Plans Built Skytwister Helicopter Design
By Nev Walker – Ayr Nth Qld 4807 – December 2000
Enclosed is a photo of my SKYTWISTER helicopter – NW plan modified light helicopter, which I have had in the air for around the last 10 months.
This machine is one of two Skytwisters built in my engineering workshop over the last 2 1/2 years; the second machine is due to be inspected within the next 2 months.
The helicopter in the photo is single seat and powered by a Rotax 618 engine. Its maximum take off weight is 380 kg, and carries a 105-kg pilot with 50 lt of fuel.
I believe that this single seat light helicopter is the first plan modified homebuilt experimental helicopter legally flying in Australia. Rego number VH-ULH.
SkyTwister Notes From Ben to Adam (Redback Aviation)…(1990’s)
The new design tube tail contains a belt system. I feel this is the most maintenance free, dependable, strong and affordable drive there is for a light helicopter. With over 200 flight hours logged and the belt still looks brand new. I’m not sold on heavier commercial gearboxes, drive shafts, carrier bearings, plus the weight of the shaft drive system.
Poly Chain cog belts can be used for the primary and secondary drive. But the cost for these systems are very expensive! (EDITOR: now days, as an option, you can get off the shelf motorcycle belt drive sprockets that might work).
The sprocket-chain drive is low cost, easy to set-up and adjust, plus the O-ring racing chain needs no lubrication. All the professional moto-cross, hill climbing and racing bikes use this type of O-ring chain and they totally abuse them all year round.
The horizontal stabilizer is adjustable with 17° and works very well. The all extruded “Fleck” rotorblade system (now being sold by Vortech with a stronger 6061 spar) tracks in super smooth without the need for trim tabs. It was surprisingly easy due to the consistent weight, balance and blade finish.
Time Life Schedules? Well, we have been working on tracking this, but at the moment – we haven’t got enough hours up – so for now, a bit of common sense and manufacturers specifications should be a rough starting guide.
Fuel consumption is currently around 4 to 5gal per hour on the two stroke engine. This depends on what type of flying you are doing – “All Hover” or “Mostly Cruising” which uses less.
All cruise and general performance specifications are similar to the Mini 500, Angel CH7, LoneStar, Ultrasport etc…though top speeds (VNE) are more moderate for safety.
400-450 main rotor RPM seems to be the sweet spot and works best with the SkyTwister. The Exec 90 weighs around 900lbs dry and uses a higher 500 RPM in their design. The blade size, symmetrical airfoil type, with the SkyTwisters weight, rotor system design are things that determined what works best in rotor blades.
I prefer my drive system but ultimately, it’s up to the builder. While it may look a little complex, I built it this way so that the ordinary backyard mechanic (like me), can build my helicopter design.