B317

DESIGN: UniCopter ~ Engine - Cooling

Outside Craft:

Long-EZ ~ Pusher Prop

George Shell's Downdraft Cooling System Excellent pictures.

Text from the above web page;

"N10LZ's downdraft cooling system uses ram air inlet scoops for engine cooling and the NACA scoop for carb air and accessory cooling.

The two inlet scoops have 4-inch circular openings to feed ram air into two separate high pressure plenums. Shaped from urethane foam, the scoops are glassed onto the top cowling directly in front of the cylinders. The plenums are typical sheet aluminum fabrication using standard gasketing for sealing to the top cowl. The installation is simple, uses mostly factory-supplied holes, without the need for complicated ramps or diverters. A Kevlar manifold is installed over the entire NACA scoop opening to funnel air to the carburetor, oil cooler, fuel pump, and alternator. A Brackett filter is mounted in the manifold for filtered air to the carb. 3-inch scat tubing is used for the carb and oil cooler. Note the customer Kevlar air channeler upstream of the oil cooler. 1.5-inch hoses are routed to the fuel pump and alternator diodes. Carb heat is provided by two half-shell muffs on port exhaust stacks. Exhaust stacks exit straight, avoiding hot air blast to prop. Except for the cooling scoops, the only cowl modification was to install a slight bubble to the lower cowl for clearing the carb air/heat box. Original exhaust cut-outs in lower cowl will be reshaped and glassed over later.

N10LZ uses the Audio Flight Avionics AV-10 and 4-line display for engine monitoring. CHT bayonets are installed in the factory ports on the bottom side of the cylinders. EGT bayonets are located 3 inches below the exhaust ports.

Cooling performance has been outstanding. Even at high angle climbout (98 MPH IAS), CHT is 340 F, EGT is 1100, and OIL is 170. Airflow in the plenums is well balanced. CHT spread amongst cylinders is never more than 20-25 degrees. EGT spread is 100-150. Cooling numbers are lower during cruise flight. Still in primer only, N10LZ is a fast bird and sees no adverse effects from these cooling mods. Performance is 225 MPH flat out, 200 MPH at high cruise, and 180 MPH at economy cruise (2400 RPM @ 4,000 feet). Paint, wheel pants, and spinner should gain another 10-15 MPH.

N10LZ's engine is an O-320 E2A (160 HP), outfitted with Klaus Savier's LSE electronic ignition and propeller. "

UniCopter:

Ideas:

Consider using the DESIGN: UniCopter ~ Rotor - Disk - Pusher Prop Assist as the cooling fan. If the UniCopter is intended to have a fast forward speed then during hover the engine is not working hard and a lower air flow may be acceptable.

Consider locating the fan on the inout shaft to the intermediate gear reduction. Locate it just back of this reduction and baffle so that the air is drawn in for outside just in front of the final reductions. The air will flow by the final reduction, by the intermediate reduction and on to the engine.

If a pusher prop is not to be used then consider discharging the air alone the bottom of the tail boom. This will assist in offsetting torque - pitch cross-coupling See:0842. OTHER: Flight Dynamics - General Cross-Coupling - Torque ~ Pitch

Another Idea:

Re Cruise:

Wrap the sides of the air scoops forward and inward as much as is aerodynamically viable to cause as much air as possible around the scoops during cruise.
The forward velocity will still drive air into the engine compartment.

Re Hover:

The large positive pitch of the blade roots while retreating will drive air into the scoops. This means that any pitch change between just before 270º and just after 270º does not have to be radical.

The alternating air pulses of the two rotors may want to send the air back and forth between the two scoops. Consider having baffles or flaps between the port and starboard sides. Alternatively, just divide the sides.

The horsepower expended doing this will be partially recovered by not using a dedicated fan.

Consider having the exiting cooling air be a little higher.:

Thoughts related to the use of the Lycoming Engine:

If hover OGE requires less than the maximum full-time horsepower then it may be possible to endure short (< 5 min.) climbs without forward velocity. This is because full-time power will only be required during forward flight and the forced air-cooling may mainly come from the forward flight and propeller(s). Perhaps the root of the rotors can provide some forced airflow to the engine etc.

Thoughts related to the use of the Hirth engine ( which is not intended to be used):

Crazy idea: Have a system that consists of water bottle plus necessary piping and controls etc. that sprays a small mist on the engine near the exhaust port, while the engine is running. The evaporation should give considerable cooling.

Not so Crazy Idea:

Locate a large heat sink between every exhaust port and the exhaust pipe.
The portion of this heat sink that goes between the exhaust port and the exhaust pipe could have thin sides to it and a water passage between these side walls. This water passage would be connected to piping, pump and radiator.

Additional Information:

There is an excellent article on air flow requirements in the EAA Sport Aviation magazine of Aug 203.

Thoughts:

The majority of the air will enter via the forward facing scoops on both sides. The fins on the final reducers will cool them. Some of the air will flow to the central gearbox and then all air will flow down the firewall. Some of the air may enter from above.

The air will flow through the engine in the reverse of the conventional direction, It will flow up through the cylinder head, then aft and exit inline with the openings where it would normally enter the fuselage of a plane. I.e. in line with the cylinder heads.

A small fan could be located at the end of the crankshaft extension. It would be driven via an overrunning clutch. When the pusher prop was feathered, thei fan will provide the flow of air, but during fast forward flight (when the engine is operating at max.) The side scoops and the pusher prop will probably create a flow that is faster than that of the fan. At this time, the fan will be freewheeling in the fast airflow.

Have the cooling air, and perhaps the intermixed exhaust, exit the fuselage at the location of lowest pressure. This location might be just behind the secondary gearboxes. The highest pressure is probably the area in front of the rotorhub and secondary reduction and this is the input. This should reduce the parasitic drag of the twin rotors, somewhat.

More Thoughts:

The Operator's manual says cooling is by air pressure. Does the Robinson use air pressure or suction?

An Idea: Locate this on a separate page, if it still looks good after reflection.

A small ducted fan is mounted on the same axle as the propeller. The ducted fan has a fixed pitch whereas the propeller has variable pitch. This ducted fan constantly draws air from the engine. Does negative pressure cause a problem? During hover, the air is drawn from above the engine and from the final reduction ports. During fast forward flight, these ports will tend to 'ram' air into the engine compartment.

The blade cutouts could be overwraped with and airfoil. This airfoil has a large range of pitch change. It is spring loaded so that the trailing edge wants to be high. As the blade is in the advancing region and the cutout is passing over the engine, a cam causes this airfoil to be trailing edge low. This will tend to force air into the engine compartment.

When overwrap is on the retreating side and the forward velocity of the craft is slow, the trailing edge will want to spring up but because the spring is weak the air flow will set the actual angle. When overwrap is on the retreating side and the forward velocity of the craft is higg, the trailing edge will spring up and the air flow, which is faster will hold it up. This will result in a small amount of lift, plus it will cause a small amount of drag which will want to assist in the rotation of the rotor.

Intermeshing configuration: Since the overwrap airfoil is spring loaded so as to cause the trailing edge to be high when on the retreating side, much of the downwash from the advancing blade, on an intermeshing configuration, will be absorbed by the lowering of the trailing edge.

Fans should be driven with or by rotors. Consider place two cooling fans on X-shaft between final gears and intermediate gear set. Alternatively; could a single fan be drive from the movable longitudinal shaft, with speed up? As this shaft is raised to engage the rotors it could also engage the fan.

Using Synchronizing Gears:

Roots Blower Concept:

If there is a consideration for large plastic gears between the two hubs, for use in synchronizing the rotors, then consider using the intermeshing of these gears as a type of Rootes blower. The closing teeth could be used to inject air into one area and the opening teeth could be used to extract air for an aerodynamically isolated area.
Forward flight will also assist airflow if the rotors are turning inside back. (i.e. non-breststroke)

This has been linked to from Electrotor. A concern might be that of foreign objects getting caught up in the closing teeth.

Same Page; Different Craft: ~ SynchroLite

Last Revised: December 23, 2009