Prototype Help

[hiflyer]

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.

[femmpaws]

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.

[hiflyer]

I am using 23012

[femmpaws]

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...

[femmpaws]

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

[Dana]

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.

[femmpaws]

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

[stolflite]

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.

Took the liberty to make a call to the phone # you added to another post and talked to Rich.
What a refreshing conversation that was, thoroughly enjoyed the time on the phone.
Well I was going to use the 30-A-618 but after his help and encouragement I have opted for the 25-518, won't need flaps so
will not need the A(cusp).
Looking forward to working on the plane again after a year in stall mode, with the help from fellow builders sharing ideas and encouragement I can start again.
just need to get my shop heater to work now and then I can press on.
Look forward to more visits with you in the future, thanks for taking the time to encourage and help
regards from another Riblett fan
rich

[Kurt Flunkn]

Looking for help in developing a prototype.
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.

I'm shocked that this turned into a discussion on airfoil selections and NO ONE responded to the original request for someone that is good with metalwork. Good luck hiflyer and I hope you get a lot of help with your new design!