Aerobraking landing

[Zaz0]

I don't know if it's already known but I can't continue aerobraking at OB 1.5.4 when I reach ~100 knts at landing, it maintains speed while nose-up and aerobrakes opened.

Edited June 30, 2016 by Zaz0

[david.lind]

+1

1,5,4 beta

[Andrei]

Not intending to start an argument, but is that an issue? 100 knots is quite a significant speed (~185 km/h), and those delta wings produce quite significant lift. So being able to continue holding nose up should be expected. Or did you mean that aircraft will not slow down below 100kts under those conditions?

[Zaz0]

My fault, I wrote "can" instead "can't" at first post, fixed now.

 

I can't continue aerobraking ;) the aircraft do not slow anymore when reached ~100 knots.

[Andrei]

Ah, now makes sense. It's strange indeed then. In addition to lift to keep the nose up, there should still be quite a bit of drag to slow you down.

[nomdeplume]

Any particular conditions you tested this in? I normally push the nose down gently before 100 knots (as I've broken it before by letting it come down on its own, and I believe steering it down yourself is the real technique) but I tried it last night and it came down on its own.

[Davee]

I don't know if it's already known but I can't continue aerobraking at OB 1.5.4 when I reach ~100 knts at landing, it maintains speed while nose-up and aerobrakes opened.

 

Just curious - are you exceeding the 14 degrees max AOA on initial contact with the runway?

[Zaz0]

Just curious - are you exceeding the 14 degrees max AOA on initial contact with the runway?

 

Negative, I landed following markers showed at HUD with the APP mode and maintain nose up condition (without tailstrike)

 

I'll try to replicate (IIRC happens me allways) and link here a video, track or acmi

[stinkx]

I was able to duplicate this independently with 111 knots and a google search led me to this post. Happened in the built in landing quick mission.

[tweet]

The simplest way of looking at slowing a jet on landing is that aerodynamic drag is used via aerobraking to the speed it either loses effectiveness or the nosewheel cannot be kept off the runway. Then mechanical braking (also drag) is used to bring the jet to a full stop. Each is used where it is most effective in normal operations. The way to stop the aircraft in the shortest distance is to lower the nosewheel to the runway after touchdown, extending speed brakes, reduce lift by raising flaps, and stomp on the brakes until anitskid starts cycling. Of course, in a fighter you will also greatly increase the likelihood of blowing tires and/or melting down the brakes/wheels/tires and start a nasty ass fire. But if you have to stop right now...so be it.

 

Most high performance fighter and trainer aircraft that do not use a drag chute use aerobraking. Aero braking is only effective at higher speeds and most jets lack the pitch authority to keep the nosewheel off the runway much below 100 KIAS. The purpose of aerobraking is to slow the jet in the most efficient manner possible without relying on wheel brakes until lower speeds. Most fighters lack powerful wheel braking systems due to the high weight. It is a design tradeoff that allows the weight needed for a massive set of brakes to be used for mission and/or performance enhancements. It takes rather robust brakes to handle the thermal energy produced at high speed. The drag, however, of a big delta wing is very effective at high speeds. So, aerobraking is used when it is mostly effective, above 100 KIAS, and wheel brakes are less effective. The nose is lowered to the runway at 100 KIAS and wheel brakes are applied. The amount of energy from 100 KIAS to taxi speed is a small fraction of what it would have been from say a 155 KIAS touchdown speed. Less massive brakes are needed to dissipate that smaller amount of energy.

 

All of that said, the Mirage shouldn't be able to keep its nose up much below 100 KIAS but if it can then you should notice a distinct reduction in deceleration as the the jet slows. It sounds like everything is about right with the flight model other than the possible excessive nose authority at low speed.

 

The matter of the airbrakes (or speedbrakes?) open should have some effect but they too will lose effectiveness the slower the jet is.

[Azrayen]

tweet, to add to your general considerations (above): :)

 

SOP on M-2000 is no airbrakes on approach/landing (the delta wing is an efficient enough airbrake + the aibrakes kill too much lift during approach already at high AoA)

 

Airbrakes after landing (i.e. wheels on runway) is possible but seldom used, again for not-so-great efficiency at "low" speeds (< 150kt) + possibility of undesirable side-effects on pitch (at a time when you want precise control to avoid tail strike)

 

Airbrakes when aircraft has all 3 gears on the runway is not that effective either.

 

= = = = = =

 

I understand that the carbon-carbon wheel brakes of the M-2000 are quite effective at high temperature. Plus the M-2000 is a lightweight fighter compared to its peers. Both makes me think its wheel-braking is probably better than that of the mean of comparable fighters.

 

= = = = = =

 

Drag chute (or tail hook) on the M-2000 are "emergency" devices. A M-2000 can carry one, or the other, or none (if using Eclair pod). It's all about choice, and relates to the relatively tiny size/weight of the airframe.

[bkthunder]

I bump this with a little more details on the issue:

 

Not only the Mirage will continue to roll indefinitely at 105 kts if the brakes are not used, but even if I slow the airplane down with brakes to e.g. 80kts, and then release the brakes, the aircraft will continue to go at 80 kts forever. So it seems that there is just a total lack of drag at slow speed or when on the runway. I did notice that the engine at idle produces noticeable thrust that makes the aircraft move forward on its own, and I haven't tested how a landing would be with the engine off. Anyway can the marginal idle thrust really make the aircraft maintain 105 kts while aerobraking??

[=OPS=Slider]

Another possible reason why you can't slow down is the engine, which now even on IDLE is pushing you, because if you noticed that, normally on idle fuel flow on the ground should be 14kg/min, now it's 16kg/min, which means there is still a bit of thrust even if your throttle is in IDLE position. When I was on the ground I could easily go above 40 knots "without" thrust ("without" because my throttle was on IDLE but in game it wasn't), then I used brakes so I'm not 100% sure if you can reach 100 knots, but now it's a good time to check this out.

[zerO_crash]

Drag chute (or tail hook) on the M-2000 are "emergency" devices. A M-2000 can carry one, or the other, or none (if using Eclair pod). It's all about choice, and relates to the relatively tiny size/weight of the airframe.

 

I wouldn`t be so sure about that. It would seem that chute is used a fair bit, as it allows to avoid tear and wear on the wheel brakes by trading it in for a chute speed reduction.

 

Take a look here([ame]

[/ame]), at the end, the pilot pulls the white lever (on the left) to open parachute. No emergency or such. In most cases planes have parachutes to use them, or they simply don`t have them. There are some other videos out there where you can see a Mirage 2000 landing with parachute, and I`m fairly sure it´s not for training, as you can imagine using parachute is a theoretical matter, not something you need to practice.
Edited July 13, 2016 by zerO_crash

[Frederf]

The only issue I have with aerobraked landings is that I lose control of pitch decelerating through ~100 knots and smack the tail. I defy anyone to land and hold ~14 AOA using neutral-to-forward stick range until the nose gear falls despite holding the stick all the way back as it happens.

[Davee]

Negative, I landed following markers showed at HUD with the APP mode and maintain nose up condition (without tailstrike)

 

I'll try to replicate (IIRC happens me allways) and link here a video, track or acmi

 

I was able to reproduce your landing . . . . continued right to the end of the runway nose up and speed steady without slowing. Nose never came down despite below 100 knots. The landing was on the numbers at touchdown.

 

Finally had to apply brakes to get the nose down.

[Whirley]

I was able to reproduce your landing . . . . continued right to the end of the runway nose up and speed steady without slowing. Nose never came down despite below 100 knots. The landing was on the numbers at touchdown.

 

Finally had to apply brakes to get the nose down.

 

similar here. Can't seem to slow below 100 knots with only aerobraking.

[Azrayen]

I wouldn`t be so sure about that.

Well, I'm actually :)

Parachute landing is non-standard in FAF.

Simply because it's painful to manage it after if not needed.

Of course, safety first. If in doubt, if problem, if overweight, if... (insert number of degraded conditions) then pull it out.

[zerO_crash]

Well, I'm actually :)

Parachute landing is non-standard in FAF.

Simply because it's painful to manage it after if not needed.

Of course, safety first. If in doubt, if problem, if overweight, if... (insert number of degraded conditions) then pull it out.

 

Gotcha, the videos I`ve seen are mostly non French, guess that explains it.

[Zeus67]

We are aware of your problem but we are waiting until 1.5.4 is stable enough to check for it.