Dave. The optimal setting for the spring is 13 degrees up as specified in the service memorandum for rigging the E model elevator.
It makes the plane fly like originally designed for the lower gross weight 415-C but allows to pull through to a stall when needed. Hartmut To: [email protected] From: [email protected] Date: Thu, 18 Mar 2010 04:18:02 +0000 Subject: [ercoupe-tech] Re: split elevator Let me add that the low-speed warning spring bracket has three positions that would allow the owner/operator and A&P to tailor the onset of resistance to a lower, intermediate, or higher airspeed. I don't know the spread, but it could only be a couple of degrees and a couple of MPH. Since I've been flying a split-elevator 'coupe without the spring and have added the spring during the restoration project, I'm inclined to set it at the higher setting so the plane feels the same as before until I'm just below stall speed. My thought are, "flare up to the spring, pull through the spring to do a stall". Anybody else have any knowledge of the optimum setting? Best, Dave --- In [email protected], William R. Bayne <ercog...@...> wrote: > > > Hi Hartmut, > > Comments interspersed below, > > William R. Bayne > .____|-(o)-|____. > (Copyright 2010) > > On Mar 17, 2010, at 17:26, Hartmut Beil wrote: > > > > > > > William. > > > > I read in my FAA approved flight Manual 56 miles true air speed as > > the lowest power off speed for 415-E and G models. This is meant for a > > gross weight of 1400 pounds. > > A 13 degree up elevator should get you down to 60 Miles in any Coupe. > > Maybe less even. But not much. At least this is what the books are > > saying. > > I agree. > > > My split elevator stop holds the elevator 13 degrees up > > OK, I believe you so far... > > > and when I let the plane settle to the speed it gives me then , I fly > > 60 -65 indicated. > > OK, I would interpret your words "...let the plane settle to the speed > it gives me then..." as indicating that you are level, power off, > where you are approximately at 13º "up elevator" and at that point of > aft yoke travel beyond which which your "low speed warning cushion" > spring will make itself known. You are flying 4-9 mph above the stall > speed of 56 mph. > > It seems evident that you have to pull the yoke further back (into the > "low speed warning cushion" range) in order to bring the plane to that > point in a power-off glide where you should get a mild jouncing or > buffeting at or about 3 mph above the minimum speed. In this I presume > minimum speed and stall speed to be identical. > > What is your observed sink rate over this range? > > > That is the published approach speed for a Coupe. So all would be > > good on final, but I would not be able to flare if I would not be able > > to pull over the spring stop into a region where I can get still the > > nose up. > > Actually the the Ercoupe Instruction Manual (as referenced in the > Flight Manual for the 415-E and G) says, on p. 6: "A good airspeed > reading during the approach...is between 60 and 70 mph." As the ground > is approached the flight path is leveled off so as to reduce the > vertical velocity. At the same time the airplane is held off in the > conventional manner until it loses its flying speed." > > At an approach speed between 60 and 70 mph you are still carrying the > excess flying speed of 4-9 mph before stall. Personally I favor the 70 > mph (True Air Speed) approach, which would give me 14 mph excess flying > speed above stall. Once I flown my approach so as to be level one foot > above the runway at 60 mph, 65 mph or 70 mph, I can reduce power and > STILL slowly move the yoke back so as to reduce sink to zero. If I am > sufficiently skilled, I can do this at a rate that the plane stays > exactly one foot above the runway. > > If I reduced power enough, at some point the excess energy thus used to > stay off the runway is gone and the plane gently sinks to touchdown. I > presumed, perhaps incorrectly, that this "touchdown speed" would > general correlate with "stall/minimum speed" at gross weight. I could > be wrong. > > > This is what the 20 degree up elevator gives you. You can pull wayy > > beyond the limitations of the earlier models. Makes for better, > > shorter landings. > > > > Now imagine what a 9 degree elevator stop leaves you when you sail > > engine off with 60 Miles or less to the runway. Little or nothing. > > Per what I have written above, what "little" is available at 60 mph > should still be "enough" to flare the arrival level before touchdown. > > > Now you need to add power to get the prop wash push down the tail. > > That seems not natural and requires planning. Airmanship. Not everyone > > is able to do so. These folks will have a rather hard landing and > > learn to come in fast. > > I respectfully disagree. Power should not be necessary to land as I > have described. > > > Coming in fast is mostly ok, but when you have a short runway or > > other not so favorable conditions, you may want to come in slower. > > With the split elevator, you can do that. > > To my knowledge there are no published figures for ground roll for the > 415-C and CD at 1260 lbs., the 415-D at 1400 lbs. and the 415-E & G > with the split elevator at 1400 lbs. I certainly agree that the split > elevator may be able to get you down to 38 mph at touchdown...I just > have not personally experienced or witnessed that particular feat. > > > It is not about the stall speed. The stall speed is determined by > > wing load. It is about being able to have elevator travel left beyond > > the slow speed cushion. > > > > When I pull the elevator full back, power off, the speed go down to > > 38, then the plane breaks. With power on and just me in the plane and > > almost empty tanks, I see speeds around 30 until the stall breaks. > > I'll take your word on all this. > > > You can not get into these low speeds with a 9 degree elevator > > limitation. > > Agreed. If you don't fly off a 1200' strip, though, of how much > practical use is the ability to touch down slower than 56 mph? > > > > The spring stop that comes with the split elevator is there so you > > don't get that low in speed inadvertently. > > But you do have to enter that realm in a normal landing, and only the > pilot's "feel" separates "enough" from "too much". > > > > The split elevator makes the Ercoupe more like the other airplanes > > that you can stall if you want to, thus flare nicely in ground effect > > at low speed > > If I can keep the nose wheel off longer than the mains, I'm happy. > > > , but it still follows the safe design philosophy that you shall not > > be able to stall the plane in a normal flight regime. > > Could you word your point here another way? I do not understand. > > > > So you keep having an elevator stop at 13 degrees, and then not. > > Whoa! 13º "up" elevator in a 415-C or CD is NOT the same as 13º "up" > elevator in a 415-E or G. Per the Ercoupe Service Manual the elevator > area of earlier model Ercoupes is 9.6 sq. ft. Per the Forney Service > manual the elevator area is 7.5 sq. ft., or some 22% less. Accordingly > the response of the different models to yoke and elevator movement is > not directly comparable in the manner inferred. > > > Your choice how to fly it. > > Agree 100%. > > > > Hartmut > > > > > > > > > > To: [email protected] > > From: ercog...@... > > Date: Wed, 17 Mar 2010 16:48:48 -0500 > > Subject: Re: [ercoupe-tech] Re: split elevator > > > > > > Ed, > > > > The "Stall Speed" given as Item #1, p. 10 of the 415-D Manual is 58 > > mph (power off, with "up" elevator limited to 9º). > > This is presumed as being at 1400 lbs. gross weight because data in > > Items 2, 3 and 4 are "at 1400 lbs., gross weight". on this and p. 11. > > > > The "Stall Speed" given on p. 10 of the 415-E & G Manual is 60 mph > > (power off, with "up" elevator limited to 20º). > > This is verified as being at 1400 lbs. gross weight on p. 11. > > > > Since the 415-D does not have the "split elevator" and later models > > do, I would presume that substitution of the "split elevator" reduces > > "minimum speed" (or touchdown speed) at any given weight on comparable > > airframes by (a mere) 2 mph. > > > > Two strictly personal observations: > > > > 1. I prefer the "look" of the earlier elevator (with a trim > > tab) > > 2. I HATE change in yoke "feel" with the "low speed warning > > cushion" spring (and associated mental adjustment in the flare) > > > > Any "cost to benefit" ratio calculated on above 2 mph difference would > > make the "goodness" of this conversion all but impossible to justify. > > > > What am I missing, here? > > > > Regards, > > > > William R. Bayne > > .____|-(o)-|____. > > (Copyright 2010) > > > > -- > > > > On Mar 17, 2010, at 06:21, Ed Burkhead wrote: > > > > > > > > I don't think there are enough no-longer-needed split elevators > > available to meet the demand. > > > > Now, if someone were to set up an Ercoupe elevator conversion > > "factory" with PMA authorization and convert a bunch of elevators, we > > could improve the entire fleet. > > > > Or, would it be (under current regulations) that each owner would > > "fabricate" a replacement part him/herself, using a skilled mechanic > > as his/her assistant? > > > > But, then, demand also depends on cost. Back before you all caught on > > to the goodness of the split elevator idea, I wanted one but couldn't > > justify the cost to benefit ratio. > > > > Ed > > > > > > > > > > Hotmail: Powerful Free email with security by Microsoft. Get it now. > > > > > _________________________________________________________________ Hotmail: Free, trusted and rich email service. https://signup.live.com/signup.aspx?id=60969
