- Cyrus says: thanks for clearing this up guys. from reading the FAQs in the website I got the impression the coupe sank like Lake aircraft (due to the exposed engine up top, the wing floats, heavy weight of construction). But they don't feel like they do. It doesn't make sense that they should have a high sink rate. (besides 'high sink rates' are for people who build expensive kitchens!) Maybe this impression should be modified in the FAQs. 9 or 10 : 1 ratio would be better than a C150.
Be careful not to confuse 'glide ratio' with 'sink rate.' The sink rate (which messes up the glide ratio) is a
low airspeed phenomenon. Where a C150 will hang around all day at 60MPH like some kind of kite, the
Ercoupe like other high-performance aircraft, needs to have the airspeed kept up to glide well.
One reason Cessna pilots tend to prang Ercoupes (and Mooneys and Bonanzas and even fat-wing
Cherokees and Tri-Pacers) is that they are used to a much 'floatier' plane. All of the latter planes
will develop a vicious sink rate on final approach if the pilot doesn't keep the nose down and the
speed up. 'Push to the runway,' as Rich Stowell says. On the other hand, it takes me a few
landings to re-master the slowness of the 150 or 172 approach.
- Why did some planes get modified to have extra back elevator, on a spring loaded resistance device, so that the planes could be stalled? when do you need to stall a coupe? on landing?
You're speaking of the split-tail, and to understand why it exists you have to understand the evolution
of the design.
The first 415C had a low gross weight of only 1260 pounds. Not much to take mom along...not bad if
it was dad and the kid.
In the quest for more useful load, the 415D had to have its up-elevator limited even more to maintain
the stall-proof/spin-proof rating in all circumstances at the new weight of 1400 pounds. The trade-off
was that you could no longer slow down as much to land, because at the lower speeds you no longer
had an elevator that was effective enough to flare.
I hear conflicting stories about the 415CD. Some say it was a result of people not liking
the 415D, and wanting to give up the useful load in favor of landing habits. Others claim
that a 415CD is a plane that was part of the (considerable) back-stock of 415C's sitting
at College Park unsold which was converted to a D specification before being sent to
dealers and thus going 'into service.'
The 415E had a re-designed elevator, the famous 'split' elevator, which had 20 degrees of up-travel,
even more than the 415C (which had 13). Here was an elevator which remained effective when
pulled against the spring limit back down below 50MPH IAS but was not so much more effective
at cruise that it made it possible to stall the airplane any more regularly. This design soldiered
on through the whole Alon series as well as the Mooney M10 Cadet (both models, the one
with the H-tail and the one with the Mooney tail.
Yes, the M10 will stall, because Mooney wanted it that way. It was, after all, intended as a
trainer, a low-end addition to the Mooney line. I recall that it wasn't any machinations with
the elevator that made the M10 stall...it was the addition of a couple of stall strips on the
leading edges. The M10 will spin, too, but is placarded against such foolishness since
recovery is in doubt.
That, in a nutshell, is that tale of our tails.
Greg
