|Thrust (kg)||50 to 146|
|Weights (kg) and loads|
|Wing Load (kg/m2)||30|
|Powered||110 to 200 sec|
As it already occur several times in Soviet pre-WWII history, purges and re-organizations added new problems. RNII lost its Flight-Trials Grounds. There were no more experienced test-pilots (S.P.Korolev was in prison). It was necessary to find an organization within Aviation-Industrial complex capable to carry out flight trials of the aircraft. Help came from the OSK Factory N°1 NKAP. A.Ya.Scherbakov, head of the OSK was involved with "Project 218" as a designer of pressurized cabin. Glider-pilot V.P.Fedorov was invited as a trest-pilot.
Aircraft was carefully evaluated. Tail section (damaged by acid) was rebuilt. New landing ski was installed. Rigid tail skid got a shock absorber. New cowling for fuel tanks was developed.
Flight trials of RP-318-1 (designation of rebuilt RP-318) took place in November-December 1938. The engine was replaced by its weight equivalent. First three flights were dedicated to the center of gravity studies: with empty tanks, 50% of fuel, 100% of fuel drained gradually to imitate its consumption by the engine.
After those flights RP-318-1 was installed in the L.S.Dushkin laboratory for engine installation and trials. Soon several problems with the ORM-65 engine were revealed. First of all, there were only three ORM-65s built, and two of them were allocated to the "Project 212" winged rocket (cruise missile). This brought some limitations on use of the engine for a RP-318: no provision for multiple start, overheating of the engine head, few unreliable sealings. Acceptable for a missile, ORM-65 needed to undergo serious modifications before it could be used on the manned aircraft.
Modified engine was designated RDA-1-150. It was 2kg lighter than the ORM-65, had improved cooling system. Number and design of injectors was changed. Intermediate 'starter' engine regime (fuel flow at 8...10% of normal) was introduced for the first time. Monitoring of the engine operation was improved. Though still very basic, it was a step forward from couple of ORM-65's wires burned by flames and disrupting the electric current to lights on the pilot's instrument panel.
Experiments with multiple ignition (additional air-hydrogen burner with electric start) were successful, but tight design limitations of the RP-318-1 created problems for its installation. Total number of engine firings was more than 100, including 16 after installation on the RP-318 (July 21, 1939). On October 3 A.Ya.Scherbakov sent to People's Commissar of Aviation Industry a request for permit to fly RP-318-1 with the rocket engine fired.
KB-29 NKAP airfield at Podlipki (Moscow Region) was chosen for trials. In November 1939 aircraft was installed on the edge of the field, partly covered by birch and fir trees. Team had to perform systems tune-up and to work with kerosene and concentrated acid under deep freeze conditions, with very basic fueling equipment and rudimentary accommodations: wooden package box used to transport the aircraft served as a "field laboratory and workshop".
For more on-ground firings were performed. All were successful, but on January 3, 1940 supervising commission ordered more unpowered flights and demanded to perform more study of the airframe shape (remember, that wooden SK-9 glider was built in 1935, five years ago). No damage or degradation of wooden parts were revealed, but speed was restricted by 150km/h.
In February three flights were performed. RP-318-1 (pilot V.P.Fedorov) was tugged by R-5 biplane (pilot Fikson). In two last flights RP-318-1 was fueled (50% and 100%), and engine was tried in the 'start' regime. It was found that sound of the engine is clearly heard by pilot in the open cockpit. This allowed to monitor the engine operation by it's sound as well.
Members of the supervising commission, who had little idea about engines (and especially such an exotic variation as rocket engines of 30s) expressed excessive skepticism mixed with curiosity. To keep them at the safe distance, some (smoking) acid was spilled on the snow...
First flight with rocket engine fired at full power took place on February 28, 1940. It took since early morning until 5 p.m. to prepare the snow-covered airstrip, fuel the RP-318-1 (40kg of acid and 10kg kerosene), fill the nitrogen bottle to 130kg/m2, check the fuel system for leakage absence. Flight crews were in cockpits: N.D.Fikson as a pilot of the R-5, A.V.Pallo as an observer and A.Ya.Scherbakov as a tag winch operator - in the rear cockpit of the R-5. V.P.Fedorov - pilot of the RP-318-1.
At 5:28 p.m. both aircraft took off, and 31 minutes later at altitude 2800m RP-318-1 was released. It took some time for N.D.Fikson to bring R-5 into an optimal position for observation, and at altitude 2600m V.P.Fedorov fired the engine. First, gray smoke indicated ignition of the powder charge. Shortly its place was taken by blurred flame with brown smoke showing that the engine is running in the 'start' regime. And, finally - spear-shaped bright flame near 1.5m long with little smoke...
After gradual acceleration of the RP-318-1 left the observers far behind, and all efforts of the R-5 pilot to keep up with the experimental machine failed. Once it was out of sight, N.D.Fikson, A.V.Pallo and A.Ya.Scherbakov turned back to the airfield to meet the rocket-plane during its landing.
From V.P.Fedorov report:
Start of the ZhRD was normal, the glider speed was 80km/h. In 5...6sec speed was increased to 140km/h. During following climb speed was reduced to 120km/h. Engine was working during 110sec. During the climb altitude increased from 2600m to 2900m. Climb rate was 3m/sec. Handling and stability of the rocket-plane with fired engine are good. Start of the ZhRD does not deteriorate handling of the aircraft. Acceleration is smooth. Noise in the cockpit from the ZhRD is not irritating is is more muffled than during ground trials. The feel of acceleration and flight with the ZhRD fired is more appealing than on a prop-driven aircraft with the engine boosted to maximum power.
On March 10 and 19 two more flights were performed without an accident. During those flights the engine start was filmed from the R-5 observer's cockpit.
Than the Spring came. Melting snow made the airfield unusable and delivery of the acid to the plane virtually impossible. No more flights were performed. In the Fall 1940 RP-318-1 was transported back to the RNII and disassembled.
It was planned to continue trials with modified RDA-1-300 engine. Plans included rocket-powered takeoff using jettisonable wheel cart. But this project was pushed aside by RAS and RDD rockets. In 1941 priority was given to RDA-1-1100 engine for Bolkhovitinov's BI rocket fighter.
In August 1941 RP-318 was burned. The Rocket Institute was preparing for evacuation, and old wooden airframe was worthless.