Pitot Tube Problems

[Giving Wings]

Has anyone on this group had a pitot tube come loose? We operate two 2021/2022 SLSAs and have gone through three pitot tubes. It seems that the dimple and sharped machine screw method of retaining the tube is suceptible to failing. We have seen the machine screw point worn down and the dimple enlarged and then the tube is free to work itself out from the tiny plastic tubing holding it into the airplane. On one flight it almost departed the airplane. Both engine/prop combinations have been dynamically balanced. The airplanes usually go through 5-7 start ups and shut downs a day. Any ideas? Thank you.

 

[seagull]

That is not the norm. My pitot tube is over 1600 hours, been out / off the plane in that time frame on several occasions. No signs of wear or fatigue.

 

[Piper J3]

I understand your frustration… if the sharpened machine screw loosens, the pitot tube will unscrew from friction in the spinner bushing. Unfortunately, the prop spins in the direction that allows the pitot tube to completely disengage. I speak from experience…

I have an aluminum split-pinch block on the back of the gearbox for mounting the pitot tube. See photo attached… It is custom made and not for sale. Evolutiontrikes sells a 3-blade E-Prop for the RV-12 and it incorporates an aluminum split-pinch block for mounting the pitot tube. The design is very similar to the mounting block that I have. I’m not certain if E-Prop is willing to sell the mounting block as a separate item, but an email would confirm. [email protected]

Maybe if there is enough interest, E-Prop will do a special production run and list the mounting block as a separate item for sale…

 

[Giving Wings]

I understand your frustration… if the sharpened machine screw loosens, the pitot tube will unscrew from friction in the spinner bushing. Unfortunately, the prop spins in the direction that allows the pitot tube to completely disengage. I speak from experience…

I have an aluminum split-pinch block on the back of the gearbox for mounting the pitot tube. See photo attached… It is custom made and not for sale. Evolutiontrikes sells a 3-blade E-Prop for the RV-12 and it incorporates an aluminum split-pinch block for mounting the pitot tube. The design is very similar to the mounting block that I have. I’m not certain if E-Prop is willing to sell the mounting block as a separate item, but an email would confirm. [email protected]

Maybe if there is enough interest, E-Prop will do a special production run and list the mounting block as a separate item for sale…

I'd love a different way to retain the Pitot tube. "Pinching" the entire tube sounds like the way to go. I will reach out to Larry and see if he will sell one to me. Perhaps, Aric @ Van's will can approve the change for our S-LSA.

 

[Bob Y]

Not sure what vintage pitot you have, but at some time in the past couple of years, Van's has changed to a thicker-walled FF-1202-1 pitot. My friend, who had the older FF-1202 version, had the same breakage as you experienced. Apparently this must not be that uncommon an issue, but for whatever reason Van's didn't deem it necessary to issue a service letter for this change. The increased thickness is quite noticeable.

 

[JeffG]

Not sure what vintage pitot you have, but at some time in the past couple of years, Van's has changed to a thicker-walled FF-1202-1 pitot. My friend, who had the older FF-1202 version, had the same breakage as you experienced. Apparently this must not be that uncommon an issue, but for whatever reason Van's didn't deem it necessary to issue a service letter for this change. The increased thickness is quite noticeable.

The FF-1202-1 was a change to stainless steel tube, which also has a thicker wall. That was in August 2022. When my pitot broke on 8/5/22, the FF-1202-1 wasn’t listed in the store yet. Found out when I called about the status of my order for the old type. The new one shipped the same day.

I cut a lengthwise notch with a dremel cutting disk rather than drilling a divot using the threaded plastic block as a guide. I would have switched to a split block, like in post #3, if I could have got one. A friend had one at the time that was apparently a Van’s test sample that never went to production.

 

[CessnaTPA]

I understand your frustration… if the sharpened machine screw loosens, the pitot tube will unscrew from friction in the spinner bushing. Unfortunately, the prop spins in the direction that allows the pitot tube to completely disengage. I speak from experience…

I have an aluminum split-pinch block on the back of the gearbox for mounting the pitot tube. See photo attached… It is custom made and not for sale. Evolutiontrikes sells a 3-blade E-Prop for the RV-12 and it incorporates an aluminum split-pinch block for mounting the pitot tube. The design is very similar to the mounting block that I have. I’m not certain if E-Prop is willing to sell the mounting block as a separate item, but an email would confirm. [email protected]

Maybe if there is enough interest, E-Prop will do a special production run and list the mounting block as a separate item for sale…

Hey Jim, I'm having a hard time visualizing how your split pinch block is keeping the pitot tube from spinning. It looks like it's just pinching the tube.

 

[Piper J3]

Hey Jim, I'm having a hard time visualizing how your split pinch block is keeping the pitot tube from spinning. It looks like it's just pinching the tube.

The split line is centered on the pitot tube. Top portion of block if bolted to back of gearbox. Bottom portion is like a connecting rod cap and is held (tightened) with two thru-bolts from top. The cap portion pinches the pitot tube and prevents movement and rotation. Very solid...

 

[CessnaTPA]

The split line is centered on the pitot tube. Top portion of block if bolted to back of gearbox. Bottom portion is like a connecting rod cap and is held (tightened) with two thru-bolts from top. The cap portion pinches the pitot tube and prevents movement and rotation. Very solid...

Ok, how did you bolt the top portion to the gearbox? Drill and tap the gearbox? Do you have more pics? I want to fabricate something similar. I appreciate the idea.

 

[Piper J3]

Ok, how did you bolt the top portion to the gearbox? Drill and tap the gearbox? Do you have more pics? I want to fabricate something similar. I appreciate the idea.

It bolts to the gearbox with same bolts as the nylon mounting block. I don't have drawings. Contact [email protected] to see if they will sell Rotax 912 aluminum mounting block for pitot tube.

 

[Piper J3]

Finally took some photos.... This is aluminum split-pinch pitot tube mount that is included with 3-blade E-Prop. The E-Prop has a carbon fiber pitot tube that runs in a ball bearing supported by a separate tube and not dependent on the spinner. In fact, the prop / pitot tube can be ground-run without the spinner.