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Aerodynamics: Twin vs Single Engine Performance

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cDuck28Z

Member
Joined
Aug 29, 2015
Messages
8
Location
Virginia
Good Evening,

First post here, but a long time follower. I've been designing a light experimental twin engine based off of the CriCri design, but I've run into a fairly (what I hope to be basic) problem of simple aerodynamics. I've used a simple Static Thrust Calculator (1), but keep coming up with a question based off of the available HP and published top speed of the CriCri (2).

My question is this: How can the CriCri have a top speed of 138mph (3) with the dual 15hp engines, each producing 95lbs of static thrust, and a theoretical top speed of of 53mph (Solo 210 isn't on the list, but I used the 'Lightning Aircraft 150D2-B' (with a 30x10 prop) as my baseline because it's also about 15 HP)? No matter what combination I run, there's nothing that really even brakes 1/2 of the speed/power combination of the published CriCri statistics (3)?

Is the speed from this rough calculation doubled or is it just not accurate for a twin engine? Is there a more accurate to estimate top speed/power/thrust than this simple calculator?


References:
(1) http://p51.christiani.nl/staticthrustcalculator.htm
(2) http://www.rotaryforum.com/forum/attachment.php?attachmentid=67042&d=1267623273
(3) http://Hstrial-mpierce7.homestead.com/cricri_infopack.pdf (also Wikipedia)
 
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