg. Slightly higher for ram effect and an efficient inlet.

Turbocharging and turbonormalizing limits the ability to lean, which should be done in accordance with fuel flow tables, especially in aircraft with fuel controllers; the TSIO-520 and 550 series have specific fuel schedules, particularly at higher power settings. Leaning is generally best done at 75% power or less, or in accordance with EGT and CHT.

Use of a single point EGT system is ineffective as cylinders tend to vary considerably, and if leaning close to peak, you may have some cylinders lean of, some rich of, and some close to; at high power settings that can result in detonation. Multi-point injector systems with balanced injectors are a much better bet, especially given the cost of engines.

quote:

Originally posted by sns3guppy:

A normally aspirated airplane at 10,000' will pull just shy of 20" Hg. Figure 1" per 1000' pressure altitude, with standard pressure sea level at 29.92". Therefore, at 10,000', 19.92" Hg. Slightly higher for ram effect and an efficient inlet.

Turbocharging and turbonormalizing limits the ability to lean, which should be done in accordance with fuel flow tables, especially in aircraft with fuel controllers; the TSIO-520 and 550 series have specific fuel schedules, particularly at higher power settings. Leaning is generally best done at 75% power or less, or in accordance with EGT and CHT.

Use of a single point EGT system is ineffective as cylinders tend to vary considerably, and if leaning close to peak, you may have some cylinders lean of, some rich of, and some close to; at high power settings that can result in detonation. Multi-point injector systems with balanced injectors are a much better bet, especially given the cost of engines.

Agree completely. Turbo system is from these guys: http://www.taturbo.com/frames.html The airplane is equipped with Gami injectors and Garmin engine instrumentation. The Garmin isn't as good as some of the other systems out there, but it should be adequate to run the engine safely. The tornado alley system requires an engine monitor and balanced fuel flow across cylinders. Leaning is then performed based on the turbine inlet temperature not the last cylinder to reach peak EGT. We're getting into religion and not science here, but the fuel flow tables that come with a Bonanza don't work for this modified system. I run the engine adequately lean to stay away from peak internal cylinder pressure, and actively monitor CHTs to keep my engine running cool.

Every turbo system is different. I'm running the engine based on recommended operating parameters by the developer of the system, and it's not a rare or unique system. There are thousands of these systems out there on Bonanzas and Cirrus aircraft The SR22 turbo (not the SR22T) run a version of this system. The intercoolers and fuel flow are deliberately set to give adequate detonation margins and to run the engine safely.

The engine isn't a TSIO550. It's an IO550B with a turbo-normalizer. Pressure is not boosted above sea level pressure; it's essentially an engine operating at sea level while at altitude.

I'm familiar with turbonormalization.

723 on a Pgh to Boston trip. IIRC it was a couple hundred MPH tail wind.

quote:

Originally posted by Puckpilot78:

quote:

Originally posted by Jager:

quote:

Originally posted by Jager:


That is not technically correct. If it is flying into the wind, it will increase throttles to maintain desired speed. If it is flying with the wind, they throttle back the engines.

There is no 'faster' to it. Commercial airlines are going to maintain a specific speed threshold.

quote:

Jager, to be technically correct, airplanes fly through air and maintain airspeed. They will often adjust their route and/or altitude to find favorable winds that give them better ground speed. They don’t just throttle up to increase speed.

Yes, they will.

Doing 500 KIAS, encounter 150 kt headwind, speed will reduce accordingly to 350 kts ground speed.

Pilot WILL increase throttles to overcome the reduction in speed - of course, observing aircraft design limitations - and more than likely will adjust altitude to avoid the headwind. But no pilot is going to crawl along at 350 kts ground speed unless they are forced to.

What you said - was exactly what I said...

You're both right, and you're both wrong. Since we're only talking about commercial airlines, the altitude and airspeed windows we operate in at cruise are relatively small. Cruise speed is a result of many factors taken in by the flight planning software dispatchers use to plan the flight. It is always going to be a balance between flight time and fuel burn and dispatchers can bias for one or the other depending on conditions.

All things being equal, when flying into a headwind they usually bias toward flight time to meet the schedule which results in a slightly faster cruise speed but greater fuel burn. Likewise, when flying with a strong tailwind they can slow us down to minimize fuel burn while keeping the schedule because of the higher ground speed. Keep in mind we're talking a spread of 20 to 30 knots here for a 737 or similar airplane, not a huge margin when you're cruising around 450 knots.

And there are plenty of times I've puttered along at 350 knots or less in a 737 into a headwind. Why, because like I said our altitude options are relatively limited. Commercial airliners typically max out at 41,000 feet or less depending on weight, so climbing above the jetstream is basically never an option. Flying below it may get you out of the wind, but jets burn a lot more fuel at low altitude so you could actually end up using more fuel than flying high into the wind. Same with trying to fly around it, the increased distance could take longer and/or burn more gas than a shorter route into it.

You also have to take into account areas of turbulence which are common when there's a strong shear between the jet and the air around it. Again this is all stuff dispatchers look at when planning a flight, and of course there's ATC and airspace issues as well.

One of the best answers so far. The old Northwest Airlines used to go to great lengths to chase favorable winds and avoid turbulence. They had their own highly specialized weather folks who worked full time on these routes and altitudes. The did not want shortcuts and hated it when you had to vector them for traffic.

So for you pilots, Does it "feel" different flying against or with the wind? Like do the planes behave differently? Maybe one way easier than the other?

Unless in turbulence, it doesn't make any difference as far as feel. The wind impacts the amount of fuel burned, and it can cause turbulence when a change in direction or speed occurs, but otherwise, there's no change in feel when flying against a wind or with it.

In fact, in a steady wind condition without turbulence on an approach to land, the airplane will be "crabbed" or pointed into the wind during the approach. When the airport becomes visible (eg, runway lights), they won't be ahead of the airplane, but will appear on the opposite side of the nose as the wind, making it appear as if the airplane is off-course, with the runway off to one side. It may be that the only indications are cockpit displays.

Modern cockpits use screens with displays of instrumentation, and all use one type of wind indicator, or another. It's often just an arrow showing the direction of the wind and the speed, and is calculated by the navigation computers. Without that, one would have to calculate winds by hand, and that's not really done any more.

I still have my "wiz wheel" that was used to figure winds and make corrections to headings. The old school way only told you what the wind was as it was based off of latest navigation fix.
So you plotted your next heading adjustment off what the wind speed and direction was.
One thing about celestial navigation is that you sure stay busy and long flights seem short.

The worst head wing I recall was enroute to Goosebay over the north Atlantic. It as over 110 and our airspeed was 280-290.
Needless to say we had to get out of that by course / altitude adjustment

I've used the E6B over the north atlantic after a nav loss before, but today there's so much data and it's so accurate, and so redundant, and most crews wouldn't have a clue how to use a manual computer or wind-calculator (and don't carry them), it's really not something that's done. Navigators are no longer carried or trained or certified or taught. Oceanic fixes are determined only by GPS/IRS, without celestial reference, and even time, distance, and heading are largely obscured by history.

The fight plans with forecast winds are generally so accurate that once updated with the takeoff time, every fix for the remainder of the flight, over the next six, seven, eight hours, is going to be within two minutes, and every fix will have heading and wind information laid out such that it can be used in the event of a loss of direct nav data (I've used it).

When I enter the flight plan in the FMS/FMC (nav computer), I also enter the forecast winds at several altitudes; the computer can look at what's planned as well as what's actually occurring and get a more accurate model in four dimensions, projected for the entire length of the trip. I typically enter the winds and temperatures for the trip with updates any time there's a 10 degree or 10 knot change in forecast data.

quote:

Originally posted by sns3guppy:

I'm familiar with turbonormalization.

Some of the folks reading this thread are not familiar, and do appreciate the explanation.

Another question for pilots. Does the fuel efficiency correlate directly in headwinds vs tailwinds? Like do you burn xx extra pounds of fuel flying 2 hours into a 100mph headwind, but would save the same xx pounds of fuel flying the 2 hours with the same 100 mph tailwind?

quote:

Originally posted by Xer0:
Another question for pilots. Does the fuel efficiency correlate directly in headwinds vs tailwinds? Like do you burn xx extra pounds of fuel flying 2 hours into a 100mph headwind, but would save the same xx pounds of fuel flying the 2 hours with the same 100 mph tailwind?

Winds aloft have no bearing on fuel efficiency. The fuel burn is a function of altitude and power setting. The only affect is has is that flying a 400 mile trip with a 100 knot headwind means you effectively fly 500 miles. Flying the same trip in reverse with a 100knot tailwind means you really fly 300 miles. Obviously flying 500 miles uses more fuel than flying 300 miles and this is where your extra fuel burn comes in.

There was reference above to navigation when flying with winds.

For the non-pilots, a quick (slightly oversimplified) explanation: the wind vector can be broken down into two components:

1. the tailwind or headwind component, which will increase or decrease the aircraft's ground speed, and
   
   
2. the crosswind component, which determines the correction angle that is applied to the aircraft's heading in order to maintain the desired track over the ground without being blown off course.

Many years ago, I was flying with an examiner, a grizzled old-timer. He was a retired captain (PanAm or TWA, I don't remember which), with something like 40,000 hours according to the local legend, and supposedly held the record for the number of trans-Atlantic crossings.

The purpose of the flight was the two-year renewal of my instructor certificate. The flght was from the Orlando area to Jacksonville. We were trundling along in the clouds. I turned the autopilot on and reached for my E6B (the "whiz wheel" referred to by a previous poster) to calculate the required heading correction for the crosswind component of the wind.

The examiner saw me grab the E6B and said, "You don't need that. Steer four degrees left."

Hmmm . . . OK, he is the examiner and he has pass / fail authority, so I tried it his way. Four degrees left. Son of a gun, the CDI (Course Deviation Indicator) needle stayed centered, we did not move off course.

We landed at Jacksonville and while we were walking in to the FBO building to grab a coffee, I asked him "How did you do that? I know that we were going from high to low pressure, so the correction had to be to the left, but how in the world did you come up with four degrees?"

He laughed and told me the trick that he learned from navigators way back. A formula involving the difference between the barometric pressures at the departure and destination, and the time enroute, a fairly easy formula that you can solve in your head.

I flew with this old-timer four or five times for two-year instructor certificate renewals, and I learned something new each time.

Barry Schiff has a series of three books that ought to be required reading for all pilots, and especially light aircraft pilots (because it's most useful in GA, which requires more actual piloting). They're called The Proficient Pilot (volumes 1-3). I can't recommend them enough.

In the first volume, I think, there's a chapter on pressure pattern navigation which is what your examiner was referring to. Take departure barometric and destination barometric, and you can get a single heading to fly for the course, and it's surprisingly accurate. Why it isn't used or referenced more, I don't know.