Dynon AOA Pitot tube connectors?

[airguy]

I'm installing the Dynon heated AOA/Pitot, and need to connect the 3/16" aluminum lines to either 1/4" aluminum or 1/4" plastic to make the run to the fuselage. I'm having difficulty finding the correct AN connectors, and don't really feel comfortable installing something less than AN for this mission-critical component. Can someone who has these installed give me a link to the correct connectors?

[roee]

I'm actually at the same spot right now, pondering how exactly to plumb my Dynon heated pitot.

An AN919-2D reducer is like a standard flared union but with 3/16" on one side and 1/4" on the other:
http://www.aircraftspruce.com/catalog/hapages/an919.php

If you go the plastic option, then that's not AN. But poly-flo tubing with nylo-seal fittings seems to be a proven solution that's been in use for some time in both experimental and certified aircraft.

With the plastic option though, one issue to be mindful of is temperature. Dynon's heated pitot nominally maintains about 80 deg C, and the plastic tubing and fittings are generally rated for a max temperature between 65 and 80 deg C depending on manufacturer. I would expect that the far ends of the aluminum tubes coming out of the Dynon pitot don't quite reach the full temp of the pitot mast itself, but I have no data on this yet. If they do get too hot, then it may be a better idea to go with aluminum tubing. Or at least a section of aluminum tubing before transitioning to plastic, one that is long enough to dissipate the heat down to an acceptable temperature at the transition to plastic.

P.S. if anyone has measured the temperature of the tubes coming out of the Dynon heated pitot, please post that data. Thx!

[airguy]

Dynon's installation literature indicates that the user should not cut the aluminum tubing shorter than 6" from the base of the pitot, to allow the tubing to dissipate heat from the pitot to a temperature low enough to prevent melting the plastic tubing.

[roee]

Originally Posted by airguy

Dynon's installation literature indicates that the user should not cut the aluminum tubing shorter than 6" from the base of the pitot, to allow the tubing to dissipate heat from the pitot to a temperature low enough to prevent melting the plastic tubing.

Oh, cool. I didn't see that. Which document & page number?

Thanks,
-Roee

[airguy]

Originally Posted by roee

Oh, cool. I didn't see that. Which document & page number?

Thanks,
-Roee

Hmmm....good question...I know I read it on their website, I'm looking for it now. Might have been in the Dynon forums??

[roee]

Originally Posted by airguy

Hmmm....good question...I know I read it on their website, I'm looking for it now. Might have been in the Dynon forums??

I looked and didn't find it in any of their documentation or the forums. But that's ok. I did my own experiment. Tonight I bench tested my Dynon heated pitot tube for the first time. Here are my observations:

The tip of the pitot mast became hot within seconds, and then the heat slowly spread aft. So it looks like the heating element is located at the very tip of the mast. I then let it do its thing for about 25 minutes, more than long enough to reach steady state (also evidenced by the fact that the duty cycle had stabilized). At this point, the tip of the mast was very hot to the touch, with temperature decreasing aft toward the base of the mast, which was only warm to the touch. The 3/16" aluminum tubes were not even warm, couldn't have been more than a few degrees above ambient, if that. You wouldn't know by touching them that the pitot heat is even on. [Sorry I don't have real temp measurements. Didn't have a thermocouple on hand. But these qualitative measurements are more than good enough.]

Given these observations, I now have high confidence that plumbing it with plastic tubing will not be an issue temperature-wise.

BTW, a few other general observations:

The current draw measured about 7.8A when the heating element is on, and about 60mA when the heating element is off.

Once steady state temp was reached, the duty cycle was surprisingly low. The heating element turned on about once a minute for only two or three seconds. Now granted, this is on the bench, with ambient air at room temperature, and no airflow. Under flight conditions the duty cycle should be somewhat higher due to greater rate of heat loss to the airstream. But still I'm surprised at how low it is, at least on the bench.

And overall, my impression of this tube so far is very positive. Well designed, well made, and works well to the extent that I've been able to test it so far. Good job, Dynon!

[terry.mortimore]

Hi guys, if you have not purchased anything yet, I'd recommend the Safety air kits. I purchased mine through Avery tools and I'm really pleased with the outcome. Quailty stuff.

http://www.averytools.com/c-124-safeair1.aspx


Hope this helps, Terry.

[jchang10]

Just to add to this old post. I just did my own first bench test with the Dynon heated pitot. I had the exact same observations.

I did measure the temperature of the heated pitot about a couple inches aft from the tip and it seemed to be a steady 127F degrees. Did this w/ an infrared thermometer. I wasn't expecting it to run that hot - too hot to touch in fact for my sensitive fingers.

I plan to email dynon support as well just to verify this steady state temperature but alas it's the long weekend. If anybody else can confirm, that would be great.

Jae

[roee]

Originally Posted by jchang10

I plan to email dynon support as well just to verify this steady state temperature but alas it's the long weekend. If anybody else can confirm, that would be great.

It's 70 to 80 deg C at the tip. Says it right in the installation guide, page 1-1.

[Pilot135pd]

Originally Posted by roee

I looked and didn't find it in any of their documentation or the forums. But that's ok. I did my own experiment. Tonight I bench tested my Dynon heated pitot tube for the first time. Here are my observations:

The tip of the pitot mast became hot within seconds, and then the heat slowly spread aft. So it looks like the heating element is located at the very tip of the mast. I then let it do its thing for about 25 minutes, more than long enough to reach steady state (also evidenced by the fact that the duty cycle had stabilized). At this point, the tip of the mast was very hot to the touch, with temperature decreasing aft toward the base of the mast, which was only warm to the touch. The 3/16" aluminum tubes were not even warm, couldn't have been more than a few degrees above ambient, if that. You wouldn't know by touching them that the pitot heat is even on. [Sorry I don't have real temp measurements. Didn't have a thermocouple on hand. But these qualitative measurements are more than good enough.]

Given these observations, I now have high confidence that plumbing it with plastic tubing will not be an issue temperature-wise.

BTW, a few other general observations:

The current draw measured about 7.8A when the heating element is on, and about 60mA when the heating element is off.

Once steady state temp was reached, the duty cycle was surprisingly low. The heating element turned on about once a minute for only two or three seconds. Now granted, this is on the bench, with ambient air at room temperature, and no airflow. Under flight conditions the duty cycle should be somewhat higher due to greater rate of heat loss to the airstream. But still I'm surprised at how low it is, at least on the bench.

And overall, my impression of this tube so far is very positive. Well designed, well made, and works well to the extent that I've been able to test it so far. Good job, Dynon!

Thank you !! I'm installing the plastic tubing right now and left Dynon support a voicemail yesterday about this but they haven't gotten back to me yet. Glad to know I can safely cut 2 inches off the top (still leaves me with 10" long tubes) and my plastic tubing won't melt.