Foresthouse wrote:
This is not correct. The braking distance is function of speed and mass.Braking distance = 1/2 * mass x speed squared / braking force
So if your mass is doubled (and the braking force and speed remains the same) then your braking distance will double.
Your formular is correct, your statement is not!
The “trick” is, that “braking force” (to be more precise: Maximum braking force with non blocked tires) is also a function of mass:
B_F= Mu_f * F_N = Mu_f*mass*g
with g= 9.81 m/s^2; and Mu_f being the friction coefficient of the tire/concrete system.
Therefore your formula becomes:
Bs= 1/2 * mass * V^2 / (Mu_f * mass * g) = 1/2 * v^2 / (Mu_f * g)
As you can see: Not depending on the mass.
To explain it physically: The maximum braking force you can apply increases when you add weight by the same amount as force required to have the same deceleration increases.
The above is true but one need to add a caveat, only those who fly on tundra tires can afford use of wheel breaks near VS !
Aircraft, unlike car will also have “breaking force” reduced by lift and increased by drag (which is proportional to weight) at high speeds, so you have to look at the D/L drag-to-lift ratio as well as the T/N firction-to-normal ratio, there is also some funky non-linear breaking from entering boundary layer and gusts on low wing load in ground effect
The impact of weight is far from intuitive,
- It impact approach ground speed (via stall speed increase and Vref increase)
- It impact flare length (via wing load as in boundary layer ground effect due to solid/fluid non-stationary oscillations)
- It impact ground roll before you wheel break (via lift/drag at high speeds and via friction/normal as slow speeds)
- It impact ground roll after you wheel break (see as explained by Malibuflyer)
- It may impact breaking efficiency (when breaks melt or solid/solid hysteresis)
Overall an increase in weight will increase your ground roll but the dominant factor is the first one (if you can approach at 0GS breaks and weight are irrelevant 
)
Finally, the funny bit do you apply breaks differently depending on weight & remaining lift or ground friction? you better do
Do you raise flaps before applying breaks and why?
Hi everyone,
As with any crash, we should not take shortcuts to reach conclusions.
As an aviation educated crowd, we know or should know better. I happen to know all facts on this accident which makes reading some comments painful.
The aircraft French registration was recent…Does this mean the pilot just got the aircraft? In this case, the answer is no so comment 2 is irrelevant.
Making fun of a detail such as the company name when someone died feels disrespectful. Is this Facebook now?
The owner pilot killed his father and has been living with this guilt since.
I feel for him and his family as we all should.
By an odd coincidence I saw the remains of this aircraft just recently. The guy at Toussus who reassembled my plane has a speciality of rebuilding wrecked PA46s, and he bought the remains. It’s in a corner of his hangar, along with several others in various states of brokenness. He told me the sad story of the crash. He has another one that met its end at Courchevel too. I’ve seen planes operate there, many years ago, but never tried it myself. Based on statistics, it sounds pretty scary. Maybe easier in a Cub than a PA46…
@davidfabry which comments are you referring to? Nothing notable posted recently.
If you have further info, you could perhaps post it so we could all learn from it.
I think David is pointing towards the early comments posted. Seems the aircraft was owned by the accident pilot since november 2020, from searching the internet. Unclear to how familiar he was with Courchevel.
That is not what he said “ Does this mean the pilot just got the aircraft? In this case, the answer is no so comment 2 is irrelevant.”
I happen to know all facts on this accident which makes reading some comments painful.
“I happed to know but I won’t tell you.” How useful is that?
@davidfabry does have a point that some of the posts in this thread do not reflect the usual high standard of respect in this forum.
OTOH it is normal to infer the aircraft was freshly acquired as the registration was recent.
Some of us, as current, past or would be altiport users, are particularly interested in the technicalities of this accident. This may or may not be linked to personal aspects, but since there was a fatality, and the pilot is alive, I agree we should strive to maintain high correctness in this public forum.
Having said that, most of the inaccurate posts were published early on in the thread and it has recently remained quite technical and civilized.
@davidfabry anything you can add to enlighten us as to what happened and assist us in staying away from such occurrences is appreciated. We would understand that if you have some personal involvement you had rather be cautious.
Thanks
Antonio
Malibuflyer wrote:
The main challenge is that deviations from perfect landing technique (which we always do) have a much higher impact than in slower/lighter aircrafts.
Exactly, and so much more at an altiport than elsewhere
