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  #1  
Old 08-16-2005, 08:45 PM
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Default The Static System

I learned a few things about static systems today. I built the plans static port with the floxed pipe on the inside. It leaked. AC Spruce sell a bond-in aluminum static port set PN 10-00229 which has a 1/4 NPT fitting on the inside. Luckily someone had a spare set (one for each side). From there I replaced the barb fittings I'd used with screw type plastic compression fittings which come with nuts and little inserts for the hard plastic pipe. This seems to be how the professionals do it.

I replumbed the ASI, VSI, Altimeter, encoder and engine monitor in the avionics shop hangar in about an hour. These fittings are fool proof and much easier to install - and they don't leak.


Anyone in S. Florida looking for a good avionics shop - talk to Larry at http://www.treasurecoastavionics.com
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  #2  
Old 08-16-2005, 11:35 PM
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Quote:
Originally Posted by John Slade
I learned a few things about static systems today.

John,

I'm sure that you know this--but for those others listening (looking)-- make sure that your plumbing lines first go upward from both your static ports and your pitot tube before turning down to go to their termini. This prevents the capture of water in the low parts of the lines as it will drain out naturally. If you are going to do IFR, I suggest a alternate static source. You can get a small air valve (toggle type-- your dentist can get this for you, if not give me a shout), mount it on your instrument panel and T it into your static line. You don't have to connect the other port to anything. When the toggle is down, the valve is closed and the static line is connected to the static ports. When the toggle is in the up (alternate) position, the valve opens the static line to the inside of the cockpit at the valve. (easier than breaking the glass on an instrument).

Not intended to give anybody static!!!!
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  #3  
Old 08-17-2005, 07:19 AM
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Good point, Rich. The second static port on the other side isnt an "alternate", it's for balancing. I should finish the job and add a proper alternate. Can you point me to one of these air switches? I do most of my dentistry by UPS these days
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Old 08-17-2005, 09:10 AM
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Quote:
Originally Posted by John Slade
Good point, Rich. The second static port on the other side isnt an "alternate", it's for balancing. I should finish the job and add a proper alternate. Can you point me to one of these air switches? I do most of my dentistry by UPS these days
John: another option: get a 1/4 turn ball valve. an instrumentation shop or even a hardware store should have one. Make sure the handle is out of the way in flight, yet accessible.

Dave
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  #5  
Old 08-17-2005, 11:44 AM
argoldman argoldman is offline
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Quote:
Originally Posted by John Slade
. Can you point me to one of these air switches?

G-d, I hate when people force me to back up what I say on lists such as this!

A source for this part is a company called American Dental Accessories.
www.amerdental.com

The part number is 05-07, description: A-dec toggle.

The price is $29.95 not including shipping. You can log into their website and order the part. They will sell to the public.

Although somewhat pricy, and the same physical effect can be achieved by a small valve, or even a fuel tank drain valve, this product will blend in elegantly swith a well done instrument panel. It is a well made piece from a reputable company.

I believe it has 1/8" barbed fittings.

My Bellanca Vikings had a similar switchs for their alternate static and I used this switch in my Dragonfly.

I'd rather switch than break.
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Old 10-18-2005, 01:39 PM
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Default Heated Pitot

I want to make a cool stainless pitot tube for the nose. Anyone know how to heat it? I can't see spending $650 on a heated tube.
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  #7  
Old 10-18-2005, 02:03 PM
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Originally Posted by neverquit
I want to make a cool stainless pitot tube for the nose. Anyone know how to heat it? I can't see spending $650 on a heated tube.
Like this?
You need a Cessna p/n 0721105-5 80w 12v element, about $60 when they are available.
...Chrissi
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Old 10-18-2005, 10:09 PM
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Now THAT's a pitot!

Mine's a tiny little thing by comparison. I'm ashamed to say its only a 1/2 inch stub of 1/4 OD pipe. (when it's at rest )
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Old 10-18-2005, 10:49 PM
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Quote:
Originally Posted by John Slade
Now THAT's a pitot!

Mine's a tiny little thing by comparison. I'm ashamed to say its only a 1/2 inch stub of 1/4 OD pipe. (when it's at rest )
Pitot envy John?
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  #10  
Old 10-18-2005, 11:08 PM
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Quote:
Pitot envy John?
Not at all. Why "drag weed" when all it does is slow you down? Another advantage - mine's so small, no-one could possibly step on it.

Seriously, I got the idea from Jeff Russell - His pitot got broken off at a fly-in. (I hate it when that happens ). Anyway, he sawed no difference on the way home, so he sawed it off straight and left it short. As far as I know there were no complaints from the missus.
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  #11  
Old 10-19-2005, 12:36 AM
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Quote:
Originally Posted by John Slade
Not at all. Why "drag weed" when all it does is slow you down? Another advantage - mine's so small, no-one could possibly step on it.

Seriously, I got the idea from Jeff Russell - His pitot got broken off at a fly-in. (I hate it when that happens ). Anyway, he sawed no difference on the way home, so he sawed it off straight and left it short. As far as I know there were no complaints from the missus.

John, m'friend,

The short pitot does work, it will even work if the hole is flush with the nose, with no extension. The problem is that there will be a greater error between actual airspeed and indicated airspeed.

This is of less importance today as we don't usually use the calculations for TAS as much due to the GS being given by GPS, however, there is disturbance that is created in front of the surface that is being pushed through the air which does effect the pressure measured by the pitot.

We test our craft in terms of the V speeds via indicated airspeed in our installations, and thus we can easily and safely get away with pitot tube variations.

The indicated airspeeds may differ significantly from plane to plane, thus using airspeed numbers, of another craft, as absolute to land and takeoff your craft, may be less than wise

In "real plane" testing the pitot tube is attached to an extremely long boom to keep it away from the effects of the surface to which it is attached.

I wonder, how the airspeed indication error changes with higher angles of attack etc with various lengths or location of pitot tubes.

Having a pitot tube mow the lawn is less than satisfactory. I may mount mine under the canard or on the nose, further back ala Cessna 310. I bought a heated Pitot from ACS for about 300$ years ago, never used it, new price for identical is $962. (I thought it was expensive then).

Venting static to the cockpit also works but has its airspeed and altimeter errors too, especially when opening vents. VSI disturbance is only temporary.

Perhaps at a cozy fly-in, side by side comparisons can be made between actual GS tests vs indications and get these tabulated with pitot-types and lengths.
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  #12  
Old 10-19-2005, 01:12 AM
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Come on, be creative, install two pitots... one out in front of each winglet where it meets the wing

And as to venting static into the cockpit... that is done in quite a few certified non-pressurized planes. It is actually pretty much standard. Our 303 has a nice label on it stating that on alternate static source, add x to the airspeed and x to the altitude to correct for error due to this.
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  #13  
Old 10-19-2005, 08:28 AM
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Quote:
Originally Posted by JonC
Come on, be creative, install two pitots... one out in front of each winglet where it meets the wing

And as to venting static into the cockpit... that is done in quite a few certified non-pressurized planes. It is actually pretty much standard. Our 303 has a nice label on it stating that on alternate static source, add x to the airspeed and x to the altitude to correct for error due to this.
Am I getting nothing but static here????

Yes, venting to the cockpit is done in many certified non pressurized aircraft, but in modern planes, only as an alternate source. If you have a Mode C transponder (probably S in your case) and static venting to the cockpit, my understanding is that it will not pass the periodic inspection as the static system must be checked and verified for continuity. Pop the alternate static source, or break the glass on the VSI, and you will get a temporary change in VSI, a permanent change in IAS and altitude the direction is determined by whether the cabin is of higher pressure than outside ambient such as with open vents, or lower such as with improper cockpit venting. If the inside pressure is the same as outside pressure, there will be no change.

Now to the concept of polypetotubemorphism

I know, I know, the stuff that you fly has multiples. It is common knowledge that they have multiples just to justify the cost of the airplane. Probably one of the pitot tubes is a dummy.-- And that silly AOA thingy-- What will they think of next to clutter up the outside of the craft and to give, yet one more impressive, but un-needed instrument on the panel (kinda like the ASI) Who needs them????? Real pilots need only needle ball and airspeed-- choose your best 2 out of the three-- What ever happened to flying by the seat of your pants and sometimes arriving safely??

Remember, two pitots yield twice the possibility of failure (somewhere I heard this with respect to two engines too)

I will now extract my tongue from my cheek.

(by the way, my Aerocanard will have an AOA in it)
It woluld look neat to have two pitot tubes, one on each winglet tip, on a 1' boom, ala Boeing 707 (F15?) style. Too bad my winglets are finsihed.
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  #14  
Old 10-19-2005, 08:44 AM
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Quote:
It woluld look neat to have two pitot tubes, one on each winglet tip, on a 1' boom, ala Boeing 707 (F15?) style. Too bad my winglets are finsihed.
Are those Pitot booms, or HF antenna's??

I used to fly EC-135's, we had HF antennas on the wing tips and the tail tip. At airshows, we'd tell people they were laser cannons.

Waiter
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  #15  
Old 10-19-2005, 12:08 PM
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Quote:
Originally Posted by argoldman
It woluld look neat to have two pitot tubes, one on each winglet tip, on a 1' boom, ala Boeing 707 (F15?) style. Too bad my winglets are finsihed.
I was actually going to put them there, and have one run the blue mountain stuff, and the other one run the steam gauge. Not for any real particular reason except for that it would look cool. And I guess if you get a birdstrike right on the pitot of one side you would still have the other. Birds on the pitot just like babies on spikes.
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