Tubing for static

[Jan Olieslagers]

Having bought my nice close-to-new Halley Apollo Fox, I was at first eager to fly it - took a good deal of doing to get all the paperwork ok - so I just flew whenever a chance turned up. Now that the first excitement is over, I've come to take a critical look around, and did find a few surprises.

One thing I never discovered is the static port on the fuselage. Looking behind the panel I found the explanation: there is NO static tubing, the relevant inputs of altimeter, vario, ASI are simply open, breathing the cockpit atmosphere. As the cockpit is everything but airtight, this is not necessarily very different from outside conditions, though.

Is this acceptable?
Certainly the instruments will get some of the cockpit dust and dirt into them, how bad is this?
And will it affect the reliability of instrument readings?

Another finding that disturbed me less: the alternator regulator and the starter relay are not at their usual location on the firewall, on the engine side. I found them after some searching on a horizontal panel between the firewall and the instrument panel. Or SHOULD I be concerned, and consider relocating these high-current components to the engine compartiment?

[kenparry]

Static pressure: it would be very unwise to assume that cabin pressure = outside pressure. Your staic source needs to be at an approved place. You are right to be sceptical.

[Genghis the Engineer]

Having bought my nice close-to-new Halley Apollo Fox, I was at first eager to fly it - took a good deal of doing to get all the paperwork ok - so I just flew whenever a chance turned up. Now that the first excitement is over, I've come to take a critical look around, and did find a few surprises.

One thing I never discovered is the static port on the fuselage. Looking behind the panel I found the explanation: there is NO static tubing, the relevant inputs of altimeter, vario, ASI are simply open, breathing the cockpit atmosphere. As the cockpit is everything but airtight, this is not necessarily very different from outside conditions, though.


Is this acceptable?

This is quite common on low performance microlights.

Is this acceptable? In my opinion no, it introduces large and unnecessary errors easily eliminated by some straightforward mods to the airframe using a few tens of (insert currency unit of your choice).

Certainly the instruments will get some of the cockpit dust and dirt into them, how bad is this?

And will it affect the reliability of instrument readings?

I've seen ~25% ASI errors and ~250ft altimeter error due to this particular design "feature" in some types. I've not however seen much tendency for dirt ingress into the instruments.

Also in my opinion the ASI and altimeter should be calibrated - doing this against GPS is most normal nowadays, takes about an hour, and the same again to sort out an insert in the manual and check that you have the IAS operating speeds correct.

Another finding that disturbed me less: the alternator regulator and the starter relay are not at their usual location on the firewall, on the engine side. I found them after some searching on a horizontal panel between the firewall and the instrument panel. Or SHOULD I be concerned, and consider relocating these high-current components to the engine compartiment?

Personally I'd like to see the starter relay as close to the battery as possible, so that when not open, the starter line is not live with potential to cause problems. If the battery is by the firewall, fine - but if the battery is behind the seats, that's where the starter relay should eb as well.

The regulator should be close to the alternator source to reduce losses, but that's no big deal so long as it's somewhere not causing a nuisance.

G

[Pilot DAR]

Jan,

A question which comes to mind, having done a lot of flight testing to get static ports right; The static port on the fuselage, what confidence do you have that it's position is correct? As I expect that this is not a certified aircraft type, what data is there to describe the correct position? If someone just "put it there", I would be very suspect.

Like Genghis, I have seen immense airspeed errors with very subtle static port location and shape changes.

[Jan Olieslagers]

Thanks for the quick replies!

So for the static, I am not surprised I'll have to acquire a couple of feet of plastic tubing, two T-pieces and an elbow, and a static port to fix on the fuselage. Any recommendations or criteria for the location? Prop slipstream would be the main concern, I should think?
Also: after thus improving my installation, should I want to re-calibrate the instruments? Actually, would they have anything to calibrate?

As for the electrics: the battery unfortunately IS under/behind the right hand seat. Placing the relay close to it seems like a very good idea, but would involve quite a bit of work. Think that IF I go for it, I'll also install a receptacle for a high-current plug for an external charger/jump starter. Don't ask me why I want that one!

[Genghis the Engineer]

I'd normally put two matched statics, one either side of the nose at a first approximation. Another option is to put them behind a static dam. A third option is a second pitot tube, on the wing, blocked up but with holes drilled around the sides. All of these work on various aeroplanes.

There's some good material on the BMAA website on how to calibrate your pitot-static system. Download TIL 027, and form AW/043.

Since there's no minimum accuracy requirement on microlights, it's much easier to accept possibly large errors so long as they're consistent, then calibrate - than spend huge amounts of time and money trying to get static positioning right.

G

[Zulu Alpha]

There is a very simple way to see whether your static is OK.

Set up a GPS to show altitude. Then, when parked on the ground set the altimeter to read exactly the same by adjusting the pressure setting.

Without touching the pressure setting go for a flight. Any static error will show as a difference between the two. Try different heights and slow and fast flight and also with a slide slip both ways. If there is no difference then you don't really need to connect the static port.

If you do connect the static port then also do the test.
I have known static ports to be very inaccurate, it just depends on their location. If its on the fuselage then its best to have two, one on each side, and connected together.

The best is the type that takes the static from the side of the pitot tube

[Crash one]

The best is the type that takes the static from the side of the pitot tube

When I bought my Emeraude, for whatever reason the ASI was reading 80kts at the flare. Crumpled tubing & pitot angled down at 20deg!! was fixed with a new pitot/static made from cupro nickel tube. Wingtip mounted as the original & pointed approx straight & level. No problem since.

[lasseb]

Any static error will show as a difference between the two

Well, so would any difference between ISA and current conditions. (except when you are on the level where you set your altimeter = on the ground)

[Zulu Alpha]

Any static error will show as a difference between the two
Well, so would any difference between ISA and current conditions. (except when you are on the level where you set your altimeter = on the ground)

I think you have misunderstood. The static error is the difference between the altitude measured on the GPS and the altimeter (not the pressure setting difference).
If the static is correct then the GPS and Altimeter should read the same at all times ie stationary, in the air, at VNE, with a side slip etc.