AoA differential port locations

[technerdian]

Hi all,

I was going to use the Dynon pitot with the AoA port but it would require fairly major wing surgery on a 1948 rag wing Cessna 170, which I want to avoid. I have decided to fit upper and lower wing ports and use the differential 2-port mode on the iEFIS MX1 for AoA.

Has anyone done this and used this mode? I'm not finding anything about how far from the leading edge of the wing to locate the ports. Any reference to articles or posts would be greatly appreciated.

Thanks,

Gareth.

[PaulSS]

There were some clever chaps on the RV Forum who had installed such a system into their machines. Basically they took a feed from the normal pitot tube and then installed a port at about 30 degrees to the chord line underneath the leading edge of the wing for the second feed. I recall one person used a football inflation adapter. The threaded part stuck out the leading edge of the wing and the pipe to the EFIS was attached to the needle part of the adapter. Another person simply used a rivet the same size as is used for a good number of the RVs' static port. Basically a static port hole in the same place in the leading edge and a tube from the back of the rivet to the EFIS.

I used the Dynon pitot tube but the RV Forum suggest those experimenters got good results

[technerdian]

Thanks Paul,

I was going to order up static ports from aircraft spruce, but I'll have a look at the RV big rivet method! I hadn't even thought to do a single offset port, which would basically emulate what you have on the Dynon pitot. I think I'll put one top and one bottom. Then I can calibrate both ways (2-port and 1-port AoA settings in the EFIS) and see if there is a difference.

Cheers,

Gareth.

[PaulSS]

I, personally, wouldn't bother with a port on top. You've already got one of the feeds you want from your pitot tube and simply have to 'T' off from that.

Installing a static port rivet or similar at an angle of about 30 degrees to that of your pitot tube will give the differential pressure required and is all that Dynon do but at a greater price

I wouldn't over-think it too much. The EFIS does all the calibration necessary and comparing one system with another won't really achieve anything. You'll have to choose which one you're going to use anyway and if you get the correct noises and indications from the calibration does it really matter? I'd just be setting myself up to drill another hole in the wrong place by putting in two ports

This is the thread: https://vansairforce.com/community/show ... 040&page=2

[technerdian]

I wouldn't over-think it too much.

That along with "That's overkill!" pretty much some up my project!

That said, between this and the cessna170.org forum (where I learned how to fabricate a replacement 1948 pitot tube from "recovered materials"), my pitot-static and AoA systems have got about $550 less expensive, which I'm loving.

G.

[rainier]

When I first designed this system many years ago I simply made a piece of wood with a hole in there - shaped so it provided about a 25 or 30 degree slope with the hole in the middle - this I simply taped underneath the pitot tube. I stuck a PVC pipe firmly into the hole that went back to the positive pressure port of the AOA sensor.
So now I had the unchanged pitot tube and the downwards facing AOA tube. The static port and the AOA negative pressure port were simply left open in this case as it was an un-pressurized relatively slow aircraft that did not have a dedicated static port.

In a nutshell - I sold the plane like that - the AOA worked a treat.

[PaulSS]

Yep, plenty of similar ideas out there; from 3D printers to bent aluminium tubes