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-   -   Low air speed (https://vansairforce.net/community/showthread.php?t=80254)

LifeofReiley 12-20-2011 08:57 PM

Quote:

Originally Posted by JohnJacobsen (Post 607979)
Nobody I know that has a D-180. Looking for a steam gage Airspeed to hook up for comparison.

Stop by the airport, we can locate one you can borrow for testing. :) I'll email my phone #.

Tony Kirk 12-20-2011 09:57 PM

Manometer Article
 
One of my fellow chapter members, John McAvoy, published an article in Sport Aviation about calibrating you airspeed system using a Manometer.

Here is the link to the article and materials on his webpage http://www.iflyez.com/manometer.shtml.

Yes, his favorite building material is different than ours, but I don't hold it against him. ;)

Vac 12-21-2011 10:42 AM

John,

Take a look at this thread: http://www.vansairforce.com/communit...=static+source .

What you're discribing might be a static source pressure error. There's some other good info on this phenomenon (provided by Kevin Horton) in the flight test section. You'll still need manometer data, but if that shows the Dynon display to be accurate, then you'll need some flight test data. It generally takes some effort to get indicated airspeed and altitude "dialed in."

If you have any questions, you can drop a PM or e-mail.

Cheers,

Vac

jjconstant 12-21-2011 11:20 AM

Is your static source in the same location and using the same pop rivet head as Van supplies? Both location and shape have a strong effect on indicated airspeed. Low indicated speed implies that you may be getting pressurized air in your static source. Deploying flaps can change your static pressures at the low end if you use differing static source locations and shapes.

All best

Jeremy

Bavafa 12-21-2011 11:30 AM

@ 35K, it seems like a big discrepancies

Is the airspeed off by a consistent amount or varies significantly?

You seem to have tested all but the instrument itself, so I would suggest to try to take that also out of the equation before messing more with the pitot/static system.

Of course, this is based on the assumption that the location of Pitot and static are on the suggested location by VANs. A quick check to make sure your pitot is not bent in a wrong angle, though doubtful since you have been checking every thing else.

Good luck

WingsOnWheels 12-21-2011 01:30 PM

I'm not exactly close by, but I have a new airspeed indicator sitting in the box at home. If you make it up to Dallas, you are welcome to borrow it for testing. Just e-mail me if you are interested.

Walt 12-21-2011 06:34 PM

If you get up this way to pick up the airspeed indicator in the above post, stop by and I'll throw my pitot static box on it and check it.

JohnJacobsen 12-22-2011 05:40 AM

The static is pretty close to Vans location. About half an inch forward. The air speed stays consistantly off thru the speed range.

Thanks for the offer to borrow an AS indicator in Dallas. I will see what I can get done down here first. :)

I have access to a pitot static test set down here.

Thank you everyone for all the suggestions and offers. Hope to have this figured out soon. This is a great community. :)

NickAir 12-22-2011 06:03 AM

Let us know what you find out. Instrument or static system.

Brantel 12-22-2011 09:00 AM

I went thru this as well.

Take a look at this thread:

http://www.vansairforce.com/communit...ad.php?t=56387

I think like post 64 is were I found the fix....


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