British Frog 100
Engine Data from AEROMODELLER October, 1950 by L. H. SPAREY
Displacement: 1cc or 0.06cu
Cylinder Head and Fins: Aluminium Pinoy Díevcast,
2 SBA holding-down bolts to Crankcase. Piston and Contra Piston : Meehanite ground and lapped.
Crankcase: Aluminium Alloy. Die-cast. Integral Fuel Tank.
Front End : Aluminium Alloy. Die-cast attached to crank Case by four IDEA screws.
Connecting Rod : Forged, Hiduminium RRöß. Crank pin Bearing : Plain.
Little End Bearing : Pláin.
Crankshaft : Steel Hardened and ground.
Induction : Crankshaft rotary valve.
Manufacturer craft Ltd., Morden Road, Merton, London, S.w.19.
Type: Compressìon Ignition. Specified Fuel : Frog " ".
Mounting: Radial, upright, inverted. or Sidewinder.
Recommended Airscrews: Free Flight
5X3 inches; Control Line 5X3 inches. Or 6X 3 inches.
Recommended Flywheel : 2% oz.
Cylinder: Steel, hardened, ground and honed.
AEROMODELLER October, 1950One of the first engines to be tested. when this series began; in 1948 was the Frog " 100 ", so that it is particularly interesting to compare the Frog " 100 " engine of today with its ancestor. This engine was altered considerably both externally and internally.
There appears to be an improvement in performance, as the new engine shows an increase in BHP of over 25 percent. It is dangerous to attribute the difference to any particular factor because the both engines were not tested under the same conditions. One factor was the fuel used in the tests and it alone may have attributed to the performance increase. In any event, it is not highly important to the average user to know the exact cause of the improvement, the salient fact is that from an engine of identical capacity the average aeromodeller’ may now expect a. much improved performance. As with all Frog engines it displays great flexibility, as it ran evenly and steadily at speeds from around 1,000 r.p.m. to 9,000 r.p.m.. In this connection it may noted that the makers claim a maximum of only 6.500 rpm. They also claim. that the engine weigh is heavier than the checked weight obtained by me. In contrast with the exaggerated claims made by some manufacturers these days, it seems that it is being realised that a modest claim is even more likely to create buyer confidence than an exaggerated one; and in the long run a much sounder form of advertisement. This tendency has been noted before ín these pages.
The: Frog engine should be of partícular interest to f'reeñight flyers, in view of the. fact that the greatest output lies around the 8,000 rspm. mark. This is the approximately the speed at which propellers usually turn in freefight flying. 1t is also not also a speed not difficult to attain if the propeller is carefully selected. Furthermore, thc speed is reasonably low, so that the engine need not rack itself to pieces in :an endeavor to obtain maximum output at some phenomenal rate of revolution.
An interesting experiment on this motor was carried out in addition to the usual B.H.P. test. The Frog 100 engine is very easily convertible to upright or inverted running, and a series of figures was. obtained for the. engine in both pusitìnns. These results showed so little variation: from one position to the other, that it can be said that the performance remains the same irrespective of the engine's position. I am not aware of any concrete facts on this subject have hitherto been available and from that point of view this information may be helpful. It must be remembered, however, that data. applicable to one type of engine may not neeessariïy apply to other engines of different design and manufacture.
While the Frog diesel engine is of quite pleasing appearance and general proportions, it does seem to be rather on the large side for its capacity. The chief criticism is that, it is too high and on taking thè engine píeces, the reason for this height is easily dìscpvered. The contra~piston is extremely long. This is probably done in order to ensure a good seal in the cylinder.
Test Engine: Frog " 100 " Mk.ll Diesel.
Fuel: "Frog PowerMix."
Starting : Extremely good under all conditions.
Running: Shows great flexibility. and :ran well at all Speeds between-about 1,000 and 9,000‘r.p.m. It was not found possible to exceed 9,600 r.p.m.
Power: The curve shows a flat characteristic between 7,000 and 8,000 r,p.m. with a. maximum output of bh.p. at around the 8.000 mark.
[The Frog 100 " engine testçd in 1948 gave 0.0575 h.p. at 8,100 1. Output declines steadily down to about 1,000 r:p.m., below which a steep drop is indicated. At 9,600 r.p.m. the output is down to 0.05 h.p.
Checked W'eight: 3.75 ozs with tank
Maker's advertised weight: 4 ozs.
Power to weight ratio : 0.304 b.h.p./lb.
Narne : Frog 100 " Mark II. Manufacturers : International Model Air
Remarks : This new Frog engine displays all the characteristics of easy starting, flexibility, and reliability, associated with the range.
Frog family of engines in the collection
Featured engine with the replacement parts required to get it to run reliably
Other Frog engines in the collection
Test run with an APC 7X4 propeller and a fuel mixture containing extra castor oil because of the tight fitting parts.
See it run after a major rebuild.