Calibrating Static Port was: Re: REFLECTOR: Cirrus v. Velocity

Wed Apr 12 11:10:17 CDT 2006

I agree with Scott B. on the necessity of calibrating  the static port.

I bought my V and the static port was way off.  My altitude was 400 ft 
off at cruise! I don't know how far off my indicated airspeed was but it 
must have been bad.

The method described below to calibrate is fairly accurate and can be 
fun also. Our static ports have a small  plate or fence mounted for or 
aft of the port,  to calibrate you will need to change the thickness and 
or the orientation. Flying this is easier and more safely done with a 
co-pilot.

You will be doing some low level flying so either you need to be 
comfortable with this or have somebody else you trust that is 
comfortable with low level flying.  Do this at an airport that the tower 
will let you do this or an uncontrolled airport that is not to busy.  
Explain the procedure to the co-pilot so he or she understands the 
procedure and objective.

1.)  set the field elevation in your altimeter when parked near the 
runway threshold.  The readings you are interested in are relative so 
the absolute reading is not important. Do not use the announced 
altimeter setting is it does not agree with the your field elevation.

2.)  You will need to fly as close to 20 ft AGL as you can. or some 
other elevation that can be verified by your co-pilot. I use 20 feet 
because the large hanger at my field is  20 ft high.   It may help to 
have somebody on the ground verify your height if your unsure when in 
flight.   The closer to the ground the easier it is the estimate.  100 
ft is very tough unless you have a radar altimeter.  Your GPS altitude 
unless you have WAAS is unreliable for this.

3.) Make a low pass at the prearranged altitude at 90 knots.  A trick to 
make this a bit safer is to dial in some up trim so it takes a couple 
pounds of down pressure on the stick to maintain level flight. This way 
if you get distracted  you will tend to climb away from terra firma.  
note the altitude and speed. 

4.) Make a low pass at cruise speed, same altitude.  This will usually 
be much appreciated by all at the airport with many requests to do 
another. Note the altitude and speed.

5.) Land and compare indicated altitude with real altitude.  When I did 
this on my plane I was indicating 400 ft AGL when actually 20 ft AGl.

The plate or fence now will usually need to be adjusted. If its aft of 
the hole, a thinner(as in height) will reduce the pressure and raise 
your indicated altitude, thicker will increase the pressure and lower 
the indicated altitude. If the fence is ahead of the hole the change in 
thickness is reversed.

Make a WAG as to the change needed and fly again.  you may need to 
adjust to some value between what is indicated during slow flight and 
cruise. Keep track of the change made so any further adjustments will 
divide and conquer the needed adjustment. Do this until your satisfied.

Once your altimeter is reading correctly out airspeed should also be 
relatively closer, unless your pitot is installed in a very bad spot.

Fly Safe.

Scott

 Scott Baker wrote:
> I have noticed that many Velocity aircraft vary in their indicated air speed
> due to either an un-calibrated air speed indicator and the position of the
> static port.  Calibrating the air speed indicator at the local avionics shop
> is a good thing to do - but that still leaves the possibility of air speed
> errors caused by the static port.  I trust the Cirrus air speed because of
> its being certified.  It's great to get a fast moving certified aircraft to
> do some side-by-side flights with the Velocity, just to make sure both air
> speed "meters" are indicating the same during formation flight.
> 200 knots indicated in the Denver area is outstanding.  The true air speed
> must be "right on up there".  I have flown the company demonstrator (310hp)
> at Front Range and at Colorado Springs - giving demo rides with 4-people on
> board and about 40-gallons of fuel - and the aircraft performed quite well.
> I've talked to several Cirrus 22 owners who have taken a demo ride in the XL
> with the Continental IO-550.  All of them seemed impressed - and most
> admitted the Velocity had a small but noticable performance advantage.  Most
> were looking for a way to reduce the cost of aircraft ownership.  Several of
> the Cirrus owners were upset with the cost of aircraft insurance.
> Sunny Eymann recently sold his Velocity XL in favor of a Cirrus 22 because
> he liked the feel of the Cirrus in a cross-wind landing - something that is
> an everyday event in Key West.  Still, he likes the Velocity - he just felt
> the Cirrus was the right aircraft for him.
> Random thoughts.
> Scott B.
>
>
> ----- Original Message -----
> From: "Tom Martino" <tmartino at troubleshooter.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Monday, April 10, 2006 10:51 AM
> Subject: RE: REFLECTOR: Take Off Performance
>
>
> 1600 Pounds.  Actually a little less now that I am removing the back
> seats.  If I push it I can darn near indicate 200 knots ... but normal
> cruise would be less.
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Al Gietzen
> Sent: Monday, April 10, 2006 8:23 AM
> To: 'Velocity Aircraft Owners and Builders list'
> Subject: RE: REFLECTOR: Take Off Performance
>
> Tom;
>
> I'm curious what the empty weight is on your Velocity.
>
> Thanks,
>
> Al
>
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