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[CORRECT AS IS] Braking effectiveness


yogipol

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Of course 1st striped white lines or before.

 

As far as I remember all performance calculations for landing according to the civil aviation rules is to be at 50ft over the runway threshold...I don't know how IT works with army, but I do still believe real Hornet does better with braking then the one we have in DCS. Just my two cents

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Is the approach speed of 125 knots the speed for 39000 pounds? I'm sure 39k pounds is structural limit not field limit to perform safe landing in your case.

125kts = 27500lbs

149kts = 39000lbs

 

@yogipol, if you compare RW performance data with the actcual landing roll you will see that the DCS F/A-18 needs a lot more runway than it should.

Btw, no need to be 50ft above the threshold and at e.g. St.Maarten even civil planes are way lower over the threshold ;)


Edited by bbrz

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That depends a lot on the plane and it's e.g. not required, (not even recommended) on the F-5 when trying to achieve the minimum landing run. It's just a note that braking is more effective with the flaps up.

 

In the F-86 manual I didn't read anything about raising the flaps either. Neither on the F nor the K. Interestingly the F-86 manual mentions that opening the canopy will increase drag and help shorten the landing distance.

 

In general you are trying to avoid any distraction during the landing run, and fiddling head down with levers and knobs after touchdown is usually to be avoided as much as possible.

 

Quite a few flights ended with the plane sitting on the runway with the gear up instead of the flaps up with this technique ;)

 

Back to the F/A-18:

 

With the very large boards hanging down I doubt that retracting the flaps would put more weight on wheels than they create drag.

Furthermore this isn't mentioned in the -1 when shooting for a minimum landing run.

 

According to the -1 the landing roll should be ~2600ft at 30000lbs.

 

With antiskid I need 4000ft and without antiskid (and the associated directional control problems) even a bit less!

 

Antiskid braking is apparently way too weak.

 

Regardless flaps add lift not drag, that’s what they are there for. Reasoning that keeping them lowered helps slow you down is wrong. If anything they increase stopping distance because they reduce brake effectiveness. Not that it really makes a difference in the hornet, but flaps are flaps, not speed brakes.

 

Fact is the hornet has a long ground roll in general because it’s meant for trapping not landing. The tires specifically are way more inflated then ground based aircraft, the brakes aren’t suited for long sustained applications, and it’s directional instability in cross winds makes aerobraking risky. It’s just built for the boat not the field.

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Regardless flaps add lift not drag, that’s what they are there for. Reasoning that keeping them lowered helps slow you down is wrong. If anything they increase stopping distance because they reduce brake effectiveness. Not that it really makes a difference in the hornet, but flaps are flaps, not speed brakes.

You clearly don't know what you are talking about. The first 5-15deg they usually considerable increase lift and only a little drag, anything more and they add much more drag than lift.

 

The reason why flaps usually extend more than e.g. 15deg is that you want to increase drag so that you can keep a higher power setting on approach and speed stability is also higher.

 

The ground roll is rather long, confirmed, but not as long as presently in the DCS F/A-18 ;)

 

Btw, if your flap drag theory would be correct, all Hawker bizjets would have serious design flaw, since they extend the flaps to much greater angle after touchdown to reduce the landing roll due to the increased drag.


Edited by bbrz

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You clearly don't know what you are talking about. The first 5-15deg they usually considerable increase lift and only a little drag, anything more and they add much more drag than lift.

 

The reason why flaps usually extend more than e.g. 15deg is that you want to increase drag so that you can keep a higher power setting on approach and speed stability is also higher.

 

The ground roll is rather long, confirmed, but not as long as presently in the DCS F/A-18 ;)

 

Interesting, that must be why they’re called high lift devices, because they add drag.

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Interesting, that must be why they’re called high lift devices, because they add drag.

Increasing lift without increasing drag? Are you rewriting basic physics and aerodynamics? :lol:

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Increasing lift without increasing drag? Are you rewriting basic physics and aerodynamics? :lol:

 

Maybe we shouldn't use them on cat shots then, if they add so much drag. There also appears to be a problem with the FCS because every time I get slow the flaps come out, if they add drag that could be really dangerous too.

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@bbrz is right about using flaps and drag to lift ratio using different flaps setting, just to give you basic idea about ground roll on B737 using flaps 30 and 40, have a look at the diagrams below.

 

The higher flap setting, the shorter ground roll is.

 

https://drive.google.com/file/d/1qUclyue7nt0wWSA7Y-4puMLEE1gANipp/view?usp=drivesdk

 

 

https://drive.google.com/file/d/1HObelWPvUc1leD30rzZVnUGzsYPp5xRw/view?usp=drivesdk

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To get back to my original question. I would really like to know why ED puts this into the wish list instead of the bug section.

 

The landing roll is more than 50% longer than it should be, so I'm curious why this is considered to be correct?

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No they increase lift, with flaps up the wings create more downforce, putting more pressure on the tires thus making the braking more effective.

 

Sorry, I should have said flaps increase parasitic and induced drag as well as lift. I can't say whether this is modeled in DCS or not.

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  • 2 weeks later...

Hornet wheel brake effectiveness

 

Hornet deceleration on ground with wheel brakes (anti skid on) is quite low on a dry runway. If someone has access to landing performance tables for the plane, it would be nice to test her against it. Wheels leave skid marks on the runway, still it decelerates as if it was on ice.

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Hornet deceleration on ground with wheel brakes (anti skid on) is quite low on a dry runway. If someone has access to landing performance tables for the plane, it would be nice to test her against it. Wheels leave skid marks on the runway, still it decelerates as if it was on ice.

 

Yeah it stops like a greased duck being thrown down a slip-n-slide.

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I noticed RL canadian CF-18 pilots deploy air brakes as soon as the wheels touch the ground so it provides some additional drag and helps slow down quicker

 

See at 0:17

 

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Never had a problem stopping the Hornet. Airbrakes out on touchdown and stick fully deflected back once under 100 knots for extra stabilator drag. Brakes under about 50 knots.

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The brakes are definitely incorrectly simulated. There's no almost difference in stopping distance between antiskid on and off braking (slightly better braking with antiskid off!)

 

Landing roll is approximately 50% higher than the flight manual values says, but since ED tagged this issue as 'correct as is' in a similar thread and moved it from bugs to whishlist, I guess we have to live with this issue :(

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Hard to tell until the own ship weights issue gets resolved.

Talking about disparity between landing checklist page and rearm window.

That being said, they might have some over heating effect being simulated that we’re unaware of.

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Hard to tell until the own ship weights issue gets resolved.

That being said, they might have some over heating effect being simulated that we’re unaware of.

I did all tests with internal fuel only, and no external loads, so no weight difference.

 

If the brakes would be overheating it would be a bug as well since they shouldn't during a normal landing well below max landing weight.

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Hornet definitely takes quite long to stop. Comparing to Su-27 even without its landing parachutes it takes more of a runway lenght to stop.

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The brakes are definitely incorrectly simulated. There's no almost difference in stopping distance between antiskid on and off braking (slightly better braking with antiskid off!)

 

Landing roll is approximately 50% higher than the flight manual values says, but since ED tagged this issue as 'correct as is' in a similar thread and moved it from bugs to whishlist, I guess we have to live with this issue :(

 

 

It's sad if they ignored a problem like this...

 

Can you point me, where I could find the data, so that I could try to make a report?

 

 

 

For those, who don't think that there is a problem, let me give you some real world data from an airliner (B737):

 

At 52000 kg landing weight (ISA / sea level ) and with no reverse thrust, on dry runway landing distance with max manual braking is 4070 ft, or 1240 meters! (vref around 136 kts)

 

This is not even the actual braking distance, since it calculates that you will land 1500ft behind the threshold.

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