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Thread: Prototype Help

  1. #1

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    Prototype Help

    Looking for help in developing a prototype.
    Plane is based on the Ercoupe, updated with larger cockpit, shorter wings andf better wing loading.
    I have the design almost complete all parts are designed and ready to cut, shape. Need someone that is good with metelwork to help build.

  2. #2
    femmpaws's Avatar
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    What airfoil are you going to be using? Harry Riblett's 30-615 would be a very good replacement for what it had. On my project I'm using his 25-816.5 for it's stall and spin resents as well as the high lift it offers.

  3. #3

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    Airfoil

    I am using 23012

  4. #4
    femmpaws's Avatar
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    Quote Originally Posted by hiflyer View Post
    I am using 23012
    I did a little looking at that NACA 23012 airfoil and think there is a better one with lower CM and a better stall. I do understand you likely have all the forming blocks made, if not all the ribs made. But I think it would be worth your time to get a copy of Harry Riblett's catalog of airfoils. http://www.aircraftspruce.com/catalo...a_airfoils.php and read it and see what he has, in the past I have talked with him on the phone and his thing is airfoils. He has helped me with a number of design issues.

    Also going up to a 15% airfoil will give you deeper spars for your wing and you will pay nothing in speed but you will get more lift meaning you will fly at less AOA so you will have less trim drag and should be a bit faster.

    I gave a copy of GA Airfoils to an engineer friend that's also a home builder and a very good one and he was shocked at the numbers he was coming up with using the Riblett airfoils over the NACA or NASA airfoils. He was coming up with higher cruise speeds and lower stall speeds on a number of aircraft he had real world numbers for. The software he uses has been tweaked till it was giving real numbers of real aircraft. The one thing Riblett says is all the NACA and most of the NASA airfoils were just for testing only and not to be flown. Riblett's are designed for use in the real world, all of his have a soft stall, not the whip stall that are found on any number of the NACA and NASA airfoils that are/have been used.

    The little plane I'm working on will carry two 200 lb people, 20 gallons of fuel, a bit of baggage, cruse around 95 to 100 mph on about 3.5 to 4 gph. It will carry 36 feet of wing but only have 42 inch of cord. Empty weight will be about 600-650 lbs with a gross of 1250...

  5. #5
    femmpaws's Avatar
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    Quote Originally Posted by hiflyer View Post
    I am using 23012
    I talked with Rich my engineer friend this evening and told him what you were doing and he told me about the nasty habits the 23012 has. It has a very nasty stall and you have to pitch it nose down a lot to recover from a stall. Meaning post stall recovery is poor and not something for a low time pilot.

    Rich and I both think if you are trying to make an aircraft that is stall and spin resistant the Riblett 25-613 or 615 would be far better. The reason why the Ercoupe was "stall and spin proof was the controls were set so you couldn't get it into a stall. Rich said the elevator was set so you had 10 degrees down and 15 degrees up to start with, then they had the rudders coupled in a way where only the inside of the turn rudder worked. So that made it a so-so aircraft. Rich knows more about the Ercoupes than I do. I know my dad has flown a number of them and didn't like them, he had a few thousand hours at that time.

    I don't understand why you want to shorten the wingspan, it's only 30 feet now, it's about the same size as a Piper Colt. If you are trying to get performance on low horsepower you need a high aspect ratio wing. Try going to 35 feet and taper the last 6 to 8 feet of the wind panels.

    I can come up with the airfoil plots for the Riblett 25-6XX for you. The 30-6XX would be better than what you are planing to use, both in stall and drag.

    I'm not trying to rip up your design! I think the Ercoupe was/is a great idea and there are ways to make it a much better aircraft. One of those is to use a better airfoil and not repeat the same mistakes they did.

    Blessing Kristine

  6. #6

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    Quote Originally Posted by femmpaws View Post
    I talked with Rich my engineer friend this evening and told him what you were doing and he told me about the nasty habits the 23012 has. It has a very nasty stall and you have to pitch it nose down a lot to recover from a stall. Meaning post stall recovery is poor and not something for a low time pilot.
    A lot of people criticize the 23012 as having a nasty stall and it looks that way on paper, but many successful (and good handling) planes have used this airfoil. One good example is the Taylorcraft, which has very benign handling, an excellent beginner's plane... and far better performance than the Cub, with its USA35B airfoil.

  7. #7
    femmpaws's Avatar
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    Quote Originally Posted by Dana View Post
    A lot of people criticize the 23012 as having a nasty stall and it looks that way on paper, but many successful (and good handling) planes have used this airfoil. One good example is the Taylorcraft, which has very benign handling, an excellent beginner's plane... and far better performance than the Cub, with its USA35B airfoil.
    Yes the 23012 does well if it's lightly loaded. The Taylorcraft does well with that airfoil because it has light wing loading around 7.5 PSF They also did things like putting wash out in the wings to help control the stall. Harry Riblett simply states DO NOT USE ANY OF THE NACA FIVE DIGIT AIRFOILS! The reason why CG Taylor used them was that's all he had to work with at the time. Yes the 23012 is a lot cleaner than the USA-35B

    With the 23012 it starts to get nasty when you get over 10 pound per square foot wing loading and becomes real bad at 12 PSF. What happens I'm told at high wing loading a bubble forms on the top of the wing and when the wind stalls you lose that bubble and all the lift causing a whip stall. And to recover you have to pitch the wing highly nose down to reattach the airflow. I'm not even going to say anything about spins.

    An Ercoupe had 142 Sf for wing area and a gross weight 1400 lbs giving it a wing loading of 9.85 pounds per square foot and you plan to shorten the wing span so that's going to push the wing loading up. Rich liked the idea of giving it a 35 foot wingspan and tapering the last 6 feet of the wing panel, or just leave it alone and put one of the Riblett airfoils

    Yes there are a large number of European aircraft that use the 23012, 23013, 230XX but they are mandated to have low wing loading.

    You have not really said what the mission for the aircraft is or how close or far from the Ercoupe you are moving. Are you looking to have a stall and spin resistant aircraft?

    Please spend a few bucks and the time to read Harry Riblett's GA Airfoils. http://www.aircraftspruce.com/catalo...a_airfoils.php There are far better airfoils then what NACA/NASA came up with.
    Rich even says call him 360-298-5942

    Kriss

  8. #8

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    femmpaws
    I have had a copy of Harry Riblett's book for some time and very impressed with what I see. I know two Sonerai owner that removed the airfoil that it was designed with and went with if I remember right the 35-415. Both reports soft to self recovering stalls and also reported a 8-10 mph increase in cruise and also lowered the landing speed.
    Well I now am in the process building a stol replica of the Feiseler Storch and want to use the Riblett wing. So far I've got it down to the 30-A415 or 30A418.
    Would be interested in running some numbers by someone else and interested proving Harry knew what he was talking about.
    thanks in advance, would Rich consider being contacted by me also?

  9. #9

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    Airfoil

    I haven't cut the block or created any ribs at this point.
    Reduction of the wing span was to increase wing loading, the Ercoupe wing is very light and does cause some stability upset in bumpy air.

    If I recall thye RV's also use the 23012

    I am not opposed to looking at other options, but do plan on maintaining the anti stall/spin of the Ercoupe

  10. #10
    femmpaws's Avatar
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    Rich is like me an aircraft nut and would need likely be glad to help. Seeing how you are fallowing after the Storch I think Rich would likely push you to the 25-6XX The Storch is not a clean airframe to start with, so it's not going to be a fast plane. Having the max thickness at 25% is going to work for you when it comes to your stall and spin resistant needs for STOL work And if you were really want all out STOL I would use the 25-8XX it's high camber line helps it make a lot of lift at some flat angles of attack

    The reason I'm using the 25-816.5, is in part do to the short wing cord of 42 inches and the wingspan of 36 feet will tend to offset the drag of the high camber

    I forget who it was but they built a Zenair 701 clone and left out the slats. Their plane stalled about 5 knots faster but was also 15 knots faster in the air at cruise then they added VGs and got it so the stall was 3 knots faster and was 12 knots faster at cruise...

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