Outstanding!!!
As usual, Tarver's Citation Revival Spa did not disappoint!

Mike -

You know that there is no replacement for displacement!

...and I know you will correct me about jet engines not having displacement and have some fancy saying like "In Thrust we Trust!"

Thanks for the free lessons on BT!

A friend with an ultra said it has been so hot on recent trips he wasn’t able to get up FL450.

If that happens in Ultra, how often does it happen in the V mile? Seems like the big range numbers are only possible up there, right?

Hotter than ISA+10?

The climb chart says no step climb at MGTOW to FL450 even at ISA+10, though it just barely makes that. Maybe their plane is underperforming for some reason?


I've not gone to FL450 yet, mission didn't require it so far, but my climb rate at FL430 has been decent, 400-500 FPM even in ISA+5. My AOA wasn't over about 0.28 or so, where 0.35 is max climb, so I had some margin. I felt like I could go to FL450 decently. My weight has been below MGTOW some, though, which is less than the Ultra.


Well, not exactly. Getting the most range is somewhat complex.

One issue is that doing a direct climb to FL450, even if the chart says so, might not be a good idea. You will end up slow and at high AOA and it will take a LONG time to reach cruise speed. Like 15 minutes in some cases, it seems excruciating. So you are better off leveling a bit lower, keeping the speed and increasing it in level flight a bit, then step climb up to the next level. This is particularly true in a headwind, which is exactly when you want to extend your range.

The fuel specifics at FL410 and FL430 are not that much worse than FL450 since you are going faster. Again, in a headwind it helps to go faster.

The real trick to long range is to operate at less than max cruise thrust (MCT). Get to altitude quick, accelerate, then reduce throttle to long range cruise (LRC). This changes with headwind component and with weight, so it takes a bit of monitoring. What this means is that you will be generally faster and lower at the start, and end up higher and slower at the end of the leg.

Another factor is headwind versus altitude. When you start to get into the 40s, headwinds can start to decrease. For example, the headwind at FL410 might be 100 knots and FL450 might be 60 knots. Then it makes a lot of sense to get to FL450 as quickly as you can. Other times, the wind gradient is not as favorable.

Another factor is routing. The upper level winds can be such that a non direct route can reduce your headwind component substantially particularly on a long flight where being off course 150 miles is very little distance. I've done that a few times where 3% more distance yielded 10% more speed.

In the tailwind case, you usually have all the range you need and thus optimizations are not needed, but if you are trying to fly across the country, then you find the fastest wind core and throttle back to ride the winds.

Here is an example (Ultra, FL430) of the power setting guidance in the manual for maximal range:

Thrust is approximately proportional to the square of N1 speed. As the tailwind increases, go slower, as headwind increases, go faster. As weight declines, go slower.

Finally, being able to climb quickly and descend late help a lot. A KDFW to KJFK flight is simply not going to get the range you can do with a flight from rural areas. Also, good weather helps to reduce the need for alternate fuel.

As you can see, lots of factors. This is how one operator, FL350, MCT, urban airports, says the plane can only do 1200 nm, and another operator, FL450, LRC, rural airports, can say it goes 1800 nm, and it is the same plane.

Mike C.

I think he mentioned it was warmer than IsA +15, so pretty warm!

I am surprised no one has made a route planner to surf winds for best times and best speeds. I do what you described quite a bit. Amazing how well it can work out if you are doing long legs.

In the 40s so far, I haven't experienced over ISA+7. This is even flying out of Florida on really hot days.

Maybe out west there is ISA+15?

When temps are really hot, your true altitude is higher and your fuel flow is lower, so flying lower flight level is not as bad as it sounds. FL450 on ISA+15 could be 47,000 ft high.


The airlines do this.

Also, the North Atlantic Track (NAT) system does this every day.

I just do it with looking at winds aloft on skyvector.com, and then playing with routes on fltplan.com for best times. It is a bit hit or miss, but works well enough. It tends to works best when there are concentrated high speed winds in the winter, and not as well with broader slower winds in the summer.

Mike C.

That's the thing about writing a dissertation....there's always more that can be said.

I think foreflight does this. On one trip it suggested going 500 miles north of a direct route. Added 100 miles but kept me out of a stiff headwind with a crosswind-tailwind instead.

I think foreflight does this. On one trip it suggested going 500 miles north of a direct route. Added 100 miles but kept me out of a stiff headwind with a crosswind-tailwind instead.

When you click the Routes button it’ll give a suggested route. I believe that is wind optimized.

When you click the Routes button it’ll give a suggested route. I believe that is wind optimized.

And it's a lot of fun continuously explaining to ATC that you don't want to accept their rerouting

Really wish there was a way to put in your flightplan notes that you have a reason to be flying your filed route that they will actually acknowledge

As you get further from the equator (and closer to the poles) the troposhere thins and you hit the tropopause lower. There is typically a temperature inversion in the tropopause. It's not uncommon to see ISA+15 in the upper 30s and lower 40s in the higher latitudes (such as north Atlantic routes).

This counts as my best new thing I learned today.

I will keep that in mind when flying at higher latitudes.

Mike C.

Reminds me of Mike Tyson's face tattoo.