Flap extension

nimdave

Non-Member
I am working on a stretch project that will be licensed Exp Exibition. I am working on extending the flaps from 52 to 81 inch’s long, shortening the aileron a few inches and moving it to the end of wing after a squared wing tip mod. I am concerned about additional twist of the rear spar and would like to get drawings that would show reinforcement to account for this. Any guidance would be appreciated..
 

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Not sure how you will end up with an 81 inch flap and shorter ailerons. My stretched which is per STC has a 90 inch flap. My aileron is 102 inches just like Super Cubs and is moved out to the wing tip attachment point. Which is squared off. Look at the pictures I just posted and you will see the rear spar reinforcement. The stretched wing also has more ribs, compression struts and drag wires than a Cub wing. Also the false spar area is boxed in with aluminum panel the whole flap length. And, the STC calls for two actuators linked together for each flap. I love having a 90 inch flap. I can make approaches in the 40's with good visibility.
 
Not sure how you will end up with an 81 inch flap and shorter ailerons. My stretched which is per STC has a 90 inch flap. My aileron is 102 inches just like Super Cubs and is moved out to the wing tip attachment point. Which is squared off. Look at the pictures I just posted and you will see the rear spar reinforcement. The stretched wing also has more ribs, compression struts and drag wires than a Cub wing. Also the false spar area is boxed in with aluminum panel the whole flap length. And, the STC calls for two actuators linked together for each flap. I love having a 90 inch flap. I can make approaches in the 40's with good visibility.

I joined the inner left flap to the inner right flap for the left wing and kept the 33.5 hanger spacing. This allowed use of inner aileron position for outer flap hanger providing 81" flap. Not extending the wing just squaring. Not looking for a super stol, stol is enough and dont want to kill my cruize speed. As far as exp there are other mods I am planning such as turbo charging/normalizing, gear change to Supercub gear, matco brakes, etc.
 
I did have to move several hinge brackets. My wing span is a bit over 37 feet. The cruise difference was around one mile per hour. Plus, it flies much better on the step at 2200 rpm. Good luck on your project. Post pictures.
 
Wow thats nice that you did not loss much cruise speed. I assumed since a Supercub is so much slower it was due to the wing span.
 
Wow thats nice that you did not loss much cruise speed. I assumed since a Supercub is so much slower it was due to the wing span.

Super Cubs are slow because they have more angle of incidence. They get shorter take off distance but slower cruise.

And, Denny is correct.
 
I would not shorten a PA20/22 aileron from my experience. Moving it outboard to the tip of a squared wing does help give it adequate aileron response though.
 
Wow thats nice that you did not loss much cruise speed. I assumed since a Supercub is so much slower it was due to the wing span.

Cub gear is one of the big things that slow them down. PA 12s and Pacers will slow down quite a bit when you start adding Cub gear to them. If you put spring gear on a Cub you can increase cruse 10-15 mph. The angle of incidence is not that big of a factor, info from PA12 pilots that changed to cub incidence the tail will just fly different But now windscreen angle can effect speed. Covered gear and fairings can get you some speed. Every plane is different and one small change on any part of the plane can have effect on the entire plane. If it is only a few inches just push that last bay out to match the Aileron length. If you want to strengthen the rear spar area look at a full wrap around false spar like Javron does. " Just for clarification what do you mean by additional twist of the rear spar ".
DENNY
 
I would not shorten a PA20/22 aileron from my experience. Moving it outboard to the tip of a squared wing does help give it adequate aileron response though.

That was my thought on shortening moving to the tip will improve enough to make up for it. I also have a Certified pacer with the squared tips and yes it does suffer due to unaileroned wing ends.
 
My experiences regarding increased drag.

I flew my converted Pacer years on Univair gear covered with fabric. When I removed the fabric the change in cruise speed was not noticable. Recently, I converted my gear to Super Cub gear with the Trimmer STC and I was pleasantly surprised to find out that my cruise speed was not noticably changed. (If you look at the Pacer gear and compare it to the Super Cub gear the cabane vee obviously adds drag but you eliminate a major strut on the Pacer gear. You also clean up the belly significantly. I found the outcome is a wash). I change my tires every summer from my 25 inch Goodyear's to my 29 inch Bushwheels, my cruise speed is not noticabibly effected. Collectively, these changes make some difference. But, not anywhere near 5 mph, for my plane. It all comes down the the inverse square law. Increased drag is not proportional to decrease in speed.
 
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Cub gear is one of the big things that slow them down. PA 12s and Pacers will slow down quite a bit when you start adding Cub gear to them. If you put spring gear on a Cub you can increase cruse 10-15 mph. The angle of incidence is not that big of a factor, info from PA12 pilots that changed to cub incidence the tail will just fly different But now windscreen angle can effect speed. Covered gear and fairings can get you some speed. Every plane is different and one small change on any part of the plane can have effect on the entire plane. If it is only a few inches just push that last bay out to match the Aileron length. If you want to strengthen the rear spar area look at a full wrap around false spar like Javron does. " Just for clarification what do you mean by additional twist of the rear spar ".
DENNY
Well I would think increasing the length from 52 to 81" would produce more up lift at the back of the wing through the hinge supports and false spar causing additional twist between the 2. That is the false spar and rear spar especially in the fuel tank area with no ribs to carry that load to the front spare.
 
Well I would think increasing the length from 52 to 81" would produce more up lift at the back of the wing through the hinge supports and false spar causing additional twist between the 2. That is the false spar and rear spar especially in the fuel tank area with no ribs to carry that load to the front spare.

Years ago (like back in the 1960s) a lot of folks would rig the flaps on TriPacers with some reflex to get more speed, kind of like the Maule MX-7, until they started finding rear spars with a twist at the inboard end. That practice has long since been discontinued!
 
Well I would think increasing the length from 52 to 81" would produce more up lift at the back of the wing through the hinge supports and false spar causing additional twist between the 2. That is the false spar and rear spar especially in the fuel tank area with no ribs to carry that load to the front spare.

Boxing in the false spar area along the flap area and adding 1 inch angled aluminum to both sides of the aft spa will meet the increased load requirements. Another safety solution is to lower your flap extension speed speed a few mph. Air speed has the biggest effect on loads. That may be why using reflex flaps are problematic. They are used at cruise speeds. Remember the STC allows for 90 inch flaps.And, was engineered and tested.
 
Boxing in the false spar area along the flap area and adding 1 inch angled aluminum to both sides of the aft spa will meet the increased load requirements. Another safety solution is to lower your flap extension speed speed a few mph. Air speed has the biggest effect on loads. That may be why using reflex flaps are problematic. They are used at cruise speeds. Remember the STC allows for 90 inch flaps.And, was engineered and tested.

I keep comparing to my son's Maule M5, it has longer flaps and shorter ailerons than mine (and a 1.5" longer cord) will have and uses 1 bell crank. The flaps are however fully skinned. I plan to fully skin mine and use 1 bell crank at the stock location. I do plan to reinforce the rear spar with trimmed angles as well which I believe are there to prevent spar buckling.
 
I keep comparing to my son's Maule M5, it has longer flaps and shorter ailerons than mine (and a 1.5" longer cord) will have and uses 1 bell crank. The flaps are however fully skinned. I plan to fully skin mine and use 1 bell crank at the stock location. I do plan to reinforce the rear spar with trimmed angles as well which I believe are there to prevent spar buckling.

I think Maule gets away with a shorter ailerons by increasing it's cord. The stock Pacer actuator is on the inboard hinge. My 90 inch flap has three hinges, I chose to used one actuator on the middle hinge. A long flag with an inboard actuator may place a significant torsional load on the flap.
 
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I think Maule gets away with a shorter ailerons by increasing it's cord. The stock Pacer actuator is on the inboard hinge. My 90 inch flap has three hinges, I chose to used one actuator on the middle hinge. A long flag with an inboard actuator may place a significant torsional load on the flap.

I fully agree with you and was planning to use the actuator at the center hinge point but after realizing the Maule with the longer flap with longer cord was using the actuator at the same location as the pacer. I think fully skinning the flap as the Maule will account for the twisting of the flap.
 
I fully agree with you and was planning to use the actuator at the center hinge point but after realizing the Maule with the longer flap with longer cord was using the actuator at the same location as the pacer. I think fully skinning the flap as the Maule will account for the twisting of the flap.

I agree, a metalized flap will better withstand torsion.
 
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