Pitot Leaks

Hello Gents

This week end I flew my RV-4 in formation with a friend of mine ( Also an RV-4 ) and we started checking our IAS/TAS/GS as we were moving along and to my surprise his IAS/TAS were 12 knots higher than mine on the same GS.

Mine were IAS/TAS ; 140/148 knots at 4500' and 2450RPM and his were exactly 12 knots higher at the same altitude and RPM.152/160 .

I think mine are a little low for an RV-4 with an 0-320 with around 175HP. so after talking with a friend who an engineer on the C Series ( Scott here on VAF ) he told me that I may have a leak in my pitot lines..

I have a Dynon Skyview with the Dynon pitot installed and used these to do the connection to the Adhars..

http://www.steinair.com/storedetail.cfm?productid=532

Are these good enough to provide a good seal or should I use something and if yes...What should I used??

Also what did you guys used to make the connection at the pitot level ( Connecting the pitot line and the AOA line)???

Thanks

Bruno
[email protected]

I fixed the leaks in my system by putting some DC4 lubricant on the outside of the plastic line and then reinserting the tube into the connector. Technique curtesy of Walt.

Stein's fittings work great.

I would recommend to use a Pitot-Static test set and inspect your system if you have a leak or indication failure.
You can easily troubleshoot that system with isolating parts of the tubing.
The fittings from Stein are great. I always use teflon tape on the threads of fittings.

kai

wrigley's spearmint gum!

It is always good to do leak checks on both pitot and static. The static system is much more sensitive to leaks than the pitot however. You might notice that for certified aircraft, the regs list a static system leak rate, but leave the pitot leak rate up to the aircraft manufacturer.

It takes a pretty significant pitot leak to cause an error in airspeed. It is always possible that a pitot tube is set up to close to the wing which could cause an error, but more likely it is a static system error. If you both set your altimeters to the same altitude on the ground, then did a similar side by side test, would the altimeters read the same? If so, then it is a pitot problem. If not it is a static system problem. The static port can be a source of large errors if not set up properly.

It also might be your friends airplane and not yours.

Static errors are the most common cause of IAS errors in my experience.

Do you have the standard pop-rivet head in the location described in the manual?

MY RV-4 had been modified with a flush static vent and didn't read correctly until I glued a pop rivet head over the flush vent. Some have experimented with dams etc to adjust the static pressure to the true, free-stream value.
The same goes for checking for static leaks as cabin static could easily give a 5-10 knot error.

He said the alt was the same as the other airplane he was formating on so likely the static is fine.

sblack said:

He said the alt was the same as the other airplane he was formating on so likely the static is fine.

Click to expand...

Missed that. Yes if the altimeters were matched, then either pitot location or a leak.

sblack said:

He said the alt was the same as the other airplane he was formating on so likely the static is fine.

Click to expand...

I wouldn't rely too much on that. A 5% error in IAS due to static error at 120 knots is equivalent to a 50 ft altimeter error. That could easily be lost in the other errors when comparing altimeter readings.

E.g.At 120 KIAS at sea level the static pressure is 1.00 atmospheres and the Pitot pressure is about 1.02 atm.. It doesn't take much of a static error to cause a significant airspeed error!

It's very easy to check for a leak.
tape over the drain hole in the pitot.
Slide some snug fitting vinyl tubing over the pitot. Use tape to make it air tight.
Drop the vinyl down, then up, in a "U" shape.
Add water to the free end. You should see the water higher in the free end than the pitot end. IF the water levels are the same (or rapidly get that way) you have a leak. Don't let water actually enter the pitot.

Hello Gents

First, thanks a lot for all the replies, it is very interesting.

Kai: I would recommend to use a Pitot-Static test set and inspect your system if you have a leak or indication failure

It is in the ''To Do'' lists as I want to get the A/C IFR Certified, it will have to be done, for sure next spring but I might have the machine hook up to see if I have a leak without going thru the whole test before I park the A/C for the winter.. ( I don't fly it in the winter ) so It will help find any leaks and check the system.

Mark: Do you have the standard pop-rivet head in the location described in the manual?

I have the Flush Type I would say, The Static Port are 2 little hole on either side of the A/C about midway to the tail ( I didn't build the A/C but could look at the plans and see if there is a note on that ) but there are definitely no Pop rivets heads installed

I will check our altimeters on the ground next time I fly with my buddies and compare. It will give us a good idea on who's might be off.

Bob: I'm not so sure I understand the way you're doing this test but I remember reading about it. Would you have any pictures of this set up??

I also check all the line today and blew air thru them to make sure there wasn't any obstructions.( Yes I did disconnect them before doing that ;-)

From your experience, what will be a ''standard'' IAS/TAS for an RV-4 with an 0-320 at 4500', 2450 RPM,Temp 13C /56F, Altimeter 30.52.

Today on a test flight,Mine were 130/142 with winds 290/11(10 KNOTS Headwind), HDG 275 and GS of 132 knots. Heading in the opposite direction ( 095 ) reading were the same except the GS was 152.

I'm off to work tomorrow, back on Thursday so I will try to have another look at the Static/Pitot lines again as soon as I can.

Keep on posting your feedbacks, it is really appreciated.

Thanks

Bruno
[email protected]

RV-4 said:

I have the Flush Type I would say, The Static Port are 2 little hole on either side of the A/C about midway to the tail ( I didn't build the A/C but could look at the plans and see if there is a note on that ) but there are definitely no Pop rivets heads installed

Click to expand...

My experience was that the pop rivet head bought up my indicated airspeeds by 5-10 knots and they then read pretty close to the truth.
All I did was cut the head off the pop rivet and glue it on with some cyano-acrylate glue keeping a pin done the holes to stop glue entering the tube.

Mark Albery said:

I wouldn't rely too much on that. A 5% error in IAS due to static error at 120 knots is equivalent to a 50 ft altimeter error. That could easily be lost in the other errors when comparing altimeter readings.

E.g.At 120 KIAS at sea level the static pressure is 1.00 atmospheres and the Pitot pressure is about 1.02 atm.. It doesn't take much of a static error to cause a significant airspeed error!

Click to expand...

The other smoking gun is that he just re-installed the pitot and he has not had significant airspeed errors in the past (this airplane has many hrs on it). That makes me think that it was the last thing he worked on. But your point is well taken. I guess he needs to test the whole p/s system.