Pattern Help

[Jim Ivey]

Earl
 Back in my C5A Flight test days. I remember the pitot tubes on the test planes mounted on a boom and 15 feet in front of the radome to get the pickup out into clean air.My group did the preflight and calibrations of the pickups including angle of attack and sideslip.   The on board ships pitots were mounted on either side of the fuse about a foot away from the skin just aft of the cockpit.There was 2 on either side, one pilot and one copilot. The pilots pitots were plumbed together,one on either side, and measured the average of the ram air for airspeed . The salt shakers were plumbed together,one on either side, and presented the average vacuum for altitude. This arrangement provided for side slip and angle of attack variations and gives a more correct readings.
Having said all this you might benefit by getting the pitots out in clean air with longer tubes and use a pitot on each wing. Plumb them together and run the single tube to the sensor.  Since one wing panel moves ahead of the other and moves in a circular motion during a snap I think you would have more representative data with a averaging system.

Just food for thought.

Jim Ivey 
> 
> From: "Earl Haury" <ehaury at houston.rr.com>
> Date: 2005/01/14 Fri PM 04:24:14 EST
> To: <discussion at nsrca.org>
> Subject: Re: Pattern Help
> 
> Bob
> 
> Correct on instrument methodology. You may be correct regarding observed readings also. 
> 
> However, very high roll rates seem not to generate the same speed reading effect. The pitot extends about 3/8" forward the center of the wing LE in my installation. I've not seen any difference in normal speed data with it varied 1/4" or so from that position.
> 
> Pressure anomalies will definitely affect the altitude sensor, however I don't see the same "signature" on downline snaps. I've not been specifically looking at snaps to this point, the data were generated flying the P-05 sequence. I plan to look at this further in a different (more expendable) airplane with a G sensor also. Possibly that sensor can be oriented to provide pitch load and thrust (longitudinal) accel / decel info. (Should receive sensor in the next couple of days.) BTW, data rate is 10x/sec.
> 
> Earl
>   ----- Original Message ----- 
>   From: Bob Richards 
>   To: discussion at nsrca.org 
>   Sent: Friday, January 14, 2005 2:38 PM
>   Subject: Re: Pattern Help
> 
> 
>   Earl,
> 
>   I'm not familiar with that device, but I will make two assumptions. 1) The altitude transducer works on barometric pressure. 2) The pitot tube works just like on a full scale plane.
> 
>   I suspect the unexpected zero airspeed has to do with the airflow at the tip of the pitot tube not being parallel with the pitot tube due to the high rotational speed of the snap. In an extreme case, the airflow traveling perpendicular could actually cause a vacuum in the pitot tube.
> 
>   If the altitude measurement works on barometric pressure, there must be a static air source. I suspect the vertical speed anomaly is caused by a change in the static air pressure due to the sudden change of airflow around the airframe, including the static air source.
> 
>   Just guesses.
> 
>   Bob R.
> 
> 
>   Earl Haury <ehaury at houston.rr.com> wrote:
>     While recently evaluating engine / prop combinations (very top secret), I noted something that looks useful regarding snaps. During both up and downline snaps the speed signal drops to zero for a period of time roughly equivalent to snap duration. It appears that possibly airflow separation from the wing includes the pitot tube. Upline snaps also show a marked decline in ascent rate during the snap. 
> 
> 
> 


=================================================
To access the email archives for this list, go to
http://lists.f3a.us/pipermail/nsrca-discussion/
To be removed from this list, go to http://www.nsrca.org/discussionA.htm
and follow the instructions.