William, I carefully read your mail about the Coupe 'glide ratio', and found it very interesting. I consider this topic really important because it is related with security.
There is one thing I would like to know, and is the sink rate in numbers (for example in feet/minute) , when the Coupe is gliding like a refrigerator as all pilots say (you referred as 'alarming' rate of descent). I heared several times this comparison with a refrigerator, but this is the first time I hear it the way you expressed, and it sounds marvelous (I am referring to the phrase "In computer lingo, this isn't a bug, it's a feature! Learn to use it."). I think it has to do with something basic, but important, as to know the plane we are flying. Just that. The plane is, as it is. It is in our hands and mind the capacity of understanding it, how it behaves in different conditions, configurations, and that is not free. We have to invest some time to know how 'the machine' works and fully understand it. Thank you very much in advance for all your help. Happy 2010 to all of you ! Daniel Arditi Ercoupe Argentina. N.B: I have sent this mail twice because it seems that the first one had a word in its subject that forced it to go to the spam folder. ________________________________ From: William R. Bayne <[email protected]> To: Techlist Ercoupe <[email protected]> Sent: Wed, December 30, 2009 12:35:41 AM Subject: RE: [ercoupe-tech] Glide Ratio All, I agree that it is possible to get tangled up in terms on almost any subject, but it would be my presumption that when someone asks about "Glide Ratio" their interest is in the "proper" speed to establish in case of significant power loss. They seek that single speed that offers the most options for a safe landing, on or off airport. In that context, the speed which gives the best forward progress for each unit of altitude lost would seem "best". Air speeds (presumed accurate) over 70 mph are accompanied by progressively greater drag for a given sink rate, which reduces possible glide range. Air speeds below 65 mph are accompanied with progressively higher "angles of attack" which similarly increase drag for a given sink rate, also reducing possible glide range. Without regard to the accuracy of one's air speed indicator or VSI, setting up a glide at idle from 4000' (estimating operating weight and noting altimeter setting and OSA Temp so as to correct to "standard day" conditions) should enable a pilot to observe his "sweet spot". There should be a 5-10mph "range of airspeed" where feet lost per minute varies least at that operating weight. I define the highest speed within this range as MY "best glide speed for greatest distance" in case of engine failure. It is a good idea to know this speed for your plane. In this context, as Ed points out, at such speed the coupe's (best) "glide ratio" should be both safe and more than adequate. ≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈ There is a big difference between the "average" Ercoupe pilot and the "proficient" Ercoupe pilot. As the saying goes, NEVER EVER confuse luck and skill. Anyone operating from a 1,200' grass strip where it gets hot in the summer HAS to be really proficient at air speed and sink management and get lots of practice. If one flies off a 3,000' plus hard surface runway, it is still possible to pace off 1,200' and practice until you routinely land and stop within that distance. It's not a difficult skill, but it conscious effort is necessary to acquire it. Landing at minimum speed without braking uses 1,500-1,800' of runway, but pucks and tires last forever. If both airspeed and ground speed are consciously managed, occasional firm use of the brakes (to clean the rust off the discs) should confirm that 1,200' landing capability is maintained and instantly available when needed. ≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈ Very few Ercoupe instructors demonstrate the high sink rate in a coupe and instruct students use. While they should certainly not try to teach that which they may not understand, I do not believe such instructors "sign off" fully trained students. A pilot's first full stall can be terrifying, and fatal if no instructor were along. With experience we learn that any danger is solely from ignorance. As recovery from stalls is taught and becomes routine, the danger of ignorance is replaced by that of complacency. The stall, followed by a spin at an unrecoverable altitude, still kills with regularity in other designs. Remember the debate over whether flight instructors should teach spins? In the "old days" the spin was a way to descend through a cloud deck in a "controlled" manner without instruments ;<) It was an arrow in the quiver many today lack that Ercoupes don't need. I would urge every Ercoupe owner personally unfamiliar with the "high sink" rate part of the operating envelope to explore it with an instructor observer. Again at 4000' AGL or so, reduce the throttle to idle, ease the Ercoupe's yoke to the rearmost position, and set trim to maintain that configuration. You should be flying straight and level with excellent lateral control and the "glide ratio" of a refrigerator shoved out of a high rise window. This is normal for an Ercoupe, but "different" from most aircraft. In computer lingo, this isn't a "bug", it's a "feature"! Learn to use it. This stable, if excessive, rate of descent without flaps is no less easy and predictable than stalls (or spins in other aircraft). If you have a VSI, the indicated rate of descent should be alarming. That's appropriate. Just like the spin in other aircraft, an Ercoupe's high sink rate rewards understanding and respect with utility. Whenever in "high sink" mode without power, always fly at 2-300' above "normal" altitude. This "cushion" of altitude can and will be exchanged...altitude for speed. Some distance from touchdown the nose is lowered such that AFTER the "altitude for airspeed" exchange the coupe will be on or above the desired "glide slope" with forward speed at or above 65 MPH TAS and still in the air. Proficiency in this part of the Ercoupe's "operating envelope" requires understanding, instruction and practice, each in full measure. The presumption is always that you will need this skill most to make the best possible off-field landing following loss of power. It can also be useful in the landing pattern, particularly when experiencing high, gusty crosswinds. Here, of course, you still have power available; and the option of a go-around if things are not going well. Nonetheless, any approach entailing a "high sink" segment followed by a "normal" segment is, in the overall, NOT a "stabilized approach". Instead, think of it as a "two-part" approach; each segment carefully and properly synchronized with the other. Proficiency in this part of the Ercoupe's "operating envelope" requires understanding, instruction and practice, each in full measure. The Ercoupe landing gear in proper operating condition has a full 12" of movement available, much of it with shock absorption. Few other designs have such combined capability. So long as forward speed is sufficient to have reduced the approach sink rate to less than 500 FPM before arrival on a hard surface, no damage should result. That said, "arriving" while descending 500 FPM is more suited to military aircraft on carrier operations than to light planes not making an emergency off-field landing. Understand, I'm NOT an instructor; but I did read available information and then teach myself how to use it as described. Regards, William R. Bayne .____|-(o)-|____. (Copyright 2009) -- On Dec 29, 2009, at 16:12, Jerry Eichenberger wrote: > > > Ed - > > I never use the term "best glide speed" because it doesn't define what is > best. > > Do you want the best forward progress for each unit of altitude lost, or do > you want the best (least) sink rate? > > So, I use either Minimum Sink Speed, to describe just that; or Best L/D, > which is best lift over drag, to describe the speed that produces the > farthest forward progress per unit of lost altitude. > > Don't mean to be hyper-technical, just trying to make these terms clear. > > Jerry E. >> -----Original Message----- >> From: [email protected] [mailto:[email protected]]on >> Behalf Of Ed Burkhead >> Sent: Tuesday, December 29, 2009 4:45 PM >> To: 'Techlist Ercoupe' >> Subject: SPAM-LOW: RE: [ercoupe-tech] Glide Ratio >> >> >> Hartmut wrote: >> > One way to find out your sink rate is to fly your Coupe >> > with an VSI and read the numbers at certain airspeeds. >> > I found That 65 to 70 gives you the least sink rate. 70 to >> > 75 might give you more distance without much penalty >> > to the sink rate. >> > If you find yourself having the best glide at 80 to 85, >> > check your static system. >> >> The VSI is also good for finding maximum endurance airspeed as that is close >> to the minimum sink airspeed. >> >> For figuring the best glide speed, you need to take into account forward >> progress (true air speed). That’s exactly what a glide ration is, forward >> motion compared to vertical motion. >> >> With my faulty ASI, the best glide ratio airspeed was at 85 indicated on >> that faulty indicator. I think that the ASI is at fault more often than the >> static system but either could be the cause of errors. For my plane, a new >> ASI brought the numbers back exactly (less than half a mph) to what exact >> calibration shows was correct. >> >> Ed
