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Thread: Javron Cub Building for Dummies

  1. #81
    wireweinie's Avatar
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    Quote Originally Posted by pittsdriver View Post
    I've used these on my last three builds. They work great and are easy to mount. I use push to connect fittings for the whole pitot system. The will even slip on the aluminum tube on that pitot tube. They work great and make things simple. The plastic ones work fine and are much lighter than the metal. You can get them local in the sprinkler supply section as they are used for drip irrigation. www.mcmaster.com/tube-fittings/for-tube-od~1-4/
    Have you pumped these up or down on a test box to see how 'gas tight' they are? There are strict limits for leaks on the pitot and static systems.

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  2. #82
    pittsdriver's Avatar
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    They are designed for high pressure air systems so yes I think they can seal tight. I have used them on 6 or 7 airplanes and they do not leak and make for an easy install.
    Vans RV7 finished 2008
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  3. #83
    wireweinie's Avatar
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    How did you test them for leakage? If they seal properly then great. But if you just installed them without checking the system for leaks then you can't trust your airspeed or altitude readings.

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  4. #84
    pittsdriver's Avatar
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    The same way I test any other pitot static system with a vacuum gauge. Why do you think these fittings aren't any better than compression fittings. These are way better and you can pop the line apart any time you want.
    Vans RV7 finished 2008
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  5. #85
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    I really like those quick connect pneumatic fittings. Much easier to deal with than the nylon compression fittings. Festo is a good brand.

  6. #86
    wireweinie's Avatar
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    Quote Originally Posted by pittsdriver View Post
    The same way I test any other pitot static system with a vacuum gauge. Why do you think these fittings aren't any better than compression fittings. These are way better and you can pop the line apart any time you want.
    As long as they meet the leak test criteria then have fun with them.

    Web
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  7. #87

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    Quote Originally Posted by skywagon8a View Post
    Very nice, but where is the static port? This is a pitot/static system. Both air sources are required for accuracy. Look at the two ports on the back of your airspeed indicator. One is labeled P and the other is S. The S is also connected to the rate of climb and the altimeter instruments. The location of the S​tatic port on the airplane effects the accuracy of all three instruments.
    This is the pitot tube you should have with the static ports attached to it. https://www.aircraftspruce.com/catal...ickkey=3046038
    Attachment 58357
    Thanks for the feedback. I was planning on venting the static port to the cabin. However, in seeking to support my response to your comment. I was coming up somewhat empty. I thought Piper had done that with the supercub but it appears they stopped the practice at some point. The final nail in the coffin was this from Tony Bingelis in The Sportplane Builder:
    Some builders (ugh) install the altimeter and the vertical velocity indicator with absolutely no static line connections. They are merely attached to the instrument panel. The instrument's static opening in the rear is left open to the cabin or cockpit atmosphere. This is sloppy practice even for a strictly VFP Putt-Putt, and provides, at best, very nervous and inaccurate gage readings.
    So, here is the new and improved bracket. Sadly, I was unable to use the original bracket as the screw holes are different between the two types of pitot tubes.

    Click image for larger version. 

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    Thanks again for the input.

    Sam
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  8. #88
    wireweinie's Avatar
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    You do what you decide is best but that line he gave you about sloppy practices and inaccurate readings is a load of crap. I can't swing a dead cat without hitting a fabric airplane with no static ports. And some of the pilots of these aircraft are the best in the world at operating in remote and dangerous geography and would tell me in no uncertain terms if the instrumentation I just installed was inaccurate.
    If it makes the recertification tests easier, I'll plumb the static connections on the instruments/encoders together to give one connection point for the test box. But I will still leave it under the instrument panel unless there is already an external static port installed.

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  9. #89
    pittsdriver's Avatar
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    That pitot static tube works great. I have them on the last three Cubs I built. Venting into the cockpit causes inaccuracies. Put an inspection hole next to it in case you ever need to service it. It is also easier to put it on after covering.
    Vans RV7 finished 2008
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  10. #90
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    Vented to inside and based on my GPS airspeed is within 1 MPH. Keep it simple. You are not building a rocket ship to go to Mars, just a 100 mph Cub. Just my opinion and all that rot.

    Bill
    Very Blessed. "It's not an obsession, it's a passion"
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  11. #91
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    Quote Originally Posted by Bill Rusk View Post
    Vented to inside and based on my GPS airspeed is within 1 MPH. Keep it simple. You are not building a rocket ship to go to Mars, just a 100 mph Cub. Just my opinion and all that rot.

    Bill
    He already has it in Bill and one nylon 1/4" tube only weighs a couple ounces so why not use it. The Aussie Cub I built had it vented to the cabin and the ASI and Altimeter were always a little twitchy. When I rebuilt it after the wreck I put one of these pitot's in it and it is now rock steady. Talked to Jay a few times in the last few weeks and he said you guys had another epic Alaska adventure.
    Vans RV7 finished 2008
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  12. #92
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    The Clipper had the static ports open behind the panel as did the early Pacer. The Tri-Pacer started off with the static on the pitot and then Piper found that they worked better if installed on the belly in the aft fuselage. Before we rebuilt my Dad's Clipper (basic same fuselage as a Pacer/Tri-Pacer) he always complained about the inaccuracy of the airspeed indicator. At rebuild we installed the staitc ports per the Tri-Pacer drawing and his AS is accurate and doesn't vary in winter, summer, window open, closed, vents open closed etc.

    First thing I noticed when I flew the first CC18 Top Cub, the airspeed was accurate, Cub Crafters figured out where to put the static port.

    Mark Erickson was certifying the Super 18 and discovered the inaccuracies of the AS indicator with flaps down. Where was the pitot/static tube? Right in front of the flaps where it got disturbed air when the flaps were deployed. Moved it outboard and it worked fine.

    Most people in tune to their aircraft don't need airspeed. People ask me all the time what speed I land at, I have no idea, it is by feel and I am not looking at the AS. I do use it compared to GPS ground speed when looking at an off airport spot to help judge if I have a tailwind or not. An accurate airspeed indicator is not a necessity but it is nice if it works accurately in my book.
    Steve Pierce

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  13. #93
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    Quote Originally Posted by pittsdriver View Post
    He already has it in Bill and one nylon 1/4" tube only weighs a couple ounces so why not use it. The Aussie Cub I built had it vented to the cabin and the ASI and Altimeter were always a little twitchy. When I rebuilt it after the wreck I put one of these pitot's in it and it is now rock steady. Talked to Jay a few times in the last few weeks and he said you guys had another epic Alaska adventure.
    A 1/8" tube weighs even less. The tube only transfers pressure, free flow doesn't need a consideration.
    N1PA

  14. #94
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    Quote Originally Posted by skywagon8a View Post
    A 1/8" tube weighs even less. The tube only transfers pressure, free flow doesn't need a consideration.
    Most are set up for 1/4" tubing so Trying to mix and match fittings becomes a pain. I'm with Steve KIS. I've flow several airplanes with and without static ports and it seems like with things are more accurate. I also agree airspeed indication isn't really important but it is nice especially for training.
    Vans RV7 finished 2008
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  15. #95
    skywagon8a's Avatar
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    Quote Originally Posted by pittsdriver View Post
    Most are set up for 1/4" tubing so Trying to mix and match fittings becomes a pain. I'm with Steve KIS. I've flow several airplanes with and without static ports and it seems like with things are more accurate. I also agree airspeed indication isn't really important but it is nice especially for training.
    Don't disagree, only pointing out it is a pressure sensor not a flow. I'll not enter the training discussion.
    N1PA

  16. #96
    Bill Rusk's Avatar
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    Pittsdriver

    Yes, I agree, already in, and certainly not a bad thing, I was just pointing out (for someone else that might read the thread) that you could get away without it. And, as you pointed out, it can be added after the fact if it does not work the way you hoped.
    Yes, Jay and I had a pretty epic adventure coming back from Alaska. Good fun. I haven’t posted anything about this summer yet, but I will. Trying to figure out how to do a video. Hopefully I’ll have something in a few days.


    Hope you’re doing well


    Bill
    Very Blessed. "It's not an obsession, it's a passion"
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  17. #97

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    Thank you all for the comments…especially the differences of opinion. I think it adds to the discussion.

    I should have added that another factor in my decision to redo it was that it was a little work now. But if I kept my original plan, it would be much more difficult to change it later. Some time in the (very far, it seems) future when I’m flying, I can play around with this status set up and straight cabin static to see what, if any, the impact is.

    Thanks again,
    Sam
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