speed brakes vs gear down

[alistomalibu]

Question 1:
Which of the following actions provide more drag during level flight? I mean, which of the following actions need more engine power to compensate the increased drag?
· Gear down
· Speed brakes

I think it depends on the actual speed, since speed brakes are more effective at high speeds

Question 2:
The following procedure is a valid procedure?
Situation:
You have to land and you need to burn fuel, because you are near the MLW. You are NOT in an emergency situation.
Action:
Maintain a flight level with speed brakes extended, some degree of flaps down and high N1, in order to obtain a high fuel flow value.

Asking for the 737, but it could apply for other types as well
Thanks

[TopBunk]

OK, a first stab at an answer:

1:

Which of the following actions provide more drag during level flight

I would go for the gear everytime, without question.

2:

Situation:
You have to land and you need to burn fuel, because you are near the MLW. You are NOT in an emergency situation.
Action:
Maintain a flight level with speed brakes up, some degree of flaps down and high N1, in order to obtain a high fuel flow value.

See 1: Greater drag as a single action is achieved with gear. Therefore to combine gear with your other actions will result in an even quicker fuel burn off and hence landing.

[Thunderbug]

Answer 1.

Generally the gear gives you the best amount of drag. On my aircraft type (A320) though you cannot drop the gear until below 25,000' and less than 250kts. There are no such limitations for the speedbrakes. The gear makes a lot of noise in the cabin, especially at high speeds

Answer 2.

Most aircraft have some warning indication of flying with power against speedbrake. Have been in just this situation. We descended early, slowed down and flew level with Flap 2 for about 20 miles. Deployed gear slightly early. Worked very well.

T'Bug

[alistomalibu]

Topbunk:
MCT thrust is enough to compensate the drag created by speed brakes and gear during level flight?

[A321COBI]

Question 1:
speedbrakes to nothing for me and the gear would come top
question 2:
with the contrast you will get a warning indication however there is nothing wrong and the gear + brakes work fine together
cheers

[kuobin]

If your flight is long enough ,you may try to use higher curise speed then you will not waste those fuel.

[ggofpac]

Question 1:
Which of the following actions provide more drag during level flight? I mean, which of the following actions need more engine power to compensate the increased drag?
· Gear down
· Speed brakes

I think gear

You have to land and you need to burn fuel, because you are near the MLW. You are NOT in an emergency situation.

Assuming u done everything during crz to increase fuel burn eg, lower cruise level etc. Start early descend, if atc permits slow down and extend flaps. Depending how much fuel u need to burn, lower gear.
But if u are early and not tight on time...by all means just take up a hold.
I personally don't like the idea of speedbrakes to lose fuel. I only use it if i need to lose height and also

Most aircraft have some warning indication of flying with power against speedbrake

too.

[kijangnim]

Greetings
In my carreer I used twice the speed brakes to increase fuel flow thus my weight, you just need 1/8 of speed brake, which is not a lot.
The advantage is that you are not limited by speed , you can modulates the fuel flow, and in case of engine failure you just have to push the speed brake lever

[alistomalibu]

Hi
Thanks for your answers
I would like to post another question

• What could be the disadvantage of using Speed brakes (Flight detent position) during level flight? (constant speed and high N1)

[welliewanger]

What could be the disadvantage of using Speed brakes (Flight detent position) during level flight? (constant speed and high N1)

Speedbrakes are another system, which wears out with use.

Passengers can get disconcerted if the wing doesn't look like a wing for too long.

Speedbrakes are noisy.

To burn more fuel, fly lower or faster. IMHO a much slicker solution.

[Cough]

MCT thrust is enough to compensate the drag created by speed brakes and gear during level flight?

I suspect with 2 engines running, you may exceed Vmo in this situation.

[captjns]

After flying lower and faster I arrived at an airport circa +500 kgs. 10,000 above the aerodrome with flaps 5 gear extended 180 knots did the trick for about 8 minutes. Lower speed less noise to disturb the passengers.

[alistomalibu]

Again, thanks for your answers
I would like to review two sentences from previous posts

“The gear makes a lot of noise in the cabin, especially at high speeds”

“Speedbrakes are noisy”

• Which one is noisier? Gear or Speed brakes in flight detent position?
• Which one generates more vibration?

The AOA at which stall occurs is increased with Speed brakes.

• Could it be an advantage against the use of gears?

[cortilla]

I had exaxctly that situation a few years ago. After fuelling and pax numbers it seemed we would be over max landing weight (by about 500 kilos ish if i remember). So flew much faster than normal but neither the captain nor I were too comfortable with this. What if we needed the fuel at the other end (we'd taken min fuel anyway). However a few shortcuts and stronger than forecast tailwinds meant we made fuel.

Once we'd learned that destination was cavok (or near enough anyway) and alternate was also wide open. decided to descend about 100 odd miles earlier than we would have done. Pottered along at FL140. Level change to get down as quick as possible. Still wasn't enough.

Also had a few LMC's before we left origin so we ammended the zero fuel weight in the descent to the actual ZFW, that helped.

Final thing to do was drop the gear at about 12 mile final. According to the FMC we dropped under MLW at around about 800' agl.

At no time did we think to use speedbrake against power. Never thought of it and even if we had thought of it i don't think we would ever have done it. Speedbrake against power really goes against everything i was taught about flying a jet efficiently.

[Thunderbug]

alistomalibu

Which is noiser.... speedbrakes or gear?

I would say the gear, but it is not quite as simple an answer on my A320. The gear is usually dropped about 150-160 Kts and the noise is noticable, but only just, and passengers register it as the gear going down just prior to landing. Gear being deployed at higher speed is very noticable as it creates vibration and noise. For passengers it is also an unusual sensation that can get some of them concerned.

Speedbrakes create some noise and vibration. The A320 also makes a "howling banshee" noise as the speedbrakes deploy, this slightly noticeable in the cabin and very noticeable at ground level. Passengers don't tend to react as it is felt to be acceptable and normal.

Must correct you on one thing........

The AOA at which stall occurs is increased with Speed brakes

With speedbrake deployed the Stall AOA will be LOWER. You are disrupting the airflow over the wing with speedbrakes so the stall occurs at a higher speed and lower AOA. This effect is very noticeable on the A321. Deploy the speeedbrake and the flight instrument display of where the low speed protection will kick in shoots up by approx 40kts! This is usually dealt with by stowing the speedbrake, reducing the speed below the slat limit speed, put out Flap 1 and then redeploy the speedbrake.

Gear does have the advantage of not affecting the stall speed

[alistomalibu]

Thanks thunderbug for your answer

I was asking these questions to know the criteria of choosing one or other option in the event you have to burn more fuel. I was looking for the advantages and disadvantages of each of the options. (Speedbrakes extended or Gear down)
Your comments were very helpful. Thanks

Regarding the AOA with Speedbrakes extended:

I found the following paragraph in the article “Understanding the angle of attack”
pilotlab.net/library-2/systems-performance/understanding-aoa-part1.pdf

“Wing-mounted speed brakes or spoilers have the opposite effect. They reduce the lift at a given AOA; they also reduce the maximum lift achievable but, surprisingly, increase the AOA at which stall occurs.”

[Romeo E.T.]

on the B737 I prefer to use speedbrake, for when I am done burning off the extra fuel I can stow the speedbrake again, with the gear, even though it does produce a bit more drag, it is also a lot more tricky to retract, ie you can lower it at 270kts, lots of noise, lots of drag, but to retract it (should that be necesary) you have to slow right down to less than 235kts.

[Type1106]

Cortilla,

Speedbrake against power really goes against everything i was taught about flying a jet efficiently.

Just a thought, but what do you think you were doing by:

Considering flying faster than optimum?
Descending 100nm early and 'pottering along at FL 140'?
Lowering the gear early?

If you find yourself in the situation you were - needing to 'loose' 500kg - no matter what action you take to achieve that it certainly isn't going to be efficient!

[cortilla]

Type 1106

very true. Not very efficient whatever you do but speedbrake against thrust is just something I would hate to do personally. Also as stated very uncomfortable and noisy and possibly disconcerting for pax. I'd always choose an early descent over speedbrake or gear against thrust. But obviously you'd need to consider everything lower down such as wx. In our situation the captain and myself felt early descent was the best option in this case.

[alistomalibu]

In my carreer I used twice the speed brakes to increase fuel flow thus my weight, you just need 1/8 of speed brake, which is not a lot.

Was this during cruise?

What do you think about using speedbrakes (Flight detent) against power, during a non precision approach? (Before the procedure turn, but a few miles before the IAF and during outbound too)
Approach based on a VOR/DME located at the airport

Thanks