pilot engine(n = noun.artifact) - a locomotive that precedes a train to check the track;
is a kind of engine, locomotive, locomotive engine, railway locomotive

N  experiment, essay, analysis, screen, trial, tentative method, t=atonnement, verification, probation, experimentum crucis, proof, (demonstration), criterion, diagnostic, test, probe, crucial test, acid test, litmus test, crucible, reagent, check, touchstone, pix, assay, ordeal, ring, litmus paper, curcuma paper, turmeric paper, test tube, analytical instruments, empiricism, rule of thumb, feeler, trial balloon, pilot balloon, messenger balloon, pilot engine, scout, straw to show the wind, speculation, random shot, leap in the dark, analyzer, analyst, assayist, adventurer, experimenter, experimentist, experimentalist, scientist, engineer, technician, subject, experimentee, guinea pig, experimental animal, protocol, experimental method, blind experiment, double-blind experiment, controlled experiment, poll, survey, opinion poll, epidemiological survey, retrospective analysis, retrospective survey, prospective survey, prospective analysis, statistical analysis, literature search, library research, tryout, audition, discovery, measurement, evidence, deduction, induction, abduction, experimental, empirical, probative, probatory, probationary, provisional, analytic, docimastic, tentative, unverified, unproven, speculative, untested, on trial, under examination, on probation, under probation, on one's trial, on approval, check it out, give it a try, see how it goes, Run it up the flagpole and see who salutes.

air engine, aircraft engine, airplane pilot, automatic pilot, automobile engine, auxiliary engine, bogie engine, branch pilot, combat pilot, diesel engine, donkey engine, engine, engine block, engine cooling system, engine driver, engine failure, engine room, epitrochoidal engine, external-combustion engine, fanjet engine, fighter pilot, fire engine, four-stroke engine, four-stroke internal-combustion engine, gas engine, gasolene engine, gasoline engine, heat engine, internal-combustion engine, ion engine, jet engine, locomotive engine, otto engine, pilot, pilot balloon, pilot biscuit, pilot bit, pilot blacksnake, pilot boat, pilot bread, pilot burner, pilot chart, pilot cloth, pilot experiment, pilot film, pilot flag, pilot ladder, pilot lamp, pilot light, pilot program, pilot project, pilot valve, pilot whale, pilot wheel, radial engine, radiant engine, ramjet engine, reaction engine, reaction-propulsion engine, reciprocating engine, robot pilot, rocket engine, rotary engine, search engine, semiradial engine, senior pilot, sky pilot, steam engine, stunt pilot, switch engine, tandem engine, tank engine, test pilot, traction engine, trunk engine, turbofan engine, turbojet engine, valve-in-head engine, wankel engine, wankel rotary engine, water engine