3. Flying at 400 mph with a Corvette V8 Engine

Date: May 13, 1998 01:56 AM
Author: Doug Marker (dmarker@zeta.org.au)
Subject: Point 3) Flying at 400MPH with V8 Corvette Engine (Rev 10 20-Aug-01)

The CarterCopter prototype is currently using a water cooled V8 Corvette LS6 Racing Engine that at peak output is capable of 340 HP.

Index

Low Lift-to-Drag Ratio
High Efficiency Computer Controlled Propellor
Engine Heat Output Issues.
Two Stage Low/High Turbo Charging
Future Preference for New Aero Diesel Engines.

The Low Lift-to-Drag Ratio. (no longer applicable)
The CarterCopter has had a Corvette LS6, that uses a specially designed computer control system with monitors to monitor Prop efficiency via a number of measurements. It will also uses a newly designed two-stage turbo-charging to gain the efficiency needed at high altitudes.

There are a number of related points worth comprehending in order to accept the CC to achieve its projected results. These include :-

That the L/D ratio for the CarterCopter is very high (sets new records)
That Jay will achieve better than 90% (perhaps up to 94%) efficiency from the 7' 10" diameter prop
That the engine will deliver a constant 340 HP at high altitudes

The L/D story is a long one but is achieved by using the unloaded rotor and the high aspect ratio wings and also because of the very efficient streamlining of the CC craft.

The rotor causes very little drag as explained in the Point 1 answer. The wing offers about 1/5 th the drag of a certified single engine general aviation plane.

The combination of the low-drag rotor and the wing drag is very low. This combined drag of the rotor and the wings is approx 50% of an equivalent fixed-wing plane - when added to the fuselage drag the CC reduces overall drag by close to 20-25% off an equivalent fixed-wing craft.

High Efficiency Computer Controlled Propellor. Jay has designed a very lightweight highly efficient pusher prop that delivers a very even thrust across the entire blade section. It is designed to provide the needed thrust at sea-level and to be also able to deliver very high thrust in the thinner air of high altitudes.

It is expected to set new records for prop effiency. Like the rotor, the blades are hollow and mounted on an I-Beam spar the two blades, the hub and the I-beam spar are a mono construction.

The blades can tilt + or - 25 degrees using the same twisting (warping) technique as in the main rotor. This is that the inner section (lengthways) of each prop blade is hollow and not attached to the center I-Beam spar but the outer half (lengthways) of the blades are rigidly attached to the I-Beam spar. So to change pitch the blades are twisted around the centre spar which warps with the twisting action.

An onboard computer monitors several key flight parameters and controls both the pitch of the prop blades and the engine speed so as to provide absolute maximum efficiency of thrust, and fuel efficiency. If one looks at the pictures of the prop it can be seen that the prop is shaped to 'churn' through thin air at maximum pitch.

It also needs to be understood that the engine is capable of 340 hp which helps the CC to achieve the thrust needed at low and also at high altitudes such as 40,000 ft where the atmosphere is much thinner. The 300 HP will allow the CC to achieve the high airspeeds quoted.

If the CarterCopter flies as predicted (225+ mph at sea level), then it will have little difficulty flying at 400+ mph at 40,000+ feet providing that the the turbos deliver as promised and that the craft pressurization meets spec. If the rotor is stable at sea-level at that speed then the high altitude flying will be a 'breeze'. The reason why the CC has to go so high to get the speed advantage is because of the significant reduction in air atmospheric pressure from sea-level to 40,000+ feet (i.e. one fifth or better atmospheric pressure at 45k than at sea-level). If sea-level air is 'syrup' then the air at 45k feet is 'methelayted spirits'. Any craft could fly faster if it can 1) reach the altitude, 2) efficiently 'churn' or 'blast' through the thin air, and 3) keep the engine sufficiently cool (which is why a liquid-cooled engine was chosen).

(On the CarterCopter the 2-stage turbos and the big efficient computer controlled prop get to 'pay their rent' when flying at high altitude.

Engine Heat Output Issues.

If one looks at the body of the CarterCopter, one can see that there is a large air-scoop underneath to take in cold air and the hot air has been designed to be 'sucked out' around the prop spinner (this is working well enough). At full power the engine compartment temperature is slightly better than was predicted and well within tolerance.

Two Stage Low/High Turbo Charging. (outdated)
The engine will use a low-pressure turbo-charger that feeds a high-pressure turbo-charger - there will be an intercooler between the two turbos and a further cooler between the high-pressure turbo and the engine.

These are expected to deliver the needed manifold pressure at high altitudes and allow the engine to in turn deliver the needed 340 HP to drive the high L/D craft at 400 MPH cruise speed (40-45 k feet) at an estimated 18 mpg.

Quote from Jay Carter : To obtain the horsepower needed in thin air, the powerplant is a compound turbo charged water cooled piston engine.

Note:
a piston engine is very efficient relative to a gas turbine, it is very difficult for gas turbines to maintain horsepower ratings at high altitudes.

Two turbos in series -- a large low pressure and a smaller high pressure turbo with an intercooler and aftercooler -- are used to efficiently obtain the needed manifold pressure for 300 hp at 45,000 ft altitude.

A water-cooled engine is generally more efficient and easier to cool than an air cooled engine at high altitude, high horsepower outputs.

Our Corvette LS6 engine weighs 300 lb excluding the turbochargers, turbo coolers, radiator and coolant.

Future Preference for New Aero Diesel Engines. The CC team have also begun evaluating potential diesel engines of which at least 3-new and very interesting designs are in development or testing. The advantage of diesel is the even greater efficiency (and lower fuel cost) over petrol, the use of non-volatile fuel, the removal of the electric ignition system (always a possible point-of-failure), and less moving parts.

The version of the CC to be used for the world record attempt at distance, will almost certainly use a diesel engine.

Doug Marker

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D.Marker email: dmarker@zeta.org.au
R.Anderson email: cartercopter@casagrande.com