William, Thanks again, for a thorough explanation of the Coupe's landing gear systems..... One point I wouild add is that Fred designed am almost foolproof system to prevent balooning....that is , when the nose strut is fully conpressed, and the static tail height is correct, the wings are now at a no lift angle of attack, having no more lift ( of very little lift), preventing balooning. I think the flight manual points out iot is safe to land the Coupe at speeds up to 120 mph without balooning, as the wing is now in a zero/negative angle of attack.
The only negative thing I can think of is that If one decided to take off without setting the trim to take off position, the coupe's controls must be pulled back slightly inorder to provide positive lift and take off. Besat Regards, Harry ________________________________ From: William R. Bayne <[email protected]> To: [email protected] Sent: Sat, August 21, 2010 2:05:07 AM Subject: Re: [ercoupe-tech] nose gear cable Bart, As you have pointed out, there are many types of airplanes. Following the initial unstabliized approach (first pilot error), I can visualize how a pilot COULD induce oscillation such as you describe with improper control inputs at high landing speeds...emphasizing the word PILOT in "Pilot Induced Oscillation". I would expect "heavy iron" (relative to lightplanes) such as the T-33, T-38, C-130 you spoke of to be more susceptible to PIO (no such experience). When aircraft of considerable mass "arrive" with an excessive descent rate the design shock absorbing capacity of the landing gear is exceeded. The extent of their rebound, or "bounce" should be directly proportional to the energy not dissipated by the landing gear (or structural collapse) ;<) Among light aircraft there are significant differences in landing gear design. Modern designs with transverse spring-type main gear and "classic" designs with bungee-style elastic components do NOT dissipate excess energy but almost immediately push the aircraft back into the air. Pilot perfection (or close to it) is mandatory if embarrassment is to be avoided. The common term for such undesirable characteristics is "unforgiving". In airframes with the Alon/Mooney "spring" style main gear, the only energy dissipated is from sufficient distortion of the gear to scrub tires. If the aircraft is EXTREMELY mishandled prior to "touchdown", "spring" gear can become bent. Factory shims exist to correct this (to a point) ;<) So here is where I preach the "Ercoupe gospel". Ercoupe design resolves many of the deficiencies of other aircraft. It has "good manners". Perfect landings should be both easy and frequent. Main gear trailing arms on other planes tend to be shorter (with less effective oleos). The Ercoupe's oleo-dampened long trailing arms and nose strut offer a full foot of oleo shock absorption (presuming no snubber on the nose and proper servicing/operation of nose and main oleos). Effective oleo action is only available from immediately after liftoff until immediately after touchdown. The Ercoupe nose strut taxi spring and main gear rubber donuts have NO shock absorptive capability. Each come into "play" only after the weight of the plane has fully depleted available oleo action. Paul described how a newly minted Private Pilot suddenly and unexpectedly augered Paul's coupe into the runway nose wheel first (even with a snubber fitted). His coupe didn't bounce because his nose and main oleos absorbed much of the excess energy (as Fred Weick intended). I guess we can take this experience as proof that an unflared Ercoupe "arrival" at up to 500 fpm should not result in damage (don't try this at home, folks!). The condition Ed described is much more common, where poor pilot judgment in the flare causes the aircraft to "balloon" some feet back in the air from the runway surface even as airspeed is "scrubbed off" below that necessary for flight. Without power, it will literally fall to the runway once lift is gone. Full power (in ground effect) can restore sufficient airflow over the wings (almost immediately) to salvage such a situation (if the engine doesn't quit). This situation is right up there with "Russian Roulette" as a gamble. You suggest that the shortened oleo action due to a snubber is of no consequence. For discussion let's assume design operational nose strut travel at 12". Let's also assume that we have a snubber that reduces that 12" oleo travel exactly five inches, or to 7" (I have seldom seen two of the same length). With the nose strut unloaded and fully extended both with and without a snubber the strut must rise (compress?) some distance to offer some dampening effect (resistance). If we presume that we have little or no effective dampening in the first three inches of travel, then of our 12" of travel in the unsnubbed strut there may be only 9" of "effective dampening" travel. Our snubber removes 5" of the above 9". We are left with an effective length of 4"! That would correspond with a reduction of oleo effectiveness of some 55%. Whileearly availability of steering authority is desirable in almost any circumstance, I am unable to envision the unsnubbed strut as more prone to damage or as a contributing factory to an accident. That said, I would try to avoid landing on water, mud, soft sand or freshly plowed ground if a better choice were available even if a snubber were fitted. You have to play the cards you're dealt the best you can when the s..t hits the fan. What should be first and foremost in our minds is the extremely high percentage of Ercoupes with evidence of a crumpled firewall (either physically evident or somewhere in the airframe log). Damage results from an improper rate of descent or inadequate directional control at the moment of impact. When initial contact occurs is of little consequence. It would appear evident that every bit of effective nose strut shock absorbing capability that was designed into this aircraft has proven inadequate to prevent substantial damage from "real world" conditions for a very large number of the fleet still in operation. It seems fundamentally illogical to reduce nose gear oleo action and efficiency given preceding considerations, but achoice is there. Main landing gear spacers similarly reduce effective main gear oleo action, but that's an entirely different evaluation. The spacers remedy a clear and present danger (low tail) most commonly associated with the presence of ERCO's 5" single fork and wheel (standard on the 415-E and G) or the Forney double fork with 5" wheel (standard on all but the very first Forneys and all Alons and M10s and a common retrofit throughout the fleet). A "bad" landing on the mains is exceedingly rare, whereas Ercoupes that are not near level on level ground exhibit crosswind and "hot landing" unpredictability that many pilots (wrongfully) believe to evidence an Ercoupe design deficiency. I see such "tradeoff" as well worth while. Some bristle whenever I speak of pilot competency or proficiency, yet no one sees themselves as a "unsafe" pilot. Aviation is "safe" but it is not without risk. So where is the line drawn? It isn't. We each set our own standards. I believe our reach should always exceed our grasp. If we cannot recognize risk in it's many forms we cannot effectively manage it. If I must gamble in going aloft, safety is my two-sided coin. Knowledge on the one side and skill on the other, but never enough. Who among us has "enough" knowledge? Who among us has "enough" skill? Regards, William R. Bayne . |-(o)-| . (Copyright 2010) -- On Aug 20, 2010, at 11:43, [email protected] wrote: > >Remember the dynamics for a PIO are: Nose wheel contact first. Resultant >force >rotates plane around the lateral axis (wingtip to wingtip), mains then hit the >runway with enough force to bounce the aircraft into the air, pilot pushes >yoke >forward to lower the nose (typically over corrects), nose wheel contacts >runway >- and the cycle is repeated. I would think it would be easier to make nose >wheel contact with the runway with a fully extended nose strut as in one with >no >cable. >If you want, I will demonstrate a PIO for you but we'll have to use someone >else's airplane. It's a little tough on airframes. >
