Cowl Flap Mod
Had the first free weekend in a long time so I took advantage and modified my cowl flap as per the previous post - Don't worry Dan, I have a cover which returns the exit to stock configuration in about 10 minutes.
I basically moved the hinge line of the flap forward 4" by cutting out the lower rear portion of the cowl exit area. By allowing the flap to deflect a max of about 30 deg I've increased the exit area by 22 in^2 for a total of 69.1 in^2 when fully open and reduced to 32.6 in^2 when fully closed. Stock exit (minus exhaust) is 47.1 in^2.
I used engineering graph paper to trace the inlet shape and calculate those areas for a total of 61.75 in^2 resulting in ratios (exit/inlet) of :
Stock: 0.762
Flap Fully Open: 1.11
Fully Closed: 0.527 (most likely a bit higher since the flap is probably leaky around the sides - I'll fix this)
which leaves the stock ratio right in the middle of the adjustment range where I wanted it.
I don't have a plot of my test today as my datalog battery died shortly after T/O.
WIth flap open I started with #2 cyl at 350 deg as in previous tests and a WOT Vy climb to 6K PA. Temp climbed to 360 by 300 feet then started decreasing and stabilized at 345 by 1500 ft and steadily decreased down to 330 at 6K. OAT at Sea level was 77 deg F. Changing from flap fully open to closed resulted in a 150 FPM ROC increase.
In a Vy climb with flaps fully closed CHTs climbed to high 370's, low 380's then decreased to 360's by 6K. An average 30 deg hotter than with flaps fully open during climb
Flap fully open in level flight with a fixed throttle setting gave 2300 RPM @ 152MPH. Flap closed to stock exit area resulted in a stabilized speed of 153 MPH. Fully closing the flap gained another 2 MPH to 155MPH. CHTs at 155MPH flap closed were 309, 313, 324, 319
In level flight with fixed throttle setting closing the flap from fully open increased CHTs by an average of 5-10 deg with corresponding airspeed increase of 3 MPH.
-Overall the flap is far more effective in this configuration than the original which is expected given the wider range of adjustment.
-A climb rate penalty is the price for better cooling (DUH)
-With lower OAT climbing with flap closed is acceptable
-Drag reduction realized with flap fully closed with marginal CHT penalty.
- OT was 175-180 throughout all flight regimes
modified cowl flap:
I will say there is significant pressure trying to open the flap from the fully closed position. As it is I had to maintain positive pressure on the cable knob to keep the flap fully closed. It will be interesting to measure the pressure changes as a function of flap position soon.