My Zodiac 601HD as a touring aircraft

By Alan Cozens

Comments on weight, CG, stability and working out the weight and balance which will provide a few guidelines to builders.

My Zodiac is a standard ‘to the drawings’ HD/Rotax 912 machine built from a Canadian kit, with but 2 key changes - the Rotax is moved forward a little and the tailplane span is increased by 2 feet. These changes are important to be sure of meeting the JAR/VLA longitudinal stability requirements now required by the PFA, which do not apply in the USA or Canada. Fundamentally the need is for the aircraft in normal trimmed condition to return to level flight after the stick has been pushed forward (or back). This at max. aft CG.

Since my test flying started in July 95 at Goodwood, I have flown 130 trouble free hours, and begun to enjoy the touring the aircraft was intended for. With visits to the Scilly Isles, Guernsey (twice), Alderney (twice), Ostend and evening venturing north of Manchester, I have really got to know its good points and its limitations. Much of the flying has been over the Channel in conditions of zero horizon and poor visibility (despite good forecasts) when you need all the help you can get from the natural stability of the aircraft.

For touring it is essential to have the maximum possible ‘lift’ capability, because lots of fuel and baggage are heavy but essential accompaniments. The very light Rotax 912 helps in this respect, but even with the engine/firewall moved forward nearly 4 inches, maintaining the PFA safe (and legal) max. aft CG position of 16.1 inches from the datum has presented problems. To visit places like the Scillies and Isla, where there is no fuel, you need to carry plenty, and I have the optional wing locker tanks. This inevitably displaces all the baggage and the 12 lb liferaft to the aft locker behind the pilots, which worsens the aft CG problem. Because my wife Margaret and I are both light we can generally stay legal (and insured!). Frequently during flight we pump fuel from the wing tanks (aft of the CG) forward to the main tank, as that forward fuel and weight is consumed. Having the long range tanks in the leading edges should be considered by current builders, as it has a helpful ‘double whammy’ effect the CG position.

I encourage all builders to study my weight and balance table (below) and substitute their own aircraft target weights, crew weights, fuel loads, baggage requirements etc. Two indicators should appear - KEEP IT LIGHT THE CG FORWARD. If you do not follow these maxims you will end up with an aircraft of limited range that cannot be safely loaded to PFA requirements - a nice Sunday afternoon flyer but little else! To be fair , that is all that the original VW machine was capable of but it can do much more!

WEIGHT & BALANCE - G-BVAC ZENAIR ZODIAC 601HDPFA 161-12504

BASIC WEIGHT AND CG: Weighed by Southern Air at Goodwood - 672 lbs/11.65 ins. Datum LE at inner wing section. See Southern Air weighing report GW 695/22.6.95 Basic weight includes full engine oil (3.5L) and full coolant (3.5L) and approx 1.5 lbs unusable fuel.

EQUIPMENT LIST: VHF Comm Narco 810. Transponder Narco AT 150. Garmin GPS 150. Sigtronics SPA 400 I/Com. Wing tanks 2 x 25 L. Battery Gill G.25 (22 lbs). Cockpit seats. GSC 66” 3 blade propeller (wood)

CORRECTIONS: Nil.

NOTE! This aircraft has following modifications from standard; firewall extension of 80 mm and tailplane span extension of 24".

SAMPLE FLIGHT LOADING CALCULATIONS Note: max AUW 1200 lbs

1. TYPICAL FORWARD CG

2. TYPICAL AFT CG

Case 1 is legal, being within 10.5 to 16.1 in CG limits for the 601 HD currently set by the PFA. Case 2 is not legal being outside the aft limit.