Fuel Efficient Flying
Combines Best of
(from PRIVATE PILOT magazine, March 1980)
by Dennis Shattuck
EVERY SAILPLANE pilot has this secret wish to have a sailplane that would self launch, motor around to sniff out thermal activity and then soar with the best. Not so much different is the powered-plane pilot's repressed desire to have an airplane that combines an excellent cruise speed with absolute minimum fuel consumption. In short, the soaring pilot wants a sailplane that acts like a powered plane and the power pilot wants an airplane that is as efficient as a sailplane.
Both requirements would seem to indicate an aircraft with high aspect ratio, glass smooth wings, a relatively low output but efficient power unit, light wind and power loadings and a well-streamlined fuselage of minimum crosssectional area with fully enclosed cockpit. If this description fits the concept of what's popularly described as a "motorglider," then the reader has a good point of reference from which to start.
The motorglider, literally a glider with a "motor," or reciprocating engine, attached, has been around for some time, but is just now beginning to experience the same sort of super sophistication that pervaded sailplane design 20 years ago. While motorgliders have yet to achieve the 40-45 to I glide ratios of today's competitive sailplanes, there are a few in the upper 20s and low 30s that make recreational soaring extremely interesting as well as much easier to obtain.
The lightweight powered airplane, on the other hand, has not developed. Instead, production-oriented design has led us toward higher wing loadings and thus greater dependence upon the engine to keep us aloft. How many pilots trained in Cessna 150s know that the airplane is a pretty good glider, capable of soaring flight when conditions are right? We know of one C-150 that soared for four hours with engine off in a low mountain wave not half-an-hour's flight from its home base.
The lightly wing- and power-loaded aircraft was a development of the 1930s, especially in Europe, where gasoline costs were high (even then) and engines heavy and expensive. Thus the single- and duo-seat Klemms and Miles airplanes achieved "floater" status without consideration for soaring flight. These aircraft would take off and land in short distances, fly fast and efficiently on 25-40 hp engines, and generally provide enjoyable recreational flying for their pilots. In this country, the Taylors, Aeroncas and Piper Cubs achieved somewhat the same status. Interestingly, those aircraft are still prized today for their low operational cost and enjoyable flying qualities!
Not surprisingly, the European aircraft makers again are leading the way into more fuel efficient flying . . . at least for the recreational flyer. We're seeing the development of the motorglider concept encouraged by economic conditions, and we're seeing pilots rediscover the joy of flying (and soaring).
One such motorglider to reach our shores in the last two years has been the PZL SZD-45A Ogar (greyhound), a product of Poland but by no means one of those odious Polish jokes. Of unique design, for a sailplane, it resembles greatly a Republic Seabee that's been too long at the exercise/slimming salon. It has that same pod-and-boom look with a pusher engine mounted at the rear of the wing. Seating is side-by-side for two under a snug swing-up canopy, and a T-tail at the rear completes the unusual format. What's even more unusual about the Ogar is the fact that it's good at both soaring and power-flying; it's both a motorglider and an airplane that acts like a sailplane.
On the power flying side, the Ogar claims a cruise speed of more than 90 knots (104 mph) on only 3.1 gallons per hour (32.26 miles per gallon!), Range is 200 n.m. (230 statute miles), in the pure power-cruising mode, but this can be extended by use of either maximum economy cruise power settings or by utilizing some free lift along the way.
As a glider, the Ogar does well enough for all but the devout soaring enthusiasts. With its 28:1 glide ratio it has soaring performance better than any of the current two-place training sailplanes, and equal to or better than most other two-placers and this with a draggy profile, open engine cooling ducts and a stopped propeller. Its large, 57.4-foot span wing has generous wing area, 213.9 square feet, and efficient aspect ratio of 15.5:1. Minimum sink is 200 feet per minute at about 44 knots (50 mph), a very respectable figure for a 1540-pound airplane, giving further clue to the Ogar's polished efficiency.
Charley Gyenes of Aerosport, Inc., is importing the Ogar along with several other European-made sailplanes to his Elsinore, California, facility. But Gyenes is not the usual importer . . . he doesn't practice the "ship 'em, sell 'em and forget 'em" tactics accompanying some foreign-made products. Gyenes believes in adapting the product to suit the market. In this case, the Ogar arrives in the U.S. without engine or instruments. A U.S.-built engine is installed, along with U.S. (mostly) instruments and avionics.
Gyenes has worked with, and tested extensively, the engine manufacturer, Revmaster, Inc., to obtain a package best suited to Ogar operation. Equipped with a turbo-supercharger the engine delivers outstanding performance at both low and high levels, something no other motorglider powerplant can claim. It can be equipped with either a controllable pitch metal propeller or a fixed pitch wooden prop (obviously, the wood prop is less expensive, less weight and less complex).
The first Ogars, delivered to the U.S. with a German version of the same engine, but without turbocharging, performed rather anemically, thus prompting Gyenes' continuing program of improvement. The modifications do not alter the gliding performance of the aircraft (in fact, they may improve it slightly) which was its strong point in the beginning. However, with the stronger engine and the Ogar's better performance as a powered aircraft, Gyenes now feels he has a package that will be appreciated by Western Hemisphere flying enthusiasts.
Now, a bit of detail on the vehicle itself:
Airframethe Ogar is officially the Zaklady Szybowcowe Doswiadczalny model 45A, design from the Polish national aircraft industry's experimental glider works. It emerged in the early 1970s, the prototype making its first flight in 1973. The fuselage pod is molded fiberglass, the boom extension that supports the tail is an aluminum tube. Two major internal bulkheads of wood carry the loads of wings, engine, tailboom and landing gear.
The sailplane is wood and fiberglass and separated into conventional horizontal stabilizer and elevator segments. The vertical fin is blended into the tailboom with fiberglass and the rudder also is fiberglass covered. Controls are pushrod-actuated.
CockpitThe Ogar has dual stick controls and seats are side-by-side. The seats are semi-reclining and very comfortable, while vision out of the bubble canopy is extremely good. A single pushpull throttle is in the center of the conventional instrument panel, but the fuel shut-off is on the left side. However, there's a spoiler handle on each side of the cockpit. The landing gear retraction handle is in the center between the two seats; a removable pin is used to safety lock the control in the down position. Rudder pedals for both sides may be adjusted fore and aft in flight. The canopy hinges up and back for entry/exit.
The instrument panel features the usual flight reference gauges, plus variometers for soaring use, on the left side, the engine condition gauges on the right. There's limited space for radio equipment on the right side and beneath the panel.
Baggage, oxygen tanks and take-along equipment can be accommodated in a generous area behind the seats. The area is placarded for up to 110 pounds.
Fuel TankA 30-liter (7.926 gallons) fuel tank is built into the upper fuselage area behind the cockpit. The back cockpit wall has a vertical stripe left unpainted, through which the gasoline
quantity may be seen. Tick marks for the various quantities are painted across the stripe, making an effective, never failing fuel gauge. A single filler point is atop the fuselage.
Landing GearA single main wheel under the fuselage, a steerable tailwheel and two outrigger wheels comprise the Ogar's ground support system. The main wheel is retractable in flight by mechanical means. A spring-assisted cockpit lever moves the wheel up or down. (No wheel-up warning system, other than handle position, is fitted, however.) Tail and outrigger wheels are fixed in place. The outriggers, sprouting down off each wingtip, are fiberglass rods which flex easily to absorb shocks as the Ogar is taxied over lumpy terrain. Outriggers that retract to a trailing position are under development, Gyenes says, and these might add a point or so to the glide ratio, once installed. The tailwheel steers with the rudder to provide directional control on the ground.
WingWhile the wings are basically wooden structures, they are glass-fiber covered for smoothness and protection against the elements. They utilize a Wortmann FX-61-1261 airfoil at the tips, blending into a Wortmann FX-61-168 airfoil at the roots. These are excellent high lift/low drag ratio airfoils akin to those used in many high performance sailplanes. They are characterized by rather sharp leading edges and downward cusps at the trailing edges.
The wing is assembled from two separate components and these can be removed/installed like those of any sailplane for transportation ground. As they are heavy panels, it takes at least two men to lift each 29-foot section, and another to position and fasten it on the fuselage. A folding wing option, such as used on the Fornier RF-5B Sperber motorgliders to reduce the span to 36.8 feet, would allow it to be stored in a normal width hangar.
AiIerons are internally hinged, no-slot panels of narrow chord but generous length. They are effective enough at low speed, probably because of the long span, to pick up and balance a wing at around 8-9 mph airspeed. The Ogar has no flaps, but does have vertically actuating spoilers on both the top and bottom sides of the wing. These spoilers are extremely effective for glide path control. Both ailerons and spoilers are pushrod-operated.
Engine The Volkswagen-based, four-cylinder opposed, air-cooled engine is built up from new components by Revmaster, Inc., of Chino, California. Revmaster utilizes so many of its owndesign modifications that it is more accurately a Revmaster engine than a VW conversion. The R-2100-D version used in the Ogar has dual ignition, 125 cubic inches (2170 cc) displacement, turbosupercharging and develops 78 horsepower at 3200 rpm and 34 inches of mercury manifold pressure.
It features a built-in electrical system with 20-amp alternator and geared starter. A large oil cooler fits horizontally beneath the oil sump. A Revmaster/Posa fuel injection carburetor meters fuel to the engine and is fitted with a mixture control. Dual Bendix D2000 magnetos are fitted to a special accessory drive at the rear of the engine.
Fitted with turbocharger and the Maloof/Revmaster two-position controllable propeller, the engine has an installed weight of 215 pounds. As installed in the Ogar with the above equipment and accessories, the R-2100-D would cost nearly $5000 retail. A noncertified engine, it is designed and sold for the use of sport aviation builders who need a strong, lightweight powerplant.
Propeller The Ogar is equipped with a fixed-pitch, wooden prop but a Maloof controllable pitch metal propeller can be ordered as an extra-cost option. The wood prop works well, especially when pitched more for climb than for cruise (this would be ideal for the pilot who intended to use his Ogar for mostly soaring). The Maloof propeller, developed in conjunction with Revmaster especially for use with the Volkswagen-based engine, is a real gem. While the Maloof prop is basically a two-position propeller (high for cruise, low for takeoff and climb), it will hold a selected engine rpm. However, it does not feather for gliding flight.
PZL Ogar Motorglider
New, FAF, Elsinore, California .................................................................. $38,000
Equipped as flown ....................................................................................... 41,500
Wingspan ..................................................................................................... 57.4 ft.
Wing area ............................................................................................... 213.9sq. ft.
Wing aspect ratio .............................................................................................. 15.5
Length overall .............................................................................................. 26.0 ft.
Height overall ................................................................................................ 6.6 ft.
Weights and Loadings:
Gross weight 1540 lb.
Empty weight (standard aircraft) 1054 lb
Useful load 486 Ibs.
Payload, full fuel 438 lb.
Fuel capacity 30 Itr (7.93 gal.)
Oil capacity 1 gal.
Baggage area capacity 110 lb.
Seats 2, SBS
Wing loading 7.2 Ib./sq. ft.
Power loading 19.74 Ib./hp
Revmaster-VW R-2100-D, four-cylinder opposed, air-cooled, turbo-super charged; injector-type carburetion; 78 hp at 3200 rpm and 34 in. Hg. manifold pressure.
Maloof/Revmaster controllable pitch, hydraulic, metal hub and blades,
Maximum allowable speed 118 kt. (135 mph)
Cruise speed, 75% power, optimum altitude 90 kt. (104 mph)
Range* at cruise, 75% power 200 n.m. (230 s.m.)
Fuel consumption at 75% power 3. I gph
Economy cruise, 50% power, optimum altitude 76 kt. (87 mph)
Range* at economy cruise 300 n.m. (345 s.m.)
Fuels consumption at 50% power 2.0 gph
Stalling speed 37 kt. (42 mph)
Rate of climb 600 fpm
Service ceiling 20,000 ft.
Takeoff over 50-ft. obstacle 1000 ft.
Landing over 50-ft. obstacle 1150 ft.
*No allowance for climb, descent or reserve.
32301 Corydon St.
Elsinore, CA 92330
Phone (714) 674-1584
Ray Maloof is a Southern Californian who wanted a better propeller for sportbuilt aircraft. Hartzell and McCauley constant speed props being too heavy, he set about designing his own controllable pitch prop. He uses very high quality materials, builds the props to air craft standards, and is on the verge of becoming a full-fledged manufacture At this point, they are classed "experimental," like the Revmaster engine but conceivably they could be certified at a future time.
The Maloof prop's blades are move by engine oil pressure working again springs in the hub. An electrically operated solenoid varies the oil pressure to establish rpm. Engine speed, measured at the flywheel, either from the alternator or, if not so equipped, by a sensor mounted on the crankshaft flange. The electronic controller sort out the information engine speed and energizes the oil pressure solenoid accordingly. A side benefit of this electronic controller is its ability to flash; red panel light when the engine reaches restricted rpm readings (1800 to 2400 and above 3600 rpm).
The controllable prop gives the Ogar its best combination of climb and cruise performance, allowing the pilot to spool the engine down to 2800 rpm for cruise, yet rev up to 3200 for maximum power at takeoff. Then, all he has to do is monitor manifold pressure for the desired power output.
Power Management For takeoff, the Ogar-Revmaster pilot dials up 3200 rpm and runs in 34 inches of manifold pressure. The turbocharger takes a few seconds to spool up and the pilot has to be careful not to overboost the engine as the turbo develops more and more pressure. The engine can be run to 3300 rpm and 38 inches (which produces 85 hp) for emergency use, but this is not recommended as a steady diet.
Once off the ground, the pilaf retracts the wheel and sets up cruise climb power at 2900 rpm and 30-31 inches. At gross, and with 50 mph indicated airspeed, the setting nets 400 to 500 feet per minute. On a test flight, we climbed to 2000 feet AGL in five minutes, and to 4000 feet AGL in 10 1/2 minutes.
At cruise altitude, the throttle is reduced to whatever fuel consumption/power percentage the pilot wants. A 2850 rpm/31 inches setting at 5000 feet MSL showed us an airspeed of 90 knots, this approximated 75% power. Gyenes reported that fuel consumption at that setting, leaned properly, would net about 3.1 gallons per hour. At 2800 rpm/25 inches, or 65% we saw 85 knots, and at 2800/21 inches, we were getting 76 knots. Gyenes reports 2.0 gallons per hour at this 50% power settingover 43 miles per gallon.
Descents can be made with the prop in either position, with the throttle backed off only enough to allow the engine to stay warm. With a redline of 118 knots, plus the availability of spoilers if faster descents are necessary, the Ogar pilot has no problem with taking care of his engine and getting the plane down, too.
As a matter of precaution, to prevent thermal shock, i.e. too rapid cooling, the Revmaster turbo engine always is allowed to run for a few minutes at low powersettings. This lets it cool evenly, at a slower rate than if it was suddenly switched off.
"Ogar" means "greyhound" in Polish.
Photos: Dennis Shattuck
Soaring FlightDespite its size and weight (for a sailplane) the Ogar is an excellent soaring aircraft. The Wortmann airfoil wing is no doubt the key. It seems to possess good qualities at both ends of the performance scale. Stalling speed is only 42 mph, and it sinks at only 200 feet per minute when the engine is off. The 28:1 lift/drag ratio is exceptionally good for this type of airplane.
Along with Gyenes, we sampled both powered and non-powered regimes of flight and found them completely acceptable. The Ogar will thermal at 50 mph, out-climbing a number of production pure sailplanes along the way. As a cross-country cruiser, it does well, too. The seating position is quite comfortable and the view fantastic.
Control pressure requirements are moderate, as would be expected for a big bird, but tend to become more firm as speed increases. Ailerons require an authoritative hand on the short stick for rapid deflection movements at speed. Pitch control is lighter and more sensitive. Rudder also is sensitive, but needs relatively more force. In all axes, the response to control inputs is quick, but not fast.
Ground Handling Here is where the power-only pilot may have a problem, while the soaring-oriented pilot will not. The Ogar balances nicely on its two centerline wheels if it is taxied at 10 mph or more, and can be taxied along on one or the other wingtip wheels, too. On takeoff and landing runs, the pilot must remember to level his wings, however, to keep the outriggers from contact, lest they drag him into a groundloop. There's plenty of authority in rudder and ailerons to do so, and the transitioning pilot needs good instruction in this phase of motorglider operations.
A cable-operated brake is fitted to the main wheel, and this will stop the Ogar in reasonably short order. Aerodynamic braking is not possible as the craft sits in a level attitude while on the ground. That single wheel retracts flush with the Ogar's belly but has no covering doors.
In retrospect, the Ogar, while a more complex machine than the pure sailplane, seems to offer a great deal more flexibility of operation. The handiness of self-launching for a day of chasing thermals is far more interesting than having to wait for the availability of a towplane and pilot.
As a cross-country machine, it seems to have reduced appeal, although its abilities for economical transportation are certainly attractive. Gyenes' Ogar buyers have flown themselves home from Elsinore to Connecticut and Alaska, as well as other points in the U.S., all without complaint or delay.
So, if the idea of an airplane that can act like a high performance sailplane, too, seems interesting, take a long look at the Ogar . . . it fills the bill.