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I don't buy it, Wayne. However, this input should give Ed an opportunity to regale us with yet another of his many conversations with Fred Weick on the subject. Don ________________________________ > From: [EMAIL PROTECTED] > To: [EMAIL PROTECTED]; [EMAIL PROTECTED]; [email protected] > Subject: Re: [COUPERS-FLYIN] > Date: Mon, 16 Oct 2006 06:08:31 -0700 > > ----[Please read http://ercoupers.com/disclaimer.htm before following any > advice in this forum.]---- > Fellow Coupers:: > It has been a long time since I flew an Ercoupe without manual rudder control > input, but as I recomember it, the reason we want to let the nose strut to > fully extend upon touchdown is for the nosewheel to make terra-firma contact > at the same time as the main gear. Done right in a crosswind, the nose wheel > will be aligned with the runway, and the aircrafts momentum, at the moment of > touchdown the strut begins to take the forward weight of the airplane and > compress, the robust main gear moves the aircraft line of thrust > configuration to the line of momentum, (The cross wind vector) the > controllable nose wheel slips gently though the fingers of the highly > experienced airframe controller, allowing the strut to fully compress, > causing a properly rigged Ercoupe tail to rise to 75 inches, and the negative > angle of incidence of the tail surface to effectively cause the aircraft to > quit flying, and pass on down the runway centerline bleeding off speed and > forward momentum in the process. > Is that about right? > Still doesn't answer the cable restraint question. I never have figgured > that out, I think the nosewheel should be below the turbulent airstream > created by the propeller. hence, no need for the cable at all, the > nutcracker does all the work of a restraint cable, that is if the bumper is > on correctly, and the nutcracker cannot go "over center." > Wayne W. > ----- Original Message ----- > From: Ed Burkhead<mailto:[EMAIL PROTECTED]> > To: [EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]> ; > Cflyin<mailto:[email protected]> > Sent: Monday, October 16, 2006 5:17 AM > Subject: RE: [COUPERS-FLYIN] > ----[Please read http://ercoupers.com/disclaimer.htm before following any > advice in this forum.]---- > Dr. R. Beeman wrote: > >>>>> If you land an Ercoupe on the mains in a crosswind and wait "...until > >>>>> the coupe itself swivels straight down the runway..." please tell me > >>>>> specifically what force will cause the aircraft to "swivel straight > >>>>> down the runway"? > The answer is there is no magical force available to an Ercoupe or a spam can > for that matter. A spam can uses rudder to counteract the crab just before > touchdown, but a rudderless Ercoupe must use the runway itself to counteract > the crab, for if the Ercoupe pilot tries to take out the crab before touching > down, he'll simply fly away from the centerline. > The only counterforce to a crosswind crab that a rudderless model of the > Ercoupe possesses is the force exerted through the nose wheel touching and > counteracting the cocked main gear. This is what the POH calls for and this > is all there is. There is no automatic swivel straight down the runway and if > you wait for it before planting your nose wheel you'll be cutting > daisies.<<<<< > Doc, > Please review Chapter 17 of Stick and Rudder, which in my copy starts on page > 312. > Yes, there IS an automatic swivel, straight down the runway. > The force that rotates the airplane to line up with the direction of travel > is exerted through friction with the ground. > The friction vector comes at an angle along the direction of motion. It can > be represented by two vectors at right angles, one along the longitudinal > axis of the aircraft and one directly sideways. > |\ > | \ > | \ > | \ > | \ > | \ > | \ > | \ > -------à > When touching down in the crab (whether the nose gear touches at the same > time or not), there is a side load on the tires – they are not lined up with > their motion. > The tires do start to rotate and almost instantly stop providing resistance > along the vector of the aircraft’s longitudinal axis. But, the frictional > push is at an angle and part of the force may be vector diagrammed as being > from the side of the aircraft. > It is that side vector which pushes sideways on the main gear – and the main > gear is behind the aircraft’s center of gravity. So, there’s a sideways push > on the rear of the aircraft. > But, if the nose gear has already touched, any sideways vector on that is > almost instantly relieved because the nose gear will turn and align itself > with the direction of motion. So, there’s no sideways push vector on the > front of the aircraft. (This is why we must not hold the yoke firmly when > landing – a fingertips only grip will allow the nose gear to turn to line up > with its travel across the ground.) > Summary: There’s a sideways push to the rear of the aircraft but no sideways > push on the front of the aircraft. So, the aircraft rotates. > When the aircraft is in line with the direction of motion, all sideways > vectors disappear. > Side notes: the mass of the aircraft is concentrated near the center of > gravity. The structures far from the center are light weight. So, the > aircraft automatically rotates quickly. The sideways force vector is > relieved quickly and is not very violent. An egg in a saucer in your lap > will probably stay there. (Please use hard boiled eggs for your personal > testing.) J > If this isn’t adequate, I’ll try to hand draw, scan and send a proper vector > diagram of the forces involved later. (I’ve got to get my daughter up and > get her to school.) > Ed Burkhead > http://edburkhead.com > ed -at- edburkhead???.com (change -at- to @ and remove "???") > ============================================================================== > To leave this forum go to: http://ercoupers.com/lists.htm > ============================================================================== > To leave this forum go to: http://ercoupers.com/lists.htm ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
