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No slow Super Cub

StudentPilot479

Registered User
I just started flying a different Super Cub than usual. Similar, but it weighs a bit more with PSTOL flaps and a cargo pod. The ASI seems to be quite accurate, but the plane starts mushing when I slow to below 55 mph. It also feels (and looks) like the plane is plowing through the air even when light.

A couple people have suggested increasing the wash out, my mechanic saying shorten the rear strut one turn. It is a trip to get the plane to the mechanic, so I was hoping to get some guidance as to how much the wash out should be changed. Will it be a process of one turn at a time then a test flight? Are there ideal measurements for wash out we can check to save some time? Is there another issue that may be causing issues?
 
If you really are a student, get an experienced pilot to fly with you. Airspeed indicators are notorious for being inaccurate, lessening wash can lead to unpleasantness, and lengthening the rear strut increases wash in any case.

Almost any Cub should feel just fine at 55 mph. With full flaps on a very heavy 160 Cub we indicate 42 on final. It is probably an honest 45 or so -
 
Looking at your past posts you had an almost identical issue with a cub back in 2016. So I will start with the question I asked back then, where do you live? You need to find a A&P or IA to look at the plane. Rigging wings over the internet is dangerous. What tests did you do to make sure you ASI was accurate?? Post a picture of the plane most all have a history and someone here may know it.
DENNY
 
This is a good discussion of wash out and wash in. You do know the difference? The discussion is about model airplanes but it also applies to "real" airplanes.
https://nebula.wsimg.com/1619e15352...12BE8653E72CA9A0B&disposition=0&alloworigin=1
Wash out and wash in effects aileron control at stalls, your mechanic shouldn't be suggesting this for what you have described.

Your situation sounds more like a loaded CG issue. Try loading some weight in the baggage compartment for starters. Move the CG aft. Are you still a student pilot after ten years?
 
Find a cub driver who has a few minutes in one fly it and see.
The only ones with a halfway decent airspeed indicator is the tip cubs with a real static system. Heck my airspeed shows 0 on final. I guess I have a slow cub


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Knowing what trim setting stabilizes this Cub in level flight would help inform. Both with and without flap settings as well. For example, does it require more than normal forward or rearward trim? Are the elevators needed to assist and increase angle of attack in level flight or can the range of trim handle it? Things like that.

Gary
 
Interesting links on rigging. Posting to read this later after I’m through being on fire in icing conditions in the magic box..
 
Re: rigging.
Please, before going through extensive rigging and testing, just get in cruise, trim for level flight, take hands off the stick, and make sure your ailerons both go to trail. In my short life I have found four sets of mis-matched ailerons, compensated for by increasing wash on one wing, and decreasing on the other. Nobody does stalls any more (my friends say it is impossible with VGs) but when I put these aircraft into a full stall, they always drop a wing, and it can get violent with VGs and power on.
Flying today in a 160 Cub with 29" tires - approach at 45 mph full flaps. Stalls at 41 indicated with flaps up.
Don't like the tires much, but the aircraft is a screamer - goes up like an elevator!
 
What? Now you have me worried - will a Taylorcraft go uncontrolled in a stall if a wing doesn't drop?

A Cub properly rigged can be controlled with the rudder all the way through a stall. My Taylorcraft experience is only single seat and L2 - neither seemed all that deadly.
 
No worries here Bob....Taylorcraft has the best rudder. But given it's head at higher wing loading it will stall (can be a leading edge first discontinuity then aft) and let you know it's happened. They have taken many with them to Earth forever. VG's fix that.

My expectation is the wing in any aircraft will stall or at least loose lift and alert the pilot before the tail looses authority, as demonstrated by some slatted or slotted wing aircraft.

With far aft CG any can go flat.

Gary
 
All Super Cubs fly a little different. Some are pigs and some are sweet. In my experience the angle of incidence has a lot to do with this and those numbers can be all over the place from the factory. I would check rigging and get an experienced Cub pilot to fly it. Empty weight is another contributing factor.
 
A very experienced local Cub pilot had two PA-18's on conventional gear. One was a "dog" compared with the other. It was consistently that way he said. Never did hear if the wing incidence was different.....maybe never was checked. With today's lasers and levels it would be interesting to find out why. They looked the same to me and rode in only one of them.

Gary
 
What is the cause of different wing incidence? How would that be possible with proper production tooling/jigs?
 
Mark, Chuck or Pierce will maybe chime in at sometime and explain it. Just had the conversation with Chuck on a fuselage. Pipers tolerance was 4.4 to 5.2 degrees of incidence from my understanding.
 
Also consider the engine CL relative to the airframe CL - mounts/fittings/sag - can change flight behavior. Centerline mod apparently does so why not the factory's airframe tolerances including engine and wing incidence?

Gary
 
I assume they would get busy and weld frames outside of the main jig after tack welding cause I have measured them all over the place and the fast ones seem to be the dogs and the slow ones fly really slow. No matter what I have run across several that I wanted to keep and others that didn't fly as good and the angle of incidence of the wing has been the common denominator.
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I just realized my reply did not go through... it is 160 HP, 85 mph cruise at 2400 RPM with an 8242 Borer prop. 31s, a pod, and PSTOL flaps. 55 mph on final is okay, but as soon as it decreases below that I need 1500-2000 RPM depending on weight and how slow I go (down to 45mph) to fly a 'normal' approach.

The plane is based 200+ miles from the A&P who maintains a fair number of Cubs (hence the long trip). I forgot the previous thread. That had the answer so I can see if there is a gross error. That Cub had a very forward CG for a never determined reason, and ballast or a load never made it fly better either. The same owner sold that plane because it was not enjoyable to fly and recently decided to buy another Cub...he has bad luck with finding nice flying Cubs.

Stalls empty with 20 gallons of fuel were gentle, wings level, with a descent. Clean the speed was indicating 50, the nose would dip until 55mph, then the nose would come up until 50, repeated ad nauseum. Full flaps was the same, but 45 to 50 mph. My first thought was that they ASI was off, but at altitude the ground speeds upwind and downwind were about what was expected with the forecast upper winds. Landing both ways with the windsock limp only had a 1 and 2 mph difference from indicated on approach. Trim is about neutral or a little nose up in cruise. Slowing to 65 mph does not have quite enough trim nose up, but once the flaps are extended several turns of the trim handle towards nose down are needed.

I often make the trips for maintenance for the owner as they are always busy, neither of us has an intention of actually doing the work ourselves. I was mainly curious because this is the first Cub I have flown with PSTOL flaps, but it seema at odds with what I have read about them. The owner and A&P both reacted to my comment about the plane needing power to not sink on what had been a normal approach with a wait and see attitude. After taking the Cub home, the owner is now thinking of having me take it back to adjust the wings, which was also suggested by another Cub pilot, and now the A&P also says they can shorten the rear struts when I have time to take the Cub back. I think they may have said 'adjust the wash', so my error, they were talking about shortening the rear strut so the wingip would take a 'bigger bite'.

I suppose my question is really: is this the best way to go about this? Is there anything else that could be causing the difference is approachea (ie PSTOL flaps)?
 
Unless you have had proper stall spin training you have reached you level of expertise and should have someone that is capable of spinning a plane to venture further. If you have then here are things to ponder. Are you doing power on or power off stalls? Where is the trim when you stall? If you are doing a power off stall with a lot of nose down trim you may not be inducing enough AOA for a proper stall instead you are just doing a controlled decent. Go to altitude and do full flap, power as needed level flight, keep rolling in nose up trim to relieve stick pressure and see how slow you can go before you drop a wing hard. The Pistol flaps are going to cause a lot more drag so you are going to need more power. Your numbers are all over the board. How slow can you fly 1 foot off the runway with full flaps and power as needed to stay off the ground? Do you normally do power on or power off landings? It is hard to do this over the computer so be very careful with any advice. DENNY
 
After taking the Cub home, the owner is now thinking of having me take it back to adjust the wings, which was also suggested by another Cub pilot, and now the A&P also says they can shorten the rear struts when I have time to take the Cub back. I think they may have said 'adjust the wash', so my error, they were talking about shortening the rear strut so the wing tip would take a 'bigger bite'.
Before you fly 200 miles to shorten the rear strut in order to take a 'bigger bite, get a smart level. Place it under the wing root rib. Then place it under the tip rib. The tip rib should be nose down in relation to the root rib by 2 1/2 degrees. This is to ensure the wing root area stalls prior to the wing tip area providing more aileron control in a stall. And reducing a tendency for one wing to drop prior to the other in a stall.
 
My airframe from the factory had a really flat AOI, (too flat for a thrust line mod) which made it faster than any other Super Cubs around (easily cruised at 110 mph with stock covered gear and 31's and a BBW) but it wouldn't slow down very well which led to its eventual total rebuild and now it slow and won't speed up.
 
The cub I have now flew a little bit like a yard dart when I first got it. Well rigged, straight flyer, just wouldn’t slow down like it should. I had come from a modded up, pstol flap, good performer to this stock, unmolested 150hp pancake breakfast cruiser. In order to be able to use it like the other without spending tens of thousands on mods, I went to taking weight out of it, mainly off the nose. Turns out it had all the heaviest accessories you could put on one.

This isn’t for everybody, but by deleting the generator, starter, flywheel and belt I took nearly 40lbs off the nose…..
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Delete the spinner and change the borer for a plastic prop and it took about another 15lbs off the nose. Completely different animal with the CG back and the nose lighter. Just a thought.
 

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If you are going to set your washout with a digital level the difference between the butt rib and the outer aileron bay rib is - 2 degrees.

Good Luck - Jerry



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Cubflier, Thanks for looking that one up. I had seen that several times before, just wasn't sure which post it was in. Cold winter nights are usually the best time for me to reread all the old stuff looking for the pearls of rigging. DENNY
 
Cubflier, Thanks for looking that one up. I had seen that several times before, just wasn't sure which post it was in. Cold winter nights are usually the best time for me to reread all the old stuff looking for the pearls of rigging. DENNY

The washout part is an easy one to explain but the real mystery is that number 1.843 degrees. It requires a very long winded discussion and at some point this winter might deserve a thread all by itself. It's the most misrepresented number when it comes to rigging and at some point it would be nice to have everyone understanding where that number came from and what it really means.

Take Care - Jerry
 
If you are going to set your washout with a digital level the difference between the butt rib and the outer aileron bay rib is - 2 degrees.

Good Luck - Jerry



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What is the source of these numbers? Does anyone really believe that Piper specified angles to 0.001 degree on anything they ever built? What is the use of such a specification without an associated tolerance?
 
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