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airspeed indicator pitot placement

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mdnanwelch7(at)hotmail.co
Guest

Posted: Sat Dec 11, 2010 1:22 pm Post subject: airspeed indicator pitot placement

Kolb guys, and specifaically Xtra drivers,

   

  

   I'm getting close to drilling the underside of my nosecone (like...in a few minuntes),

 and I was wondering if anyone has an opinion about the best place to mount the front of the pitot

 tube.  I have the following pitot (from Dynon--unheated);

  

 http://www.aircraftspruce.com/catalog/inpages/heatedAOApilot.php

  

   The "L" shape of this pitot places the intake hole 1 1/2"  (3.8cm) down from the mounting surface.

 Can't change that.  My question is;  considering the wedge shape of the Xtra nosecone....

 how far ahead of the front edge would you think would be good enough.  One inch?  Two?

  

   I appreciate all input, but please realize the uniqueness of the Xtra nosecone, compared to 

 other Kolb aircraft.  In other words....just becasue your's may work well on a Firestar, etc, etc,

 I don't want to assume it'll work that same way on an Xtra.

  

 Thanks,   Mike Welch

  

 		 	   		    [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Dec 11, 2010 1:39 pm Post subject: airspeed indicator pitot placement

http://www.aircraftspruce.com/catalog/inpages/heatedAOApilot.php

Thanks,   Mike Welch



*************************



Mike W/Gang:



Most of us use 5/16" 6061 tubing.  Bend it the way we want it, and go fly.



I found a new Kollsman Pitot/Static system for a WWII Stearman Biplane, 

still in cosmoline and wrapped in the original oil paper, for $12.00 from 

Wag Aero.  Mounted it on the right wing lift strut.  Works like a charm.



Pitot tube will work in most places you can dream up to mount it.



-Popular is on the apex of the nose cone.



-Wing lift strut works for me.



-Leading edge of a wing.



-Bottom of nose cone.



Sure you want to spend that much money for a pitot tube?  



john h

mkIII

hauck's holler, alabama

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

mdnanwelch7(at)hotmail.co
Guest

Posted: Sat Dec 11, 2010 2:01 pm Post subject: airspeed indicator pitot placement

Hi John,

  

   Thanks for the reply.  Re: the cost, I already spent it years ago, back when I 

 used to make boat-loads of money.  It came with the Dynon D10A EFIS I have.

 (I bought 5, since they were such a good deal...I have two remaining, using one on 

 the Kolb)

  

   My concern is.....if you place it in "disturbed" air (like that bouncing off the leading 

 edge of the nosecone), the you're going to get an inaccurate reading.  I realize just

 about any ol' place on the airplane would work okay, I was just wondering if anybody 

 has found out what it takes to get 'out ahead' of that split airstream hitting the leading 

 edge of the Xtra nosecone.

  

   I went out in my shop and held the pitot 'roughly' in position.  It looks to me like

 1" ahead could be okay.  (It's ALWAYS at least 1 1/2" down).  The problem with it

 sticking out in front of the nosecone is it will be a great knee catcher!!

  

   My thinking is 1" in front of the leading edge would be fine, 1 1/2" would be more

 than I need.  The final ram air point would end up at ...1" ahead & 1 1/2" down from

 the leading edge.

  

   My apprehension is I don't want to start cutting holes in the nosecone, only find out 

 I should have done it differently.

  

 Mike Welch 

 

  		 	   		    [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Dec 11, 2010 2:43 pm Post subject: airspeed indicator pitot placement

Mike/Folks:



Probably the best place for pitot performance is right on the apex of the 

forward end of the nose cone, but like you said, it takes a beating from 

everyone that passes by, especially little kids that can reach up and hang 

on it.  When we used 5/16 or 1/4 tubing, we spliced a piece of polyurethane 

tubing to allow the pitot tube to bend without breaking.



I have flown with a 2" X 5/16 pitot tube in the nose of the nose cone. 

Worked great.



Seems like the nose cone might produce a bow wave off it, but I do not know 

for sure.



If I was going with the Dynon System, I would put it on the leading edge of 

the wing between the mid point and the outboard end.  Out of the way from 

spectators and flying in clean air.  Check out a DeHavilland Beaver or 

Otter.  That is where they place their pitot/static system.



john h

mkIII

hauck's holler, alabama

****************************************

  My concern is.....if you place it in "disturbed" air (like that bouncing 

off the leading

edge of the nosecone), the you're going to get an inaccurate reading.  I 

realize just

about any ol' place on the airplane would work okay, I was just wondering if 

anybody

has found out what it takes to get 'out ahead' of that split airstream 

hitting the leading

edge of the Xtra nosecone.

Mike Welch

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

mdnanwelch7(at)hotmail.co
Guest

Posted: Sat Dec 11, 2010 3:51 pm Post subject: airspeed indicator pitot placement

> Probably the best place for pitot performance is right on the apex of the 

 	  Quote: 	
		   forward end of the nose cone

 john h

 mkIII

 hauck's holler, alabama

 
	


John, and others,

 

  My favorite preference would be the apex of the nosecone.  While I was

waiting for replies, I did a 'google' search and came across a guy that was

installing the exact same pitot (Dynon) in his Zenith high-wing airplane.

  

   I don't know where he got his pitot installation directions, but he mentions he

 was supposed to put his pitot inlet 6" below the wing, etc, etc.  He built

 an airfoil shaped extension that slid on the notched area of the Dynon pitot.

 He says he ended up with only a 4" extension (in addition to that other 1 1/2"??).  

 Maybe he got 5 1/2" overall.  (I can't re-find him to verify any of the perticulars.....)

  

   I'm thinking I'm going to try to build one of those airfoil shaped extensions.

 That way I can lower the inlet, rather than go too far forward.   BTW, the extension

 would look like a Kolb plastic wing strut airfoils, only smaller, and a lot shorter, and 

 made out of aluminum.

  

   Thanks for letting me bounce all these ideas off ya.  Headed out to my shop 

 to see what I can come up with.

  

 Mike Welch

  

 PS.  Boy, we had a windstorm blow in here a couple of hours ago.  COLD, and the wind

 is ahowlin'!!!  They say maybe snow in a few hours.  It if does, it'll be flying sideways at 40!!

 		 	   		    [quote][b]

kuffel(at)cyberport.net
Guest

Posted: Sat Dec 11, 2010 9:44 pm Post subject: airspeed indicator pitot placement

Mike,

  

 << place it in "disturbed" air (like that bouncing off the leading  edge of the nosecone), the you're going to get an inaccurate  reading.   My apprehension is I don't want to start cutting holes in  the nosecone, only find out I should have done it differently. >>

  

 Standard practice says probes mounted on leading  edges should be at least as far forward as the radius of the mounting  surface.  Know from direct experience mounting a dual tube pitot/static  probe directly on the front of the nose of a Mark IIIC which  violates this practice produces massively inaccurate airspeed indications  (low).  For a Dynon "L" why not try to emulate a wing mounting  and try several inches *behind* the nose tip.  For minimum messing  with your cone you could experiment with soft bent aluminum tube and  ShoeGoo to see if 5" or 10" etc puts the probe in relatively smooth  air.  I would start with as far back as reasonable.  You want the  probe to be below a relatively flat surface (as in a wing mount) so  the air is not accelerating at the probe tip.  The probe and mounting  surface don't have to be horizontal, just relatively parallel to each  other.

  

 Tom Kuffel

 Whitefish, MT

 

 



   [quote][b]

mdnanwelch7(at)hotmail.co
Guest

Posted: Sun Dec 12, 2010 3:38 am Post subject: airspeed indicator pitot placement

Hi Tom,

  

   Thanks for the help.  After I last replied to John H, I went out to my shop

 and built an extension that lowers the pitot inlet 4".  So now, with the normal

 1 1/2" "L" drop, and my added 4" drop, I end up with 5 1/2" down from the 

 mounting surface.

  

   It looks to me like that 5 1/2" lower, and maybe 1" ahead of the front of the 

 nosecone should be sufficient to be ahead of the 'bow wave', especially considering

 the wedgie shape of the Xtra nosecone.

  

   I got the extension mostly finished last night.  The only thing left is to cleco on

 the nosecone, raise to tail to approx. flying position, and get a fairly close idea of 

 the angle between the underside surface of the nosecone, and the slipstream.

   Once I have a good idea of the angle, I can cut the extension's lower edge to 

 make the pitot point toward the best in-coming air.

  

   I'll take a picture and post it later.  

  

   Thanks again, Tom, for your pointers.

  

 Mike Welch

  

   From: kuffel(at)cyberport.net

To: kolb-list(at)matronics.com

Subject: Re: Kolb-List: airspeed indicator pitot placement

Date: Sat, 11 Dec 2010 22:20:19 -0700



     Mike,

  

 << place it in "disturbed" air (like that bouncing off the leading edge of the nosecone), the you're going to get an inaccurate reading.   My apprehension is I don't want to start cutting holes in the nosecone, only find out I should have done it differently. >>

  

 Standard practice says probes mounted on leading edges should be at least as far forward as the radius of the mounting surface.  Know from direct experience mounting a dual tube pitot/static probe directly on the front of the nose of a Mark IIIC which violates this practice produces massively inaccurate airspeed indications (low).  For a Dynon "L" why not try to emulate a wing mounting and try several inches *behind* the nose tip.  For minimum messing with your cone you could experiment with soft bent aluminum tube and ShoeGoo to see if 5" or 10" etc puts the probe in relatively smooth air.  I would start with as far back as reasonable.  You want the probe to be below a relatively flat surface (as in a wing mount) so the air is not accelerating at the probe tip.  The probe and mounting surface don't have to be horizontal, just relatively parallel to each other.

  

 Tom Kuffel

 Whitefish, MT

 

 



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pj.ladd(at)btinternet.com
Guest

Posted: Sun Dec 12, 2010 8:04 am Post subject: airspeed indicator pitot placement

preference would be the apex of the nosecone>>

 Hi Mike,

 if you do, cut the tube off about an inch or so from the nose cone. Push a  short length of plastic tube over the short stump and fit the pitot into the  other end of the plastic to make a bendable joint.

 If you don`t someone will walk by and snap off or bend the tube or if you  are really unlucky, tear the fitting right out of the nose cone.

  

 Cheers

  

 Pat

   [quote][b]

pj.ladd(at)btinternet.com
Guest

Posted: Sun Dec 12, 2010 8:56 am Post subject: airspeed indicator pitot placement

The "L" shape of this pitot places ....>>

  

 Hi Mike,

  

 I fitted the pitot under the nose cone as plans and  although it seemed to work OK I wiped it off 3 times standing the Xtra on its  nose while learning to fly the plane. ( I missed the training  wheel).

 I then fitted it to the top of the nose cone but it  didn`t seem to be very accurate. John H suggested the root of the flying strut  about 4 inches from the fuselage. That worked just about the same. I suspect  that it is not very accurate but I just live with it The GPS provides any ground  speed I want  and  the only time that I really need airspeed is the  approach and landing and as I suspect with most people the angle of the  needle rather than the figure which it is pointing is what you work on. That and  the seat of your pants.

  

 Incidentally if you want a good laugh.

  

 During the summer I flew in a Rans with  a guy while in France on holiday. We took off and I noticed, sort  of subconsciously that during the climb out he seemed to be flying much  faster than I do in the Xtra. I didnt have my bifocal glasses with which I  usually fly and couldn`t see the numbers on the ASI but the angle of the  needle seemed wrong. Halfway up the climb out the Frenchman gestured for me to  take over. I did and hauled back on the stick to bring the climb back to my  usual speed. There was a shout of `Merde!` from the other seat and a hairy arm  shot out and forced the nose down. I had totally forgotten that the speed was  not calibrated in mph or even knots but in kilometers. I had pulled the nose up  in a fully loaded machine on a hot afternoon climbing hard from a small field  and dropped the speed back to about 30 mph. The quick action of the pilot kept  us flying but we must have been right on the edge of a stall and no doubt a spin  ending in a crash. i flew around perfectly OK for about an hour but I noticed  that the guys hand was never far from the stick. That put a dent in the old  entente cordial I bet.  How stupid . Just shows that old man gravity is  waiting all the time for you to make that silly misjudgement.

  

 Cheers

  

 Pat

   [quote][b]

by0ung(at)brigham.net
Guest

Posted: Sun Dec 12, 2010 9:01 am Post subject: airspeed indicator pitot placement

I'm getting close to drilling the underside of my nosecone  (like...in a few minuntes),

and I was wondering if anyone has an opinion  about the best place to mount the front of the pitot

tube.  I have  the following pitot (from Dynon--unheated);

 

Thanks,    Mike Welch



 >>>>>>>>>>>>>>>>

  

 i am probably too late to be of help... but i would  put it at the rear edge of the nosecone, center, bottom, just before the  transition to the fabric.   this way the air will have time to  stabilize and become a laminar  to bottom surface.    too  close to the leading edge of the nose will be more disturbed,  and you  would have to have a forward extension to clear the high pressure bubble at  that location.

  

 my 2 cents worth

  

 boyd young

  

  

   [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Dec 12, 2010 9:23 am Post subject: airspeed indicator pitot placement

---

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

slyck(at)frontiernet.net
Guest

Posted: Sun Dec 12, 2010 9:34 am Post subject: airspeed indicator pitot placement

Boyd, well said.  I stuck mine under the nose and only wiped it off once.  Doesn't make much difference your skill levelwhen you lose the noise maker and plop it into knee deep alfalfa.  Trust me, your MkIII will skid along for a few feet with the tail raised.

The plus side is that I replaced it with an improved mount.

Wonderful experiences I've had over the years.  Uneventful flying is SOOOOO boring. 

BB



On 12, Dec 2010, at 11:59 AM, b young wrote:

 	  Quote: 	
		   

  I'm getting close to drilling the underside of my nosecone (like...in a few minuntes),

and I was wondering if anyone has an opinion about the best place to mount the front of the pitot

tube.  I have the following pitot (from Dynon--unheated);

 

Thanks,   Mike Welch



 	  Quote: 	
		  >>>>>>>>>>>>>>>

 
	


i am probably too late to be of help... but i would put it at the rear edge of the nosecone, center, bottom, just before the transition to the fabric.   this way the air will have time to stabilize and become a laminar  to bottom surface.    too close to the leading edge of the nose will be more disturbed,  and you would have to have a forward extension to clear the high pressure bubble at that location.

 

my 2 cents worth

 

boyd young

 

 

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Dennis.Kirby(at)kirtland.
Guest

Posted: Mon Dec 13, 2010 11:21 am Post subject: airspeed indicator pitot placement

Hauck: << I have flown with a 2" X 5/16 pitot tube in the nose of the nose cone. >>

 

 

Mike, John, and All –

 

One of my Tony Bingelis books says that a pitot tube sticking our 6 inches ahead of the structure (either wing leading edge or nose cone) should be in undisturbed air.  So that’s how I did mine.  Must be some margin in there, if 2 inches works OK for John H.

 

Also, I agree with the advice to mount the 5/16 alum tube on a small piece of polyurethane tubing, to allow the pitot tube to bend without breaking.  This has saved mine many times.  Mine is mounted on the tip of the nosecone, right at knee level.  

 

At airshows, I tell the kids not to stand in front of it because if someone in the cockpit pushes the little red button on the top of the control stick, it fires a laser which will shoot a hole right thru your body.

 

(hehehe … simple amusements)

 

Dennis Kirby

Mark-III, 912ul

Sandia Park, NM

 

 

 [quote][b]

mdnanwelch7(at)hotmail.co
Guest

Posted: Mon Dec 13, 2010 12:06 pm Post subject: airspeed indicator pitot placement

> So that’s how I did mine.  Must be some margin in there, if 2 inches works OK for John H.

  

     



 

 	  Quote: 	
		  At airshows, I tell the kids not to stand in front of it because if someone in the cockpit pushes the little red button on the top of the >control stick, it fires a laser which will shoot a hole right thru your body. 

Dennis Kirby 

Mark-III, 912ul 

Sandia Park, NM 

  
	


 

  

 Hi Dennis,

  

   As I previously mentioned, I'm not using a 5/16" tube, I have a Dynon

 pitot tube (see attached photo).  I made the extension, which is the white

 part, and that now places the pitot inlet 5 1/4" lower, and about 3/4" ahead

 of the Xtra nosecone leading edge.  I would find it difficult to believe that 

 that location wouldn't work well. (with regard to oncoming air)

  

   Because of the very sharpish nature of the Xtra's nosecone wedge, I can't 

 imagine it produces very much of a bow wave like you could expect from a typical 

 wing leading edge, or possibly like that on a MkIII Classic's more round nosecone.

  

   Regarding having it bumped at airshows, etc.  First of all, I'll have a 'remove before flight'

 tube slid over it, with an extra 3-4" of foam rubber, making it LOOK like it sticks out 5".

 Secondly, maybe I can build a little taser circuit that will dissaude kids from kicking it.

 Nothing funnier than watching a 10 year old holding onto 20K volts.

  

   "Teach a boy electricity, and he can electrify the world.  Hook a boy UP to electricity,

 and HE'LL be electrified for the rest of his life."    (just kiddding)

  

 Mike Welch

 MkIII

  

  

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Mon Dec 13, 2010 1:04 pm Post subject: airspeed indicator pitot placement

Spruce sells a pito tube that you can mount where ever and  the tube twists one direction to stay and the other to come out. Allowing you to  remove it around klutzes. Its pretty cheap too.

 Larry

  

 Note: If you forward this email, please delete the  forwarding history, which includes my email address.

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