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CH601XL Pitot Location

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Dave Nixon

Joined: 20 Sep 2007
Posts: 25

Posted: Thu May 01, 2008 8:31 am Post subject: CH601XL Pitot Location

I now have about 20 hours logged.  And from the first, my Indicated AS has been a pretty consistent 

 10 - 12 kts high.  Trying to get more cruise out of the Jabiru 3300 and the adjustable, Sensenich prop, 

 I did a series of static run-ups.  Finally got the prop half-way decent and noticed that my Dynon was

 Indicating 15 - 20 Kts on full throttle (on the ground, tied down) and when I backed RPM off, the IAS

 came down also.  So, when I went flying today, I measured speed over ground vs. Indicated and 

 sure enough, it indicated higher than actual.  

 Other than moving the Zenith pitot out two more bays, does anyone know of any other fixes??  Out two

 bays would put it in the same bay with aileron bellcrank access cover. 

  

 Thanks, Dave Nixon 

 N107R Flying

  

           [quote][b]

amyvega2005(at)earthlink.
Guest

Posted: Thu May 01, 2008 8:50 am Post subject: CH601XL Pitot Location

what airpseed indicator instrument do you have?

Juan



--

amyvega2005(at)earthlink.
Guest

Posted: Thu May 01, 2008 8:53 am Post subject: CH601XL Pitot Location

What static RPM do you have on the Jabiru at full throttle at start of take off? It should read 2850 to 2900. 2950 at climb out at 70 to 75 mph.

AT 3000 PA on a dead air day fire wall full throttle should get you 3250 to 3300 rpm.



Juan



--

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu May 01, 2008 11:23 am Post subject: Re: CH601XL Pitot Location

Where is your static port? Is it on the fuselage or out on the pitot tube?



To check and see if it is a static or pitot problem tie it down and rev it again. When it is showing you are moving when you aren't have someone cover the ports one at a time. 



If the problem is a steady state you might be able to adjust it out of the Dynon. Of course the Dynon might show you backing up when you are on the ground with the engine off. 



 	  Dave Nixon wrote: 	
		  I now have about 20 hours logged.  And from the first, my Indicated AS has been a pretty consistent 

 10 - 12 kts high.  Trying to get more cruise out of the Jabiru 3300 and the adjustable, Sensenich prop, 

 I did a series of static run-ups.  Finally got the prop half-way decent and noticed that my Dynon was

 Indicating 15 - 20 Kts on full throttle (on the ground, tied down) and when I backed RPM off, the IAS

 came down also.  So, when I went flying today, I measured speed over ground vs. Indicated and 

 sure enough, it indicated higher than actual.  

 Other than moving the Zenith pitot out two more bays, does anyone know of any other fixes??  Out two

 bays would put it in the same bay with aileron bellcrank access cover. 

  

 Thanks, Dave Nixon 

 N107R Flying

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

Tim Juhl

Joined: 21 Mar 2006
Posts: 488
Location: "Thumb" of Michigan

Posted: Thu May 01, 2008 12:46 pm Post subject: Re: CH601XL Pitot Location

To check the static you might also disconnect it at the back of the dynon so your reference is in the undisturbed air of the cockpit.  Other than that, many steam gauge ASI'S won't even read a speed under 40 kts so the phenomena may be common in other aircraft but not observed because of the lack of sensitivity of the instruments.  Look at the position of the pitot on production aircraft - they will have much the same relationship to the prop location as your XL.



Check out this webpage on how to use your GPS to determine your true air speed.  It might be helpful - http://www.csgnetwork.com/tasgpscalc.html



Tim

_________________
______________
CFII
Champ L16A flying
Zodiac XL - Jabiru 3300A
Almost done! It'll fly in spring!

A.F.Rupp(at)att.net
Guest

Posted: Fri May 02, 2008 7:35 am Post subject: CH601XL Pitot Location

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Fri May 02, 2008 8:19 am Post subject: Re: CH601XL Pitot Location

A.F.Rupp, Your post comes up blank on the web forum version.



DO NOT ARCHIVE

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

lgingell

Joined: 10 Jan 2006
Posts: 50
Location: Lake California Airpark 68CA

Posted: Fri May 02, 2008 8:36 am Post subject: Re: CH601XL Pitot Location

I put a "collar" (piece of plastic tubing about 5mm long) on my static port near the holes (about 3mm aft I think).  This changed the airflow on the static port and decreased my IAS  a few knots.  I'm still reading about 5 knots high.



I haven't disconnected the static in flight, but there is quite a bit of pressure (my shirt gets sucked down at the canopy sides), so I don't think it would help diagnose much in flight. However on a ground test, it would.



You cannot adjust this on the Dynon. Nor do i think you'd want to.



Dynon changed their minimum IAS registered from about 38 knots down to around 15 in their v3 software. I had used the old and the new.  I didn't notice any difference except the IAS starts to show eariler on the takeoff roll, which is nice.



I suspect the prop draft over the pitot is quite different on the ground, and may not reach it in the air.  Putting the pitot further outboard wouldn't be bad, but I'd first consider moving the static port on to the fuselage (and maybe using one on each side). I even bought the vans static kit planning to do this....)and then bought an RV7A kit to go with the static kit! - another story!!)



I get about 2650RPM static with my Jabiru 3300. I'm a bit over propped with my wooden sensenich 51" pitch, but it works nice in cruise, and I can still get to 3250rpm at full throttle (10.5gal/hr!).



Cheers,

..lance

XL/Jab3300/Dynons

_________________
Zodiac XL/Jab 3300
http://lancegingell.com

Tim Juhl

Joined: 21 Mar 2006
Posts: 488
Location: "Thumb" of Michigan

Posted: Fri May 02, 2008 9:16 am Post subject: Re: CH601XL Pitot Location

On my Cessnas the static port was on the side of the fuselage just behind the cowling...  The alternate static air was drawn from the cockpit.



On my Champ, the static port is located with the pitot like the XL and has a little collar on it (like a thick washer with a set-screw) set forward of the holes.  You can move it back and forth to fine tune the system - another thing you might check is to make sure paint or gunk  hasn't clogged the holes.



To me, an ASI gives at best a relative indication of speed and I don't worry too much about the accuracy as long as it is consistent.  There are so many factors the effect true air speed that you can't get too excited about it.  My GPS gives me the best indication of actual progress.



Tim

_________________
______________
CFII
Champ L16A flying
Zodiac XL - Jabiru 3300A
Almost done! It'll fly in spring!

Dave Nixon

Joined: 20 Sep 2007
Posts: 25

Posted: Fri May 02, 2008 11:14 am Post subject: Re: CH601XL Pitot Location

Thanks for all of the help on the Pitot system. After contemplating the Dynon D180 and my mechanical 2 1/8" UMA ASI systems ( UMA is backup) (both are doing the same thing, indicating high) and looking it all over real good, I decided to move it. When I called the factory and talked with Caleb, he said No Problem.  So I moved it outbaord of the #7 rib  but the hole through the skin is about 40mm from the wing spar rivet line instead of the 150mm per plans. Caleb was surprised when I told him that the plans called for 150mm. During the pitot examination, I found that the leading edges of the tubes were slightly sandblasted and starting to rust. I presume that this is from the prop wash.  My vent tube, next rib out, has no signs of sandblasting. 

After finishing the move I tested the system and all seemed to work fine during ground runup.  Unfortunately, unless you are doing a racetrack route, GPs is not much good because that gives you ground speed.  The FAA wants you to record accurate VSO, VX and VY.  Can't do that without a reasonably accurate IAS system.  So its off to breakfast tomorrow with three other planes and I will see then how much improved the IAS is. They are the ones who tipped me off in the first place last Saturday. I will keep you all posted on what I find. 

Dave Nixon   (18 Hrs down, 22 Hrs to go)

A.F.Rupp(at)ATT.NET
Guest

Posted: Fri May 02, 2008 4:51 pm Post subject: CH601XL Pitot Location

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