2. Doing Vertical Take-offs and Landings with an Unpowered Rotor



Date: May 13, 1998 01:32 AM
Author: Doug Marker (dmarker@zeta.org.au)
Subject: Point 2) Doing vertical take-offs and landings (rev6 - 02 Nov 1999)


Index


The CarterCopter's High-Inertia Rotor. To understand about the ability of the rotor to store energy it would pay to read Point 1 answer first.

The CarterCopter rotor is a 'high-inertia' rotor. This means it stores rotational energy because of its weight and design. The 110 lbs of depleted uranium (55lbs in each blade tip) allows the rotor to hold sufficient rotational energy when spun at approx 525 RPM, to lift the Cartercopter at a typical weight of approx 2,600 lbs, up to a height of 50 ft + a forward distance of 75 ft at 50MPH.

In slow speed flight the CarterCopter rotor spins at approx 275-300 RPM (depending on gross weight at the time). During high-speed flight (above 100 MPH) the rotor will spin at between 75-150 RPM as it gets unloaded. When landing or taking off the speed should be between 400-525 RPM. Jump take-offs are to be performed at about 525 RPM main rotor speed.

To commence a vertical take-off the CC uses a prerotatror set for slipping mode, to firstly spin the rotor up to 150 RPM which takes about 45 seconds. When at that speed the prerotator cluch is switched to non-slip mode and the full engine power is applied it takes about another 45 seconds to spin the rotor up to pre take-off speed (currently set to be 525 RPM).

The craft is sitting on its wheels (brakes on) and is angled forward in one of two recommended take off attitudes - 1 = normal shallow angle take-off, 2 = high-powered jump take-off. The undercarriage is adjustable to allow the CC craft to change its forward leaning attitude on the ground without the pilot having to make external adjustments.

The pilot pulls collective steadily taking pitch to a max of 10 degrees over about 4 seconds, then eases back to about 4 degrees which is the normal forward flight pitch setting. The rotor by this time will have dropped back to near its normal flight rotation speed (275-300 RPM).


Helicopter Takeoff - Gyroplane Slow Flight. The craft is actually behaving like a helicopter during the first few seconds of flight. Air is drawn down through the rotor as collective is pulled.

The pitch increase must be controlled so as to not slow the rotor too much while at the same time gaining adequate altitude at an acceptable rate. At the same time the pusher prop is at full power and causing the CarterCopter to fly forward.

The faster the CarterCopter flys forward the more the horizontal stabilizer (tail wing) tries to level the craft. Also the pilot will be pulling back on the cyclic stick to tilt the rotor back as well as to start reducing collective.

At the end of the take-off manouvre the rotor tilts back far enough for the rotor airflow to transition from down through the rotor to up through the rotor. Collective is reduced to 4 degrees and the CC is now flying as a gyroplane.

The whole craft has shifted from flying forward in a nose down attitude to flying in an almost level attitude with the rotor tilted slightly rearward (a normal Gyro position).


Transition to Fixed-Winged Flight. Near 100MPH and depending on gross weight, the rotor will be 'unloaded' and the CC will have transitioned to aeroplane flying mode.

Takeoffs should be one of the easiest manouvres assuming the CC is facing mostly into the prevailing wind. This style takeoff is what all good helicopters normally do if conditions permit. The difference with the CC is that the pilot does not have to worry too much about forward cyclic as 1) the CC rotor cannot be tilted any further forward than 90 degrees to the mast which is why the CC is angled forward for a jump take-off, 2) Unlike a helicopter, the CC has a pusher prop that under normal circumstances is at high thrust during take-off.

To land, the pilot would normally come in at a steady descent at a low trajectory and adjust rotor tilt and collective to cause the rotor to spin up over 400 RPM (low collective and increased rearward tilt).

When near the point of landing the pilot will flare out and if done at the right height should flop gently down with minimal forward roll (pelican landing).

A true vertical landing is for the experienced pilot as pilot only has approx 5 seconds of lift inertia in the rotor if descending vertically. Pilot has to be sure he/she is committed to the vertical landing.

A go-round is of course quite feasible but requires a higher level of skill in that the pilot has to know he/she has enough room to clear obstacles and get the rotor to spin up again.

The pusher prop would be operating at maximum thrust in attempting a go-round.

Achieving it cleanly is a good balance of rotor collective, rotor tilt, remaining energy in the rotor and prop thrust.

Jay Carter wants to do a demo where he switches off the engine just prior to landing, then as soon as the nose wheel touches the ground, pull collective, go up to 40-50 ft, fly forward 150 yards and land again dead-stick.


Again - I hope this has helped explain aspects of vertical take-off and landing of the CarterCopter.

Cheers

Doug Marker


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- 04 Dec 1998
Created: 01 Dec 1998 - Updated: 2 Nov 1999
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