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Keller (Perfromance) Flap question. Needing more tension some how??

Aktahoe

Aktahoe

Registered User
Truckee, Alaska
Anyone here running the Keller (Performance) flaps? There is not enough tension in the flaps to keep them up, not to mention keep them flapping when on the ground in the wind. Yes, just park it into the wind but thats not a real solution. Adding a spring will only create more unwanted tension in the handle. The cables are tight.

Another issue we have addressed is the need for scuff tape at the bottom seem on the backside where they come apart to extend. Scuff tape and baby powder seems to work until they wear in a bit but the excess sag in the flap is a concern. In all positions there is slack to the extent that Im concerned when in flight 10 and 20 degrees won't really have flap extension due to how loose they are. Anyone have this experience?

AKT
 
I used two flap retract springs on my build which holds the flaps up in the shop, will be a while before it flys. The retro fit aircraft are doing the same with two flap and was recommended to me for my build.
LiteCub
 
The problem surfaced very early on my project. Bare wings had droopy flaps even with three springs attached. Coincidentally the flap cable tension was alarmingly high. My spring setup included a single spring and another pair of springs attached to a single bridle cable. All the springs pulled perpendicular to the short leg of the bell crank in the attached photo. It would work better if the springs were attached to the front spar and pulled on the long bell crank arm from the front (where you see the flap rod attached). Tahoe already knows that I elected to use a flap return system like in a Cessna instead of bungee springs. My flaps lock in the up position so the thumb button must be depressed to pull flaps on. The pair of springs on the bridle have been removed. My cable tension is down from 110# to <80#. You can see some more pics on the flap cable tension page on my build site.

Coincidentally, a stock piper flap bell crank has equal length legs. My Keller flaps are 9'2" and have a deeper chord than stock Piper so it isn't unreasonable to find that the stock operating system is being overwhelmed. Lengthening one leg on the bell crank exacerbates it. Adding springs isn't the ideal solution in my opinion. But that's all it is, an opinion. Loving the experimental category!
 

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I notice that you have the long flaps. My Backcountry has the same length flaps. The wings came with two flap actuation bellcranks which are tied together with a short cable. There is a spring on each for a total of two springs per wing. They do the job. Maybe the Kellers are heavier? In flight the long flaps require more muscle to extend to maximum deflection, which required me to lengthen the flap handle for extra leverage.

I used this tape between the flap and trailing edge of the wing: https://www.aircraftspruce.com/catalog/cspages/teflonantichafetape.php?clickkey=491290
 
Hello Aktahoe,

Your flaps are longer and deeper in cord than the standard Piper OEM size flap. Holding bigger, longer, deeper cord flaps up is a problem regardless of which style flap used. The simple Piper style flap deployment system is not closed loop like the Cessna style and was not really intended for bigger, heavier flaps. With that said, it is easy to remedy, all you have to do is add more spring tension. You can do this by a few different methods: add pre-load to your existing spring(s), add more springs, use stiffer spring(s). The more spring tension the harder it will be to pull the flaps down in flight. There is not a safety issue with the flaps drooping when on the ground, air loads will retract them. I realize that it is undesirable, but all these modified bigger flaps extend beyond the original Piper flap deployment design concept and suffer that same consequences.

The double slotted flap system we are working on to get STCed (we are almost done by the way) utilizes the original Piper flap return springs just like the OEM flaps. What I am trying to say is the droopy flaps are not particular to the double slotted flaps, the same problem exists with over sized Piper style plain flaps. The double slotted flaps are slightly heavier than the OEM style flaps witch does add a little to the problem.

I can’t really comment on what flap return springs Back Country uses, they might not be stiff enough. I don’t know what Back Country uses for flap bell crank(s), they appear to have less mechanical advantage than the Piper style, I know they use different flap hangers. There could be other factors involved that I am not aware of in your particular installation.

Thanks,
Doug
 
Doug, any idea on time frame for getting them STC'd? I realize you're dealing with the FAA, but any guesses? Looking forward to them being stc'd. Good job!
 
The more spring tension the harder it will be to pull the flaps down in flight.
Click to expand...

Assuming that the spring tension is just enough to positively counter the flap weight, wouldn't the force to overcome the spring still be small compared to aerodynamic loading, and therefore not be really noticeable?
 
If 150# of spring force is insignificant to you? Yes. The bigger question is how the aggregate tension from the springs and the air pressure load the system that was designed for much shorter, smaller chord, smaller total area flaps. The inability of the springs to hold the flaps is a symptom of a bigger issue. Maybe not as much with stock wing replacement flaps as it is with our 9'+ deep chord flaps on the Backcountry wings using Backcountry brackets. This thread is already mixing Kevin and my big flaps with single stage Backcountry flaps and stock replacement Performance STOL flaps. The three are not equal.

And to be clear, the Backcountry wing option for Keller flaps uses Doug's flaps only. The hangars and return strings are by Backcountry. This is not Performance STOL's problem to fix. And that isn't meant to pin it on Backcountry, either. It's just the evolution of cool parts and the users having to learn as we go.
 
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If 150# of spring force is insignificant to you? Yes.
Click to expand...
I have no idea what the required spring force is, but I looked at a set of Keller flaps last weekend and if 150# is required it's on a mighty short lever arm. Still, those flaps aren't made of cast iron:lol:, but they're BIG, so the aero forces have to be significantly greater than the static force required to hold them up. I have no idea what the actuating force on the flap handle might have to be. I do know that in my -12, I pull the first notch holding very close to the handle fulcrum, and it's no big deal. Second (last) notch is a different story, but still not at all difficult. I have standard -18 flaps, extended a few inches to the fuselage per the Crosswinds STC.

I bet the actuating mechanism could be designed such that the mechanical advantage is low for small flap deflections, and larger for full flaps?

Respectfully - - -
 
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I have 94" Keller flaps on my cub with stock bell crank I use a little stronger spring and had to preload it to 22lbs to hold up the flap...the handle forces are no more then a stock cub and I have no issues... yes they move a little when taxiing on rougher stuff and if you need to park with the wind on your back just pull a little flap on.
 
If I pull 40* flaps in a Cessna I know I have 40* flaps out whether I'm parked or flying at 90mph. With my Backcountry flaps pulled to my third notch my aft flap surface is at 70*. What will it be in flight? That will depend on how fast I'm going. My flap control mod solved the droop. There's more to the problem than droop.
 
maybe cessna style tracks are the answer...

then the weight of the flap is held in the up position by the track grove alignment, not just by the cable tension....(also the force when down is on the track grove, not all on the cable system..)

would think since cessna have 2 groves to move one piece, you might need an extra grove to make the second piece follow along...??

just thinking out loud....
 
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No, the simple system's effective limits have been exceeded. Tahoe asked how to hold the flaps up but also referred to the inability of the control system to hold the flaps when deployed. That you don't have that problem with your single stage flaps does not make our problem less real.

My cable tension concerns have nothing to do with flap handle operation. I can pull the flap handle just fine. The problem is more akin to trying to remove a Caterpillar axle bolt using a 1/4" ratchet and a 3' cheater bar.
 
I have standard cord double slotted flaps 110" long and two Piper springs (1 is heavy duty and the other is the stock spring) and my flaps stay up good. All the original bell cranks were used in the stock location. I have extended the arm on the flap handle by 1" were it rotates around the pivot point. I am not getting as many degrees as I would like with the stock bell crank and I am going to machine new bell cranks to further deploy the flaps. Right now I get about 55 degrees full flaps on the ground and in the air I would guess that it drops to around 50 degrees.

I do have a problem with spring interference that needs to be addressed also when flaps are fully deployed. I would rather fly then work on the airplane so it has been this way since October

Greg
 
Hello RaisedByWolves,

We are getting close. All we have left to do is the static structural test. It is our hope that we will have the structural testing done within the next 2 months at which point we should have the STC.

Since we do not have PMA we will need to get that prior to being able to sell any certified flaps. My best guess at this point in time is that we should be ready to sell certified flaps by the first of the year.

Thanks for the interest,
Doug
 
ksecub said:
Hello RaisedByWolves,

We are getting close. All we have left to do is the static structural test. It is our hope that we will have the structural testing done within the next 2 months at which point we should have the STC.

Since we do not have PMA we will need to get that prior to being able to sell any certified flaps. My best guess at this point in time is that we should be ready to sell certified flaps by the first of the year.

Thanks for the interest,
Doug
Click to expand...



Great job! Thanks.
 
On our SQ2 it wasn't the staying retracted at static, it was how much they would actually stay down on approach that was the problem. As soon as your flyin the air will push the flaps up. On the ground at full flaps it would look like its a set of barn doors hanging down, yet even at a 30mph or less approach speed they were barely deployed. We had to add a lot of spring tension to fix this. Then we had to brace the stock sq2 flap handle as it bent going into full flaps at 25-30 mph.
Was it worth it? Well now we can come in on final with the airspeed not even registering and still be flying. So I'm going to say yes.
Do I like the extra effort to have to pull them on? Hell no! Though with the current rigging design it's the only way to keep them down and actually doing their job on final.
For those doubting the few extra degrees making a difference, try adding more spring and do a couple approaches. These flaps combined with the SQ2 slats are incredible. No longer now do I have to have a huge angle of attack to slow down my over the fence speed.
I can have a steep perfect nose down approach while still safety coming in at slower then airspeed readable speeds. No more hanging on the prop trying to look over the side of the nose.
Love the flaps, very much dislike the rigging set up. Would love to somehow have a system that only used springs to retract not deploy the flaps.
That if they were in full flap position they would be down as much as they are on the ground at static.
We still aren't there, but I don't want to add any more stress or spring tension.


Sent from my iPhone using Tapatalk
 
Springs don't do anything but pull my flaps up, and not very well. If I was starting over I'd convert to an overhead flap handle with push rods and get rid of cables. I believe that's what Cubcrafters does in Carbon Cubs but I've never seen it.
 
I forget how the rigging is inside our wings but it was too loose of springs that would cause the airflow to push our flaps back up on approach. We have zero cable slack as well.
Yea rods would be way better.


Sent from my iPhone using Tapatalk
 
If you have springs pulling your flaps down, your system is totally different than any that I have seen or heard of. Certainly not a Piper or Cessna design. Springs pull flaps up and cables pull them down or as in a Cessna up as well.
 
I checked out Jay's uncovered Cub that he had in the Javron booth. I played pulling his flaps full down with my hand on the trailing edge, they returned fully retracted every time. I asked Jay why everyone was complaining about the spring tension being to soft. He chuckled and showed me an extension that he added to the bell crank giving the spring a little more leverage.

Glenn
 
cubdriver2 said:
I checked out Jay's uncovered Cub that he had in the Javron booth. I played pulling his flaps full down with my hand on the trailing edge, they returned fully retracted every time. I asked Jay why everyone was complaining about the spring tension being to soft. He chuckled and showed me an extension that he added to the bell crank giving the spring a little more leverage.

Glenn
Click to expand...

Wish he would share that with backcountry or Kellar.



Sent from my iPhone using Tapatalk
 
skywagon8a said:
If you have springs pulling your flaps down, your system is totally different than any that I have seen or heard of. Certainly not a Piper or Cessna design. Springs pull flaps up and cables pull them down or as in a Cessna up as well.
Click to expand...

We have cables yes. The inside the cockpit set up rigging is all stock cub stuff I believe. The cables do pull the flaps on and springs pull them back.
For whatever reason with how backcountry first set up our flaps the cables would let the flaps be pushed up on approach. I wasn't in the hangar the day my old man changed things. I just got there and he said go try this. Then they worked. I was assuming it was a spring change because of how much harder you have to pull to put them on now?...
Or maybe the springs are only on the return side and now the cable pre-tension is so tight we needed the extra stiff springs to stop them from being pulled down on their own?... I don't know ill have to pull off some inspection covers and look.
All I know is the used to be pushed almost all the way retracted by the air on approach.
Now they are still pushed up some, but at least they are actually doing their job when I pull them on.




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