Landing with Speed Brakes?

[bmcconnaha]

On 9/22/2011 at 11:49 AM, jetdriven said:

I dont see how anyone would need speedbraked an a non turbocharged Mooney.  A J can descend 1000 FPM and slow from 175 KTS to 100 in about 2 miles or less even with 18" of MP set.

They have their use in a J or an ovation, just like they do in a turbo.  I don’t use them often for enroute descents, with the exception of I fly over a class C often that’s close to my home airport, and they occasionally keep my high.  Few nights ago, they kept me at 12500 for a bit, but let me down sooner than they usually do, so no brakes needed.  Where they are useful to me is coming into the airports I do that are surrounded by terrain.  They are nice to deploy once I’m clear and let it come down rapidly. Usually have them stowed long before I’m at 1000 agl and am slowing down for the gear drop.  Not a need, but nice to have.  

[carusoam]

On 7/23/2022 at 9:39 PM, Verle Cox said:

 

Wow…

Holy necro post you pulled up there Verle…

Unfortunately, this thread is more than a decade old…

 

Being rude, and not knowing the audience, and missing the decade… cost you an extra point.

 

Best regards,

-a-

[Peter Rejto]

Old post or not, it’s an interesting read.

I have mechanical speed brakes in my J and have never had an issue since they were installed back in 1992....controlled by a lever near the trim wheel. Dead simple.

Funny thing a few years ago during a BFR with an instructor not too Mooney experienced. I pulled on the speed brakes approaching the airport to more easily get slowed down and to get to pattern altitude.....and eventually I put down the gear. After the flight to instructor told me he was waiting for me to possibly forget the gear since I was somewhat below the gear down speed when I did activate the gear. I suppose that is something worth keeping a bit in mind. The speed brakes might somewhat mimic the feeling of the plane getting slow with the gear down. I think the feel is quite different as well as the sound (and of course, there is the normal gear warning horn). Still, perhaps worth keeping in mind?

Peter

[M20F-1968]

A few years ago I was falling with a high time Mooney pilot  who flies Ovations and Aclaims often.   Were coming in  and landing a strong crosswind and he introduced me to planning crosswinds with  speed rates deployed,  full flaps,  and of course gear extended.   The extra drag makes the airplane feel heavier  and allows you to carry more power for the same airspeed.   It seems to not be affected as much by the crosswind.   I have done  a go around in this configuration  in my F model (now more like a J)  and it does climb,  albeit somewhat more slowly.  I retract  speed breaks for us because their quick,  gear second,  and flaps last.  

 I don't use speed breaks all the time when landing in a cross wind, but for the  landings with higher crosswind component and  gusty winds they do seem to be helpful.

John Breda

[PT20J]

Speed brakes add drag. They are too far aft to affect lift much. It seems like deploying speed brakes and countering the drag with more thrust from a higher power setting is kind of like driving with one foot on the brake and one on the gas,

Skip

[donkaye]

23 minutes ago, PT20J said:

Speed brakes add drag. They are too far aft to affect lift much. It seems like deploying speed brakes and countering the drag with more thrust from a higher power setting is kind of like driving with one foot on the brake and one on the gas,

Skip

You are ABSOLUTELY right.  Using speed brakes in a crosswind and gusty situation is VERY dangerous in my opinion.  As I mentioned in a writeup on my website (https://donkaye.com/useful-aviation-articles), I experimented with speed brakes on a gusty windy day for extra stability.  I hit a downdraft near the ground, and even with full power in a Bravo it was necessary to retract the speed brakes in order to get better control of the descent rate.

[Fly Boomer]

7 hours ago, donkaye said:

I hit a downdraft near the ground, and even with full power in a Bravo it was necessary to retract the speed brakes in order to get better control of the descent rate.

So the speed brakes were reducing lift, and you got more lift by retracting?

[carusoam]

If you watch the flow of rain around the deployed speed brakes…

You can see a wide band of expected airflow get disrupted…

A total of about 3X the length of the brakes themselves….

 

If this flow disruption eliminates the lift of that section of the wing….

It would be similar to temporarily snipping off a length of wing…

Only just snipping the lift, and none of the drag….

 

When the lift is removed in that region…. The AOA gets increased to maintain altitude by increasing the lift of the rest of the wing….

The increased AOA comes with plenty of induced drag….

The side affect of flying with a higher AOA… you are now somewhat closer to the critical AOA…. Where the stall will occur…

Slowing down on final approach to the runway…. The gap between IAS and Vso is getting narrower, speed brakes deployed closes the gap more….

Bumpy air with a closed airspeed / stall speed gap… can be sporting….

 

At slower speeds the speed brakes are less effective, compared to higher speeds…. But, they still interrupt a lot of air flow….

PP thoughts only, not a CFI….

Best regards,

-a-

[PT20J]

47 minutes ago, Fly Boomer said:

So the speed brakes were reducing lift, and you got more lift by retracting?

No, speed brakes create drag. They have a minimal effect on lift because they are located so far aft of the 25% chord line. That’s why you can take off (or go around) with them deployed.

What Don was describing was most likely caused by windshear. To counteract that effect, he needed to accelerate to regain airspeed and the speed brakes impede acceleration by increasing drag.

Skip

[donkaye]

2 hours ago, Fly Boomer said:

So the speed brakes were reducing lift, and you got more lift by retracting?

Speed brakes immediately increase the descent rate by 200 ft/min.

[PT20J]

30 minutes ago, donkaye said:

Speed brakes immediately increase the descent rate by 200 ft/min.

Exactly! Because speed brakes increase drag, they increase the power required for level flight. So, unless you increase the power, the airplane will descend. So long as the aircraft is not accelerating (which requires an unbalanced force) the lift is unchanged and still equals the weight.

[Fly Boomer]

9 hours ago, PT20J said:

the aircraft is not accelerating (which requires an unbalanced force) the lift is unchanged and still equals the weight.

I'm having trouble with this.  If lift and weight are unchanged, why did Don's airplane descend with speed brakes?  Sounds like lift was reduced, and therefore weight exceeded lift, and he descended.

[PT20J]

1 hour ago, Fly Boomer said:

I'm having trouble with this.  If lift and weight are unchanged, why did Don's airplane descend with speed brakes?  Sounds like lift was reduced, and therefore weight exceeded lift, and he descended.

You are not alone. It is common misunderstanding that a change in lift is required for an airplane to climb or descend.  According to Newton's second law, an unbalanced force causes an acceleration (Force = mass x acceleration). So if the lift is not equal to the weight, the airplane will be accelerating upward or downward. But if the airplane is descending at a steady rate (200 fpm in Don's example) then the airplane is not accelerating and lift must equal the weight. What is happening when the speed brakes are deployed is that the drag now slightly exceeds the thrust and the deficit is made up by gravity as the airplane flies down hill.

Skip

[midlifeflyer]

20 hours ago, Fly Boomer said:

I'm having trouble with this.  If lift and weight are unchanged, why did Don's airplane descend with speed brakes?  Sounds like lift was reduced, and therefore weight exceeded lift, and he descended.

He's actually right. Once the speed brakes are out and the airplane is stabilized in unaccelerated flight,  by definition, weight = lift. Speed brakes, flaps, open the door, whatever. Unless the airplane is accelerating or decelerating, by definition lift = weight. Level, constant airspeed and rate climbs and descents are all a load factor and lift:weight ratio of 1. Descents are not the result of weight being greater than lift. They are the result of insufficient power to maintain altitude at a given airspeed. 

The problem your question points out is that drilling down into the lift vs drag equation may be adding an unnecessary level of complexity to a simple operational reality. Speed brakes add drag. Like any other addition of drag If we maintain altitude, it will slow us down. If we maintain airspeed, we will descend. 

 

 

Edited August 2, 2022 by midlifeflyer

[kortopates]

The Lift the wing produces at any AOA and airspeed is unchanged. But deploying the Speed Brakes causes the aircraft to slow without a change in pitch. Since speed is reduced, the net lift is reduced. But by overcoming the additional drag of the speed brakes with more power, it get back the loss of speed, the loss on lift can be restored. It’s not that the ability of the wing to produce lift for any AOA and airspeed has been compromised.

In contrast, Spoilers differ from airbrakes in that airbrakes are designed to increase drag without disrupting the lift distribution across the wing span, while spoilers disrupt the lift distribution as well as increasing drag.


Sent from my iPhone using Tapatalk

[Fly Boomer]

13 minutes ago, midlifeflyer said:

Speed brakes add drag. Like any other addition of drag If we maintain altitude, it will slow us down. If we maintain airspeed, we will descend. 

Okay, I think that clicked.  Thanks!

[carusoam]

Sooooo many variables!

Anyone any good with multi-variate regression?

Collect gobs of data, and generate an equation that defines what you get with all the combinations of the variables…

 

Best regards,

-a-

[midlifeflyer]

4 hours ago, carusoam said:

Sooooo many variables!

Anyone any good with multi-variate regression?

Collect gobs of data, and generate an equation that defines what you get with all the combinations of the variables…

 

Best regards,

-a-

Great idea. Then we'll be able to figure out exactly what airspeed and descent rate will result from a -1.275° pitch with speed brakes 

[midlifeflyer]

18 hours ago, Fly Boomer said:

Okay, I think that clicked.  Thanks!

It's not the easiest concept. Just the other day, I was asked what I would do if left too high on a VFR base leg. I said speed brakes. My friend was surprised since we were already slow enough. 

[Fly Boomer]

2 hours ago, midlifeflyer said:

It's not the easiest concept.

I get that gear is pure drag and, while flaps may contribute to lift, they are also "draggy", but I just had it in my head that speed brakes were primarily a lift killer.

[AeroEng]

I'll add that if you are having issues with bouncing on your landings, you may want to check your shock discs.  I was bouncing now and then, until I had the discs replaced.  New discs made a night and day difference.  Landings were completely smooth.  I was shocked at how effective the refreshed discs were...

[midlifeflyer]

3 hours ago, Fly Boomer said:

I get that gear is pure drag and, while flaps may contribute to lift, they are also "draggy", but I just had it in my head that speed brakes were primarily a lift killer.

...and my friend had exactly the opposite in his head, that it was a speed killer. 

[PT20J]

2 hours ago, midlifeflyer said:

...and my friend had exactly the opposite in his head, that it was a speed killer. 

It's sort of how you look at it. Since the predominant effect is an increase in drag, if you maintain airspeed the airplane will descend and if you maintain altitude, it will slow down. 

[Raptor05121]

6 hours ago, Fly Boomer said:

I get that gear is pure drag and, while flaps may contribute to lift, they are also "draggy", but I just had it in my head that speed brakes were primarily a lift killer.

Don't confuse speed brakes with spoilers. Spoilers "spoil" the lift. Speedbrakes just do drag.

[midlifeflyer]

7 minutes ago, PT20J said:

It's sort of how you look at it. Since the predominant effect is an increase in drag, if you maintain airspeed the airplane will descend and if you maintain altitude, it will slow down. 

We both said that.