sjhanc

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kcollier,
I have done a lot of 4 blade testing with both gas engines and electric brushless motors. I hate to burst your bubble but the engine you want to use is about 40-60 cc too small for a scale sized prop on your Mustang. The main problem is the power pulse the gas engines punch the prop with requires that the hub and blades be over-sized in construction to avoid a catastrophic blade loss that will destroy the entire plane if (MORE LIKE WHEN) it happens. This heavy, thick hub and blade construction needs lots of excess horsepower just to turn it, and a lot more horsepower for scale like performance. My big gas 4 blade prop is a wall ornament (22-14 blades), it needs a 110cc twin for adequate flight performance.

I have had, however exceptionally good performance with the Varioprop (Germany) brand with electric brushless motors turning them. An 80 mm diameter or larger motor can spin them but you need to carefully match the motor's top rpm (KV) with the design top rpm the manufacturer lists as max for their product. I used the 22.6 inch diameter blades (max 4900 rpm for 1 minute) but found that the electric motor over revved the prop during the takeoff (stalled blade airfoils) and again at high speed even with the pitch set at 18 inches. I bought a set of (19.9 inch diameter) Spitfire blades rated for higher rpm's but they didn't look as good as the 22.6 inch Hamilton Standard set. The 19.9 blade set worked very well for takeoff power (pitch set at 18 inches) and high speed flight (130+mph). Current draw was high (140-165 amps) during acceleration but dropped dramatically during cruise even at 120+mph (65-85 amps). As an electric motor approaches its maximum rpm it unloads and current draw goes way down if you are using a clean airframe like the P-51. Round motored planes are going to be operating close to the motor's max current rating all the time because of the airframe drag, but they have more room for batteries. P-51 planes typically don't have enough internal room for the large (24 cell, 10,000 mah) LiPo packs needed for 10 minute duration. My P-51B weighed 29.5 lbs with a 24 cell 6600mah pack and gave me 5-7 minute flights.

If you are going to want to stick to gas power then you need to use the 100 inch wing span class of plane and 100-120cc twin cylinder motors for power. At that size it all gets easier, especially if you can keep the gross weight down below average (hard to do with gas power).