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

WindOnHisNose

BENEFACTOR
Lino Lakes MN (MY18)
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
Vetterman vent pre.jpg

Installation, looking toward the front of the aircraft
Vetterman vent looking fore.jpg

Installation, looking aft
Vetterman vent looking aft.jpg

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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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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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.....:p


Man, I crack myself up!
 
How about CO? Great idea but I would run the CO detector for a while to make sure nothing is sneaking in there.

sj
 
alot more streamlined than draggin a set of these around.
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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
 
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
 
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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I myself was considering an electric bib for rides in Jim's CC on the New Year's Day jaunts....
 
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
 
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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
 
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.
 
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
 
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.
 
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.
 
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
 

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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
 
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
 
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
 
Wait….so if we put three NACA ducts facing rearward on each rear window, the cub will go faster?? 🤣


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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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