the invention relates to a two cylinder engine fig1 with the cylinders in tandem arranged concentrically instead of side by side as is common in conventional engines . one cylinder and piston comprising a double acting charge pump the other cylinder and piston a double acting power plant . the pistons are rigidly connected by a piston rod 6 . the engine can fit into a slender sailplane fuselage though a 7 + inch wide door . the power piston does not carry any side load ( connecting rod force component ) permitting a larger piston clearance . the benefit of this design is that the engine can run at full power right from the start without the need of a warm - up run . this feature will be appreciated by sailplane pilots when the ground is coming up fast and power is needed right now . super charge is achieved by the charge piston which has a larger displacement than the power piston . a second means of super charging is provided by the inlet ram tube . the ram tube provides over 120 in lb of kinetic gas energy at full throttle resulting from the near full vacuum of the rising charge piston . full throttle is used only for takeoff . it provides added internal cooling by the excessive gas “ washing ” through the cylinders . the charge piston down stroke also delivers excessive volume ( 40 %) for the same purpose . it is effective for the down stroke of the power piston , whereas the ram tube delivers the largest volume for the upstroke of the power piston . this makes an almost balanced power output for both upstroke and down stroke . a smooth near sinusoidal oscillation of the engine requires that both cylinders operate at about the same output level and the center of gravity of the engine be approximately at the piston center . ram tubes have very limited effect in standard two stroke engines mainly because the exhaust is always open to atmospheric pressure . the reed valves have been designed to work at a much lower stress level than in conventional 2 stroke engines . the valve opening stretches over the width of the plenum box and therefore provides large gas passage even though the valve travel is a mere 0 . 25 inch and resulting in a gas velocity of less than 90 ft / sec . the valve is a 5 layer kevlar composite 3 . 0 × 5 . 4 × 0 . 016 inch . 70 % kevlar fabric 30 % epoxy by volume . the pressure control valve in the exhaust system 1 fig3 controls the supercharge pressure . this valve is designed to open a very large gas passage ( 0 . 18 in × 37 in ) with only a small movement of the valve plate ( 0 . 18 in ). this small movement permits the valve 1 , fig3 to open and close very rapidly . response time of the valve can be calculated using formula 2 . the valve is designed to close in less than 40 ° of crank shaft rotation . ( about 2 millisecond ) the total force of the springs 5 are determining the supercharge pressure which is adjustable by the pilot using a control cable 4 . instead of making the spring load adjustable , it may be preferable to set the spring load to a fixed value and install a mixture control on the carburetor , to insure a smooth low speed operation . the engine tends to runs lean at low speed under supercharge . gas deflector 3 prevents turbulent gas flow . the weight of the valve ring and the volume of the exhaust box can be fine - tuned for best power output and minimum exhaust noise . valve : titanium sheet 6 . 25 × 5 . 2 × 0 . 032 inch . weight : 0 . 7 oz . exhaust box : 6 . 5 inch diameter , 1 . 75 inch long . spring rate ( total ) 4 . 8 lb / inch the exhaust valve is still shut at the instant when the cylinder exhaust ports open . this traps much of the exhaust noise in the closed exhaust system before the gas flow opens the exhaust valve . this provides considerable noise reduction and produces a much lower tone ( lower frequency ) than a high speed 2 stroke engine . the gas exits at a relatively low speed through the long narrow slot in opposite directions from under the valve plate and this may also have a beneficial effect on the noise . 4 piston rings are installed at both ends of the piston for heat transfer . both ends are capped with an s . st . plate 0 . 040 in thick held in place with 6 aluminum rivets . because the oscillating mass of the piston assembly is considerably greater than in a conventional engine , the consequence is higher dynamic forces ( acceleration ) of the moving parts . the resulting mechanical forces on the drive mechanism however benefit from this fact since the accelerating forces always work in the opposite direction to the gas forces on both ends of the piston stroke . the resulting up - stroke force especially is considerably lower by this arrangement as shown on the force diagram fig . 5 . bearing loads drop with increasing engine speed and are cut in half at about 3000 rpm as shown in fig5 . f ( a ) represent the gas force and p ( a ) represents the combined effect of the gas force and the accelerating force and is the actual load on the upper connecting rod bearing . the heavy weight of the piston assembly causes a near sinusoidal change in the load on the engine mount spring . ( 3 . 15 lb ) all other vibration whether from the engine or the prop are at a frequency higher than the engine rpm and are therefore absorbed by the spring mount . this telescoping mount greatly reduces the transmission of vibration into the air frame and is imperceptible at the pilot seat . the lower the spring rate the better the vibration insulation to the airframe . there is no danger of resonance even at idle speed . resonance is an issue with most airplane engine installations . formula 1 can be used to calculate engine oscillation and designing the spring mechanism . the location of the bottom cylinder and cylinder head is near the periphery of the propeller and therefore benefits from the strong turbulent cooling effect of the prop blades passing in front of the cylinder . the upper cylinder tends to run cooler than the bottom cylinder because of the cooling effect of the charge cylinder and the upper structure of the engine acting as a heat sink . the charge cylinder receives cooling from both inside and outside which aids in extracting heat from the cylinder head . additional cooling can be effected by running the engine at full throttle . full engine power is obtained at 70 % throttle . at full throttle some fuel mixture is circulated though the cylinders providing additional cooling and reducing the possibility of overheating . this could be helpful when taking off from a soft field when it takes a long time to reach flying speed . a considerable weight saving was achieved on the compact by rewiring the standard ignition system according to fig . 4 . it permits the use of a small starter motor and small starter battery . the 4 magneto coils are connected in series in the start position of the switch . this quadruples the power to the start sparkplug and lets the engine start at a much lower cranking speed . q = piston weight / total weight minus piston weight [ 0 . 063 ] r = crank radius ( half of piston stroke ) [ 2 inch ]