HUD acceleration vector after last patch

[Frederf]

Math isn't my strong suit so all I ask is once it's sorted out :book: you pass it onto us laymen in a simple format.

 

Like;

 

chevron above = going faster

chevron below = slowing down

 

:thumbup:

 

That has to be it. Perhaps if you view the chevrons relative to the horizon instead of relative to the FPM you get some indication of energy. For example if your FPM is 1° down and chevrons are even with FPM (constant velocity) then of course (specific) energy is going down.

 

What would be interesting if the chevrons are calibrated in such a way that constant-energy climbs and descents where the kinetic decrease rate and potential increase rate (decelerating climb) are exactly opposite in magnitude if this will result with the chevrons being equal to the horizon.

 

So for example an acceleration (chevron above FPM) but in a dive (FPM below horizon) could be equal energy (chevron at horizon).

[jojo]

No, because it's not an airliner. So with 30 degrees dive you wouldn't see the horizon anymore.

This is why the reference is the FPM.

[Luzifer]

True, it doesn't mesh with the other HUD videos shown on this forum.

 

Which just means... that oft-quoted p.66 in that document simply does not apply to the Mirage.

[jojo]

It's a starting point. They convert total energy into vertical velocity and then into potential vertical flight path (climb or descent)

For airliners, if the > < are at +10 degrees you can climb at +10 degrees and hold your speed = 1:1 scale.

For fighters you can't do that. The thrust to weight ratio is so high that each time you engage MIL or AB power the > < would jump out of the HUD.

So there is a scale down

 

Test:

Set the plane into stabilized flight: > -O- < and the whole thing on horizon -------> -O- <---------

Don't touch throttle, pull the stick: > < instantly goes below FPM. So everything is fine.

 

But you have the misconception that climbing means losing speed.

It depends on throttle setting. The plane is powerful enough to accelerate into climb. It depends on power setting.

Edited August 27, 2016 by jojo

[Frederf]

I'm still confused. Assuming a constant velocity climb the > < should be above the FPM. Constant velocity, increasing height --> increasing energy.

[jojo]

No. The reference for > < is the FPM.

So for a constant velocity climb at +10 degrees you have > -O- < at +10 degrees.

 

The thing works as expected. No bug here.

The only thing that changed recently was chevrons travel amplitude...

[Azrayen]

jojo, Frederf is confused because the concept of "total energy" is used.

 

All other things being equal, more altitude = more (potential) energy. So he thinks (I guess) that all other things being equal, more altitude = chevrons displayed higher.

 

There is, if I understood correctly, the misconception. The chevrons are not a "total energy gauge" with a fixed scale.

They indicate, in relation to the FPM, wether the longitudinal acceleration is positive (chevrons above FPM) or negative (chevrons below FPM).

With no acceleration (nor decceleration), the chevrons are aligned with the FPM.

 

++

Az'

 

PS: "The thing works as expected. No bug here." => agreed :)

[Sarge55]

jojo, Frederf is confused because the concept of "total energy" is used.

 

All other things being equal, more altitude = more (potential) energy. So he thinks (I guess) that all other things being equal, more altitude = chevrons displayed higher.

 

There is, if I understood correctly, the misconception. The chevrons are not a "total energy gauge" with a fixed scale.

They indicate, in relation to the FPM, wether the longitudinal acceleration is positive (chevrons above FPM) or negative (chevrons below FPM).

With no acceleration (nor decceleration), the chevrons are aligned with the FPM.

 

++

Az'

 

PS: "The thing works as expected. No bug here." => agreed :)

 

This is how I have been understanding the function of the chevrons based on how I understand the manual and in sim flying.

 

(Complete layman WRT aircraft)

[Frederf]

Then don't call them energy carets, call them acceleration carets because that's what they show.

[Azrayen]

Not our choice. It's how they're called IRL. ;)

[bkthunder]

No. The reference for > < is the FPM.

So for a constant velocity climb at +10 degrees you have > -O- < at +10 degrees.

 

The thing works as expected. No bug here.

The only thing that changed recently was chevrons travel amplitude...

 

The point is what you mean by constant velocity. Is it Mach number?

Because for sure, I have the > < above the FPM while in a 20º climb and my indicated airspeed is decreasing.

[Ramsay]

The point is what you mean by constant velocity. Is it Mach number?

AFAIK the 'energy' chevrons display how the total energy is changing

 

E= mgz + 1/2 m v^2

 

so no IAS or mach numbers involved, just total velocity and height.

 

but I'm only reading from p66 though, so perhaps misinterpreting something ?

 

http://www.developpement-durable.gouv.fr/IMG/pdf/hudF.pdf

 

Google translate version

 

Potential gradient:

=============

The potential gradient of information is another major interest of the head up displays; it is one of the basic concepts initially defended by the engineers of French test

(Klopfstein, Wanner, ...).

 

Recall that the potential gradient is indicative quantity derived from the total energy of the plane, obtained by the following calculation:

 

The total energy is:

 

E = mgz + 1/2 mV^2

 

It defines the total height:

 

H= z + V^2 / 2g

 

The derivative provides the total rate of climb:

 

W = dH/dt = Vz + V/g dV/dt

 

Using that Vz = V sin γ, one can define a total slope (or potential) such that W = V sin γt

(Assuming W <V, otherwise the total slope is 90 °: this case exists for the aircraft with a thrust / weight ratio greater than 1; it indicates that the aircraft is capable of climbing to the vertical continuing to accelerate).

 

The total slope is given by:

 

sin γt = sin γ + 1/g dV/dt.

 

The potential slope of the plane corresponds to the slope that can be flown with the current thrust, while maintaining speed.

 

This information is usually presented as an offset to coincide chevron with the wing of the velocity vector when the potential slope is equal to the total slope.

The angular separation between the horizon and the Chevron is directly equal to the potential gradient.

The angular difference between the velocity vector and the chevron represents the difference between the current slope and potential gradient: it appears the path acceleration measured by an accelerometer.

 

Chevron potential slope allows control of the speed and thrust delivered by engines ; it also allows the control of the work of the autothrottle when the airplane is team.

The potential gradient as an aid in steering considerable, especially at low speeds (Stabilization of the approach, resolution of the instability of propulsion, passing thunderstorms, go-around).

 

It is also a safety element in the event of failure during takeoff, since it allows the direct control of the maximum possible slope without the risk of degrading the speed.

 

Edited August 30, 2016 by Ramsay
Add google translation of Potential Gradient, fix typos

[jojo]

The point is what you mean by constant velocity. Is it Mach number?

Because for sure, I have the > < above the FPM while in a 20º climb and my indicated airspeed is decreasing.

 

The HUD displays Calibrated Airspeed (CAS).

https://en.m.wikipedia.org/wiki/Calibrated_airspeed

 

So with the same speed "true speed", the more you climb the lower will be the displayed value, because of lower air density.

[Shadow_1stVFW]

The point is what you mean by constant velocity. Is it Mach number?

Because for sure, I have the > < above the FPM while in a 20º climb and my indicated airspeed is decreasing.

As is expected. A constant angle climb will result in a lowering airspeed. Between air density, temperature and a host of other things. That's why we shift to indicated Mach number after climbing high enough. indicated Mach number increases with altitude as well.

 

It's probably not really what you're looking for, but when you climb out, you need to set an initial climb attitude, 20 degrees by your example, leave the throttle at full military, and then use your nose attitude to maintain a constant airspeed, I use 300 until I intercept 0.75 mach. I use the energy carrots to assist with fine nose attitude adjustment, though you could use airspeed or mach number.

 

Sent from my SAMSUNG-SM-T707A using Tapatalk

[Frederf]

The point is what you mean by constant velocity. Is it Mach number?

Because for sure, I have the > < above the FPM while in a 20º climb and my indicated airspeed is decreasing.

 

Surely the actual number driving the calculation physically is the Vz (velocity, longitudinal component) value held by the INS.

 

I'm sure a blocked pitot system wouldn't affect it while a faulty INS would.

[Azrayen]

energy carrots

:megalol:

 

Thanks Shadow. Now my colleagues look at me with kinda little fear: "what's with him?" :D