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Improving Take Off Performance?

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Well-Known Member
Sep 5, 2011
Ok, I have a friend who has a Kolb Firestar 2 which is tandem configuration, with a 503UL (50hp) with C Gear Box with a 3.0 to 1 ratio and a 71/72" Warp Drive Prop. 6500rpm / 3.0 = 2166.6 rpm for Prop. It's a (3) Blade.

A 72" x 22 at 6500/3.0 = 2166.6rpm Pitched for 2066.6rpm (3) Blade = 430.83 lbs needs 49.632 hp!

He wants to put a 670 (93hp) on it to increase his takeoff Performance for better Stol in the OutBack using the same 72" Prop & Grear Drive.

A 670 (More Weight & Cooling) with same 72" x 41 at 6500/3.0 = 2166.6rpm Pitched for 2066.6rpm (3) Blade = 430.83 lbs needs 92.496 hp!

A 72" x 33 at 6500/3.0 = 2166.6rpm Pitched for 2066.6rpm (4) Blade = 523.15 lbs needs 90.401 hp!

With a Take-off distance with a 503UL: 250 ft. Will you really Gain that much Shorter Takeoff Distance with the Higher 93hp Engine using the same 72" Length (3) Blade Prop or does he need a better prop?

Plane Specifications: https://www.pilotmix.com/firestar-ii

MTOW: 725 lbs (329 kg) 725 lbs = 328.9 kg / 10kg = 32.8 kw is needed = 43.98552 hp (44hp) needed.

Empty weight: 325 lbs (147 kg) <---- A little Less since he took out the 2nd Seat.

Useful Load: 400 lbs.

Stall speed: 30 kts (35 mph) (56 kph) <--- Can that be Improved! How much for a better Bush Plane?
Cruise speed: 61 kts (70 mph) (113 kph)
VNE: 74 kts (85 mph) (137 kph) <--- 503 50hp is probably pushing it close to the VNE.
Climb: 800 ft/min (4.1 m/s)
Take-off distance: 250 ft (76 m)
Landing distance: 300 ft (91 m)
Engine: Rotax 503 (50hp)
Fuel consumption: 4 GPH (15.1 LPH)

Using Static Thrust Calc at 77F:
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