Wicked Stick

Wicked Stick

Well Known Member
I'd like to check for any leaks in my Pitot and Static lines before riveting on my top skin and starting to bond the windscreen. [RV-8]

I'm looking for ways to provide pressure to the pitot system and vacumn to the static port so I can monitor the Altitude and Airspeed readings on my AFS 3500 EFIS.

It's my understanding that if I can get less than a 100 foot drop of altitude from 1,000 feet in one minute I'm good with the static lines and if I get less than 10 knots of airspeed drop I'm good with the Pitot.

What local "home-made" tools have others used to create vacumn around the static port and pressure attached to the tip of the pitot ?
 
crude method

Here is the most crude method you will find. I tapped into the lines by inserting a t fitting and extending a long tube out to where I could reach it. For pitot I just blew into the tube and noted that both my steam gauge and my 3500 presented exactly the same numbers. For static, I taped over the ports then sucked out the air (with my mouth) until both my steam and efis read 1000 ' above the airport. I then folded over the tube and clamped it. It took more than 15 minutes to loose the 100'. I won't fly into airspace that requires a pitot/static check until I have someone do my test properly but I feel confident that my system is working since a have 2 separate instruments that agree for each test and the system seems leak free.

Also, you can search the site for manometer. You can build one and do a fairly accurate calibration of the system if you so choose
 
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andrew phillips said:
Also, you can search the site for manometer. You can build one and do a fairly accurate calibration of the system if you so choose
Click to expand...
Dave
I've got a manometer in the hangar I use for setting the carbs on the Gold Wing that you are welcome to borrow
Jack
 
USCANAM said:
Dave
I've got a manometer in the hangar I use for setting the carbs on the Gold Wing that you are welcome to borrow
Jack
Click to expand...

Thanks Jack, I appreciate the offer.


Rockyjs said:
Dave,
Here is a link to the one I made. It's been used by other pilots at our field. Very accurate! This will work for vacuum and pressure. I use a blood pressure ball to control the air.

http://www.iflyez.com/manometer.shtml
Click to expand...
In the spirit of building my RV for recreation and "Education", I think I'm going to build the manometer from the link above and give that a whirl.
 
I tested my pitot line with the same rig I used for testing the fuel tanks. I hooked a keg pump to the fitting inside the fuselage and secured a balloon over the pitot. When the balloon stayed inflated overnight, I knew there were no leaks in the system. Thus, I only had to worry about the connection at the instrument panel. Don't laugh, it worked perfectly.
 
Follow up home-made pitot static check.

I connected a hose over the pitot under the wing, and blew into it (slowly) until I reached about 180kt indicated on the EFIS (AFS 3500). Then I pinched the hose shut and capped it off. When trying to cap it, a little leaked out but once capped, it settled on 160kt. Then I waited a little over a minute and I only lost 2 knots. From what I was told by an avionics guy at a nearby field, this was well within spec. (10 kts in 1 minute is considered o.k.)(Cool, I'm way better than that.)

Next I tried checking the static line. I went and got a suction cup from the hardware store, drilled a hole in the middle, and glued it to a piece of clear rubber tubing. Then I covere'd one static port with electrical tape, and proceeded to slowly suck on the hose with the cup on the other port. Well, it had a big leak. :mad: Like a recent post, I too had leaks at the static port and side of the fuselage.
So, I crawled back into the "tunnel of love" (RV-8) and discovered I had forgot to use sealant where the line attaches to the port. (duh) :(
So, I removed the lines, coated everything with sealant, and put it all back together. Once dry, I checked it again.
It was good to go after that. The avionics guy says that at 1,000 feet you should have no more than 100 feet loss in 1 minute, so I was really happy cause I never saw it go down more than 10 feet in 3 minutes.

One question though, I notice that as I would suck and bring the altitude indication up, the airspeed would also go up with it ?????? Is that normal ?
 
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Wicked Stick said:
One question though, I notice that as I would suck and bring the altitude indication up, the airspeed would also go up with it ?????? Is that normal ?
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Yes - the ASI measures the difference between the pitot and static pressure, and converts that difference into an airspeed reading. At sea level, under standard conditions, if you decreased the static pressure to increase the altitude by 1000 ft, the ASI should read 148 kt. If you took the altimeter up to 2000 ft, the ASI should read 207 kt. Obviously one could damage the ASI if the static pressure was decreased too much without also sucking on the pitot line. For example, if you sucked hard enough on the static line to take the altimeter up to 20,000 ft, the ASI would read 536 kt. Our ASIs aren't built to take that.

Also, be careful to release the vacuum slowly, so the ASI and altimeter innards don't get spun around too fast.
 
Thanks Kevin,

I was very cautious about the speed at which I let air pressure in and out.
The most I brought the altitude up to, was about 3,000 feet.
That's when I notice the airspeed was in the red zone and I brought it back slowly to 1,000 for the time check.

I'll have to do it again and note the airspeed at 1,000 and 2,000 to see what the indicated airspeed reads.
I currently have the plane here at the house, which is approx. 40 feet above sea level, and I could set the alt to a nearby airport's current reading when trying this. Or, should I just set it to 29.92 ?
 
Kevin Horton said:
Obviously one could damage the ASI if the static pressure was decreased too much without also sucking on the pitot line.
Click to expand...

Sucking on the Pitot ??? When flying/climbing the air pressure goes down in the static system the higher we go. The air speed forces air "in" the pitot tube. So, wouldn't I want to blow into the pitot instead of suck ? I'm confused now. lol,... Please explain for this non-rocket science guy that I am.
 
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Wicked Stick said:
Sucking on the Pitot ??? When flying/climbing the air pressure goes down in the static system the higher we go. The air speed forces air "in" the pitot tube. So, wouldn't I want to blow into the pitot instead of suck ? I'm confused now. lol,... Please explain for this non-rocket science guy that I am.
Click to expand...
The ASI has a diaphragm inside, with static pressure on one side of the diaphragm and pitot pressure on the other side. The difference between those two pressures moves the diaphragm, and the movement is translated into ASI needle movement. If the pressure difference across that diaphragm is too great, you could damage the ASI internals.

Sitting on the ground, the ASI sees ambient pressure on both sides of the diaphragm. The difference between the two pressures is zero, and it indicates zero airspeed. If you accelerated to 250 kt, at sea level, the pressure on the static side of the diaphragm would still be the same (29.92 inHG), but the pressure on the pitot side would be 33 inHG, or giving a pressure difference of 3.1 inHG.

If you are doing a static system test at sea level under standard conditions, and apply vacuum to bring the altimeter up to 3000 ft, the pressure in the static system is 26.8 inHG, or 3.1 inHG less than the pitot pressure on the other side of the diaphragm.

Now, imagine that you wanted to bring the altimeter up to 20,000 ft. The pressure on the static side of the diaphragm will now be 13.75 inHG, giving a difference across the diaphragm of 16.17 inHG (the pitot side is still at 29.92 inHG), and the ASI would read 536 kt. ASIs for RVs aren't built to indicate speeds that high, so it would probably be damaged. If you wanted to prevent it from being damaged, you would also apply vacuum to the pitot system to prevent the pitot pressure from being too much higher than the static pressure.
 
ASI-operation-FAA.png


Thanks Kevin, Found a picture of the diaphram part and had forgotten about the ASI having to use both references. (doh)
 
testing

In regards to my own aircraft, I had a difference of at least 200' between my altimeter and altitude encoder. Since I fly under and in a Class B veil; it's of great importance to be corrected... as well as a legality.

As it turns out, my altimeter was correct (which I suspected) and the encoder was off. The pitot setup had a very small leak which is actually okay, but the static has to be leak proof, and it was. My altimeter is a tso'd six pak variety, and the encoder is Ameri-king. Some will hit right on, and some don't..........according to the technician. You can have up to a 125' variance max. Mine was tested to 20,000'

L.Adamson --- RV6A
 
Easy to put togeter, easy to use airspeed tester

I've made a simple device to test airspeed indicators because it was bugging me that everybody claims different speeds when I fly with them and we never know whose is in error, or both of ours.

Using a latex pressurizing bulb like those used on blood pressure testers and an anolog meter calibrated in inches of water the tester is very simple and is dead on accurate. Here is the basic set up, but this kit is very expensive. If you order just a guage off ebay and get a pressurizing bulb you can be into one of these pretty cheaply. The bulb is nice because it has a thumbscrew on the side so you can slowly bleed the pressure down to what you would like to measure and then seal it off while you go look in the plane. Mine has a rubber hose so we can use it on typical pitot tubes, and an AN termination so it can go onto the nipple that our homemade pitots screw onto. I'll take a picture of it at the hanger today. Everybody uses mine and it has paid for itself over and over. Total price, about $40.

(If you happen to have an extra airspeed indicator laying around you can use it instead of, or in addition to the guage)
 
Bryan Wood said:
Using a latex pressurizing bulb like those used on blood pressure testers and an anolog meter calibrated in inches of water the tester is very simple and is dead on accurate. Here is the basic set up, but this kit is very expensive. If you order just a guage off ebay and get a pressurizing bulb you can be into one of these pretty cheaply.
Click to expand...

Hopefully these devices are much more accurate than the spec sheet claims. The unit in the link is good to 100" of water, with a claimed accuracy of 2%. It isn't clear in this spec sheet, but normally accuracy numbers are with respect to the full scale reading. 2% of 100" of water is 2" of water. An error of 2" of water at 180 kt is an 8 kt error.
 
Kevin Horton said:
Hopefully these devices are much more accurate than the spec sheet claims. The unit in the link is good to 100" of water, with a claimed accuracy of 2%. It isn't clear in this spec sheet, but normally accuracy numbers are with respect to the full scale reading. 2% of 100" of water is 2" of water. An error of 2" of water at 180 kt is an 8 kt error.
Click to expand...

Yeah Kevin, no kidding. I just linked to that to give an idea. The one I use is a little more serious and came from a former aviation background. When I was looking around the guage sold for around $20 on ebay. If you happen to have an airspeed indicator you can use that in place of the guage.
 
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I don't know about just using another airspeed indicator, but want to ask opinions on this:

Of the methods discussed so far & short of having an actual certified & calibrated test set; which would be the most accurate?

-well built water manometer
-mechanical gauge calibrated in inches of water
-and then I'll throw in a third one, say an MGL Avionics ASX-1 spec'ing airspeed accuracy at +-1% at 85mph, altitude +-30' at seal level

I'm just wanting a method to ensure round gauge & encoder accuracy to the best I can attain, in between 2 year certifications.
 
GrayHawk said:
I don't know about just using another airspeed indicator, but want to ask opinions on this:

Of the methods discussed so far & short of having an actual certified & calibrated test set; which would be the most accurate?

-well built water manometer
-mechanical gauge calibrated in inches of water
-and then I'll throw in a third one, say an MGL Avionics ASX-1 spec'ing airspeed accuracy at +-1% at 85mph, altitude +-30' at seal level

I'm just wanting a method to ensure round gauge & encoder accuracy to the best I can attain, in between 2 year certifications.
Click to expand...
I'm a fan of a water manometer, but it is a bit bulky. If you can measure the water height with 1/16" accuracy, that amount of error represents 1 kt of error at 50 kt, 0.5 kt error at 100 kt, and 0.3 kt error at 150 kt. I think in practice you can probably measure more accurately than 1/16".

You also should use distilled water, or at least water that you are sure is quite pure. And be sure the manometer is vertical. If the temperature is very warm, you could also correct for its affect on water density, but that is a second order effect.
 
Here is an example of the guage that I'm using. It is made by Dwyer Instrument and has tolerence of 2% at full scale deflection. I think this one has a range of 0-20 inches of water which is a good range for the RV's airspeed, but one with a scale of 0-15 inches of water might be better. Mine happens to be ranged from 0-50 inches, but it was used on Airliners in its past life. But what the heck, it still works for a quick check, and certainly finds leaks while it gives a decent reading on airspeed.
 
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