Especially EdwardB, Cybertom and John (but any and all ideas welcomed from anyone):

Specific numbered questions follow below, after "Background".

BACKGROUND

Am considering a Flair Moth build and my first engine choice is the Desert Air DA 50 R (50 cc) gas engine rather than the Laser 150 or 180 glow for several reasons.

DA-50-R is newer, computer designed, spark ignition (better reliability), recommended by Toni-Clark.com models in Germany, produces much less fuel residue, eliminates hgroscopic and toxicity fuel issues, and probably would eliminate the need to add much if any nose weight (more below on weight). My philosophy for the "big moth" is to put the "added nose weight" into engine power if possible.

Other issue is my 9750 foot above sea level Nordic ski center parking lot, my flying site (in summer and fall) 10 minutes from my home (live to Nordic ski).

According to Richard Shelquist's website

http://wahiduddin.net/calc/calc_da_rh.htm

this Nordic flying site has about 26% less density altitude and produces 29% less relative horsepower for a normally aspirated engine than Cybertom, EdwardB and other fellows who fly more or less at sea level. These numbers come from a typical summer day basis Gainesville, Florida, the Spring site my son and I fly at. The huge bipe wing area of the Flair Moth, light construction and wing loading make the plane a strong candidate for my altitude up here.

Lift is proportional to density altitude, but proportional to the square of velocity. For example, if moth stall speed is 25 MPH in Ohio, it's 28 MPH (3 MPH of additional speed) up here, which is a negligible increase. But my engine power rating has to be 29% higher than sea level fliers. Another good reason for the DA-50-R, which Desert Air says is for a 14 to 18 pound aircraft.

Need to know if the DA - 50 R will fit under the Moth's fiber-glass cowl.

Height from crankshaft center to top of head for the DA 50 R is 5.49 inches or 139.4 mm.

Width of DA 50 R cylinder is 3.77 inches or 96 mm.

Length, distance from thrust washer to back edge of engine mount is 6.7 inches or 170mm.

Unfortunately, for Laser 150 I could only find height (from crankshaft center to cylinder head top): 3.97 inches or 101 mm.

QUESTIONS

1) Given the numbers above, would the DA 50 R (inverted) fit within the Moth fiber- glass cowl? The biggest concern is whether the width of the DA 50 R head is too large.

2) The Laser 150 weighs 29.5 Oz, and the DA 50 R (with mounts) weighs 50 Oz, a difference of 20 .5 Oz or 1.28 Lbs. EdwardB, can you tell me fairly precisely how much lead weight you had to add to the nose of your Moth (with Laser 150 in place) to get proper CG, and whether it was close to 21 Oz?

3) I gather that there are "engine bearers", wooden rails installed for the Laser 150 crank-case side lug mounts. The firewall is probably not adjustable for the Moth. The DA 50 R mounts flat against the firewall, and the wooden rails would have to be cut off flush to the Flair Moth firewall in my case. Can you envision a problem with DA 50 R length (above) of 6.7 inches (170 mm) for a "flush to the firewall" installation?

4) Recommended props are 22X12 or 24X8. Up here, a 22X16 or 24X10. EdwardB noted the “tip over” taxi issue during his maiden. Would a 22 or 24 inch prop exacerbate ground handling or ground clearance problems?

5) Since gas runs hotter than glow, might have to enlarge vents in the cowl for cooling. Can you for-see any engine cooling issues with the Moth cowl?

Thanks fellows for your help and any other ideas/suggestions/criticisms.