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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Thu Feb 08, 2007 7:03 am Post subject: ASIs

 	  Quote: 	
		   From: Barry West [barry(at)pgtc.com]

 But there must be  something wrong with 

 the airspeed indicator.  Does anyone have any suggestions?


	


A way to find out if it is the ASI or the static port (or cabin pressure) is to fly in a radar controlled zone with your transponder mode C then ask for altitude check. If the given altitude is the same as what you can read on your altimeter, the error is a under or over pressure in the static port (or cabin). If not, then your ASI needs calibration.



Cheers,

Michel

<pre><b><font size  color="#000000" face="courier new,courier">

_________________
Kitfox 3 - Jabiru 2200

smokey_bear_40220(at)yaho
Guest

Posted: Thu Feb 08, 2007 8:49 am Post subject: ASIs

Hi Michel!



--- Michel Verheughe <michel(at)online.no> wrote:



 	  Quote: 	
		   A way to find out if it is the ASI or the static

 port (or cabin pressure) is to fly in a radar

 controlled zone with your transponder mode C then

 ask for altitude check. If the given altitude is the

 same as what you can read on your altimeter, the

 error is a under or over pressure in the static port

 (or cabin). If not, then your ASI needs calibration.

 

 Cheers,

 Michel


	


This of course depends upon your Mod C being

calibrated and the local controller having adjusted

for the current pressure.  Why not ask him for an

airspeed readout while you are at it?  Fly cross wind

for the check.



BTW, if you ever looked right as you begin to rotate

for takeoff, the altitude goes down for a moment.  It

is due to the pressure building under the wing in

ground effect and getting to the static port, where

ever it is.  Changes the ASI too.



All of these pressure gauges are approximate and have

variable accuracy.  Never 100% and not = to a fun

meter anyway.  But is is "professional" to get close

first, then the heck with it.    Fly the thing.



Kurt S.

 

Now that's room service!  Choose from over 150,000 hotels

in 45,000 destinations on Yahoo! Travel to find your fit.

http://farechase.yahoo.com/promo-generic-14795097

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Feb 08, 2007 8:56 am Post subject: ASIs

Don't forget to tell them why you want the altitude check otherwise they

will just read your transponder  altitude right off their radar screen.

Most cases that altitude is presented as it comes from your transponder.  

At least one airliner has crashed (not Kitfox VFR conditions)  because of

that false info.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Thu Feb 08, 2007 10:20 am Post subject: ASIs

On Feb 8, 2007, at 5:46 PM, kurt schrader wrote:

 	  Quote: 	
		   This of course depends upon your Mod C being

 calibrated


	


Well ... yes, Kurt and Noel. My thinking actually comes from my first 

blunder. The previous owner of my plane flew only G airspace. Here, 

near Oslo, it's pretty much controlled so the first thing I did was to 

install a transponder mode C. On the first flight, I asked the local 

tower: "Radar check, please!" He gave me my position and altitude. 

"Cool!" I thought, "this is exactly what my altimeter shows! It must be 

pretty accurate."

Then, later one, someone told me: "Not quite so! It only means that you 

were both using the same QNH."

Indeed, because both altimeter and the transponder's altitude encoder 

are connected to the same static port.



In this case, we wanted to know if the ASI needs calibration, or if it 

is a static port problem. I suggested then a process of elimination. 

Knowing that the indicated airspeed is wrong and assuming that the 

altitude encoder is correct, if the indicated altitude matches the 

reported altitude, then one would assume that the static port is not 

really sensing the static air pressure. Does that make sense?



Kurt, of course, one could ask the controller for airspeed read out, 

but then, it would be ground speed and usually we can find that from 

e.g. a GPS. In any case, it won't tell if it is most likely an ASI 

problem, or a static port problem.



Incidentally, I also have a static port problem, my indicated airspeed 

is too high by about 5 MPH. And yes, I have the port aft, left side of 

the fuselage, as recommended by Denney (Skystar, in your case! 

When I have a bit of time, I'll try to have a double port, one on each 

side.



Cheers,

Michel

_________________
Kitfox 3 - Jabiru 2200

barry(at)pgtc.com
Guest

Posted: Thu Feb 08, 2007 10:34 am Post subject: ASIs

I have not installed the transponder yet.



Barry



Original Message:

-----------------

From: Michel Verheughe michel(at)online.no

Date: Thu, 8 Feb 2007 16:00:34 +0100 (CET)

To: kitfox-list(at)matronics.com

Subject: RE: Re: ASIs

 	  Quote: 	
		   From: Barry West [barry(at)pgtc.com]

 But there must be  something wrong with 

 the airspeed indicator.  Does anyone have any suggestions?


	


A way to find out if it is the ASI or the static port (or cabin pressure)

is to fly in a radar controlled zone with your transponder mode C then ask

for altitude check. If the given altitude is the same as what you can read

on your altimeter, the error is a under or over pressure in the static port

(or cabin). If not, then your ASI needs calibration.



Cheers,

Michel

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lcfitt(at)sbcglobal.net
Guest

Posted: Thu Feb 08, 2007 11:39 am Post subject: ASIs

I have a spreadsheet off the web for anyone wanting to check the ASI with a 

manometer.  It is a simple device made up of  a plastic tube bent into a U 

and secured in a vertical position.  Add enough water to fill the curved 

part of the U then connect one end to the Pitot tube with some tubing and 

begin dropping water in the open end.  It only needs to be 8 inches or so in 

length after the bend.



I found that my ASI is definitely not linear but accurate at about 95 mph 

and deviating at lower and higher speeds in a linear fashion.  A graph of 

the deviation looks like a bow tie.



If there is any interest, I will post it as an attachment.  It shows my 

numbers.



Lowell

---

Fox5flyer
Guest

Posted: Thu Feb 08, 2007 1:02 pm Post subject: ASIs

Please post it Lowell.  Thanks,

Deke

do not archive



---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 09, 2007 7:23 am Post subject: ASIs

How much do you guys trust the altitude feature of your GPS?  Just check and

see if your altimeter approximates the reading on your GPS before and after

take off and that should give you an idea as to how effective your static

ports are.  If the altimeter reads high, say 10% then your ASI will probably

also read too fast.  Probably close to 10% too high.



Also how long has it been since any one has calibrated their Altimeter ??



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Fri Feb 09, 2007 8:46 am Post subject: Re: ASIs

ASI, hummm...



I use to worry about mine.  Ya, I have the static port on the side, but I have a transponder also.  I remember when I had my transponder calibrated for use, they wouldn't do it unless I changed the altitude indicator, seems the higher graduate was broken.  But otherwise it worked just fine, I jokenly said, that's the nose bleed level, I don't go up that high, they didn't care, so I got a used one and put it in.



Back to the ASI, I can care less what mine says, wide open I go 90kts GPS.  At least that is what my ground speed comes out to, at about 100ft off the ground and taking a 4 point average.  I still don't care about ASI when crusing.  Ok, when do I care about the ASI, when doing a base to final turn 20ft off the ground and over the numbers, yup, I glance at it to make sure I'm at least 60mph, it's amazing how nice our foxes slow down doing a 60degree turn over the numbers.



How about the altitude indication, again I don't care to much, the only time is to make sure I'm at proper altitude, lets say 1000 over structure or when I'm told to fly at a certain altitude for sequencing.  Other than that I know what I need to fly to approach to land without looking at that round dial.  I sometimes chuckle to my wife when doing a short approach and when turning base to final just over the lights, or fence, whatever your discription is, I end up being right on the vasi lights when I level out on the final.



On the altitude indication, have you ever got off the ground at less than 200ft and hold full throttle and push forward on the stick and run along the ground 2 ft off and hit about 80 indicated and pull up and look at the altitude indicator, it doestn't move, what???  yup, all of the sudden when your at about 200ft it will finally move.  All these guages are for a guide, think of them as running on a rubber band and the response is going to be after you have already done it.  If you fly as much as I do, over 250hrs a year, you will begine to realise this is very true, you end up not even relying on them, just using them for a reference.



I also Bass fish and I have a nice Ranger boat.  When I was doing turnaments I would want my boat to go faster to impress the other person in the boat, so what I did and a lot of other guys did with their boat was to enlarge the hole in the outdrive for the speedo, wow instand speed increase, sure impressed the fella that you had for a partner that day.  I think when we pull the static port off the back of the panel and use cabin static, we are doing the same thing.  Try it if you haven't, you pull the static off the guages and you have instant speed increase.

smokey_bear_40220(at)yaho
Guest

Posted: Fri Feb 09, 2007 11:46 am Post subject: ASIs

--- kitfoxmike <customtrans(at)qwest.net> wrote:



..........

 	  Quote: 	
		   How about the altitude indication, again I don't

 care to much, the only time is to make sure I'm at

 proper altitude, lets say 1000 over structure or

 when I'm told to fly at a certain altitude for

 sequencing......


	


Well, there goes my theory that if I cruise at a hard

altitude, +/- 250 feet, I'll miss both the VFR and IFR

traffic.  



Kurt S.



Ha ha



Do not archive

 

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barry(at)pgtc.com
Guest

Posted: Fri Feb 09, 2007 11:54 am Post subject: ASIs

Here is my airspeed caliration from the initial flight testing.  It is 

essentially the same after installing a static port.  Not yet having a 

transponder, I don't know about altitude.  Like most of you, I never had any 

concern about calibrated or indicated airspeed but it would be nice to know. 

Maybe the problem will be resolved when the transponder is working.



indicated        0    20    40    60    80    100    110

calibrated       0    21    42    60    80    95      102



Barry



---

Bill Willyard

Joined: 10 Jan 2006
Posts: 34
Location: Grandville, Michigan U.S.A.

Posted: Fri Feb 09, 2007 12:04 pm Post subject: ASIs

>How much do you guys trust the altitude feature of your GPS?

    

   Not much. Not even close to field elevation and fluctuates while the GPS is stationary.

    

   Bill W.

   Do not archive

   

 

    

    [quote][b]

_________________
Bill Willyard
Classic IV 912UL

smokey_bear_40220(at)yaho
Guest

Posted: Fri Feb 09, 2007 10:03 pm Post subject: ASIs

Hi Barry,



I assume your were still on the ground at 20 knots? 





Seems that you are getting some compression at the

static port at low speed and suction at higher speeds.

 Your static port position and fuselage pitch attitude

probably are doing that, ie, you need a different port

location?



Another possibility is prop wash effects.  That can be

tested by doing airspeed checks in climb and glide. 

No change in accuracy at a given speed = not prop

wash.



In all cases, a static port out on the wing strut well

below the wing and out of propwash instead of on the

fuselage would help.  Harder to make this change

though.  Wish I had done it this way....



You might occasionally see aircraft with some small

object like a little 1/8th inch high "V" or buldge

very near the static port used to modify the boundry

layer and gain accuracy.  This takes a lot of testing

to make work.  Something that can be done with a

little tape for testing and hardly noticable for a

perminate fix after you found a shape that worked, but

involves a lot of time.



Kurt S.



--- Barry West <barry(at)pgtc.com> wrote:



 	  Quote: 	
		   Here is my airspeed caliration from the initial

 flight testing.....

 

 indicated    0    20    40    60    80    100   110

 calibrated   0    21    42    60    80    95    102

 

 Barry


	




 

Bored stiff? Loosen up... 

Download and play hundreds of games for free on Yahoo! Games.

http://games.yahoo.com/games/front

colind

Joined: 10 Jan 2006
Posts: 32
Location: Sydney, Australia

Posted: Sat Feb 10, 2007 7:09 pm Post subject: Re: ASIs

Hi!



How many of you have a static chamber fitted to your Altimiter air-line, or is your Alt simply connected directly to a single static port? If you do have a static chamber, how many feed lines/static ports have you got connected to it? Alternatively, if no static chamber, how many static ports have you connected via "tee and branch" to your air line?



Because the air pressure at each point around the surface of the aircraft is dynamic during the various phases/states of flight, ie: as the airframe alignment changes relative to the airflow, and at different power settings, etc, etc; trying to measure the static air pressure by just one port is problematic, no matter where you locate it. If you sample the pressure at several locations, and then mix these in a static chamber, the extremes tend to cancel out and you develop a stable, relative atmosphere where the pressure closely reflects that in still air away from the airframe.



For the static chamber to work, you need at least 2, preferably 3 or more static ports, located in diverse points around the aircraft, plumbed individually back to the chamber. The static chamber should be at least 1ltr (1 quart (very roughly)) in volume, and be of rigid construction.



Probably preaching to the converted here, but it really does improve the accuracy of the Altimeter (as long as you then set the QNH, or Area QNH correctly).

Regards



Colin Durey

Sydney

_________________
Colin Durey
Sydney
+61-418-677073

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 11, 2007 3:33 pm Post subject: ASIs

I have tried similar thing on floats but closer to ten feet then climb until

airspeed bleeds off a bit.  Yes I did notice the altimeter didn't move until

I was about 200-300 feet up and then it started to climb and make up for

lost time as it were.



On changing the airspeed indication of your plane with the static port

disconnected that depends on whether or not your biggest  leaks are in the

front or the rear of the plane.  If your plane actually pressurizes a

little, (airleaks in the front) then the ASI will read lower.  If your plane

depressurizes slightly (air leaks in the rear) then your ASI will read

higher. If you say you don't have air leaks then you are a fisherman and as

we all know all fishermen are liars except for you and me.  I'm not so sure

about you. 



 The problem I had was just after getting up on step the ASI was all over

the place.  Once I got to flying speed, and off the ripples of the water the

ASI smoothed out to usable performance.  As I said in an earlier post I

found the static port fitting was well beyond loose.



About the only time I check my ASI like yourself is when landing.  These

little planes can get into some small locations and it is easy to bleed off

too much airspeed.  I tend to set up to land a bit hotter than is really

necessary.  Loosing airspeed isn't too hard.... Building it up again takes

time.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 11, 2007 3:36 pm Post subject: ASIs

Around here when a Kollisman is set properly the altimeter is supposed to be

within 20' of the registered airport altitude.  The adjustment is easy to

make.  Invariably other deviations will come form the static set up.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 11, 2007 3:37 pm Post subject: ASIs

The faster you go the more Bernoulli effect on your static port.  I wouldn't

worry about it.  Your ASI seems accurate around the approach speed.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 11, 2007 3:44 pm Post subject: ASIs

Mine is usually within 20 feet  of home altitude MSL ( I live at 15' MSL)  fluctuations are not too  noticeable.  Changes generally occur over days not  seconds but if I  were to see fluctuations I'd give the altitude feature and GS  indication a zero.

  

 A few years ago, before 9-11, I  saw a stationary GPS jump location by more than thirty miles in a few  seconds.  The next day all was normal again.  Remember who controls  the GPS constellation and trust it accordingly.

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 11, 2007 3:51 pm Post subject: ASIs

Attach the static port to the wing strut maybe 2/3 the way to the wing and

route the tubing down the back of the strut and into the plane.  If you have

the strut fairings you can route the tube inside the fairing.  The tubing

can be held in place either with Cora Seal or even nylon zip ties at several

locations.



Noel

 	  Quote: 	
		   

 In all cases, a static port out on the wing strut well

 below the wing and out of propwash instead of on the

 fuselage would help.  Harder to make this change

 though.  Wish I had done it this way....

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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