Bud K

Bud K

Well Known Member
The wife and I were cruising home after spending July 4th with friends in California. The A/P was flying the plane and we were in smooth air. My wife wanted more air and opened her air vent all the way. Suddenly, the airplane began to climb until the A/P corrected. She looked at me and said 'Sorry'. Then she shut her vent completely and the airplane suddenly began to sink, again before the A/P corrected it. We played with the vents several more times and the effects were very predictable.

I had no clue that the aerodynamics of the RV-7 were that sensitive to pressure variations from the air vent. It was actually pretty fun, from a scientific perspective.

Anyone else have a similar observation?
 
Sounds like your AP may not be properly connected to your static air system or maybe there is a cabin leak into your static system.
 
Static leak. Or pitot, depending on your AP may have both inputs. My TruTrack does.

Did either the airspeed or altitude jump also???

Try flying level without AP and open/close vents rapidly while watching the AS, and alt.
 
Last edited:
Plumbing leak?

I'll have to check it out a little closer and do some experimentation. For some reason, the wife wasn't too keen on experimentation while she was on board.
 
Not the Autopilot!

My RV7A does exactly the same thing, with or without the autopilot on. I don't think it has anything to do with the static system (why would that affect the flight characteristics when hand flying). More likely it is the result of a sudden redirection of a small amount of air from over the wind root to inside the cabin. I did not install the supplied Van's air vents... used the upgrade aluminum eyeball vents from Van's.

Bob Cowan
N743RV, 300 hrs
 
As you describe it , it is functioning normally

The vent definitely affect the flight of the plane and when you change the configuration of the plane its flight state changes and you autopilot correctly detects the change and "corrects" altitude to the lavel it was told to maintain.

When I race, one of the race prep things I do is install flush inlet covers in the NACA openings. Those openings affect speed even if the internal control is closed. The same is true of the air pickup out of the baffle for the cabin heat. I have covers for that and the blast tube ports for racing and there is a measurable difference in speed. It is strange to see builders go through a lot of effort to build a plenum independent of the cowl in the interest of preventing leaks (which reduces the cooling air volume) and then cut a ~2" hole in the back for a heater air source.

Bob Axsom
 
I had the same thing happen to me on July 4th a couple years ago. I also posted and discovered that my tru-trak altitude hold was vented straight into the cabin so any pressure change inside the cabin affected the pitch of the airplane.

I've discovered this is totally normal and all was well but I had an encoder issue that I tried to tie into the anomaly you describe. Of course, they were unrelated. You sure can learn a lot on this forum. :D

http://www.vansairforce.com/community/showthread.php?t=73951&highlight=Peculiar
 
It's my Tru-track

tkatc said:
I had the same thing happen to me on July 4th a couple years ago. I also posted and discovered that my tru-trak altitude hold was vented straight into the cabin so any pressure change inside the cabin affected the pitch of the airplane.
Click to expand...

I finally had an opportunity to fly and experiment with my vents again. You have it right, its my Tru-Trac/Altrac autopilot. I was able to duplicate the condition only when the A/P was on and holding altitude. My steam gage air speed indicator did move a bit. I too have the upgraded aluminum eyeball vents. Glad to know I don't have to track down a static leak.
 
You must log in or register to reply here.