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Static Ports

Sig600 said:
I can't believe I'm asking this question, but I can't think of a good answer...

In an unpressurized vessel (i.e. an RV) why can't you get a source of static air from within the plane itself? Something like an open port within the empennage?
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The air that goes around the aircraft is accelerated as it goes around the fuselage, just as air is accelerated as it goes around the thicker parts of the wing airfoil. Bernoulli's Law tells us that the static pressure of this accelerated air is lower than the ambient pressure. The cockpit is exposed to the lower pressure air around the fuselage by the small leaks around the canopy. Thus the air inside the fuselage is usually a bit lower pressure than the ambient pressure. The air pressure in the fuselage also varies depending on whether the fresh air vents are open or closed.

RVs with leaks in the static system typically have IAS that read roughly 10 kt too high in cruise. The altimeter would also read 100 to 200 ft too high.
 
different ports

Mike S said:
O.K., are you cutting them in half first? so they look like the setup in this photo I borrowed from David?

20072010001.jpg
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Hey Mike:

I am referring to the wing mounted mast type pitot-static devices. The O ring is sized to slide over the tube and adjust the static pressure in flight. The picture you posted shows one method of tuning the fuselage mounted static ports...

Sorry for any confusion!

Carry on!
Mark
 
I have a flush mounted static, drilled a hole in the middle of a #10 screw and I believe my IAS is on the slow side. Time to test this again and see if I can get it more correct. I like the low pass test and see what the altimeter says.
 
Fly a GPS box and compare it to the TAS on your EFIS if you have one. Thats the easiest method.

try to do your runs under the same conditions (i.e. Temp/QNH/Throttle/rpm/mixture) that way its easy to compare.

Low level with all the levers forward is the most fun too! :)
 
Phil said:
Does anyone have any experience with the Cleveland ports installed in the RV-10 standard location?

http://www.cleavelandtoolstore.com/prodinfo.asp?number=SPF50

These are what I installed early in the project without having talked to others about their static port choices on the -10. I wish I had gone the SafeAir route, but I'm curious to know if anyone has experience with these.

Thanks,
Phil


spf50_lg.jpg
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I have these static ports as well and can not quite figure out If there is a quick connect coupling available for the barb end. I look up the safeair1 kit and stein air's kit but could not decide which one is better. Did anybody use either kit. What is your recommendation?
 
G34U said:
I have these static ports as well and can not quite figure out If there is a quick connect coupling available for the barb end. I look up the safeair1 kit and stein air's kit but could not decide which one is better. Did anybody use either kit. What is your recommendation?
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Give Stein or Jed a call at SteinAir.

I can't quickly put my hands on the details, but they do carry additional parts not on their web site and can set you up will everything you'll need.

All my parts that I got from them are setting in a box at the airport.

bob
 
I used Tygon tubing from Cleveland. The 1/4" hard static lines slide nest into the larger 3/8" tygon tubing.

They probably air-tight on their own, but I went ahead and mixed up a batch of pro-seal and put it on the 1/4" tubing before inserting it into the tygon. I believe it's completely air tight now.

Phil
 
Well I just ordered the Safeair1 static ports and are going to give them a try. I spoke with them and they claim that they are machined to replicate the Pop rivet and to sit at the same distance from the fuse as the Pop rivet style. They also came with the snap fittings, tubing etc for both the pitot and static system, and have a compression connection to the port. Time will tell how accurate they are.
 
Those are the ports I have and while the kit is awesome, I had poor accuracy. Your results may vary. I think it is hit and miss with any off the shelf solution. It takes verification and fixing if needed.

Bill.Peyton said:
Well I just ordered the Safeair1 static ports and are going to give them a try. I spoke with them and they claim that they are machined to replicate the Pop rivet and to sit at the same distance from the fuse as the Pop rivet style. They also came with the snap fittings, tubing etc for both the pitot and static system, and have a compression connection to the port. Time will tell how accurate they are.
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I just did a static test by doing a low pass and my the result was not what I had hoped. My altimeter drops about 70-80 feet at around 100K.
My static ports are flushed with the skin, so I am going to change them to a slightly raised and see how that will work.

Any one has a good reference as how much it should be raised pass the skin in a RV7?

Happy new year to all.
 
Those side skins are 0.025. And assuming you don't put any primer on the inside of the skin (I did initially but later removed it with scotchbrite in favor of alodine) they'll poke out 0.030.

Phil
 
Phil,
Are you flying and if so, how is the result with 0.030 protruding out?


Thanks and happy new year
 
I think this is posted elsewhere but for convenience I will go through the history of this again.

For well over a decade we made static ports with flat faces. These were intended to mount on the inside of a bare skin. They had a .025" step on them that transitioned into a 45deg. taper up to an ultimate thickness of .035". We had zero complaints about the ports until the RV-10 kit came out. Either due to different airflow, or more sophisticated and redundant ability to monitor the system, their became and issue. As I remember a builder added the head of the pop rivet in van's kit to the face of our port and the problem was minimized. This indicated that the port was not far enough into the airstream. Listening to several other builders we concluded that the ports were often installed different than the intention. I will separate out the common mistakes for those who like to skim.

First is the primer. Builders have transitioned in the last two decades from keeping the skins bare on the inside to various methods of surface protection. This adds thickness and commonly even more thickness at the edge of the hole where the port is attached. Some even primed the port itself adding twice the thickness. The thicker the primer the less the port sticks out.

Second is adhesive. Many builders attached the ports with RTV or proseal rather than riveting them onto the inside of the skin. This obviously adds thickness as well.

Third is painting. Builders would often mask the port when adding paint (sometimes a lot of paint) to the exterior. It is recommended that the ports be painted unless a provision is made to allow them to protrude further to allow for paint.

Fourth is countersinking. Seldom but still present were builders that would countersink the port, but not deep enough to accept the skin dimple. The port would sit on the dimples rather than the skin.

The net result of any of these mistakes was that the flat face of the ports would not protrude out the intended .010" into the airflow. We added the dome to the port in hopes that it would stick out far enough regardless of how the builder installed it, now there is a 0.025 step with a 0.035" height radius that should protrude from any finishes added to the surfaces. We have not had any complaints since changing the design. I can't speak for other manufacturers but I am guessing that any errors are resulting from similar installation problems. Please let me know if there are other questions, or if anything here is not clear.

Thanks,
Mike
 
Mike,
I appreciate the write up and good explanation. As mentioned in my earlier post, I have just found out that my static port which is flushed to the skin (it is a Philips screw that I drilled a hole in the middle of it) is causing about 80 feet of altitude error (lower) and my IAS being lower then real airspeed using the GPS method. I am very interested in your ports, only thing that my plane is painted and I really don't want to use rivets (again due to paint) and gluing them obviously will change the designed amount that it protruded out.

So, just wondering, do you make different sizes of static port that would account for such installation and are these made more specific for RV10 or would it work just as good in a RV7A?

Thanks again for all the info.
 
Just put 2-8 ply of Scotch pieces of tape behind the port to increase the pressure until your altitude/IAS is right on. You basically have a drop of 0.08" Hg and the tape behind the port will increase the pressure. We had an increase of about 0.012" on my friend's plane and 4 ply of tape in front of the port reduced his error from -4 mph to right on.
 
Brian,
Did you install the safeair1 ports in an RV-10 or Rv7? How far do you think they protrude from the skin?
Bill
 
RV7...I will have to check my notes on the stickout.

Update:

Found the thread that discussed this:

The ports extend from the side of the fuse .051 on the left and .053 on the right.
 
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I measured the depth of the Safeair1 ports, and including the bevel, they are .087 proud from the flange. this would put them, assuming no paint, at .055 protruding from the skin. So with a little primer I would guess that yours are about where I would expect. The Cleaveland ports protrude from the skin .030, which is what the Vans rivet head is supposed to be.
 
I used proseal to attach so that took up some.

I ended up drilling and adding a pop rivet with a washer under it to get mine .081/.083 of stickout. Works much better now!!!!
 
do you make different sizes of static port that would account for such installation
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Looks like you have them fixed, but we can customize them however you would like. They work for all RV's and I would assume most other aircraft as well.

.
 
clevtool said:
Looks like you have them fixed, but we can customize them however you would like. They work for all RV's and I would assume most other aircraft as well.

.
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Mike,

Are the static ports to be proud of the skin surface sufficiently to be (mostly) out of the turbulent boundary layer? So theoretically, further out from the skin surface is better?

Bevan
 
Bevan,

That is the way that I understand it, but I am certainly no expert in this. There are likely some 'fluids guys' reading here that could answer that one??
 
Our static ports were stuck out a fair way, and we had a massive error, refer to my earlier photo.

The adding of a rivet head and subsequent filing and then adding the fence was the best I could do.

I would really like to get a good static, and anything poking out in the airflow is likely to ice up.......:eek:
 
Bit of data, and a question

Yesterday I paid attention to the altimeter while on take off roll.

I saw a drop of 20-30' as the plane accelerated-----till I had to pay attention to the actual takeoff. I do not know how much it dropped in total, prior to liftoff.

This would seem to be indicating to me that the static port is seeing increasing pressure as the plane is moving faster/getting prop wash over the port.

???????
 
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Mike S said:
Yesterday I paid attention to the altimeter while on take off roll.

I saw a drop of 20-30' as the plane accelerated-----till I had to pay attention to the actual takeoff.

This would seem to be indicating to me that the static port is seeing increasing pressure as the plane is moving faster/getting prop wash over the port.

???????
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You're right, Mike! that 0.025" pressure increase, if carried through at the same amount, would make your TAS at 8000' dalt and 200 mph TAS look like 197.8 mph. See, you didn't realize just how fast you are going!
 
Mike S said:
Yesterday I paid attention to the altimeter while on take off roll.

I saw a drop of 20-30' as the plane accelerated-----till I had to pay attention to the actual takeoff.

This would seem to be indicating to me that the static port is seeing increasing pressure as the plane is moving faster/getting prop wash over the port.

???????
Click to expand...

I've also got flush static ports and have seen the same phenomena - the altimeter shows about 30-40' low while flying a few feet over the runway at about 100 kts. My GPS/ASI calibration showed that the ASI reads about 1-2 knots slow, which is roughly consistent with Ellippse's post?
 
Mike S said:
Yesterday I paid attention to the altimeter while on take off roll.

I saw a drop of 20-30' as the plane accelerated-----till I had to pay attention to the actual takeoff.

This would seem to be indicating to me that the static port is seeing increasing pressure as the plane is moving faster/getting prop wash over the port.

???????
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Mike,
Mine was flushed to the skin (RV7A) and I was showing 60-70 feet lower when doing a low pass, just as your test. My IAS was also lower the actual. After many test with different head size and shape static port, I have got the best result by adding a 0.035 rivet head to my static port. The low pass does not change the altitude when I am at 5-10 feet off the ground and my airspeed is now within one knots accuracy.

In my case, it proved that any size flat shape static port yields the same result and I needed a curved shape in order to change it. We are close enough if you want to see what I have done.
 
Mike S said:
Yesterday I paid attention to the altimeter while on take off roll.

I saw a drop of 20-30' as the plane accelerated-----till I had to pay attention to the actual takeoff. I do not know how much it dropped in total, prior to liftoff.

This would seem to be indicating to me that the static port is seeing increasing pressure as the plane is moving faster/getting prop wash over the port.
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This could be a hint of a static source position error, or it could be a sign of ground effect. The airflow patterns around the aircraft are different when in ground effect than they are when clear of the ground. This may affect the pressure at the static port. So, if you are going to compare altitude indications to visual height above the ground, you should do this at a height of at least one wing span so can be sure your results are not affected by ground effect.
 
I have to agree with Kevin here, I have this also and many aircraft do it.

Most likely as the static is at the rear of the aircrfat it gets closer to the ground (not 30 feet of course) and all sorts of pressures will be flowing around there at the point of rotation.

DB :cool:
 
The plans make it sound like this is optional

Building the tailcone now and from the book it says:

Page 10-14 step 3

Drill the hole (indicated in the blowup) for the static source in both the F1073L & R side skins using a #30 drill. If you didn't choose the Static Kit option, the two holes can be dimpled and filled with flush rivets.


He makes it sound like the static port is highly optional?? Even if I have every electronic gadget made by man, I will still need a static port, right???

Big emphasis on the question mark. Is he saying if you use OUR static port then do this.. if using someone elses, plug the hole...
 
Bavafa said:
My IAS was also lower the actual. After many test with different head size and shape static port, I have got the best result by adding a 0.035 rivet head to my static port. The low pass does not change the altitude when I am at 5-10 feet off the ground and my airspeed is now within one knots accuracy.
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Out of curiosity, what type of rivet head did you end up using and how far off on airspeed were you originally? I think I've got about a 5-kt TAS error (reads 5 kts too low when compared to a 3-way GPS run) I'm trying to get rid of and have been suspecting that my almost-flush SafeAir ports may need some modification.
 
JackinMichigan said:
Is he saying if you use OUR static port then do this.. if using someone elses, plug the hole...
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That's what he's saying. Of course, Van's has spent a lot of time and effort figuring out the location and configuration of accurate static ports for the air frame. This is a very tricky and time-consuming thing for a a flight test organization to do. It is unlikely that you'll find a better place or configuration, so there isn't a whole lot of motivation to NOT use the Van's design. Many have tried...many have been disappointed....
 
Being the OP, I thought I would report the results now that I am flying. I installed the Safe Air 1 static ports available through Avery. They were installed in the pre-located/pre-drilled position on both sides of the fuse. They were installed from the inside out using both a small application of pro-seal and -3 rivets. My three leg GPS calibration is spot on. I see less than 1 kt error at 170 kt level flight.
 
Thanks Bill

Good to know. I also bought the Safe air kit and was hoping to hear results like this. It won't keep me from testing my own system during Phase 1, but it's good to hear of positive results.
 
I know it's an old discussion however I realized today while looking through the data that on ground with 0 Groundspeed (GPS), my EFIS records about 10 kt of airspeed when the prop is turning about 1000 RPM. I wonder if this will be consistent over the speed band. I see my clean stall at about 70kt which would support the theory of a consistent offset by 10 kt. Looks like I need to calibration runs again. I have the Cleveland ports installed which protrude the skin.
Mike
 
Michael Wellenzohn said:
I know it's an old discussion however I realized today while looking through the data that on ground with 0 Groundspeed (GPS), my EFIS records about 10 kt of airspeed when the prop is turning about 1000 RPM. I wonder if this will be consistent over the speed band. I see my clean stall at about 70kt which would support the theory of a consistent offset by 10 kt. Looks like I need to calibration runs again. I have the Cleveland ports installed which protrude the skin.
Mike
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There is a reason why analog ASIs generally don't display until the airspeed is at least 30 or 40 kt. At very low speed, the amount of pressure difference between pitot and static required for a given airspeed is extremely low, which makes it very difficult to measure such low airspeeds with any reasonable accuracy. The pressure difference goes up as roughly the square of the airspeed.

It only takes a difference between pitot and static of 0.0048 inch HG to equal an ASI reading of 10 kt. At 70 kt indicated, the difference between pitot and static is 0.235 inch HG. If there was the same error in pressure at 70 kt as there was at 10 kt, the error would only equal 0.7 kt.

But, it would be worthwhile to check for a leak in the static system. Static system leaks usually produce ASIs that over read, as the pressure in the cockpit is usually a bit lower than the ambient pressure.
 
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Kevin,

you were right I had a small static leak which I fixed. My backup ASI read then correctly but my EFIS was still off about 8 kt too much. I used the off set setting now to adjust that and it looks right now.

Mike
 
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