Speed brakes?

[PJClark]

Something odd today.  I have vacuum speed brakes in my 252/Rocket.  On descent from 11,000 they deployed just fine but when switched back to in they both hung open.  Not sure but the normally glossy red paint on the plates looked kinda frosty. They eventually both retracted and I didn't use them again...then forgot to test before I shut down back home.

It was 6 degrees F at altitude.  Anyone ever have this happen? What to do...and how would you get them open to maybe apply WD40 on the ground without the engine running and making vacuum?

[Niko182]

31 minutes ago, PJClark said:

Something odd today.  I have vacuum speed brakes in my 252/Rocket.  On descent from 11,000 they deployed just fine but when switched back to in they both hung open.  Not sure but the normally glossy red paint on the plates looked kinda frosty. They eventually both retracted and I didn't use them again...then forgot to test before I shut down back home.

It was 6 degrees F at altitude.  Anyone ever have this happen? What to do...and how would you get them open to maybe apply WD40 on the ground without the engine running and making vacuum?

When its below freezing dont use them. They get stuck. Once theyre out, no going back in until it gets warmer. 

[carusoam]

Tough way to find out you are in icing conditions...  

Ice is a known way to have challenges with the brakes...

They don’t get damaged, they just stay deployed...

You may only see one line in the POH supplement, like this...

-a-

[smwash02]

Since you've got a 252 run your electric pump to get vacuum without the fan spinning.

They should retract fine even if the rest of the system is hung up and given your report of them being frosty I'd bet they froze.

Edited March 7, 2021 by smwash02

[PJClark]

Well when I had all the new gadgets installed I ditched the electric Standby vac...it weighs way more than the engine driven and the speed brakes are the only thing left that uses vac.

I'll test on the ground on a warm airplane tomorrow...I suspect they're fine and I had some ice on them.

[kortopates]

20 minutes ago, PJClark said:

Well when I had all the new gadgets installed I ditched the electric Standby vac...it weighs way more than the engine driven and the speed brakes are the only thing left that uses vac.

I'll test on the ground on a warm airplane tomorrow...I suspect they're fine and I had some ice on them.

Me too on ditching the standby. I suspect they're fine too, glad your destination wasn't subfreezing else it may have been a whole lot more exciting. Before I avoided using them entirely in sub-freezing I thought I might get away using them  without any visible moisture flying into my favorite ski resort - but that was a mistake as you discovered. At least they tend to go back in slowly in seeminly dry air, I didn't want to worry about possiby needing to go missed in mountainous terrain with them stuck and not deployed evenly. They slowly came back down but that became a never again moment.

Edited March 7, 2021 by kortopates

[PJClark]

17 minutes ago, kortopates said:

Me too on ditching the standby. I suspect they're fine too, glad your destination wasn't subfreezing else it may have been a whole lot more exciting. Before I avoided using them entirely in sub-freezing I thought I might get away using them  without any visible moisture flying into my favorite ski resort - but that was a mistake as you discovered. At least they tend to go back in slowly in seeminly dry air, I didn't want to worry about possiby needing to go missed in mountainous terrain with them stuck and not deployed evenly. They slowly came back down but that became a never again moment.

Exactly! Completely clear air.  No ice on the wings or any exposed surface.  How odd....but lesson learned.  And if you were planning to use the speedbrakes even a little bit to get down from 11,000 feet THAT is shot all to hell!

[N201MKTurbo]

They will retract once you get down to warm air...

Edited March 7, 2021 by N201MKTurbo

[squeaky.stow]

12 hours ago, PJClark said:

Anyone ever have this happen?

Yes. Unfortunately the vacuum operated speedbrakes do this all the time when they get cold soaked. Up here in the frozen north I try to avoid using them in the winter. It has nothing to do with icing. They are extended by the vacuum servo but retracted by just a spring.  I think that the rubber bellows on the servo gets stiff in the cold and it impedes the retraction. 
In my experience they usually go down about half way, and then depending on how cold it is, they may (or may not) slowly creep down the rest of the way over a period of several minutes. 
I plan to try changing the spring at some point as it may have become weaker with age. Binding in the  cables that run from the servo to the brakes has also been suggested as a possible culprit, but unless they both start binding by the same amount, that would cause them to retract asymmetrically. In my case the cables were fine.

The good news is that if you do have to land with them partially deployed, you won’t notice a significant handling difference. The first time I used them in very cold weather (-20C) they stayed half deployed. A tiny bit more power was required on approach, but no change in landing attitude and the landing “feel” was unchanged. (Disclaimer: I am not advocating this as a technique, but I had no choice but to be a test pilot when they would not retract.)

 

[PJClark]

Pretty much exactly what happened.

[squeaky.stow]

I would be interested to know if anyone on this forum with vacuum brakes has tried changing the retraction spring and if so:

1) Did it make a difference?

2) Where did you source the part?

 

[jlunseth]

Well, they also need to come out and be serviced every several years or they will do the same thing, ice or no ice.

[kortopates]

I would be interested to know if anyone on this forum with vacuum brakes has tried changing the retraction spring and if so:
1) Did it make a difference?
2) Where did you source the part?
 

you can get springs from Precise. I have replaced most everything in mine except for the bellows. Even the sealed bearing can be replaced - but a lot of work.


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[squeaky.stow]

8 hours ago, kortopates said:

you can get springs from Precise. I have replaced most everything in mine except for the bellows. Even the sealed bearing can be replaced - but a lot of work.


Sent from my iPhone using Tapatalk

Thanks Paul.

Sounds like I have a new project for my next annual. 

Living in San Diego, I am guessing you don’t see -20C that often, but did you notice a difference in the retraction when you replaced the spring? After 35 years, mine must be a little fatigued.

[kortopates]

2 hours ago, squeaky.stow said:

Thanks Paul.

Sounds like I have a new project for my next annual. 

Living in San Diego, I am guessing you don’t see -20C that often, but did you notice a difference in the retraction when you replaced the spring? After 35 years, mine must be a little fatigued.

My favorite ski resort had me descending in well below freezing temps, perhaps not frequently to -20C. Its been years since I replaced the springs the biggest benefit or most improvement came from replacing the conduit and the bearing on one brake. I do recall I had to buy some really long needle nose pliers, made for springs, to change out the speed brake springs though.

[81X]

This happens on my 231 with the factory vacuum brakes when it’s really cold out. (That’s below about 35 here in S.C.)  Even worse is that they asymmetrically retract over about 30 seconds so it’s especially annoying with the yaw.