Speedbrake retract slow on one side

[Oldguy]

On my way into Zephyr Hills yesterday for SNF, Tampa had me descend from 9,000 to 2,000 for landing at KZPH. To avoid some of the buildup ahead of me, I put out the speedbrakes and got a nice descent rate going while keeping up airspeed as requested. When I went to retract them, right side went down nicely, but the left took almost two minutes. I had checked them during my preflight and again on the ground after landing, and everything worked well.

 

These are the PreciseFlight vacuum speedbrakes. An old log entry shows a repair where a cable was getting hung and one side was not retracting at all (don't recall which side and logs are not with me). Is it possible they have enough wear to cause them to bind when under wind pressure or do they just need a good look by my MX? I believe they have a 1,000 hour rebuild requirement and don't know when the last one was done. Currently have 5000+ on the plane. Would appreciate any and all suggestions.

 

Thanks,

John

[anthonydesmet]

Hi John,

I have the same system and mine is a little slow on the right.  Checks fine on deck but every once in awhile (not all the time) is slow to come down compared to left. Usually under circumstances like you just had.  If I use them to slow down and hold altitude, not really an issue.  If I use it to elevator down quick then that seems to be where I have the retract issue. Was REALLY slow last summer but mech went in and lubricated it and he could never duplicate it on deck so definitely under a load issue. I am currently in Thailand and my logbooks are back in Va Beach but I think they want you to use a certain type of lubricant and only in specific spots if I am not mistake).  Its better now but still a little slower than the left.  Also, in my precise flight owners manual it also talks about an overhaul.  I don't think it is 1000, I want to say it is around 600 +/-.  Hopefully someone here will chime in thats sitting with their owners manual and an answer.  But just wanted to let you know....not uncommon. 

[AndyFromCB]

You need to take out the pulleys, press out the bearings, install new bearings. IF you do not, the cables will eventually eat into the pulleys, if they haven't already. Then you'll need to put the pulleys onto a lathe to turn them a bit.

 

Preciseflight no longer maintains these vacuum brakes. Good news, other than bearings (I'll look up the size and source for you), there is not much to maintain. The valve is still available as is the rubber boot.

[Guest]

The pullies in the speed brake itself are prone to seizing due to water entry, also the cables which run from the vacuum pot in the belly out to the wings get dry and stiff.

Precise Flight has cables, Brittain has the vacuum pots.

Clarence

[jackn]

I have had this issue since day one. Interestingly, it only happens with the gear up. Gear down, the brakes come right down. I had the cables replaced when I had my TKS installed, as the sheathing on the cables was dry and cracked. The boot, pulleys, and speed brakes were fine. The cables do run through the wheel wells. I'm assuming the tires, when retracted are pressing against the cables. I'm going to investigate further, the next time I have her up on jacks.

[AndyFromCB]

I have had this issue since day one. Interestingly, it only happens with the gear up. Gear down, the brakes come right down. I had the cables replaced when I had my TKS installed, as the sheathing on the cables was dry and cracked. The boot, pulleys, and speed brakes were fine. The cables do run through the wheel wells. I'm assuming the tires, when retracted are pressing against the cables. I'm going to investigate further, the next time I have her up on jacks.

 

Might not have anything to do with gear up or down, but speed. Mine used to do that too, when would eventually retract as I slowed down towards 90 or so when the pressure on them let up a bit. Once again, bearings were shot enough to allow the blades the bend back a bit at higher speeds.

 

BTW, according to logbooks, mine went about 3400 hours before anyone did anything. 

[aviatoreb]

Mine did that on one side, and then later on the other side  - there are some tiny springs that look like they came from a chair - that you buy for like $20 with part number, that comes in an official ziplock baggie (instead of $0.02 for he same EXACT stuff from the hardware store).  They are easy to replace.

[jackn]

Good point. My airframe has 3000 hrs.

[Oldguy]

Good suggestions. I'll check the logs and supplements to see the requirements for maintenance/rebuild and have my mechanic look at the pulleys next week when I get back home. From some of your experiences, sounds like pulley bearings might need some work. Thanks again.

 

John

[Jeff_S]

Sounds like you guys with the vacuum driven brakes have more options. When my right-side speedbrake started malfunctioning (just wouldn't come all the way up) I had to pull both sides and the central controller and send it back to Precise Flight in Oregon.  The total repair including shipping was only about $800, though, so I figure anything less than one Aviation Unit is still a bargain!

[Piloto]

The vacuum speed brakes have an internal springs that force them down when retracted. When the spring beaks they may not come down inflight. Check for spring tension by slightly pulling on the blade edge.

José