scsmith
Well Known Member
I've made reference a couple of times to putting a couple of scavange holes in the turtledeck to allow cabin air to vent into the tailcone. I thought I had posted a picture before, but when I looked, I couldn't find it. So here's the picture:
The idea here is that vent air (heated or fresh air) can't come into the cabin very well if there is no easy passage for the air to get out. Also, there is high pressure along the back edge of the canopy skirt that makes a draft under the skirt and into the cabin - so that also makes it hard for air to come in through the heater tube and fill the cabin.
These two 1" holes are just aft of the rear baggage bulkhead, (F808? I forget) so that air can pass from the area around the canopy skirt into the tail cone. When the canopy is closed, the holes are not visible because they are just under the skirt.
Air then exits the airplane through the elevator horn opening in the rear deck, and out around the elevator and rudder hinge coves. Some air also exits through the rudder cable holes.
How does it work? Well, there is still some draft in the back seat, although it is much less than others. And the back seater seems to feel plenty of cabin heat making its way aft through the cabin. I think the next step would be to provide a better outlet in the aft tailcone to let more air exit the airplane.
Someone else (sorry I can't remember who) posted some pictures of a system with a fiberglass plenum around the interior side of the scavange holes, feeding a scat tube that went to a fiberglass outlet in the bottom of the fuselage. EDIT: here is a link to that work:
http://bidasst.bizland.com/heatvent.htm
The vent discussion is a little ways down on the page, after the heater box. Sorry I don't see the fellow's name anywhere on the page.
In re-reading the previous thread on this subject, about a year ago, there were lots of bits of info presented with various pieces of the puzzle. Paul Dye and a couple of others tried flying with an inspection port or other vents open in the baggage shelf, and with the rear seatback pulled forward. This obviously would allow much more air out of the cabin than my little 1" holes. But it didn't seem to help. However, there is still the problem of getting the air out of the tail cone. Several folks mentioned various exit vents on gliders, and there were a couple of pictures of NACA vents installed backward in the elevator horn inspection covers on an RV-8. So those would do a great job of letting the air out as long as the air can get from the cabin to the tail cone.
It seems like not many have put together the full combination of getting the air from the cabin to the tail cone AND letting the air out of the tail cone. The link above to the fellow that did this seems to be one that has.
So, again, I'm thinking that the next step would be to provide a better outlet in the aft tailcone to let more air exit the airplane. Stay tuned.
The idea here is that vent air (heated or fresh air) can't come into the cabin very well if there is no easy passage for the air to get out. Also, there is high pressure along the back edge of the canopy skirt that makes a draft under the skirt and into the cabin - so that also makes it hard for air to come in through the heater tube and fill the cabin.
These two 1" holes are just aft of the rear baggage bulkhead, (F808? I forget) so that air can pass from the area around the canopy skirt into the tail cone. When the canopy is closed, the holes are not visible because they are just under the skirt.
Air then exits the airplane through the elevator horn opening in the rear deck, and out around the elevator and rudder hinge coves. Some air also exits through the rudder cable holes.
How does it work? Well, there is still some draft in the back seat, although it is much less than others. And the back seater seems to feel plenty of cabin heat making its way aft through the cabin. I think the next step would be to provide a better outlet in the aft tailcone to let more air exit the airplane.
Someone else (sorry I can't remember who) posted some pictures of a system with a fiberglass plenum around the interior side of the scavange holes, feeding a scat tube that went to a fiberglass outlet in the bottom of the fuselage. EDIT: here is a link to that work:
http://bidasst.bizland.com/heatvent.htm
The vent discussion is a little ways down on the page, after the heater box. Sorry I don't see the fellow's name anywhere on the page.
In re-reading the previous thread on this subject, about a year ago, there were lots of bits of info presented with various pieces of the puzzle. Paul Dye and a couple of others tried flying with an inspection port or other vents open in the baggage shelf, and with the rear seatback pulled forward. This obviously would allow much more air out of the cabin than my little 1" holes. But it didn't seem to help. However, there is still the problem of getting the air out of the tail cone. Several folks mentioned various exit vents on gliders, and there were a couple of pictures of NACA vents installed backward in the elevator horn inspection covers on an RV-8. So those would do a great job of letting the air out as long as the air can get from the cabin to the tail cone.
It seems like not many have put together the full combination of getting the air from the cabin to the tail cone AND letting the air out of the tail cone. The link above to the fellow that did this seems to be one that has.
So, again, I'm thinking that the next step would be to provide a better outlet in the aft tailcone to let more air exit the airplane. Stay tuned.
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