Sid Wood Enjoyed your comments on air movement and if I understand your comment
<<<<< abetter scheme is to make a rear facing ramp to get the air flowing smoothly toward the exit with the exit cut off square with the slip stream.>>>>>>> would mean that the cut off of the discharge is 90 degrees to the air flow past the outlet???? Is my assumption correct? tnx jw > On Feb 25, 2017, at 18:12, Sid Wood via KRnet <krnet@list.krnet.org> wrote: > > Pete, > The idea for the larger opening size is to accommodate the increased air > volume due to engine heating. However, the exit methodology is particularly > critical to the overall efficiency for getting the cooling air overboard and > back into the airstream. Simply cutting a big hole in the bottom of the > otherwise streamlined lower cowl will not get the job done. The positive > incidence angle of most lower cowls will have air going into the lower cowl > instead of exiting. You need to create a negative pressure area at the > exit. Some designs put a down-turned lip at the forward edge to attempt > creating the negative pressure. This works, but is terribly inefficient. A > better scheme is to make a rear facing ramp to get the air flowing smoothly > toward the exit with the exit cut off square with the slip stream. That > way, maximum negative pressure is created at the exit, and the flow rate is > maximized. If the ramp is tuned right for the cooling flow, a net increase > in thrust can be obtained. Wind tunnel tests on the P-51 confirmed 8 > percent increase in thrust just cooling the water radiator. > Here is a picture of my current lower cowl during construction. > https://s3.amazonaws.com/expercraft/sidwood/144869089252d5df7076508.jpg > The 4 engine exhaust pipes exit the same ramps as for the cooling air exit. > So, there is some flow augmentation due to the engine exhaust blast. > > Sid Wood > Tri-gear KR-2 N6242 > Mechanicsville, MD, USA > ------------------------------------------------------------------------------ > > I working on the lower half of my cowling and need to know the multiplier to > size the exit area. I vaguely remember that the exit area should be approx. > 1.5 times the total size of the inlet area. Need to qualify that memory. I > have Tony Bingelis' "Firewal Forward" book, but can't find that multiplier > listed anywhere. > Any help or info greatly appreciated. > Thanks, > Pete Klapp, building N729PK, > Canton, Ohio > > > _______________________________________________ > Search the KRnet Archives at > https://www.mail-archive.com/krnet@list.krnet.org/. > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options. > To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
