Pitot test causes large pitch change indication ??

[Bill_H]

Having installed the D-1000 in my RV-12, I am testing my pitot and static system. I know the ADAHRS is working for pitch because I can push down on the back of the plane and see the pitch change. Now, when I slightly pressurize the pitot to get an airspeed indication (this is a pitot tube in the nose, not the dynon wing pitot), in order to check the pitot leakdown rate, I get large PITCH indication changes as well. If I pressurize (using a hypo syringe) very quickly the pitch down indication is very pronounced, then some significant vertical excursions and wobbling as well until it steadies out. Obviously, the plane is stationary!
Is this normal?
I have confirmed that the pitot leakdown rate (once stable - involving getting the pitot under pressure then quickly covering it with my finger!) is miniscule (one knot per minute).

When I pull a slight vacuum on the static, the same pitch thing happens, but I think that is related to the airspeed phenomena - obviously lowering the static makes the D-1000 think it has airspeed.

ALSO:
I am having trouble testing the static leak rate. Using a hypo, tubing, and "goop" around the static port still "seems" to have a leak that makes the altitude go down quickly. (or it could be a leak somewhere else.) So to test that I taped over both static ports, which tee together and then go to the ADAHRS. I disconnected the leg to the ADAHRS and blew into it - no flow resulted - confirming that both tubing branches to the static ports had no leaks under pressure. I am pretty confident about the tubing connection to the ADAHRS - it seems just like the pitot one, installed the same. But is there perhaps some sort of internal orifice in the ADAHRS on the static side that vents it down? I find no provision for a static check method in the Skyview installation manual.

I wanted advice before I try this, but I could connect the line to the ADAHARS, disconnect the other end of that line from the static port tee, and either blow or suck on it to verify that connection on the ADAHRS itself has no leaks - even do a bubble test.

Comments?

 

[dynonsupport]

So the ADAHRS shouldn't have any leaks (and that is tested here), though our AOA/Pitot has leaks - by design - to vent moisture.

On the airspeed/attitude coupling: That's also by design. The inertial sensors that are primarily used to determine attitude are aided by IAS (and when that's not available - say due to pitot icing - GPS) for best performance. That means that if you create an IAS that isn't "real", the attitude will be effected. The latest installation guide (page 5-10 in revision K) actually has specific instructions on how to perform pitot/static tests. In short, you don't want to CHANGE the IAS when the airplane is not really moving. If you have, not a big deal. You may now notice a non-zero turn rate on the ground, and the attitude might be very slightly wrong in flight for the first hour or so of flight (but you're no IMC during that time, right? ).

In any case, follow the procedure from here on out to avoid changing the IAS while SkyView is powered up. And if you can't (because you're hunting down a leak), know that simply flying the airplane for a little while will undo any erroneous effects that you might have imparted on the ADAHRS.

 

[Bill_H]

Thanks - Downloaded Version K - got it. I think I will do the zero airspeed calibration. I have not yet ran the engine and still have to do ground checks, taxi checks, and magnetic calibration so it is awhile before first flight. I have confirmed - no leaks in the pitot or static system. The difficulty with the Vans procedure is particularly applying vacuum to the static port with a hypo and tubing and "sealer goop" that doesn't really seal... That was also the problem with the pitot leak - the tubing I had fit INSIDE the pitot and I was relying on the goop and tape to make the seal. But it is all sorted out now.

 

[dynonsupport]

So the zero airspeed calibration won't fix any leak issues. It essentially shifts the "zero pressure" sensor value to make very low airspeeds as accurate as they can be at very low airspeeds.