I don't think this is a suitable question to post on main, but I'm wondering if anyone in chat has an idea. It seems that private jets almost never cruise above FL450, but why? At this moment my flight tracking website of choice tracks about ten jets at FL450 and none above that.

I first thought it was just one of those things where all manufacturers aim for the same number, much like the cruising is always around mach .82. But then some of the aircraft have their service ceiling listed at 51k feet

Is it a regulatory thing, like oxygen mask requirements?

@Sanchises don't have an answer but to me that's a good question for the main site

@Federico @Jamiec my intention is not to cause another debate, just to provide a talking point for you mods when you talk in private -- the runway friction OP hasn't come back in 2 days since he got a wrong answer in the comments that 'made sense to him', I'm saying wrong becuase I just found the answer and posted it -- so indeed for me guessing has no place in the comments

@Sanchises adding to my reply to your comment: testing those properties have nothing to do with the actual airplane speed, for example if 20 MPH wasn't deemed too slow, it would have been the better speed for the macro testing for the fast aquaplaning

@ymb1 I am a bit careful with inferring things from flight tracking websites as they're notoriously unreliable. But maybe I'll ask on main then, tonight or tomorrow

@Sanchises you can word the question in a way that bypasses the inferring part, e.g.: what typical FLs are flown by bizjets, do they fly at their the service ceiling weight/weather permitting? I've seen a few examples that might suggest otherwise

@ymb1 Interesting! I've just started reading up on tribology and it's a subject full of counterintuitive effects

@Sanchises I updated the answer if you want to clear your comment

I would expect that small deviations are easier to measure at slow speed, but I suppose in this case the high speed actually makes you 'miss' the macro texture and only measure the micro roughness at the asperities ('tops')?

Will do

@Sanchises don't know the exact why, my inner physics-compass agrees with the observation, I didn't think I mixed them -- but here's a starting point: en.wikipedia.org/wiki/Hysteresis

'Hysteresis' was the word used by the FAA AC

They refer to en.m.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis elastic hysteresis. So basically the energy required for the tires to deform around the macro texture, and thus the dissipation due to that effect

now OP's other question, is like me asking you why my computer runs at a cooler speed during a stress test than it did 6 months ago, and I provide you with nothing else -- IMO it's very hard to answer if at all

the ICAO Doc in my answer has lots of information, but without lots of details from OP, it's impossible to reach one conclusion, OP better ask the testing equipment manufacturer

So indeed at high speeds you test the macro texture by measuring the rolling resistance due to elastic hysteresis. Interesting.

yep, i checked that page while researching for the answer -- but didn't want my physics-guessing based on skimming a wiki page leak into the answer

so I just provided the facts which adequately answers OP's question as to why there are two speeds and I added how they arrived at those speeds

@ymb1 no of course. I'm also just guessing here to get some more intuition - I've never really done anything with tribology but i think I'll need it for my PhD research

@ymb1 Yes these are the kind of problems that need detailed experiments to answer - especially as rubber tires have such radically different properties with small temperature differences. I would say vtc as opinion based

@fooot Well I finally built up the courage to post my answer. It’s over on the physics stack if you want to see it prior to my humiliation :) physics.stackexchange.com/a/399817/111581

@ymb1 Nice answer on the friction question. I agree with what you were saying above as to why answers in comments are to be avoided. That’s why I told @Federico I was cool with him deleting my comments on the OP’s other question. He did the same to my comment, which I indicated was obviously not the explanation. He sounded like he was satisfied with my response and moved on. The only reason I even put it in the comment was because the OP asked what I was getting at.

Although there have also been times when I posted an actual answer which turned out to be wrong and the OP accepted it and moved on before anyone else could chime in and point out my errors.

@ymb1 Also, thanks for pointing to that wiki on hysteresis. That would probably be the best explanation as to why when you bounce a rubber ball, each subsequent bounce is not as high as the previous. The reflex doesn’t equal the original deformation.

> there have also been times when I posted an actual answer which turned out to be wrong

@TomMcW been there done that

you could say it's up to the reader to question the validity of something without a reference -- but at least answers can be downvoted, like that recent ATC altitude readout question about the pilot selected altitude

@ymb1 Yeah. I didn’t know about that enhanced mode S thing either. Very interesting

the other answers aren't wrong per se, they are right for certain locales, but they also look hurried and not backed up, a little search would have turned up the mode-s capabilities, and I was glad to find OP finding that because as I read the two answers I knew they missed the ads-b, which I believe I learnt about from av.se from one of DL's answers IIRC

Is that functionality built into ads-b?

oops sorry mode-s

I guess when I was writing about OP's comment on that answer, the mentioned ads-b on that answer leaked in :D

I am pretty sure it was DL, I'll try to find that post -- I remember DL even corrected an answer of mine about that, where one of the envisioned capabilities was to show the controller the route the pilots had programmed in the FMS, and DL said something like it was planned but got scrapped, but that was a long time ago so don't quote me just yet

That skybrary article he linked suffers from a very common phenomena on the internet. Even some reputable periodicals do it. People don’t put a date on what they posted. I’ve read articles that refer to something that occurred “last Wednesday” and have no date on them. So you don’t know if it was actually last Wednesday or ten years ago Wednesday.

Very careless

true

i haven't checked the link though, but I do come across what you describe, even on news articles on the internet

June... June what year?!

@TomMcW here it is: aviation.stackexchange.com/a/29772/14897 and do note that I got my info from the Garmin link! which good thing is still valid:

> Eventually, when the transition to ADS-B is complete, the higher capacity ES datalink will allow controllers to see not only what each aircraft is doing, but what it intends to do. The route you have entered into your navigation system will be broadcast on the ES so controllers and other pilots can see where you intend to fly. With this futuristic technology, the clairvoyant mind-reading that some pilots seem to expect from ATC controllers won’t seem so unrealistic after all.

An NBAA article from 2012 says mode S EHS is required in some European countries

but DL corrected that Garmin info in the comments as you can see

so I changed the wording to maybe one day ...

Hmmm... that’s for ads-b ES. Does that apply to mode S EHS?

¯\_(ツ)_/¯

The stuff I’m looking up isn’t clear on that point.

I'm not sure really

here's the question: Does ES require ADS-B? Or can ES work with normal SSR?

that sums up the confusion right?

Somewhere I read that an advantage is that it’s backwards compatible if that’s what you’re asking? In this Eurocontrol page they show a “basic functionality” But at the bottom of the page there are additional functionalities enabled. One of which is selected altitude

is Enhanced Surveillance the same as Extended Squitter?

@ymb1 I don’t think so