Cowl Hatch Pressure Question
03-11-2004, 12:22 PM
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Cowl Hatch Pressure Question
Hi All-
I needed to cut out a hatch on the underside of my new VF Extra cowl to slip it over the Pitts muffler exhaust pipes (Saito 91 side mounted with slimeline pitts 4007). The hatch is about 4 inches long (from firewall to just behind pipes) and about 1.75 inches wide. At that location the cowling is perhaps 20-30 deg from horizontal.
My question is: What is the likely pressure this hatch will feel during flight? There is a large cutout on the side of the cowl around the head of the saito, at least 3-4x the size of the front openings behind the prop, so I don't think there will be a big overpressure from that. I'm more worried about the airflow-induced low pressure outside the hatch. I imagine it would depend on angle of attack (worse inverted?). I glued some scrap cowl material on the inside to create a "seat" or "lip" to set it on, and was hoping I could just use trim sheets to cover the crack and hold it on (easy enough to take off and replace each time I need to take off the cowl).
Any good aerodynamics people out there willing to hazard a guess on the likely pressure the hatch will see in flight?
Thanks.
-Greg
I needed to cut out a hatch on the underside of my new VF Extra cowl to slip it over the Pitts muffler exhaust pipes (Saito 91 side mounted with slimeline pitts 4007). The hatch is about 4 inches long (from firewall to just behind pipes) and about 1.75 inches wide. At that location the cowling is perhaps 20-30 deg from horizontal.
My question is: What is the likely pressure this hatch will feel during flight? There is a large cutout on the side of the cowl around the head of the saito, at least 3-4x the size of the front openings behind the prop, so I don't think there will be a big overpressure from that. I'm more worried about the airflow-induced low pressure outside the hatch. I imagine it would depend on angle of attack (worse inverted?). I glued some scrap cowl material on the inside to create a "seat" or "lip" to set it on, and was hoping I could just use trim sheets to cover the crack and hold it on (easy enough to take off and replace each time I need to take off the cowl).
Any good aerodynamics people out there willing to hazard a guess on the likely pressure the hatch will see in flight?
Thanks.
-Greg
03-11-2004, 02:44 PM
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RE: Cowl Hatch Pressure Question
I don't think it would be much, but as long as you have scraps to seat it, why not just add a few screws into the seat to secure it? (Trim sheets will lose their stick after a while, especially in that oily area)
03-11-2004, 02:58 PM
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RE: Cowl Hatch Pressure Question
There is a slight pull on any hatch due to airflow over the hatch and still air inside the fuselage. (true Bernouli effect) Its not huge... but you do have to secure them well.
Also... if the foam padding in the compartment presses on the inside of the hatch... you can easilly pop the screw mounts. (how would I know that?
)
The combination f screws and being careful not to have the foam press on the hatch will keep it in place. Thent he trim sheet or clear packing tape will keep the oily exhaust residue from seeping in. (I will sometimes stuff a few kleenex or such into the model near a hatch to absorb anything that might leak in... when the hatch is not sealed with tape.)
Also... if the foam padding in the compartment presses on the inside of the hatch... you can easilly pop the screw mounts. (how would I know that?
)The combination f screws and being careful not to have the foam press on the hatch will keep it in place. Thent he trim sheet or clear packing tape will keep the oily exhaust residue from seeping in. (I will sometimes stuff a few kleenex or such into the model near a hatch to absorb anything that might leak in... when the hatch is not sealed with tape.)
