Copyright © Custom Flight Ltd. 2013
North Star Introduction
Thank you for looking at the North Star Kit. I want to expand on a few things covered in the specs.. You will find when reading the construction specs. that there are a tremendous number of details built into this aircraft. Details make an airplane and they are what set ours so far ahead of any similar aircraft.
The Super Cub is a good airplane but 50+ years has afforded us the knowledge to design a better aircraft. I found out after designing the North Star, that Piper had most of the improvements we used, on the drawing board years ago. They didn't proceed because the courts would view improvements as admitting there was a fault with the original design, bringing on all kinds of liability problems. Few people know they even shipped Super Cubs with toe brakes to Europe, while in North America, we couldn't have them for the above reason.
When I designed the North Star I had four parameters in mind. It had to be stronger, more durable, fly better, and be easier to work on.
There were weak spots in the Cub that were known but really show up when raising the gross weight. The SC is a J3 with a higher gross and a bigger engine. The distance between joints on the longerons behind the cockpit was too long on the J3, so for the SC small tubes were welded in from the top joints to the mid span of the lower longeron. This stopped the longeron from bowing up or down. Then tubes were welded across the bottom from this new joint to the new joint on the other side. Now the longeron can't bow sideways, but it can still bow towards the centre of the fuse. Oh well, it's good enough. If you hired a structural engineer to design a new fuselage and he brought you these drawings, you would think he was a lunatic. Obviously the Piper engineers were not lunatics, what happened? Two forces govern production airplanes: the certification and the bottom line. It would have been an expensive violation of the type certificate to redesign the structure, cheaper to put "band-aids" on it. We didn't have these restrictions so we added an extra set of diagonals to the fuselage, shortening the spans in a structurally sound way. This also solves the known weak link at the tail spring mount area. Two other weak spots were related to crash protection rather than flight loads. The diagonal in the cockpit ceiling handles extreme loads in tension only. If in compression it can pop violently down and penetrate the pilot's head. Adding a cross brace up there solves this problem. The other area is the side bay of the fuselage immediately aft of the fire wall. A very hard landing can cause the weight of the engine to swing down compressing the bottom longeron, making "s" curves in the floor. In a crash the firewall can be pushed back breaking the pilot's ankles! Again a cross‑brace instead of a diagonal makes this less likely.
One North Star owner recently called me and exclaimed "You just saved my life!". He ran out of gas and hooked a wing tip on a tall tree while gliding to a frozen lake. This put him in the vertical nose down landing mode. So vertical that there were no skid marks on the ice, just an impact. He crawled out from under the wing with only a few bruises. The airplane was a total wreck, the cockpit was the only area not crumpled. He said he didn't understand the strength I was talking about until that day. He immediately ordered another North Star.
The wings are similarly strengthened with the spar reinforcements copied and improved from the Pawnee crop duster. Many more durability and other enhancements are listed in the
With more structure comes more weight. Many aerodynamic improvements were made to compensate for this. Some of the changes seem small but their cumulative effect is amazing, you have to come and fly one to believe it
The landing gear legs are 3" taller to give higher angle of attack for better takeoff.
The sheet metal on the top of the leading edge is extended to about 4" aft of the front spar. This gives a truer airfoil shape without the concave fabric between ribs in this critical section of the wing. It's true that in normal flight the fabric billows up into the low pressure, but in a stall the fabric collapses and full stall recovery and lift cannot be had until the fabric billows again. This happens in short order but if the fabric is already held up by the leading edge metal recovery happens faster. Take that theory one step farther. A wing stalls in stages and not only that, sections of wing are stalling and un‑stalling repeatedly as the angle of attack increases. It's a very dynamic environment. The higher the ratio of stalled area compared to un‑stalled area the "more stalled" the wing is. Now if your wing recovers a bit faster, then it follows that the localized areas fluctuating between stalled and un‑stalled will spend less time stalled, thus delaying the total wing stall.
The back of the fuselage is not the typical "peaked roof" as seen on most Cubs. Piper flattened the back on the agricultural models to facilitate a hopper door. By chance, since the back more closely followed the wing shape, they found the "A" models had a slightly lower stall speed.
The trailing edge of the wing is extended. NASA did a study and found that aspect ratio, (that which gives lift), is mostly determined by the length of the trailing edge. Tape yarn to the underside of the leading edge and it will track straight back in cruise. Slow the airplane down and it will swing outboard until just before stall it will be at about 45*. If you have a round tip the pressure is lost off the tip. If your trailing edge is longer the pressure stays under the wing longer. Droop tips try to hold the pressure but block visibility and can shadow ailerons in sideslips. This wing has, therefore, 3 feet more effective span on each side. (This longer effective span places more leverage on the rear spar and necessitates reinforcements to the rear spar, another weak link). The longer trailing edge also gives us the room to slide the aileron outboard 2 feet. This makes it more effective since it has more leverage due to the greater distance from the aircraft centerline and it doesn't have the round wing tip out past it resisting roll. The aileron, like the flaps, also has greater cord and better airflow through the slot. This along with the better response means less deflection is required which means you are less likely to stall the aileron in slow flight. Also it gives room to make the flaps longer.
It's interesting that the Cub wing tends to stall at the tip first, even with the designed in washout that is supposed to cure this. We have little or no tendency to stall a wing tip and drop into a spin, and we rig all the North Stars flat, no washout. Even in extreme nose up, high bank, climbing turns with full power and full flap,( most airplanes will stall the top wing tip and roll out of the turn onto their backs) the stall causes the airplane to settle into a cruise attitude and un‑stall. The nose rarely even goes below the horizon!
The flaps are larger, 2' longer and 4" wider cord than cub flaps. The increased size of the flaps is only a small part of the performance improvement. A Cub style flap does not work well no matter how big you make it. The slot design/hinge geometry is not good. The slot is much to small to allow the required volume of air to pass through it, and even if it were larger, the existing slot geometry (radiuses and angles) can't direct the flow where it's needed. The superior hinge geometry, and the redesigned radiuses on the aft bottom portion of the wing ribs of the North Star, produce the improved, energised, air flow through the large slot that adheres to the top surface of the flap, making the slow speed performance exceptional. To demonstrate the difference pulling Cub flaps on requires almost no effort, (little aerodynamic effect = little actuator force), you don't get anything for free. The North Star flaps require a noticeable force to pull them down. The force is related to airspeed and deflection, you won't be able to pull full flaps on until the airplane slows. This gives you some of the tremendous control feed back, and is a self limiting feature, preventing overloads caused by reckless flap deployment at high speed. If you put these flaps on a standard Cub type wing the huge aerodynamic forces would twist the rear spar, bend the tubular compression struts, and break the wing ribs ahead of the spar. We therefore put the flap hinges in line with the compression struts and designed an "I" beam type of strut similar to what we used on unlimited aerobatic planes. Neat new idea eh! By the way the Stearman biplane and a few others copied our "new" idea. Remember the Snowball effect? When you change one thing, other things down stream must also change. Due to the higher forces we had to beef up the flap cable pulley mount locations. What does all this mean to you, other than not having to worry about structural integrity? With no flaps the North Star lifts off at 35 mph. With 20 degrees of flap it jumps into the air on takeoff at 25 mph, and climbs! This low speed means less ground wasted accelerating. Full flaps (52*), no power on approach gives 800 FPM descent. Just touch the throttle to 1200 RPM and the path flattens out giving excellent descent control. Sideslips also work and when performed with full flaps can give 1,000‑1,500 FPM rate of descent. After you become familiar with the airplane a normal approach will be full flap, 40mph, no power, over the trees, sideslip, straighten, flair, flaps off, brakes on. Turn around and you will be amazed at how little room is needed. Set up about 1800rpm, 30mph, full flap, and you can do figure eights and 360's all day, on the spot.
Control feed back is exceptional. As with any airplane it takes time to really get to know it, but once you do you will feel even the most subtle hint of a stall long before significant lift is lost.
Our Shock Struts work much better than the old bungee type. They are a hydraulic shock/coil spring combination. The long stroke and hydraulic shock damping give much superior protection from those extra rough landings.
Ask us about our energy absorbing front seat for crash protection.
Along with the kit, we supply instructions on videotape. The wings, on average, have been taking builders 65 hours each to build and 50 hours total for the flaps and ailerons. The video for the wings is approximately 12 hours long, taking you one step at a time through the assembly process. In addition, a dozen 24" x 36" blue prints with full size details of the wing are included. For the fuselage: full size patterns for the floor boards and interior panels are supplied with a video to show how to make and install the interior. This sounds trivial but the interior of an airplane like this can be very time consuming and this guidance makes it much easier. A binder is provided with 2 separate parts lists: hardware order lists with recommended suppliers and hardware location lists that tell where each bolt, pulley, etc. goes in the airplane. The binder also contains CAD detail drawings, indexed for the various areas and systems of the plane. It is set up so that new drawings can be added as we create them.
We only supply the parts we manufacture that are unique to the North Star. Parts that are readily available, AN hardware, fabric, engines etc. we don't supply. That would cost you more, we can't compete with Aircraft Spruce, Wicks, Etc.
You can also call for advice whenever needed. One advantage to our low volume production, other than the high quality, is the personal attention you can receive.
Another little known bonus, is that for sales to the U. S. there is no tax or Duty when crossing the border. The contract price is all you pay, except for the actual shipping bill.
If you want to build a superior airplane, the North Star, call us to discuss a production slot.