Cockpit drafts

gereed75 · #1 11-07-2008, 12:07 PM

Had an interesting learning experience this AM that might provide some insight on an oft discussed topic.... After takeoff in my slider -6, as speed increased, I immediately noticed a strong draft on the back of my neck that had never been felt before. After climbout and level off, the draft persisted. I tracked it to be coming from the slider slot and from an opening I have in the bagage compartment aft bulk head.

Hmm never felt that before - further investigation revealed that the right side canopy aft holdown "spike" was not seated in the poly block and there was a considerable opening in the right side canopy side skirt.

After slowing down, reopening the slider and then reclosing it properly -all drafts went away. It seems that a well sealed canopy precudes "Tail pumping" drafts and even any noticable draft from the slider rail (I am not using the plastic slider seal). I also have no disernable draft coming from the stick boots (and have not installed aileron push tube cloth seals).

Take care to have well sealed side and aft skirts and it appears un-wanted drafts are minimal. No place for air to get in or out of the "sealed" cockpit - makes sense!

flyboy1963 · #2 11-07-2008, 03:05 PM

You....
opened......
the .......
canopy......
in........
flight???????????????????????????????????????????? ???????????

that must be a BIG question. I don't even thing Van's has done it.
All kinds of scary things come to mind.
Was there much 'pull' or suction on it/ How far did you open it?

inquiring minds must know!

thx,

Perry

rv9av8tr · #3 11-07-2008, 04:00 PM

I was flying my Navion A once when it was "hotter than get out" and thought a little breeze would be nice, so decided to unlatch the slider canopy. Wow... it got REALLY noisy just having it unlatched.... decided that was not such a good idea!! Then... it would NOT relatch closed!! The air pressure on the front windscreen distorted it just enough that it wouldn't "mate up" closed!! Even slowing down to near stall wasn't enough to get it to relatch. Ended up having to land.

rv7charlie · #4 11-08-2008, 07:20 AM

Perry,

On all the sliding canopy planes I've been around (where the entire bubble moves aft), it's very difficult-to-impossible to get the canopy open more that a foot or so at most. There's fairly high pressure pushing the back of the canopy forward; that's the reason for the draft on the back of your neck if the rear skirt isn't tight. The Thorp T-18 even has a 2x6 inch door cut in the base of the rear canopy for letting fresh air *into* the cockpit. The only real issue I can think of is that the track be strong enough to handle the turbulence at the front.

The RV-4 with the tip-over is a different story. :-)

Charlie

L.Adamson · #5 11-08-2008, 06:22 PM

Quote:

Originally Posted by rv7charlie

Perry,

There's fairly high pressure pushing the back of the canopy forward; that's the reason for the draft on the back of your neck if the rear skirt isn't tight.

I've heard it, but I'm not even sure of that. After takeoff, I felt a slight breeze over the top of my head. Then I noticed that the slider lock was about 1/8" from being latched. With one hand, I couldn't get enough force to push it forward that little bit. I didn't try to slow the plane...........and just landed instead.

L.Adamson --- RV6A

rv7charlie · #6 11-08-2008, 08:04 PM

I guess I oversimplified a bit. The ones I've seen will open a few inches & stabilize there.

Similar situation with the tipups: they open a few inches & stabilize.

Anyone with a different experience?

Charlie

gereed75 · #7 11-09-2008, 06:12 AM

To clarify- just slid the canopy aft far enough to reseat the aft hold down in the poly block and re-latch the canopy properly. Just this small movement took moderate effort.

Although I did not try to open the slider beyond what was required to relatch the canopy, I got the distinct impression it was not going to move much beyond the 2" needed to realign and relatch. All done at 80 knots.

videobobk · #8 11-09-2008, 07:20 PM

As for canopy drafts, I stopped all those from the back with a really simple seal. I glued vinyl (actually a trim piece) onto the slider top rear that goes far enough back to overlap the top of the fuselage. I didn't glue the back 1/2" or so, leaving it free. What it seems to do (I haven't gotten out to really look at it in flight!) is that the incoming air gets between the slider and vinyl and creates an air seal. No drafts, anyway. This is a good time of year to think about such things.

Bob Kelly