New Smith Cub coming together
- Thread starter Seaworthy
- Start date
skywagon8a
MEMBER
SE Mass MA6
Not quite true. The airplane is tested for it's ability to perform with consideration that pilots with average ability or worse will be safe. In other words it is expected that the plane can do a better job than the pilots who are handling the controls.
When an airplane undergoes flight testing for certification, it is tested outside the parameters which show up on the final type certificate. To be certified for spins, it will be tested to recover after six turns. When it is placarded "Spins prohibited" it will have been satisfactorily tested with a full one turn spin with the recovery prior to the completion of the second turn. This is so on single engine airplanes. Multi engine planes are not spun by requirement, only if the testing personnel desire it for some reason.
MainlandCub
Registered User
New Zealand
I was wondering if the floats were what made it reluctant to spin. With all that mass down low, there must be a pendulum effect. What entry speed and technique were you using?
I have spun my stock Super Cub and it wouldn't spin from an unaccelerated stall. To get it to spin I used 60 mph and a bit of power and snatched the stick back followed by the boot of rudder. I was flying with a well forward c of g. Rotation was fairly rapid. It was on wheels of course.
Andrew.
skywagon8a
MEMBER
SE Mass MA6
Andrew,
I do not believe that the floats made it reluctant to spin. I do believe than the pendulum effect does effect the rate of turn once in the spin. All of the spin attempts were done with power at idle, trim at 1.3 Vs, flaps up, speed reduction at 1 mph/sec, at the stall full rudder, hold the full rudder and full aft stick for one complete turn then when the rudder returned to neutral the spinning stopped instantly.
The refusal to spin with the CG more forward was clearly a case of being elevator limited. The elevator was unable to apply enough down force on the tail to maintain a stall on the wing. During the attempts with the more forward CG (17.5") all indications were the same except the spinning turns were not as tight and the airspeed built rapidly to over 100 mph. Perhaps, without the floats, the CG could have been a little further forward with sucess.
Your experience and mine both indicate that the Cub wing has very good low speed, high angle of attack characteristics, in that it has a benign stall.
I have performed extensive spin testing on other airplanes using many different combinations of flap and aileron positions and power settings. I did not do this with the Cub for the simple reason being that I do not see that as being necessary for my purpose. I do not believe that it will show anything unusual or hazardous.
I do not believe that the floats made it reluctant to spin. I do believe than the pendulum effect does effect the rate of turn once in the spin. All of the spin attempts were done with power at idle, trim at 1.3 Vs, flaps up, speed reduction at 1 mph/sec, at the stall full rudder, hold the full rudder and full aft stick for one complete turn then when the rudder returned to neutral the spinning stopped instantly.
The refusal to spin with the CG more forward was clearly a case of being elevator limited. The elevator was unable to apply enough down force on the tail to maintain a stall on the wing. During the attempts with the more forward CG (17.5") all indications were the same except the spinning turns were not as tight and the airspeed built rapidly to over 100 mph. Perhaps, without the floats, the CG could have been a little further forward with sucess.
Your experience and mine both indicate that the Cub wing has very good low speed, high angle of attack characteristics, in that it has a benign stall.
I have performed extensive spin testing on other airplanes using many different combinations of flap and aileron positions and power settings. I did not do this with the Cub for the simple reason being that I do not see that as being necessary for my purpose. I do not believe that it will show anything unusual or hazardous.
skywagon8a
MEMBER
SE Mass MA6
Colin,
It is my understanding, that VGs lower the stall speed by creating a vortex which helps to hold the air flow to the top of the wing at a higher angle of attack, thus delaying the stall. So, since I was not getting a complete stall with full up elevator, how could the stall be lowered since there is not enough down force available on the tail to increase the angle of attack any higher?
The elevator travel on this Cub meets Piper's specs. I have found no other need for more up elevator power. So this is good and I see no need to install VGs. I may have a change of opinion if the plane was on wheels.
I have a friend who has a stock PA-18 on EDO amphib floats. He install a set of VGs which I flew. I could not find any evidence that they changed anything.
Perhaps if I had more rapidly pulled up the nose, and perhaps had used more power it would have whipped into a spin? I see no need to explore those characteristics since this is just a recreational Cub and not an aerobatic plane.
It is my understanding, that VGs lower the stall speed by creating a vortex which helps to hold the air flow to the top of the wing at a higher angle of attack, thus delaying the stall. So, since I was not getting a complete stall with full up elevator, how could the stall be lowered since there is not enough down force available on the tail to increase the angle of attack any higher?
The elevator travel on this Cub meets Piper's specs. I have found no other need for more up elevator power. So this is good and I see no need to install VGs. I may have a change of opinion if the plane was on wheels.
I have a friend who has a stock PA-18 on EDO amphib floats. He install a set of VGs which I flew. I could not find any evidence that they changed anything.
Perhaps if I had more rapidly pulled up the nose, and perhaps had used more power it would have whipped into a spin? I see no need to explore those characteristics since this is just a recreational Cub and not an aerobatic plane.
cgoldy
Registered User
Moogerah Queensland Australia
My experience was that (on wheels) without VG's I could only just stall the plane without power. Added VG's to the wing and the stall speed was lowered and found I did not have enough elevator authority to stall the wing. So added VG's under the stabiliser and the elevator authority improved and I was then again able to execute a stall. This was all with some weight in the back. Added gap seals and could not improve it any more than i already had so i removed them. Not very scientific I know. But I was very impressed with the VG's under the stabiliser.
skywagon8a
MEMBER
SE Mass MA6
Interesting, how many MPH did the stall speed get lowered? Did the characteristics of the stall change with the VGs? Was it softer or more abrupt?
This does make a lot of sense since the elevator/stabilizer unit needs to be looked at as an upside down wing. It's lift is in a downward direction. With the elevator in the full up position there is a sharp angular change in direction at the hinge line thus generating turbulent air under the elevator reducing it's "down" lift. It is sort of like a wing with a flat upper surface and a hinge in the middle. Most definitely not very aerodynamically smooth. Filling the hinge line gap only reduces air flow down through the slot, but most of the turbulence and loss of down lift will still be there. I will go as far as speculating that if VGs were installed on the top of the stabilizer also, in the same manner as the lower ones, that it would be easier to raise the tail earlier in the take off run when loaded tail heavy.
Placing VGs on both sides of the fin on some twin engine airplanes is known to improve rudder power thus reducing VMC (minimum single engine control speed). So, it makes sense that the same would be true on the elevator.
I have long thought that the flat tail surfaces were not very aerodynamic and could use some improvement. If the stabilizer had curved upper and lower surfaces the air flow past the hinge line would be smoother. Granted the construction would be more labor intensive and Piper's objective was to keep the cost down. Look at the stabilizer that Doug Keller came up with for his flap STC. There also would be a slight drag reduction.
I have thought that a small slat attached to the leading edge, top and bottom, of the elevator would improve the airflow over the elevator. The VGs would likely be simpler and with less drag. What are the dimensions of the VGs which you placed under the tail?
Good job! The more I look at these planes coming together the more I realize how big of a project it is.
RaisedByWolves
FRIEND
Tx
I know when ACA put the 0-390 in the scouts they made the horizontal stab in a wing shape. The Cessna cardinal has a slot on the stab too.
Your cub looks great, have you been flying floats much this year so far? Ill have to come down on wheels sometime and check it out.
Tom
skywagon8a
MEMBER
SE Mass MA6
You are correct Tom. The original Cardinal did not have that slot. The slot is the solution for the stab stalling and slamming the nose wheel on the runway. Only lost a couple of months flying on floats this winter due to cold and ice.
i did my first flights in my new tcow pa-12 this winter. i also could not get the wings to stall,i have VG's on the wing and tail and was thinking about the gap seals to try and increase my elevator authority.great info here it sounds like i'll keep my 250bucks and try the vg's on top to.
skywagon8a
MEMBER
SE Mass MA6
Colin,
See my airspeed calibration above at #50 on 10-24-2012. Below 40 indicated airspeed the accuracy changed drastically. So, even if the error is 50% you did lower your stall by 2-3 knots.
See my airspeed calibration above at #50 on 10-24-2012. Below 40 indicated airspeed the accuracy changed drastically. So, even if the error is 50% you did lower your stall by 2-3 knots.
skywagon8a
MEMBER
SE Mass MA6
I had been toying with the idea of using duct tape on the top of the elevator gap as a gap seal. Now that I have been talking this over with Colin as you've read here, I think that I will not for now. I'm liking the idea of VGs on the tail. Alternatively, I'm thinking about an idea of making a slat attached to the elevator top and bottom. Just need to refine my idea.
skywagon8a
MEMBER
SE Mass MA6
The idea
was to place a slat on the bottom leading edge to funnel the air flow around the hinge line when the elevator is deflected up. It would be attached to the elevator so that it is streamlined except when the elevator is deflected up. It likely would generate enough drag so that the VGs would be more efficient. The slat is only a thought, maybe just a pipe dream. The brain is buzzing all of the time.
The outboard section of the -18 style elevators already do some of this. Maybe we just need to think of something to make this section more powerful? What is your loaded center of gravity when you are trying the stall? Piper's rearward CG limit for a PA-12 is 18.6" aft of the wing leading edge. If the CG is forward of the limit, what you describe is normal.
skywagon8a
MEMBER
SE Mass MA6
Paul,
The light bulbs are: AR111-CW9W from http://www.superbrightleds.com/search/led-products/ar111-cw9w/ Good folks. I had one which had several segments stop working. They replaced it with no questions asked. The failure came after running for a short while before they were installed. I've had no trouble since. I suggest that you run them in on the bench.
The wig-wag unit is from Kuntzleman Electronics. http://kestrobes.com/beacon.htm#LL1
The light bulbs are: AR111-CW9W from http://www.superbrightleds.com/search/led-products/ar111-cw9w/ Good folks. I had one which had several segments stop working. They replaced it with no questions asked. The failure came after running for a short while before they were installed. I've had no trouble since. I suggest that you run them in on the bench.
The wig-wag unit is from Kuntzleman Electronics. http://kestrobes.com/beacon.htm#LL1
Jonnyo
Registered User
Fairbanks, Ak
This is Peter Annis's (skywagon 8a) Smith Cub
Hello Pete,
Would you comment on your interconnect system and fill procedure for your brake master cylinders ?
Also, what are you using to connect the rear brakes to the front ?
Thank you.
skywagon8a
MEMBER
SE Mass MA6
Jonnyo,
Those are North River master cylinders. Being a closed system, it is sensitive to temperature changes. Many users have complained about the nuisance of having to add or remove fluid. So, the two filler plugs and adapters were removed and replaced with brass needle valves which were connected to a "T" on the bottom of a reservoir.
https://www.amazon.com/Parker-Hanni...=2025&creative=165953&creativeASIN=B01BYLXPQE
The reservoir was made from a 6" long 2" diameter piece of clear plexiglas rod on a lathe.
The proper fluid level is set by opening the needle valve, pumping the brake pedal then closing the valve.
The parking brake valve is a 1/8" pipe ball valve from Ace hardware.
The front to rear connection is just a piece of steel tubing supplied by Back Country in their kit.
Those are North River master cylinders. Being a closed system, it is sensitive to temperature changes. Many users have complained about the nuisance of having to add or remove fluid. So, the two filler plugs and adapters were removed and replaced with brass needle valves which were connected to a "T" on the bottom of a reservoir.
https://www.amazon.com/Parker-Hanni...=2025&creative=165953&creativeASIN=B01BYLXPQE
The reservoir was made from a 6" long 2" diameter piece of clear plexiglas rod on a lathe.
The proper fluid level is set by opening the needle valve, pumping the brake pedal then closing the valve.
The parking brake valve is a 1/8" pipe ball valve from Ace hardware.
The front to rear connection is just a piece of steel tubing supplied by Back Country in their kit.
Jonnyo
Registered User
Fairbanks, Ak
Thank you for pointing out the details of the system, especially the clear reservoir.
Not thinking of building a clear reservoir, I installed valves at the fill points of the master cylinders and ran 2 pieces of Tygon tubing; one from each master cylinder, up the cabin wall behind the throttle. If you needed to "top off" the system you just opened the valve leading to the master cylinder ---with the brake peddle depressed and you could observe the fluid in the tubing go down.
If the brakes where dragging because of hot weather, you could open the valve without the brakes depressed and the excess fluid, in the master cylinder, would bleed into the line.
Filling the brakes from the bottom was easy because of the volume of the tube above the master cylinder.
Thanks again for your helpful posts !
Jonny O
skywagon8a
MEMBER
SE Mass MA6
Your method works well too. I like to make stuff and was able to get a piece of clear plastic rod. It was a challenge making it and it's cap with an "O" ring seal and vent hole on the lathe without cracking the plastic. Imagine drilling and boring a 1"x4" hole down the center and drilling/tapping another hole for the "T" fitting in a piece of plastic without it cracking. Interestingly long after the plane was finished a crack showed up in the top of the cap following the horizontal portion of the vent hole. There must have been some stress buildup in the plastic when it was originally formed, as there are absolutely no stresses applied to the cap in the installation. The reservoir is mounted on the front of the pilot seat with adel clamps where it's fluid level can be seen at a glance, keeping everything compact and all of the plumbing short. I used the plastic to make it easy to see the fluid level.
Olibuilt
MEMBER
Montreal, Canada
Attachments
skywagon8a
MEMBER
SE Mass MA6
It's more fun to make your own Oli.
I like the brakes in this SQ-2. Backcountry has favored toe brakes for several years. This setup is better than mine.
Sent from my iPhone using SuperCub.Org mobile app
Sent from my iPhone using SuperCub.Org mobile app
