Opinions

[bLizZuE]

I use the airspeed indicator to set my airspeeds.

 

[jhugz]

I’ve never flown a wide body, but basic physics would tend to indicate that’s not true.

“I’ve never flown a widebody but I’m going to give my opinion and tell you that you’re wrong anyway…”

Death, taxes, and Todd from JC.

 

[mikecweb]

I use the airspeed indicator to set my airspeeds.

 

[ppragman]

I’ve never flown a wide body, but basic physics would tend to indicate that’s not true.

@inigo88

I actually think @BobDDuck is probably right on this… wouldn’t a heavier airplane have more induced drag, so if you have a heavier airplane the “peak” velocity you could reach would be lower for a given thrust…

tbh that number is probably only a few knots but I have a feeling that he's right in a "technically correct is the best kind of correct."

doing a little algebra, assuming that while you're in the region where the drag curve is mostly linear (it's not, but this is a good first look at it, that's why we need @inigo88) then at the most speed you'll get for a given power setting, T = D.

so, using alpha 1 and alpha 2 and velocity 1 and velocity 2 we can solve for how these velocities are related. Basically, this shows (if I'm right... and doing public math is dangerous) that the ending velocity will really depend on the angle of attack of the aircraft. So, if you're super heavy, the only way that v2 = v1 is if the angle of attack is the same at all weights.
But again, I refer to the better judgment of the aerodynamicists.

If I'm thinking about this right though if an empty airplane does 250 kts at a given fuel flow (that is a measurement of thrust all else being equal) and the AoA is 5 degrees, and the same fuel flow gives an AoA of 6 degrees at a heavier weight, we should see an airspeed of 228kts.

1 degree AoA change doesn't sound like a lot, but it probably is though... so that would probably correspond to a pretty significant weight change.


now @SlumTodd_Millionaire - if you assume that drag doesn't change enough to matter, I think you're right, because the drag for all weights is constant... this is probably why this seems reasonable and is probably a fantastic rule of thumb.

anyone care to check my work? That was cool - thanks, I learned a different way to think about stuff.

 

[JordanD]

@inigo88

I actually think @BobDDuck is probably right on this… wouldn’t a heavier airplane have more induced drag, so if you have a heavier airplane the “peak” velocity you could reach would be lower for a given thrust…

tbh that number is probably only a few knots but I have a feeling that he's right in a "technically correct is the best kind of correct."View attachment 68819

doing a little algebra, assuming that while you're in the region where the drag curve is mostly linear (it's not, but this is a good first look at it, that's why we need @inigo88) then at the most speed you'll get for a given power setting, T = D.

so, using alpha 1 and alpha 2 and velocity 1 and velocity 2 we can solve for how these velocities are related. Basically, this shows (if I'm right... and doing public math is dangerous) that the ending velocity will really depend on the angle of attack of the aircraft. So, if you're super heavy, the only way that v2 = v1 is if the angle of attack is the same at all weights.
But again, I refer to the better judgment of the aerodynamicists.

If I'm thinking about this right though if an empty airplane does 250 kts at a given fuel flow (that is a measurement of thrust all else being equal) and the AoA is 5 degrees, and the same fuel flow gives an AoA of 6 degrees at a heavier weight, we should see an airspeed of 228kts.

1 degree AoA change doesn't sound like a lot, but it probably is though... so that would probably correspond to a pretty significant weight change.


now @SlumTodd_Millionaire - if you assume that drag doesn't change enough to matter, I think you're right, because the drag for all weights is constant... this is probably why this seems reasonable and is probably a fantastic rule of thumb.

anyone care to check my work? That was cool - thanks, I learned a different way to think about stuff.

I get where you're going, but part of me is like holy crap, you guys are making this way too complicated. If you're slow, add power. And you don't need to treat the thrust like an on/off switch.

 

[ppragman]

I would think that would apply for any engine number you use yeah?

definitely does in turboprop torque land

 

[ppragman]

I get where you're going, but part of me is like holy crap, you guys are making this way too complicated. If you're slow, add power.

I mean, I agree, but also, I like math and can't fly anymore, so this is how I live vicariously through your adventures in aviation, thinking about plane stuff while I procrastinate on my research project lol.

 

[SlumTodd_Millionaire]

So you’re saying a plane that weighs 200k more will have the same fuel flow for the same speed? I mean within the past month I’ve flown at 620k and 360k.

No, I’m saying it changes a negligible amount, so if you know the FF target, you can adjust it a small amount and get the desired speed quite easily. It doesn’t change all that much with a change in weight. With turbofans, and even turbojets, the bigger an engine gets, the more efficient it is. That means those really big engines on those really big airplanes need smaller adjustments than the smaller engines.

I get where you're going, but part of me is like holy crap, you guys are making this way too complicated. If you're slow, add power. And you don't need to treat the thrust like an on/off switch.

Good god, I always found this so annoying. Guy would push the throttles up to some estimated N1, then the speed would be 10 knots too fast, so he’d pull it back some. Then it would be 8 knots too slow, so he’d push it up again. And over and over again until he finally found the right thrust.

Meanwhile, I’d just push it up to the target FF and go back to reading my magazine, knowing I’m within a knot or two without even glancing at the AS.

 

[mikecweb]

No, I’m saying it changes a negligible amount, so if you know the FF target, you can adjust it a small amount and get the desired speed quite easily. It doesn’t change all that much with a change in weight.

I'll try to remember to look, although post peak and recession, I doubt I'll see high weights for awhile.

 

[JordanD]

No, I’m saying it changes a negligible amount, so if you know the FF target, you can adjust it a small amount and get the desired speed quite easily. It doesn’t change all that much with a change in weight. With turbofans, and even turbojets, the bigger an engine gets, the more efficient it is. That means those really big engines on those really big airplanes need smaller adjustments than the smaller engines.



Good god, I always found this so annoying. Guy would push the throttles up to some estimated N1, then the speed would be 10 knots too fast, so he’d pull it back some. Then it would be 8 knots too slow, so he’d push it up again. And over and over again until he finally found the right thrust.

Meanwhile, I’d just push it up to the target FF and go back to reading my magazine, knowing I’m within a knot or two without even glancing at the AS.

I've never been a fuel flow guy, just more of a "whatever gets the job done" type, but I never found it that hard to look at the trend and adjust as needed. It's crazy how many people who fly giant airplanes have a hard time with the concept of inertia.

 

[Stone Cold]

I'll try to remember to look, although post peak and recession, I doubt I'll see high weights for awhile.

If I think of it, I’ll look on my plane over the next few days. Our weights vary greatly like yours. We will see if our freight slows down.

 

[mikecweb]

If I think of it, I’ll look on my plane over the next few days. Or weights vary greatly like yours. We will see if our freight slows down.

Well someone has to fly that postal freight out of Memphis. (don't get me started)

 

[🦈💜]

It's clutter. You're welcome to keep volumes of paper on your side. Everything we do is electronic, no need for paper on the pedestal where it needs to be moved everytime we change a frequency or input something on the center ACARS.

In the case of the 175, it was customary at my previous shop to put the ATIS on top of the printer, and the printed PDC in the center. The top of the printer is bare and blank, seemingly designed for it.

That said, if you're able to do all the stuff you need electronically, and there's no space for paper, then I can see why you wouldn't prefer it.

Personally, I feel that in the left seat we should try not to let our personal preferences become an issue.

 

[Stone Cold]

Well someone has to fly that postal freight out of Memphis. (don't get me started)

Yeah I didn’t understand that one. Glad it’s over and hopefully y’all get back to ‘normal’.

 

[BobDDuck]

@inigo88

I actually think @BobDDuck is probably right on this… wouldn’t a heavier airplane have more induced drag, so if you have a heavier airplane the “peak” velocity you could reach would be lower for a given thrust…

tbh that number is probably only a few knots but I have a feeling that he's right in a "technically correct is the best kind of correct."View attachment 68819

doing a little algebra, assuming that while you're in the region where the drag curve is mostly linear (it's not, but this is a good first look at it, that's why we need @inigo88) then at the most speed you'll get for a given power setting, T = D.

so, using alpha 1 and alpha 2 and velocity 1 and velocity 2 we can solve for how these velocities are related. Basically, this shows (if I'm right... and doing public math is dangerous) that the ending velocity will really depend on the angle of attack of the aircraft. So, if you're super heavy, the only way that v2 = v1 is if the angle of attack is the same at all weights.
But again, I refer to the better judgment of the aerodynamicists.

If I'm thinking about this right though if an empty airplane does 250 kts at a given fuel flow (that is a measurement of thrust all else being equal) and the AoA is 5 degrees, and the same fuel flow gives an AoA of 6 degrees at a heavier weight, we should see an airspeed of 228kts.

1 degree AoA change doesn't sound like a lot, but it probably is though... so that would probably correspond to a pretty significant weight change.

Your math checks out best as I can tell. The one other wrinkle in all of this is that lots of big jets move fuel back and forth into the tail to keep a more constant (and efficient for a given wing) AOA.

 

[🦈💜]

...

Math: Not even once.

 

[ppragman]

Math: Not even once.

Hey, public math is scary!

 

[ppragman]

Your math checks out best as I can tell. The one other wrinkle in all of this is that lots of big jets move fuel back and forth into the tail to keep a more constant (and efficient for a given wing) AOA.

Presumably then for those aircraft Todd should be 100% correct and “fuel flow == airspeed” because the AoA should be constant in cruise…? But only on airplanes like those.

The MD11 does that with a tail tank, I remember learning about that a gazillion years ago when I toured the simulator in ANC as a kid, but I wonder how much of an effect you can get by moving stuff around in the wing tanks? Big jet guys are AoAs that different in level flight from flight to flight?

@inigo88 - bless us with your engineering brain! You probably would have been concerned with stuff like this with your projects at Untitled Spaceship Company?

 

[Beep]

There is no PM side. On the MAX, the engine gauges stay on the CA side. Doesn’t matter who’s PM or PF. And because the engine gauges are on my side, I’m the one who deals with the smaller screen VSD/radar/terrain display. Not your problem when you’re flying, I can back you up as PM just fine.

If you’re flying and I’m PM, your comment on “no point about me referencing N1 gauges” isn’t accurate. As a CA, I’d like the engine gauges inflight to be in the same position each time, every time. Not sure why that’s hard to comprehend.

But watch, a bunch of whiney complainers will get it changed and then “stick it” to the CAs.

Woe be the offended FO. Captain centric airline? You’ve never heard of AA then. The CA there does the before takeoff FA be seated PA.

When I transitioned to the Boeing, on the whiteboard there was a list of 5 things FOs find annoying about CAs. #1 was of course micromanaging. But either #3 or #4 was “CA shows up too early.”

Wow, that took me back, as a VX guy. I don’t see this place being a CA centric airline. The FO I’d actually given a lot of power and responsibility. Much more than at a place like AA.

“ You’ve never heard of AA then. The CA there does the before takeoff FA be seated PA. “

this info will be outdated as of January 3rd.

 

[mikecweb]

Presumably then for those aircraft Todd should be 100% correct and “fuel flow == airspeed” because the AoA should be constant in cruise…? But only on airplanes like those.

The MD11 does that with a tail tank, I remember learning about that a gazillion years ago when I toured the simulator in ANC as a kid, but I wonder how much of an effect you can get by moving stuff around in the wing tanks? Big jet guys are AoAs that different in level flight from flight to flight?

@inigo88 - bless us with your engineering brain! You probably would have been concerned with stuff like this with your projects at Untitled Spaceship Company?

yes, greatly