Excelsior 720 (oz2867)


Excelsior 720 (oz2867) by Dave Rounsaville 1973 - plan thumbnail

About this Plan

Excelsior 720. Free flight power model. Unlimited class C competition machine. Torpedo power shown.

Update 7/7/2022: Added article, thanks to RFJ.

Quote: "The Excelsior 'C' Special, by Dave Rounsaville. Your mind will 'unwind' as you uncork this K&B .40 machine. In two seconds it's up in thermal land. A ship for winning. Translucent MonoKote skin, flies in B-C.

Two AMA unlimited gas ships have really impressed me this year. The first was Bill Chenault's A-B 'Pearl 450' (Nov '72 FM) which I first saw perform at the '72 Taft USFF Championships in the hands of Dick Mathis. I liked it so much I built one for the '72 Nationals.

The other design was the Excelsior 'C' Special presented in this article. I had originally intended it for a dual purpose B-C combo using K&B .29 to .35 power. The weight came out at 33 ounces, fully Mono-Koted and the performance was excellent. However, after mounting a K &B .40 FI late this past season, performance changed to astounding! Spectators watching from a distance were inclined to think it was my FAI Power ship. I really believe it's a good deal faster!

The Excelsior C Special started out as a blown up version of my 1/2A-A performer; by far my most successful contest machine in terms of shear number of wins. The final version differed slightly from the smaller 1/2 A in slight changes in aspect ratio and moment arms. The basic relation of the wing to stabilizer area however was retained.

The original model flew 'right off the board' as they say. It made its third flight and went on to take 3rd at the NADC. Maxes were 2 minutes with a 7 second engine run, but the Excelsior appeared to max easily with only 5-1/2 seconds of power flight.

The contest season in our area usually begins with the Golden Eagles Early Bird meet at Johnsville also. Jim Kutkuhn is generally the CD and does a great job. This is one of my favorite contests as I won my first trophy here years ago. My 1/2A ship had won both 1st and 2nd the previous year. '72 saw the Excelsior C put in four straight 2 minute maxes before breaking a wing when it DT'd onto a house. (One of those freak accidents where it hits, then falls sideways, landing on a wing tip.) It was good enough for 1st place however, The wing was easily repaired and back flying the following week, another good feature of this type structure.

A few words follow on design and construction. A physical similarity can be seen between this 'C' ship and my FAI Power model featured in the July issue of FM, but the similarity ends with the planform shape. Since weight is not dictated by area as with FAI, the stab area can be increased. This big ship uses a 45% stab which makes for a less critical rearward CG position, with better ability to handle high power. The short nose and moderate tail moment combine to give quick recovery and good thermal riding capability.

The airfoils are a modified 'Head Hunter' type as with the FAI ship. I'm surprised more people don't use this type of construction suggested by Dick Mathis. Its advantages are light weight, and ease of construction and repair. With only one rib shape, building is is a snap..."

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Excelsior 720 (oz2867) by Dave Rounsaville 1973 - model pic


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