Static port

[GT280flyer]

I am working on my instruments, air speed, altimeter and vertical speed indicator and I am not sure how the static port should be plumbed. Should it be inside or should it be plumed to the outside of the aircraft? Any pointers?

[Mnflyer]

Hi, originally on the 1 2 3 and early 4's it was just inside the plane mine was a piece of clear tubing with small holes in it connect between the AS and Alt. this works but isn't the most accurate later on I think the factory offered a relocation static port kit, I did my own and it works good.

[Dorsal]

Mine is just open behind the IP (plug with a small hole), works well.

[DanB]

Many of us have the same set-up behind the panel with that fuel filter on the end of the tube. The Kitfox is not air tight so no need to toy with where slip stream is or isn't.

[GT280flyer]

Thanks guys, sounds like a simple solution to just vent them behind the panel. I should have thought of this Saturday at the fly in at Greene, there was a lot of kitfox knowledge there and some very nice kitfoxes.

[Slyfox]

I'm not trying to burst anybody's buble here, but I did a test on my static system. I have mine set up in the rear fuse where the factory says to put it. I took a valve and installed it so I can switch between inside and the rear fuse. Guess what? when I went to the inside, my indication went up almost 15mph. take that anyway you want, but I elected to put mine to the rear fuse because it reflected my ground speed on the gps more accurately.

[Dorsal]

Interesting, might have to try that. I suspect my IAS is high but not by more than a couple mph (based on ground speed and relative wind indication).

[Slyfox]

I used a three way ball valve, I think I got it from lockwood. I put it straight through and had the valve just under the panel. with the third way vented under the panel. there was a difference.

[DanB]

Interesting, might have to try that. I suspect my IAS is high but not by more than a couple mph (based on ground speed and relative wind indication).

That's what we have noticed...perhaps off by 1 or 2 MPH, but not much more. Frequently I would bring my GPS along on flights with others that have the port terminated behind the panel. our GPS speeds (as well as the round speed indicator) all matched within a couple mph. One of the things that we have done is watch the SI when we pop a door open. It certainly fluxuates the needle for a second but always comes back to rest in almost the same place.

Skyfox, that was an interesting experiment you set up being able to switch from inside to outside...even more interesting that it brought speeds into harmony with your GPS. My first thought would be that the port outside the plane would generate more of a varient. I built mine terminated behind the panel and look forward to getting into the air soon and do some testing as well. Good thread...any others do any similar tests?

[szicree]

I'm not trying to burst anybody's buble here, but I did a test on my static system. I have mine set up in the rear fuse where the factory says to put it. I took a valve and installed it so I can switch between inside and the rear fuse. Guess what? when I went to the inside, my indication went up almost 15mph.

If your static source is so out of whack as to cause a 15 mph error on a 100 mph airplane, then your altimeter is also off by something on the order of 7000 feet! (EDIT: Bad math; more like a few hundred feet)

[Slyfox]

listen to what I'm saying, when inside the cab the reading for airspeed was faster. when switched to outside static, it went down. the altitude chaged also, I just don't remember. Now that I think about it more it was more like 8 to 10 difference. Makes since with all kinds of people here saying there kitfox is real fast when it may not be because of where they are pulling their static.

[CDE2FLY]

My static port is external (pilot side just forward and below the leading edge of the horizontal stab) where building manual indicates. Similar to Slyfox, my airspeed is consistantly 8-10 mph lower than GPS groundspeed. True airspeed is often closer to GPS groundspeed. My altimeter (set to ATIS report pressure) is consistently 100 feet below the GPS indicated altitude.

[Dave Holl]

Hi
I am building my mk7 with a pressure head, ie both pitot and static in one head in the normal place on the left wing.has anyone else done this?
Dave

[Dave Holl]

here is a photo of my installation
dave

[av8rps]

My static port is external (pilot side just forward and below the leading edge of the horizontal stab) where building manual indicates. Similar to Slyfox, my airspeed is consistantly 8-10 mph lower than GPS groundspeed. True airspeed is often closer to GPS groundspeed. My altimeter (set to ATIS report pressure) is consistently 100 feet below the GPS indicated altitude.

That is EXACTLY what I found with my Model IV. Before I figured out it was off I was thinking how odd it was that everywhere I went I had a nice tailwind...(who has that luck?). Then one day when I knew I had a strong tailwind of nearly 30 mph and the GPS was showing 136 mph groundspeed, and the ASI was showing 86 mph, I figured something was wrong. Plus my gps altitude and my altimeter never made sense. So I disconnected the static port connection and just use the cabin for my static now. And I've verified my ASI and ALT are now quite accurate. The only time that changes is when I open the door in flight. But since I rarely fly with the doors open (have great vents) that's not an issue for me.

Also had the exact same problem with the Highlander I recently purchased. It used a static port on the side of the cowl just forward of the left door, and that ASI was off by about 10 mph also. Interestingly, this Highlander went through the hands of 3 different owners, and has always been equipped with a GPS, and all the owners complained the airplane was slow. Once I realized it was off and disconnected the static port and then tested it to see if it was accurate, my airspeed was much better. At 5500 rpm I can fly at about 110 mph with a G/A sensenich 2 blade composite prop, just like the factory says it will. :)

Ironically, at the low end of the ASI scale my slow speeds stayed essentially the same. So apparently the static doesn't affect it as much at the lower end? The good thing is that my stall speed still appears to match factory specs. But I have more testing to do yet to verify that accuracy.

So...I wonder how many Avid, Kitfox, Highlander guys are flying around with their ASI being off 10 mph, and thinking their planes are slower than they really are. And how many of them might be flying approaches too fast and getting a lot of float because of that, extending their landing distances considerably? (I know I was)

I personally think our planes have been getting a bad rap for being slow from owners that have never taken the time to verify their ASI accuracy. Add to that the fact that most every pilot you take for a ride will focus on the ASI and form his opinion of how fast the plane flies on that alone, assuming it correct.

[Slyfox]

that's why it's so important to do your stall test and all flight test with your asi and not anybody elses results. If you change your instruments, like your static location or the instrument itself, you need to redue all your lest. PERIOD.

[av8rps]

listen to what I'm saying, when inside the cab the reading for airspeed was faster. when switched to outside static, it went down. the altitude changed also, I just don't remember. Now that I think about it more it was more like 8 to 10 difference. Makes sense with all kinds of people here saying there kitfox is real fast when it may not be because of where they are pulling their static.

I'm no aerodynamacist, but the Kitfox fuselage is so short and bowed out at the cabin that I believe it causes an abnormal amount of disrupted airflow down the sides of the fuselage, causing the static port on the side of the fuselage to either be pressurized or in a vacuum, neither of which we want for ASI or Altimeter accuracy. Add to that issue the fact that most of us do not keep the ball centered the entire time we are flying and we could be getting some pretty wild static signals. I could be wrong, but I really think the combination of a short fuselage with sides that are far from flat, combined with an aircraft that suffers from a lot of adverse yaw, and you end up with it being nearly impossible to find an effective static port location. It would really be interesting to wind tunnel or at least tuft test a few of our airplanes. However, even then I think we'd find a huge amount of variables impacting our results due to things like bubble doors vs smooth doors, different turtle decks, small vs larger tires, wheel pants, round cowl vs smooth cowl, antenna locations, radiator scoops vs no scoop, etc, etc.

So unless you have a wind tunnel readily accessible, I would suggest for anyone insistent on using an outside static port to do so either by putting it out on the wing like the photo in this thread shows, or putting one on both sides of the fuselage and connecting them with a tee, so as to at least minimize the error caused by pressure or vacuum effects.

It is more than interesting that we all fly very similar aircraft and yet we have ASI / ALT errors that are significantly off both ways, and appear all relative to how we decide to locate our static port. Just more proof that we should all be thoroughly testing and verifying our ASI's and Altimeters as part of the 40 hour flight testing process. I've test flown a lot of airplanes over the years, and regardless of brand it is a rare case to find one accurate as originally built.

[Slyfox]

I think I'll just continue to just fly by the seat of my pants and look out the window.

[av8rps]

Yeah, isn't that the truth? Don't tell anyone, but there's times that I do an entire flight and don't remember looking at the airspeed

[Slyfox]

easy to do in these airplanes

[Slyfox]

I was landing the other day and was doing so on the sod at my airport. I was coming in on 03 and when doing so there is a good bump on the runway. I came down, sun in front of me, I didn't look out front nore did I look at the indicators, I was looking out the left door, nice to have plexy all the way down by the way. I get 2ft off and start to flair, still to fast, hold it hold it hold it, it feeeeels right, NOW. NIce flair down I come nice, than I hit the bump, up we go, I continue to hold full aft stick, I'm back in the air, wwoooo hooooo this is fun, it settles back down nice and smooth. I'm down, coool. would like to do it again, but ... I have to go to work now.

[av8rps]

Gee, I think I'm going to order a pile of dirt so I can have a bump in my airstrip like yours :D

[dholly]

Hi Tim -

Here is the Static System Installation Instructions supplement from Skystar. Maybe it will help... for reference if nothing else. Both my M-3 and 4-1200 are set up like this. FWIW, ASI in my M-3 w/ flat doors was pretty close. I haven't flown my M-4 w/ the bubble(?) (factory not LP Aero) doors yet, but I think Paul may have a good point. Will be interesting to see.

Regards,
Doug

P.S. Put up some pics in the N.E. fly-in thread!

[av8rps]

My static port was installed to those specs. So it will most definitely be interesting if you get different results than what I did, especially when it sounds like our Model IV's are very similarly equipped.

Paul

[SkyPirate]

Quote:
Originally Posted by av8rps http://www.teamkitfox.com/Forums/images/buttons/viewpost.gif (http://www.teamkitfox.com/Forums/showthread.php?p=18545#post18545)
Gee, I think I'm going to order a pile of dirt so I can have a bump in my airstrip like yours :D

I'll let you borrow my runway if you'd like ,.. north end elevation is 1100 ASL south end elevation is 625 ASL and its 700 foot long ,..trees on one side, power lines on the other but you have plenty of room it's about 45' wide between the top of the light poles to the limbs on the trees on the other side , oh forgot to mention,..there is a 250' abstruction on the south end( a slight rise in the ground )

[DesertFox4]

Chase, I hope I saved you from bodily harm.;) Posting a photo of your wife by mistake could be hazardous. LOL!!! Tell her hi for me. Still enjoying the shirt she made for me. Please be more careful in the future. You can't run very fast anymore.;)

[SkyPirate]

your a life savor Steve! thanks lol whew ,..I'll sleep easier tonight ha ha

I'll tell her you said hi :)

oh and next time I'll preview the photo lol
I'll post the runway pic when I find it lol

[DesertFox4]

Happy to help. Hope you're feeling good. Email me off line when time permits and catch me up on things.

[SkyPirate]

as promised ,..a picture of the runway ,,I'm at the south end looking north,..you can not see the top ..but it does have allot of bumps :)