Pitot tube location.

[whee]

I’m looking for a some feedback on my pitot tube location. The builder of the wings cut the hole for the mast so I guess that is set. What I’m really wondering about it the length of the mast. I’d like to cut a couple inches off it but don’t want to get the pitot tube into an area of disturbed airflow.

What do you guys think? Sorry about the low light pics. Just how it is working in a unlit hangar.

[rv8bldr]

Hey Whee

I have installed mine in the same location, although I am a loooooong way from being done.

I don't know if that pitot is a Garmin GAP 26 or not, but here are the mounting location installation notes for it:

The GAP 26 is an under-wing mounted pitot/AOA probe, it is not intended for fuselage mount
applications. For proper functionality, the GAP 26 should be mounted in a location where airflow
over the probe is relatively undisturbed (typically mid-wing span).
• The tip of the GAP 26 should be located at least 4” from, but not more than 10” below the bottom
surface of the wing. The probe tip may protrude up to 2” max in front of the leading edge of the
wing.
• Viewed from the side, the GAP 26 probe bayonet centerline should be mounted within ±5° from
parallel to the wing chord line.
• Viewed from the top, the GAP 26 bayonet centerline should be mounted within ±5° from parallel
with the aircraft centerline.
• Consider using the aircraft designer/manufacturer’s recommended mounting location (if
specified). Optimal AOA functionality results when the tip of the GAP 26 probe is located no
further back than 25% of the wing chord length from the leading edge.

I would suspect that even if it is not a Garmin, the same restrictions would apply. No idea if that helps or not :-)

Cheers

[James]

From the Dynon L-probe installation instructions:
"MOUNTINGLOCATION
The Dynon Avionics AOA/Pitot Probe / Heated AOA/Pitot Probe will work correctly only when mounted in a location where the airflow over the probe is relatively undisturbed by the aircraft. In general, we recommend you mount it at least 6 inches (150mm) below the wing and with the tip of the probe between 2 inches (50mm) and 12 inches (300mm) behind the leading edge of the wing.Typicallya pitot probeismounted about mid-wingspan to minimize the effects of both the propeller and the wing tips. Testing during the development of the Dynon Avionics AOA/Pitot Probe / Heated AOA/Pitot Probe confirmed that the standard mounting locations for the pitot probe in the Van’s Aircraft RV series of aircraft workwell for a Dynon Avionics AOA/Pitot Probe/ Heated AOA/Pitot Probe"

https://www.dynonavionics.com/includes/guides/Heated_Unheated_AOA_Pitoti_Probe_Installation_Guide_Rev_D.pdf

At least 6 inches below the wing! Ok with low wing RVs... less helpful for bearhawks.

James

[whee]

Thanks. That helped for sure. We used a Dynon AOA pitot and this location doesn’t meet their specs but their installation mostly talks about RVs, though I’d think the general rules apply.

[Ed.Meyer]

We installed our Dynon pitot/AOA on the inpection cover that is outboard of the strut. No idea if that meets specs but it seems to work fine. Put a doubler inside cover to beef it up abit.

[James]

Hi Ed,
sounds like a clever idea - just wondering how you think you'd go disconnecting the static lines every 100hrs for the inspection?
How long have you been flying with this set-up? No issues?


Thanks - James

[rv8bldr]

Ed, like you I had thought about putting the pitot on that inspection cover, but I KNEW someone (probably me) would whack their head or poke their eye out on it there. Where Whee and I have put it (inboard of the strut attach) is at least a place where most (normal) people will not be trying to walk....I hope

[Battson]

I left it full length, because my tube is located aft of the main spar. It works well, this is the same Dynon AOA pitot. Shorter may work well too.

I also liked the idea of an inboard of the strut location, to avoid head-banding (hasn't happened yet), but I didn't in the end - because I worried the prop wash would disturb the airflow to much.

[Rollie]

The mounting mast I got from Aircraft Spruce is shorter, I'm thinking about 2 inches long, maybe 3. I wanted to make sure it was outside the prop wash and figured 1/2 the prop diameter outside the end of the prop would do it so mine is a little ways outside the strut. I also was concerned about walking into it so I put it on the left wing thinking that at fly-ins and things like that people usually go to the side with the door so that might reduce the risk of that. That doesn't work for the four seaters with all those doors everywhere.

[Ed.Meyer]

That is a good point Mark. It is on the left side but I have bumped my head on it.

[mike t]

Put them on big bushwheels, won’t hit your head then!

[James]

Dynon AOA Probe, mounted into inspection panel:

With so many experience floating around this forum, I'm a bit hesitant to share my take on things, but here's some photos on how I mounted my pitot probe, plus everything I've learnt so far.

1) The $95 probe mount from Aircraft Spruce / Dynon is the long gold one, pictured above.
2) Dynon recommends the probe be at least 6" below the wing, and between 2 and 12 " back from the leading edge. It must be parallel to the wing chord, and within 5 degrees of forward.
3) I chose the inspection panel outboard of the strut, because there was nothing else in that one, and it was easy to run the pitot lines in the nose cavity. I hope I don't hit my head on it.
4) I wanted my probe to be removeable for inspections / storing the wings, which means it had to be able to be drawn back through the doubler.
5) Dynon emphasises that the probe mount must by riveted to a spar, and braced with a hefty L-bracket (included in kit). My location didn't have either of those things, so I beefed up the doubler (0.040 T6 6065), picking up previous inspection panel holes in the skin. Anchor nuts for #6 screws positioned according to rivet holes in Dynon template. There's a 40 thou packer riveted to one side of the probe, where there's no doubler.
6) I made up an L-bracket stiffner onto the rib below, which sits in the joggle of the probe mount.

I haven't worked out how to counter-sink the screws or dimple the skin panel, so I might just leave the heads proud. I haven't riveted it up yet, but when assembled with clecos, the whole assembly is pretty rigid, with only a small amount of skin flexing.

7) Downsides - yes, everything is heavy. I'm not sure how to make it lighter, and still have the probe removeable through the panel.

Anyway, hope this gives the next guy a few ideas.

James

[James]

Update:

I fix aircraft for my day job, so I'm always keen to break the rules and make up my own steps when I come home to work on the bearhawk :-)

For those of you who fit a AN5812-type Dynon pitot probe, they talk about tapping and drilling a #6 screw to hold the probe into the mount.
I thought this sounded like lots of work, so I mixed up some 2-pack adhesive (I used 3M brand 2216), and glued it in.

Then I through-drilled two 3/32 holes either side of the pitot tubes, and put in a couple of spring/roll pins.
Measure the width of the probe over the holes, and grind down the roll pin to sit just under-flush.
I sealed the hole with more adhesive.

I'd be surprised if the probe ever fell out, at the grandpa speeds I intend to fly! :-)

James

[svyolo]

I ended up mounting mine next to an inspection panel, just outboard of the wing strut. I can remove it if needed. I used an .040 doubler, with one edge broke 90 deg, and the edge bent on a shrinker to match the wing airfoil profile. Same problem with countersinking. I just countersunk the whole thing, and will use Tinnerman washers under the flush head screws. The leading edge skin still flexes a little at the forward end. If I think I need it, I will put a .025 angle at the forward edge of the doubler to spread the load span-wise on the skin. I will probably do that.

If I hit my head, I would rather let it heal, than have to fix the wing.

[James]

Yeah, good solution as well, SV - my probe doesn't have any flex fore/aft, just a little bit to the side where there's no doubler, and it's only supported by the skin. The other reason I designed it this way is in case I need to pack out the leading edge more to get the probe parallel with the chord line. I haven't drilled off and mounted the probe yet, so I'll see how it looks tomorrow. James

[svyolo]

Side to side is the only place I have a little flex. I am pretty sure an .025 or .032 angle span-wise will spread the load and stiffen it up.

[SimonNicholson]

Here is what I did a couple of days ago.

[OhioLSA]

The skin on the LSA is only 0.016, and I worried that it might flex too much. So instead of the little doubler that attaches to the adjacent rib, I made a 0.040 doubler that spans the whole bay and is attached to two ribs. It's only slightly heavier, but it sure is solid!

[James]

I never expected so many builders would pile back onto this old thread!
There was clearly a need to kick around some ideas on mounting these probes.
Thanks for the pics guys, I can see I'm on the right track.

Follow up question - how many #6 screws did you drill in to the probe?
Four? Two from each side, offset one high and one low?

Thanks, James