Dynon Pitot AOA probe

Need a 2nd opinion,

I have an older Dynon Pitot/ AOA probe installed on my RV7 which is reading 5-6 mph (True airspeed not indicated) slower than ground speed. I have trouble shot this issue back to the probe and believe it has some manufacturing defect. My plumbing lines upto the probe and back to the Dynon 180 are tight and the D180 reads calibrated per a seperate manometer gage. I have contacted Dynon support, and they agreed verbally I probably have a defective unit hence their design changes. I have an RMA number but am questioning if their offer of 1/2 price off a new unit if older that 3 years and full replacement if newer seems reasonable. Im confident mine is older than 3 years since I bought the unit from a friend who never applied it to his aircraft (its basicaly new). There have been some obvious design changes and I stated to Dynon that my probe acts nothing another new unit (I have a newer model to compare with but cant install). I am in the middle of flying off my 40 hours and the weather is closing fast. I would prefer them sending me another unit to swap out with mine and save on the downtime and some labor. Given my situation would anyone consider the "1/2 off new" a reasonable offer or would you push for a full replacement unit. I would think Dynon would benefit from being able to pull a potential defect from the field.

I like the Dynon products and have no conplaints with their service, simply want more the unit to perform the way it was advertised.

The pictures show my unit mounted to the wing and a newer unit tapped next to it.

Thanks, for hearing me out,
Steve

Steve,

If you have monometer and GPS data points, you might want to consider computing static pressure source error (which can cause the low airspeed readings you discribe). Kevin Horton has a great spread sheet that will allow you to determine if the issue might simply be caused by the configuration of your static ports? If you've already been there, done that, disregard...

Cheers,

Vac

I have the older unit, it is at least 6 years since birth, and it seems to be working just fine.

What was your method of checking its accuracy?

Updated Dynon Pitot AOA probe problem

Guys thanks for the reply I have included the static system as part of my trouble shooting checks.

I want to re-direct the conversation back towards the issue with Dynon and how I should move forward from here. The issue is wheather it is acceptable for Dynon to charge me for a new unit to replace my defective unit and wheather I have a defective unit. Im happy with the D180 product but unhappy with the technical service Ive recieved thus far on this issue. I cant see sending them my probe and paying $100 + shipping for another unit given its consider defective and they have verbally admitted its probably defective.

Please chime in with your thoughts

My testing has been as follows:
Ground testing:
Disconnected the air lines at the probe within the wing. Connected a water manometer to the air speed tube within the wing. Turned on my Dynon 180 unit and pressurized the manometer to: 4.92 inches H2O then read 97 mph IAS & 100 mph TAS, 15.94 inches H2O then read 178 IAS and 183 TAS, and finally 19.68 inches H2O and read 196 IAS and 202 TAS. (Note: OAT was 61?F and 29.97 Bar also its hard to get exactly to within .01 inches). Also the static line was pressure checked and blow out with high pressure air to be sure no water or debris.

In flight testing:
Used GPS ground speed recorded data against D180 IAS & TAS recorded data and took the delta of the average TAS vs averaged GS from flying steady for 5+ minutes at 2-180? directions. Data showed a consistent bias of 5-6 mph at 100,150,& 180 mph speeds.

Probe comparison:
I was able to use a friends new Dynon Probe to compare with. The newer probes have two very tiny drain holes placed side by side about midway along the length of the tube. My unit on the other hand has larger drain holes in-line along the bottom. I was told these have no bearing on the differences Im seeing. On mine when I cover the pitot intake hole only and blow throw the pitot tube (soft aluminum tube end) I get almost no resistance and air rushes out the AOA hole in the front as well as both drain holes. On my buddies new unit doing the same thing, there is no leak at the front AOA hole in the front but rather leaking from just ONE of the two tiny drain holes not both. In addition to this I soaped the outside of of my probe and found significant leaks along all component mating lines. This was not a calibrated test but WOW there was a significant differences between the two.

Slagergren said:

........ The issue is wheather it is acceptable for Dynon to charge me for a new unit to replace my defective unit and wheather I have a defective unit. Im happy with the D180 product but unhappy with the technical service Ive recieved thus far on this issue. I cant see sending them my probe and paying $100 + shipping for another unit given its consider defective and they have verbally admitted its probably defective.

Please chime in with your thoughts........

Click to expand...

This is probably not what you want to hear, BUT I don't think it is entirely out of line for Dynon to only credit a 2nd hand purchaser 50% of the cost. Looking at it from their point of view:
1. you were not the original purchaser(one of the pitfalls of buying used)
2. >3yrs old product (some of which are operating just fine)

Could they do better if after they test it they find it truly was a manufacturing defect...maybe.
Could they send one out for swapping to allow you to fly...maybe, did you ask for that option? Did you offer to pay for it in full, give them a credit card number to credit your account when you to return the original that is found to be defective.

BTW my old style probe works fine.

We have had exactly the same experience with our older model pitot tube. We began chasing a TAS issue three weeks ago because we are consistently seeing readings 3 percent lower than GPS values computed via spreadsheet. The same tests on the system and tube you have done produced the same results leading us to believe that there was a problem within the tube itself. To this point, we have had a very positive experience with Dynon. However when we called to pursue a solution to our problem, the tech insisted on the integrity of the design and had no suggestions. The the promised return call with more information has not been received. We were not offered the 50 percent off a new pitot tube. I think we would be happy to take the new tube at the reduced rate so long as Dynon is willing to open our tube and tell us if there is in fact a problem.