Where to place static ports

[Jch]

Has anyone placed their static ports on the sides of the boot cowl? I looked for a reference in AC 43-13 but couldn't find anything specific. Advantages-mounting on a firm surface and shorter tube runs. Thoughts?

[Av8r3400]

I plan to vent static behind the panel. These are not sealed up cabins, so why bother with an external port?

[ackselle]

I too placed the static ports behind the panel.

[DesertFox4]

I also opted for the behind the panel porting. Works very well and is very simple. I put a tee back there with a short stub of tubing with a little auto fuel filter over it to keep dirt and what ever out of the static system.
When I bought my first Kitfox, a model 3, I did the same thing to it after the static port came unglued from the side of the fuselage. This was easier than trying to reattach in the original location and worked better.

[HansLab]

Not me, I put the static in the back of the fuse.
And after some stories in this very forum about Side-slips and loosing altitude indication, I put another one on the other side of the fuse.
Never gave me problems since then (7 hours :-))

[Dorsal]

I am planning on experimenting with this as mine are behind the panel but my airspeed is also off by 3-5 mph (to high). Have the kit to do as HansLab did, won't get to it till spring though.

[n85ae]

I have a heated pitot/static tube out on the wing. Works great, easy install
and it's not affected by fuselage airflow weirdness, or inside cabin problems.
The only downside was that it was a bit pricey.

Regards,
Jeff

[Dave S]

When constructing our KF, I spent a bit of time looking into this issue and thinking about it....Then went with the factory specified location. No matter where the port is installed it is probably not going to totally avoid every possible installation effect on static error.

I thought back on certified airplanes I have flown with alternate static ports vented to the inside of the cabin. Most of the time they would read a higher airspeed on alternate source than the outside static. Experimenting with those, it became apparent that a cabin can be either somewhat pressurized or somewhat subject to pressure lower than static depending on how the air flows over the numerous pneumonia holes in the airframe. I know a Cessna or Piper is not a KF; but I have since found through experimentation that my Kitfox is subject to cabin pressure variations to some extent depending on if the side vents are open, conditions of slip, how much power or speed is being carried...and on and on - can't say anything about open doors since I haven't tried that.

There can be variations on the factory KF location too....not all static ports will be installed in the airstream the same way and a minor variation or tilt on the static disk or mounting can change things.

Having said all that, I do find that the factory location, at least on my plane, results in readings that appear to be minimally affected by installation error. My main interest was in having a static signal that would provide a reasonably accurate input for the transponder encoder....ground calibration/certification of the encoder does not guarantee that reported and actual altitude aloft is correct if there is a significant static port error....so far the ATC folks have not had an issue with me other than the time the encoder pooped and read 2,000' higher than actual:o (OK, where the heck are you!!!).

I figure if my altimeter puts me at eye level with most other traffic in the pattern it can't be too far off; and, that in combination with the transponder calibration should mean that the system is not too far off. Airspeed values come reasonably close to design numbers.

But then, we do learn to fly our planes without looking at the ASI & ALT too often:)

Sincerely,

Dave S
KF 7 Trigear
915ULS Warp

[N981MS]

FWIW
Series 6 IO-240
Static port stock location (or really close) on left side only.
Gretz aero pitot on left wing.

Accurate and never lost any readings in 700 hours or so. Never noticed any problems doors open, closed, slips, or otherwise.

[av8rps]

My Model 4 had port on right side of fuselage a bit forward of the tail section, but it was pretty consistently off, showing 10 mph too slow on ASI (Stall looked great but cruise looked poor at best). I changed static to read behind panel and now ASI reads accurate within 1 to 2 mph regardless of whether vents are open or closed.

I also have a JA Highlander that had the same error with airspeed (pretty much identical to Kitfox, showing 10 mph slow). It had a static port on boot cowl just forward of left side cabin door. I disconnected it and ran static under instrument panel and found that one to be fixed just like my Kitfox. And it didnt seem to make any difference with vent position, but it does change slightly if I have the window on top half of door open, or if I fly with door open completely.

If I really felt I had to have an external static port I would use either a combo pitot and static out on wing in relatively clean air, or I would put a static port on both sides of the fuselage teed together approx midway between tail and back of wing. Just my two cents...

[DesertFox4]

Paul- that's pretty much the same results I encountered with the static ports until I vented to behind the panel and I had ports on both sides of my first Kitfox.
My model 4 is right on with the static behind panel. Only change I can get is a slight momentary fluctuation when I open my door quickly. If I open it normal speed not much happens. My encoder is accurate also. Go figure.

[HighWing]

This is an interesting discussion. For the record I like the factory location and do have the T with ports on both sides. This location was a late decision - late 90s - as the earlier airplanes had the port behind the panel. So my installation was a retrofit on a 1998 inspected Model IV. The new location determination was made because of owner comments on their ASI readings over the years.

The reason for this post is because it seems some are getting better accuracy with the port behind the panel and some on the fuselage. A possible reason for that. On my first airplane I decided to use the water manometer to calibrate the ASI. This is done to see if the needle is pointing where it should with a precisely measured column of water creating pressure at the Pitot Tube. I found that my ASI read low on the low end giving braggable numbers for stall and it read high on the high end giving braggable numbers there as well. I think it might be entirely possible that a more correct reading - static port one location vs. another - just might be a lucky compensation for a built in error in the high end of the gauge. I doubt many of us use the GPS to help calibrate the ASI at stall so who knows actually how accurate the stall numbers are. There is a IV here that the pilot will tell you stalls at 28 mph.

Then again, since none of us use dead reckoning any more and we get used to what the gauge says and fly accordingly, is there a real issue here?

[Dave Holl]

I have built my mk 7 with a pitot static head located out on the port wing, not quite ready to fly it yet so can't say how good it will be!

[Dorsal]

Then again, since none of us use dead reckoning any more and we get used to what the gauge says and fly accordingly, is there a real issue here?

Agreed, this is one of the reasons I have not addressed mine to date. My current motivation is to get better relative wind info and just the satisfaction of knowing the instrument is correct. I will be putting the T in the back sometime this spring.

[GaryNo]

Here is what I'm using out on the wing.Pitot + Static tubes.Series 7 SS.
http://www.aircraftspruce.com/catalog/inpages/pitot15144.php?clickkey=7405

[WISDAN]

Mine is off a tee behind the panel also. All indications tested correct.

[Lion8]

I just installed two. One on each side of the fuselage, 5" up and 27"(I think) forward of the horz stab. Installing them was a real challenge. I'm still in the process of bringing this bird back to life. I took the seat out, supported the skin on the bottom, then crawled to the back. I don't have the windscreen in yet, so I rigged a block and tackle to the over head in my shop. Put the hook on my belt in the back. After I did the work, I had my son help me out by pulling me out backwards. I'm 5'7" and 175# and at 65 and not in a regular workout guy, this was tough. Not impossible, just tough. The kid got a kick out of watching me being pulled out backwards.

[jrevens]

I'm using something similar to GaryNo - a combination pitot/static mast on the wing, but I made my own.

[t j]

Lion8, if you need to get in there again to work on the static system or service the elevator tube bearing you can easily install inspection hole rings and cut a hole on the belly.

I installed the static port after I had covered and painted but before first flight. The factory did the flight testing to determine the best spot and came out with a retro fit kit right after I finished painting.

I also installed two to service the elevator tube bearing. One in front and one behind it so I can get both hands on it.

[av8rps]

I think we should all test our airspeed indicators for accuracy. With modern GPS capabilities it is far from difficult. I can't tell you how many times I've heard people that own aircraft in this design family telling others that the cruise speeds are much lower than the factory claims. And if you ask them about stall speeds they typically will state much lower numbers than is even possible. Not only is this most likely caused by a simple ASI error, but it is easily fixed if they just took the time to understand what is causing the error.

And I feel strongly that stating incorrect numbers is doing a disservice to those that are looking for information on designs they might be considering to purchase.

A while ago I saw a really good example of that on the Highlander forum; Potential buyers were hearing numbers all over the place from owners, but no one was providing any proof. So I went out on a nice night and flew my airplane at cruise speed, and took a panel picture that showed my tach, ASI, GPS, altimeter, and my VSI, and then posted the picture with a description of wind and temp conditions at the time, along with another picture showing the exterior of my plane with a general description of how my plane is equipped (tire size, gear type, prop and engine used, empty weight, etc) so everyone could see some actual proof of cruise speeds.

I say all that because my general opinion is that Kitfoxes are a lot faster than most people think they are. But we don't as a group do a very good job proving that to others that are interested in that information. Yeah, I know that a Kitfox is generally not chosen by people for its blazing cruise speeds. But kept in perspective, it is a pretty efficient little cross country cruiser (and it can land dang near anywhere to boot) that is generally underestimated by the aviation world for those capabilities.

Another good example of that is in the seaplane world; most perceive a Rans S7 on floats to be much faster than a Kitfox (on floats). But it is actually just the opposite. Now I don't know how that got started, but that was the seaplane communities general perception until I started flying my Kitfox next to the Rans airplanes in the area and starting posting proof of what my Kitfox will actually do on floats. In time, the perceptions changed and now the community better realizes how good of a choice the Kitfox makes if you want to build a seaplane.

Oh, and on a last note; I really don't think we will ever find a good place on the fuselage of our airplanes to place the static port. If you look at the proportions of a Kitfox compared to most other aircraft, the fuselage is very short and boxy, and tapers a lot front to rear. So finding an area where there is neither negative or positive pressure in normal flight in my opinion is nearly impossible. Add to the short and tapered fuselage issue the potential for some continual adverse yaw effect typical of short coupled aircraft (causing some minor lack of coordination - affectionately known as "Being a half a bubble off" ;)) and you have a scenario that in my opinion dictates that the static port be out on the wing in clean air. And even there, if you don't make an effort to fly with the ball in the center, that too will be off.

So I'll be keeping mine underneath my instrument panel...

Ok, I'll get off my soap box now :)

[SkySteve]

AV8RPS,
Nice Rant. I liked it.

[av8rps]

I think the boot cowl would be the best place of any, but my Highlander has one there and it too was off just like the one on the rear fuselage side of my Kitfox.

Maybe if you used two static ports on the boot cowl, one on either side of the fuselage and teed them together it would be better?

But honestly, under the panel is easiest in my opinion. And unless your Kitfox has an airtight cabin (is that even possible?), I can't imagine finding an area that is more pressure neutral than under the panel.

[jrevens]

From an engineering standpoint the boot cowl in general is a terrible place to locate static ports. You might be able to find a specific location there on your bird that is acceptable, but being close to the propeller & in it's slipstream is bad. Because of the swirling or rotating/disturbed air, the boundary layer can be compromised. If air is impinging on the port, pressurization or de-pressurization can occur. What you want is static ambient pressure - no suckin' or blowin'. It's the same issue in the cockpit... air rushing past openings on the fuselage can cause increased or decreased cabin pressure. I know that location works fine for some, but it can be a crap-shoot. If you're going to put it on the fuselage, the rear sides are usually the best, as proven by multiple factory built designs for many decades. One on both sides, teed together will help eliminate the issue of inaccurate pressure due to slips.
So, engineering aside, whatever works for you on your particular airplane is all that matters, I guess, so... never mind. :rolleyes:

[Av8r3400]

Putting it on the side of the cowling would mean it would need to be disconnected every time you removed the cowl to service the engine.

[Dorsal]

So that was disappointing, I spent a couple of hours and moved the Static port to the recommended location along the side of the fuselage. My airspeed went from indicating 3-5 mph too high to 7-8 too low :(
On the bright side it turns out adding an inspection port after the fact (in a location I can not reach from inside the plane) was fairly easy.

[av8rps]

I'm curious, have any of you Kitfoxers with the static port out on the wing tested the accuracy of that location?

I have a Kitfox 4 project and a new Highlander project that I could still change to that if I knew it actually was accurate. Otherwise I will make my new planes like my old ones, taking static from behind the panel...

Paul Seehafer
Central Wisconsin