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Thread: A Vetterman Application to Prevent "Tail Pumping"...and Keep Rear Passenger Warmer

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    WindOnHisNose's Avatar
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    A Vetterman Application to Prevent "Tail Pumping"...and Keep Rear Passenger Warmer

    Some time ago I began a thread on how to best keep Julie warm in the rear seat. I have installed the Atlee Dodge rear seat mod and it works well, but there is a draft that comes from the rear of the aircraft to the lower pressure in the cockpit. Larry Vetterman has developed a method of preventing this "tail pumping", using a reverse NACA duct. Grant Wallace was kind enough to install the vent (Larry, I'm not sure what you call the device...please correct me) on the belly of the aircraft during annual, and it looks good and I'll report back on the effect it should have on air flow.

    Pre-install
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    Installation, looking toward the front of the aircraft
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    Installation, looking aft
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    Grant did a super job with this. Larry is a very talented engineer, and this should be a good help in keeping the passenger warmer!

    Randy
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    SteveE's Avatar
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    A Vetterman Application to Prevent "Tail Pumping"...and Keep Rear Passenger Warmer

    I’m thinking a nice big rat snake might like to explore that hole. I’ll let Julie know ASAP so she can be on the lookout.


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    cubdriver2's Avatar
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    Your aircraft is no longer gender neutral

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    Grant's Avatar
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    Quote Originally Posted by SteveE View Post
    I’m thinking a nice big rat snake might like to explore that hole. I’ll let Julie know ASAP so she can be on the lookout.
    We dont have snakes up here, Except, of course, when you're visiting.....


    Man, I crack myself up!

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    SteveE's Avatar
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    A big rubber one might work just as good.


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    aktango58's Avatar
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    Quote Originally Posted by SteveE View Post
    A big rubber one might work just as good.


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    Do snakes like whirly birds?
    I don't know where you've been me lad, but I see you won first Prize!

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    SJ's Avatar
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    How about CO? Great idea but I would run the CO detector for a while to make sure nothing is sneaking in there.

    sj
    "Often Mistaken, but Never in Doubt"
    ------------------------------------------
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    alot more streamlined than draggin a set of these around.
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    Crash, Jr.'s Avatar
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    That just gave me a great idea for a way to add some weight to the tail of my plane for STOL contests
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    Scouter's Avatar
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    Randy can you explain further or should I call vetterman? I really enjoyed talking with him at NH in july, hes a smart man. Your saying the NACA duct is going to pressurize the cabin so cold air wont flow in as much? The heater in the CC was putting out some nice warm air yesterday on the way home from Dan Dufault. It was about 32 at 100 ft This is without the Spudcity TwinTurbo flowmaster mod
    Jim

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    Farmboy's Avatar
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    I’ll leave it to Randy, Jim, but it looks like it’s a suction vent pulling the air out, and in theory the heat in…, if no other “fresh air vents” up front.


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    BC12D-4-85's Avatar
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    Skip the ads> https://www.youtube.com/watch?v=rtEsdUzlIEk

    Facing one way it blows the other it sucks

    Gary
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    JP's Avatar
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    I myself was considering an electric bib for rides in Jim's CC on the New Year's Day jaunts....
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special
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    cubdriver2's Avatar
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    Randy, after looking again at that mod and thinking about your profession it looks like you finally found something to install on your Cub that you can claim on your taxes.

    Glenn
    Last edited by cubdriver2; 11-03-2021 at 06:26 PM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    Quote Originally Posted by BC12D-4-85 View Post
    Skip the ads> https://www.youtube.com/watch?v=rtEsdUzlIEk

    Facing one way it blows the other it sucks

    Gary
    I learned the other day that the nascar boys don’t use the term “cheating”. They instead call it “adjusting”.
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    WindOnHisNose's Avatar
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    You guys are incorrigible.

    Jim, the fellas are correct, the duct acts to lower the pressure in the rear of the cub to a pressure that is less than in the cockpit (which is theoretically lower in pressure than the rear of the aircraft). By so doing there is flow from front to back, reversing the usual flow from back to front.

    You guys are still incorrigible.

    Randy
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    Crash, Jr.'s Avatar
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    Incorrigible? You put "pumping" in the title and then showed off the new orifice in the tail of your plane. The jokes literally write themselves.

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    BC12D-4-85's Avatar
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    "incorrigible" I asked my wife what it meant. She said "you"

    Gary
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  19. #19
    BC12D-4-85's Avatar
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    I wonder how much air enters or leaves around the vertical stab trim slot fairing? Wouldn't be hard to put an outward facing lip on the slot's front to maybe suck out air. Plus if there's a fuselage hole above the tail spring mount that should be closed in my experience.

    Gary

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    Steve Pierce's Avatar
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    Quote Originally Posted by WindOnHisNose View Post
    You guys are incorrigible.

    Jim, the fellas are correct, the duct acts to lower the pressure in the rear of the cub to a pressure that is less than in the cockpit (which is theoretically lower in pressure than the rear of the aircraft). By so doing there is flow from front to back, reversing the usual flow from back to front.

    You guys are still incorrigible.

    Randy
    I knew a Lockheed engineer who did the same thing on his RV4 some 20 plus years ago. Said it worked well.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  21. #21
    WindOnHisNose's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Skip the ads> https://www.youtube.com/watch?v=rtEsdUzlIEk

    Facing one way it blows the other it sucks

    Gary
    Gary, that is a good video.

    My grandson, when he was 5 years old and wanting to play with one of his sister's toys, looked at her and said "Sharing is Caring"

    Thanks for sharing this.

    Randy

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    Quote Originally Posted by WindOnHisNose View Post
    You guys are incorrigible.

    Jim, the fellas are correct, the duct acts to lower the pressure in the rear of the cub to a pressure that is less than in the cockpit (which is theoretically lower in pressure than the rear of the aircraft). By so doing there is flow from front to back, reversing the usual flow from back to front.

    You guys are still incorrigible.

    Randy
    Sky Wagons have a similar (but small, maybe 1/2" opening) vent on the side of the fuselage near the horizontal that essentially does the same thing, I understand it was added to address Carbon Monoxide issues in the cabin.
    Remember, These are the Good old Days!
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  23. #23
    BC12D-4-85's Avatar
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    Spruce sells these rudder cable fairings. Similar to Cessna's vent, they may help exhaust air in planes w/o a metal belly to attach the gadget above.

    Gary
    Attached Images Attached Images  

  24. #24
    55-PA18A's Avatar
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    Hmmm. I'm just trying to wrap my feeble mind around this, but by lowering (i.e. increasing) the negative pressure in the cabin, aren't you just asking for problems with CO2 ? And come cold weather, I would expect any cold air leaks to increase. My understanding of the vents on the Cessna's is that they are to face forward to create positive air pressure in the cabin. But I might be wrong. ??

    Jim
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  25. #25
    BC12D-4-85's Avatar
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    Yea they face forward....CO reduction plus drying out the tail on floats maybe - I was told. Those rubber landing gear seals on spring gear tend to get loose and leak. But, who knows providing the heater pumps in lots of flow like Cessna's do. But check out their heater system and duct work compared to Cubs.

    More heater airflow for the Cub might help. Only so much flow can come in via a single 2" heater valve. Double that setup for more and use the muffler/heater in front of the engine - Sutton exhaust with extra inlet?

    Gary
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  26. #26

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    Somewhere there is an article on the Cessna tail dohickky. It was meant to add pressure to the fuselage if I remember correctly. In the early 180's the wing vents alone are not enough to keep the cabin with some positive pressure when you close off the heat/fresh air inlet with the slider plate, you will start to get a CO2 buildup. They came out with the little cowling door vents around the D model. DENNY
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  27. #27
    Farmboy's Avatar
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    Wait….so if we put three NACA ducts facing rearward on each rear window, the cub will go faster?? 🤣


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    ^^^^^^ And apparently it could be considered cheating….
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  29. #29
    BC12D-4-85's Avatar
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    Kinda' makes some sense....the ducts facing backwards. Might smooth out turbulent air flowing alongside the racing vehicle - or Cub too. In another thread I mentioned CG Taylor, that built the first Cubs, noted fabric movement or bulging out in certain places along the side of one Cub while flying nearby. He then built the Taylorcraft with the fish shaped fuselage to help minimize that drag and go 15 mph faster.

    Gary
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  30. #30

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    You guys are doing this the hard way, just install heated seat covers...
    https://www.amazon.com/Dorman-641-10.../dp/B001KQD7LC Plug into a power connection, you can get switches and thermostatic controls even and the price is cheaper than messing with the fuselage.

  31. #31
    JWE's Avatar
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    If you can spare 4.5 amps:

    https://www.gerbing.com/motorcycle-heated-vest-liner

    Keeps your body core warm.

  32. #32

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    Ok got my Cessna story a bit mixed up but kind of close. This is a better timeline. https://airfactsjournal.com/2012/08/...he-cessna-180/ https://support.cessna.com/custsupt/...df?as_id=31145
    DENNY

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    Peter when I need the extra speed to try and keep up I open my rear window a couple inches and pick up 2-3 MPH on the gps so this may be a speed mod or at least on my 11.
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  34. #34
    cubdriver2's Avatar
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    Quote Originally Posted by Douten View Post
    Peter when I need the extra speed to try and keep up I open my rear window a couple inches and pick up 2-3 MPH on the gps so this may be a speed mod or at least on my 11.
    Who knew that you doing hollow Beech tree hot airflow research would make airplanes faster? Keep up the good work

    Glenn
    Last edited by cubdriver2; 11-07-2021 at 02:47 PM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  35. #35
    Steve's Aircraft (Brian)'s Avatar
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    These comments are great…

    In our Cub we mounted one of the square Piper “vent’s” backward in the rear window… has the same effect in pulling the warm air from the front to the rear of the cabin…

    Brian
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    Scouter's Avatar
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    Last week I thought dr Randy had a decent suggestion on cabin airflow with this rear facing Naca vent idea
    i found one on amazon for 50 bucks. The carbon cub has a small access panel on the belly right under the jackscrew. I gorilla taped it into place for evaluation. I had to run to NH yesterday for parts so it would be a good test. In the cub I have a insulating board between the ext baggage and the cockpit, helps to keep the chill back there. . I had the insulation barrier in place on the way out, and was not impressed at all the heat was adequate, but overpowering. IT was 32 outside at 6.5

    Got my stuff at Woodstock and pulled the barrier down. Shortly after takeoff I can smell something hot. Its my new boots that are in front of the heater outlets. I cant put my fingers inside the outlet holes its too hot to let them stay very long. Obviously the "Randy" vent is doing something. I probably should do some before and after measurments, but this mod works. YMMV. will post a pix when I get it to a more permanent install

    Jim
    Last edited by Scouter; 11-11-2021 at 07:16 AM.

  37. #37
    RaisedByWolves's Avatar
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    Got a link from Amazon?


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    WindOnHisNose's Avatar
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    Jim, thanks for the report. It hasn't been cold enough here to adequately evaluate the change.

    The "Randy vent" isn't mine nor my idea. The credit goes to Larry Vetterman, folks. While I understand that you might be able to get it cheaper on Amazon, I would encourage you to consider purchasing this from Larry. He has made such an impact on general aviation, is quite happy to share his ideas and is always available for questions. I hope you will support him.

    Randy
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  39. #39

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    Larry new slogan is "If it Sucks its made by Vetterman"

    Just kidding, Larry is one of the best guys around and always good for a barrel of laughs too!
    I spent most of my dough on booze, broads and boats and the rest just wasted ! - Elmore Leonard

  40. #40
    SteveE's Avatar
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    Quote Originally Posted by Utah 12 Driver View Post
    Larry new slogan is "If it Sucks its made by Vetterman"

    Just kidding, Larry is one of the best guys around and always good for a barrel of laughs too!

    LOL Ray, you finally said something funny

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