Speedbrake deployment on Landing

[pauldy]

*Hope I don't sound like an annoying derp asking stupid questions.. If I sound like one please do tell so I'll shut up.. and please have this stupid thread locked*

 

 

Anyway, I was wondering... since we now have PFM for the Eagle..

 

How do we use Speedbrakes on Approach to landing?

 

I've seen dozens of F-15C Landing Videos and it seems, every pilot has their own thing.. From Deploying the Speedbrakes after touchdown, Right Before touchdown or Full Speedbrakes from Final Leg all the way down to the runway.. then there are no-speedbrake landings...

 

Weather? Aircraft gross weight?

 

So far I'm doing Full Speedbrake deployment from Final Leg.. but now, I'm trying to do a cleaner Config and will only extend Speedbrakes right after Touchdown of main wheels.. similar to ground spoilers of Airliners (I also play FS2004)

[HiJack]

I think it's a personal choice you as the pilot takes, or just as you feel the landing is commencing, the speed, and what weight you have. Have a look at these:

 

[BitMaster]

The only "static" answer to this question would that there is none.

 

It is always different, speed, glide angle, weight, headwind, tailwind, x-wind...you name it.

 

But lemme tell you this, if the Air Brake is engaged and stays there and you stabilize your airplane with it...then..hope you don't have to suddenly slow down even more, cause there is no other easy way of slowing down. So it is a good idea to try to stabilize your glide path with adequate speed without permanent engagement of the Air Brake so you still have one available if needed.

 

 

Bit

[GGTharos]

Generally speaking, if you have no need to use the speedbrake, just don't use it. Also try not to use it just before touch-down - it causes a downwards force (which you can see in-game, if you watch for it) that will increase your descent rate - so if you deploy the thing, do it well before touch-down or after touch-down.

 

There are plenty of situations where you might want to use the speed-brake, probably quite a list - for example, if you want to keep high thrust (maybe you're landing at a high altitude airport? Maybe it's hot? Both? ... short runway, or runway where you might need to go around quickly?)

 

But again - have a reason :)

 

So far I'm doing Full Speedbrake deployment from Final Leg.. but now, I'm trying to do a cleaner Config and will only extend Speedbrakes right after Touchdown of main wheels.. similar to ground spoilers of Airliners (I also play FS2004)

[Zabuzard]

Speedbrakes allow you to give the engine more power by achieving the same speed as if using no brakes+less power.With more power you achieve more engine RPM at landing speed. The more RPM you got the more controlable the AC is at low speeds and this is simulated in DCS.

 

 

 

 

So if you use your speedbrake at landing (+full flaps) your landing will be easier and safer.

[GGTharos]

Actually it can be more difficult and more dangerous.

 

The aircraft suffers more pitch issues with the airbrake open. Nozzles closing also cause problems, so don't pull idle and then power and back again (until you're about to touch down). Use the airbrake as necessary to control speed.

 

You don't need more engine power in an F-15C. You have plenty and the engine spool-up time is quite fast. Your airbrake will probably close about as fast as your engine would spool up.

 

In other words, you simply do not need the airbrake for a landing.

Edited August 19, 2014 by GGTharos

[BitMaster]

When I am lazy, high and fast and well too close to the strip to make a somewhat fashionable approach I tend to get nasty ( RC flier blood ) and deploy all there is once IAS allows and "dive" into my slide....withing 3-5 seconds I have the feeling if I am still lucky ( IAS is acceptable and AOA somewhat OK ) and can make it within parameters to come to a stop before threshold on the far side or if I really have been too lazy and too little too late so I have to go around and fly in the gentle way.

 

That's when I touch down with all out and engaged and coming over Threshold with 340km/h ( Su 25T i.e. ) and flare it off until like ⅔ down the strip before touching down and deploying the Chute

when the skid marks start to appear on the strip. Usually that works.

 

If I do this in a Fighter, there is a lot more you can do to bleed off energy, even when descending,

you just don't have to have a Cornel to speak to afterwards for this, he'd kill you if you spiral down just cuz you have been LAZY again ;)

 

In DCS you can try it all out and I think it feels pretty close to what I would expect a RL AC to behave. Since I only flew models ( but that a lot ) and only steered a MBB through the clouds

in RL with not much more to do than hold course I have to believe it's quite close and what if it doesn't work out, well, RESAWN, and try again.

Words can't tell you all the experience you can gain by trial and error.

 

I would try it all out and build up skills for landing and slow maneuvering.

[Exorcet]

With the airbrake stowed I can come in slower at a given AoA, more important though is probably getting a shallow glide path.

[LJQCN101]

Search for "F-15 Eagle Landing Runway 03R HYAKURI AIR BASE" on YOUTUBE and what you're about to see is a full overhead landing procedure with speed brake ON all the way.

 

The truth is, IRL there's no restrictions in deploying speed brake duiring normal landing.

 

${1}

 

 

I tend to extend the speed brake from the downwing leg all the way to taxi, just as the video shows, and haven't seen any harzard or difficulties in using this technique.

 

IIRC speed brake is also used to avoid a floating tendency when entering ground effect.

Edited August 20, 2014 by LJQCN101

[GGTharos]

Search for "F-15 Eagle Landing Runway 03R HYAKURI AIR BASE" on YOUTUBE and what you're about to see is a full overhead landing procedure with speed brake ON all the way.

 

The truth is, IRL there's no restrictions in deploying speed brake duiring normal landing.

 

The truth is that it isn't SOP to use it.

 

I tend to extend the speed brake from the downwing leg all the way to taxi, just as the video shows, and haven't seen any harzard or difficulties in using this technique.

 

If you don't see/know the hazards, does it mean they aren't there?

 

IIRC speed brake is also used to avoid a floating tendency when entering ground effect.

 

You use the speedbrake if you have to/asrequired. It's not SOP technique to have it out for some of the reasons that were listed.

[LJQCN101]

The truth is that it isn't SOP to use it.

 

You use the speedbrake if you have to/asrequired. It's not SOP technique to have it out for some of the reasons that were listed.

 

Sure. It isn't SOP to use it indeed. Just as you said: "as required".

 

If you don't see/know the hazards, does it mean they aren't there?

 

Good point. Then clarify it a little bit if you're more knowledgeable than us. We'll appreciate that. Especially the pitch issue.

 

it causes a downwards force (which you can see in-game, if you watch for it) that will increase your descent rate - so if you deploy the thing, do it well before touch-down or after touch-down.

 

I thought the pitch CAS was a pitch rate command system when landing gear is down (g command when landing gear is up), and will automatically compensate for the pitch-down momentum induced by speed brake or thrust reduce, done by the Pitch Trim Compensator (PTC). Will dig-in more if I have proper info.

Edited August 20, 2014 by LJQCN101

[GGTharos]

Sure. It isn't SOP to use it indeed. Just as you said: "as required".

 

Yep. The airfield you mentioned also has a relatively short runway. When landing, one of the goals is to not wear out the tyres more than necessary as an example, and this is why aerobraking is used. The airbrake being out has you slowing from the moment you touch the ground. This is speculation on my part though.

 

Good point. Then clarify it a little bit if you're more knowledgeable than us. We'll appreciate that. Especially the pitch issue.

The pitch issue isn't catastrophic so much as it might cause you to 'chase the aircraft' in good weather. It could cause more aborts than it's worth, and can make power onset for a go-around a little slower. In poor weather, eg. ILS approach, chasing the aircraft can become catastrophic.

 

I thought the pitch CAS is a pitch rate command system (or a g command system) when landing gear is down, and will automatically compensate for the pitch-down momentum induced by speed brake or thrust reduce, done by the Pitch Trim Compensator (PTC). Will dig-in more if I have proper info.

No, the CAS function is reduced (not turned off) when the landing gear is down. It's also not a perfect system, just pretty good.

The airbrake doesn't cause you to pitch-down either, so CAS wouldn't deal with it ... the brake will increase your descent rate (downward force), I don't believe there's much if any pitch changes, unlike flaps. The PTC is not engaged when the landing gear is down, that's why you have to trim. Generally, the PTC will attempt to keep the nose (W) where you pointed it.

 

So, what you'll see is the FPI 'walk down' just a bit. You might be tempted to arrest it with more thrust OR pitch, and there begins your PIO.

[Nage]

I`ve read the posts here on the matter and now i`m bit confused. Could be i was doing it wrong too.

My landing is always with brakes on cuz i always throttle up just before touch down cuz i feel that my plane is dropping to fast on glide and i think landing gears would break. My glide speed in eagle is 150-180 kts.

After all no matter what plane i fly i always use the brakes cuz of that final thrust. It does not speed up too fast with brakes on but it softens the landing.

I looked up on tube and found out that actually lot of RL pilots use it.

with brakes

${1}

 

without brakes

${1}

 

I think, that like someone said before, it`s all up to pilots decision.

For me personally any landing (with or with out brakes) that your plane is without damage and you can walk away from is good landing and procedure was good

[GGTharos]

Yes, it's all up to the pilot, but the pilot is taught how to land the aircraft properly first, and he has reasons for using the speedbrake.

 

If you're using the speedbrake all the time for no other reason than what you mentioned, your landing technique is poor.

 

Here's a couple of landing demos in-game:

 

http://forums.eagle.ru/showthread.php?t=123658

[LJQCN101]

Really nice info, THX a lot. Maybe I'll pay more attention to the PIO, or intentionally induce it for testing purpose.;)

[GGTharos]

No problem. It's usually not a huge deal in clear air (but it always increases the chances of a go-around at minimum, and an accident at worst) and it builds a bad habit for no-vis approaches, where chasing anything is ... just no. :)

 

Really nice info, THX a lot. Maybe I'll pay more attention to the PIO, or intentionally induce it for testing purpose.;)

[Nage]

Yes, it's all up to the pilot, but the pilot is taught how to land the aircraft properly first, and he has reasons for using the speedbrake.

 

If you're using the speedbrake all the time for no other reason than what you mentioned, your landing technique is poor.

 

Here's a couple of landing demos in-game:

 

http://forums.eagle.ru/showthread.php?t=123658

 

 

I watched the videos and those were nice landings but i saw that whoever was landing was playing with brakes as well, 1st video at 1:17 and i could hear it later on. I could be mistaken tho.

 

What i found interesting even more was what you wrote.

"First up, overhead break to landing. Aircraft gross weight should be less than 36000lbs for the 44th standard, in RL this standard is set by the squadron."

 

Could that be the reason for deploying brakes or not to deploy??? Squadron standard???

[GGTharos]

I watched the videos and those were nice landings but i saw that whoever was landing was playing with brakes as well, 1st video at 1:17 and i could hear it later on. I could be mistaken tho.

 

You are mistaken. You're hearing increased AoA, not an airbrake - and even if it was, it would still conform to 'as required' rather than 'use all the way'.

 

Could that be the reason for deploying brakes or not to deploy??? Squadron standard???

AFAIK not in USAF squadrons. The Japanese might have different ideas, but again, the runway they were landing on was relatively short.

 

Deploying airbrakes is technique in this case, and technique tends to be taught uniformly. A squadron may have a different climb-out SOP based on where they are based, for example 300kts in peace-time to 10000' altitude for noise abatement or other regs, and 350 from there on (most efficient climb is 350kts all the way until crossover to M0.9, then M0.9 for MIL, 0.95 for MAX).

 

This can also vary by aircraft, eg. In the A-10 you're expected to deploy airbrakes partially on landing.

 

With F-15's you'll see that the use of the aibrake is not at all consistent. You simply don't need it.

[Nage]

Thanks GGTharos for clearing things

[GGTharos]

Actually I re-watched it and he did use the speedbrake, it was used to avoid over-speeding on the base leg, so you're right - the brake was deployed for a short time :)

[LJQCN101]

Regarding the PTC:

 

The pitch trim controller adds or subtracts stabilator deflection to compensate for such aircraft variables as increases or decreases in airspeed, speed brake/flap extensions, or changes in loading. These changes are introduced without movement of the control stick.

 

ref. http://www.f15sim.com/?page_id=16

 

During my test, the pitching momentum induced by a prompt thrust increase/decrease will cause a 0.1g increase/decrease in load factor, and is compensated later on. And the g changes caused by speed brake is negligible.

 

The PTC is not engaged when the landing gear is down, that's why you have to trim. Generally, the PTC will attempt to keep the nose (W) where you pointed it.

 

Well, I just observed in the game that the PTC does not attempt to keep the pitch rate.

 

Without pilot input, the CAS commands a permanent normal acceleration of +1g. For example if you adjust your pitch to +40 degrees and maintain the airspeed, you'll find out that the nose of the aircraft gradually goes up, but the load factor remains at +1g. (Without pilot input)

 

And that remains the same when your landing gear is down. The CAS still commands +1g without pilot input, until the AOA is a little bit high.

 

Also observed a pitch-down when AOA approaches 18 units or higher when landing gear is down. Maybe there's a AOA feedback blended into the CAS, not quite sure for this one.

[Nage]

:) nevertheless, we can agree that if landing procedures are followed, we don`t need brakes.

Brakes are often used for small corrections, and after touch down to slow the plane down.

[LJQCN101]

:) nevertheless, we can agree that if landing procedures are followed, we don`t need brakes.

Brakes are often used for small corrections, and after touch down to slow the plane down.

 

Aerodynamic brake is used to slow the plane down after touch down (above 90 knots). It's more effective than a mere air brake.;)

[Nage]

Aerodynamic brake is used to slow the plane down after touch down (above 90 knots). It's more effective than a mere air brake.;)

 

Yeah, and that too :thumbup:

[GGTharos]

During my test, the pitching momentum induced by a prompt thrust increase/decrease will cause a 0.1g increase/decrease in load factor, and is compensated later on. And the g changes caused by speed brake is negligible.

 

When the landing gear is down it isn't doing anything.

 

And that remains the same when your landing gear is down. The CAS still commands +1g without pilot input, until the AOA is a little bit high.

The CAS isn't commanding 1g while you're landing. This is why you have to trim - the AoA isn't a factor, it's the speed you're trimmed for.

 

Also observed a pitch-down when AOA approaches 18 units or higher when landing gear is down. Maybe there's a AOA feedback blended into the CAS, not quite sure for this one.

The CAS is adjusting the pitch ratio (Pitch Ratio Changer, PRC) throughout the flight envelope, and there are adjustments to the roll ratio changer and ARI, but the Pitch Trim Compensator (PTC) is not operating (or at least some signals are inhibited) while the landing gear is down.

 

You can check this easily: Put gear down. Trim to fly level. If you accelerate, you'll pitch up - if you decelerate, you'll pitch down.

 

Edit/PS: There are documents out there that describe in great detail how the CAS functions in all or at least the vast majority of situations. I don't have them on-hand, but for those who want those badly, I'm sure you can find them. NASA did a bunch of research with the eagle's CAS, so they might have a bunch of publications regarding this system.

Edited August 20, 2014 by GGTharos