Sign in to follow this  
Driver170

Speedbrakes upon RTO

Recommended Posts

Hi, Can't find it in my FCOM but in what conditions will the speedbrakes deploy on a RTO? I know one of them are "reverse thrust" but any other conditions and where are they listed?

 

I rejected my takeoff below 80kts but speedbrakes did not deploy even though i used reverse thrust.

 

Cheers!

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

I rejected my takeoff below 80kts but speedbrakes did not deploy even though i used reverse thrust.

 

I think it's above 60, with reverse thrust. Either way, it should be part of the memory item actions.

Share this post


Link to post
Share on other sites

Yeh manually raise the speed brakes before intiating reverse thrust. But it got me thinking what are the conditions

Share this post


Link to post
Share on other sites

The FCOM reference is in Vol 2, page 9.20.18. As Kyle said, 60 knots.

 

RTO auto braking occurs above 90 knots with thrust levers at idle, it's possible that this speed has been used for the speedbrake deployment as well by mistake. Worth rechecking.

 

edit, speedbrakes deploy if rejected above 60 knots for me.

Share this post


Link to post
Share on other sites

Not that it matters much below 80 KIAS, they are there to kill the lift generated by the wings, but there is hardly any at that speed.

Share this post


Link to post
Share on other sites

Not that it matters much below 80 KIAS, they are there to kill the lift generated by the wings, but there is hardly any at that speed.

They also create a lot of drag, though at 60 knots that will only be a quarter of what it is as 120 knots.

Share this post


Link to post
Share on other sites

Kevin, is there an aerodynamics formula (seems awfully close to the inverse square law of light) to calculate that ?

 

I remember that the speedbrakes--called spoilers back then--were very small on the Boeing 707-320b, considering the size of the wing and weight of the aircraft, I would dare say that the 737-800 probably has more area per wing. They were strategically placed over the wing and in line with the flaps, where the wing camber was greater when they were lowered to any setting. Back then there was only talk that the main function on the ground was to transfer the weight of the aircraft to the wheels for more effective braking--the effect as a brake mechanism negligible below 80 kts. I have noticed that more emphasis has been placed of speed brakes surface in recent model aircraft.

Share this post


Link to post
Share on other sites

Kevin, is there an aerodynamics formula (seems awfully close to the inverse square law of light) to calculate that ?

 

 

It is a function of the square of the velocity of the fluid (or air) as well as several other factors: https://en.wikipedia.org/wiki/Drag_equation

 

Google is your friend.

Share this post


Link to post
Share on other sites

Kevin, is there an aerodynamics formula (seems awfully close to the inverse square law of light) to calculate that ?

 

I remember that the speedbrakes--called spoilers back then--were very small on the Boeing 707-320b, considering the size of the wing and weight of the aircraft, I would dare say that the 737-800 probably has more area per wing. They were strategically placed over the wing and in line with the flaps, where the wing camber was greater when they were lowered to any setting. Back then there was only talk that the main function on the ground was to transfer the weight of the aircraft to the wheels for more effective braking--the effect as a brake mechanism negligible below 80 kts. I have noticed that more emphasis has been placed of speed brakes surface in recent model aircraft.

It's a square law, not an inverse square law. All other things being equal aerodynamic forces increase with the square of speed.

 

Spoilers are the individual panels. "The speedbrake" is those spoilers being moved symetrically. the main reason to deploy them on touchdown is indeed to put weight on the wheels by destroying lift. But on ground the spoilers are deflected to a much greater angle than they are in flight and so they also create even more drag than they do in flight,

Ground spoilers make a significant contribution to stopping the aircraft on landing. You can test this for yourself by not arming the speedbrake before landing and not using reverse thrust or brakes. Then try the same landing with the speedbrake armed. Without the speedbrake you won't lose much speed. With speedbrake deployed you decelerate quite rapidly.

Share this post


Link to post
Share on other sites

They can actually increase the downforce. Think of the vectors and the Newtonian effect of having that air deflected upwards. More weight on wheels = more brake effectiveness = greater stopping ability.

Share this post


Link to post
Share on other sites

We did an excersise in the sim where we did three rejected takeoffs.  The first was normal with spoilers and reverse thrust, the second with spoilers only and the third with reverse only.  Not using reverse only added 200-300 feet to the distance used, not using spoilers added around 1200-1300 feet.  It really drove home the importance of making sure the spoilers get deployed promptly.

  • Upvote 1

Share this post


Link to post
Share on other sites

JoeDiamond, at what airspeed did you reject the takeoffs in these excercises, was it just before V1 ?

Share this post


Link to post
Share on other sites

JoeDiamond, at what airspeed did you reject the takeoffs in these excercises, was it just before V1 ?

 

I don't recall the exact speeds but it was at max weight for runway 20R at KSNA using flaps 25 with the reject right at V1.

Share this post


Link to post
Share on other sites

Joe diamond, after a full stop after an abort before V1 do you set the parking brake (captain) and the FO sets flaps 40 when stopped? My SOPs call for this!

Share this post


Link to post
Share on other sites

Joe diamond, after a full stop after an abort before V1 do you set the parking brake (captain) and the FO sets flaps 40 when stopped? My SOPs call for this!

 

 

What is the reason behind flaps 40? Is it for evacuation purpose?

Share this post


Link to post
Share on other sites

At this point when you stop, the captain sets the parking brake and FO sets flaps 40. Its in my SOP. I think its to prepar for an evacuation! So if you had to you wouldn't need to wait till the flaps have gone down to 40

Share this post


Link to post
Share on other sites

What is the reason behind flaps 40? Is it for evacuation purpose?

 

Yeah, it's a backup. In case a slide fails, you can, in theory, slide down the extended flap. 

Share this post


Link to post
Share on other sites

Joe diamond, after a full stop after an abort before V1 do you set the parking brake (captain) and the FO sets flaps 40 when stopped? My SOPs call for this!

 

That would depend on why you aborted in the first place.  If you thought an evacuation was a possibility then yes, but it's not something we would do by rote every time we abort a takeoff.

Share this post


Link to post
Share on other sites

A few years back, I took a ride on a B737-700 (then it was Continental) KSNA to PHOG and that small chance of a RTO at SNA was pretty big on my mind. Wow.

Share this post


Link to post
Share on other sites

Yeah, it's a backup. In case a slide fails, you can, in theory, slide down the extended flap. 

 

It's not really what I would consider a backup.  It's the only way down from the overwing exits.  No slides for those.

Share this post


Link to post
Share on other sites

I don't do high speed aborts, if I'm even close to V1 I'm go'n.   

 

blaustern

Share this post


Link to post
Share on other sites

I don't do high speed aborts, if I'm even close to V1 I'm go'n.   

 

blaustern

 

Seriously? In the sim or real life? V1 is predicated on having the available runway distance available to conduct and ACCEL-STOP.  Anything before that and you may not be able to accelerate enough to properly clear the required obstacles at the end of the runway. With that thinking, you should almost always go regardless. V1 is my cutoff. When taking off, unless I hear "V1, rotate" (In the aircraft I fly, V1 and Vr happen to be the same speed but that doesn't matter) I am stopping. I am continuously thinking in my mind abort abort abort and only when I hear those magic words (V1, Rotate) my right hand comes off the throttle on onto the yoke so there is no accidental reduction in power.

 

The FAA defines V1 as: The US Federal Aviation Administration defines it as: "the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance."

Share this post


Link to post
Share on other sites

Yes, just remember, IRL, every decision you make prior to an incident or accident will be scrutinized by lawyers. Do what you're trained to do

 

Jack Colwill

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this