Drag calculations in Bruce Carmichael style...

I made a preliminary calculations that my Max 3 has a drag of:

WING 0.134 sq ft
IND.D 0.008 sq ft
FUSE 0.125 sq ft ( + rudder...same wetted area coefficient 0.0027 )
W+B.I 0.012 sq ft
ELEV 0.031 sq ft


ALL 0.310 sq ft

Total drag coefficient based 0n wing area in 0.0120

Total wetted area dragcoefficient is 0.0015 which can be considered phenomenal !

Previously only VmaxProbe had close to similar figures and P-51D Mustang 0.0040 ( AR-5 0.0034 ).

There is no drag by cooling ( like in P-51D ) and the gear ( since it is retractable ).

That is less than half of the drag of a 3 feet longer and 1.9 sq ft more fuse cross section possessing AR-5 record setter.


NOTION; The fuse and rudder being non lift producing may have a coeffient .0025 which would yield 0.116 sq ft drag and making total drag into 0.301 sq ft. That would be 34 % of AR-5 drag and enabling to reach AR-5 speed with only 26,65 hp engine ( 213 mph ). This sounds plausible since Vmax Probe was calculated at 85% prop efficiency to go 240 mph with 50 hp. We have nowadays props that can go up t0 90% efficiency. It is also possible that my wing can be made with a lot less drag with some new foil ( instead the NACA I had as a basis ). Big wing will be serving the landing and take off behaviour...so I won't reduce the size to keep the landing more loading at 65 kg/m2. Wing being 0.120 sq ft drag the whole equation can be 0.287 sq ft ( 33 % of the AR-5 ). You see what I am getting here..checking if I could go 218+ mph with just 22 hp engine enhanced with nitrous oxide ( in theory it seems possible since with 90% efficient prop Max needs only 20 hp now with a super wing and fuse..nitrous will enhance the power output easily by 8-10 prosent ).

Who is going to say pushers have no advantage when it comes to drag issues ?

Also packing everything in a really small and yet compact size pays off.

You don't have to trust my estimate for the speed...just check the hp with 90% ( or even the 85% ) prop efficiency and use my calculated 0,31 sq ft for drag:

1 comment:

  1. I was forced to make corrections to this topic since I saw that B C used dragcoefficient 0.0029 for a non lift producing fuselage of AR-5 which is more bulged than MAX III fuse.