Super Cub Flap Adjustment

Yeah - I know - 50 degrees, plus or minus 2 degrees. When the aircraft came out of Alaska it was set for 60 degrees, and that was a delightful, if out-of-bounds setting.

Went to Cub Crafters for new wings, and came out with flaps set right around 42 degrees. Cables were so loose back there that I thought they were in danger of jumping out of the pulleys. Set them at the extreme high end of legal (read: lots closer to the Alaska value than some might) and all was happiness.

Aircraft again visited CC - flaps now at 48 and 46. First notch does nothing except take up cable slack, second brings them down maybe to five degrees.

So now I am worried - does CC know something about flaps that I don't? Is 50 degrees dangerous in some way? The thing flies just fine at 60 degrees, and is docile, if a bit shorter in the landing rollout.

Give me some of your opinions - are those slack cables back there a problem? If 46 is ok, why not 54?

And prop indexing - 180 Cub?

Anybody know of a reason for bolting the prop on so that hand propping cannot be done from the float? We have a brand new Lyc O-360, and the prop is on so that the compression stroke is 60 degrees higher than usual - or vertical, pretty much. Anybody aware of some rationale - dynamic balance, or just to prevent hand starting?

Bob,

I always rig for max deflection. I remove all the slack from both cables so that the flaps are still on the stops. This is the only way you will achieve max flap deflection, unless you grind another notch. As soon as you move the handle the flaps should start to move. If someone was dead set on 50 degrees or some other #. I would rig them like I said then hold them at 50 and mark the ratchet. Weld up the last notch and grind a new notch at the 50 mark on the ratchet. Every pilot I have asked is dead set on max deflection.

As far as deflection, the flaps are designed to balance in flight, if you get different degrees add them and divide by two that is what they will be in flight.

50 could be dangerous if you needed 60 or more to make the strip.

The props I have seen that were not indexed right (for hand proping) is because who ever installed them forgot to index them.

As far as prop indexing goes, I can't see how it would affect balance assuming the engine and prop are properly balanced as individual units (static balance). From a dynamic standpoint, I can't see how the prop knows or cares how it's "clocked" relative to the engine. I've always put mine wherever they're easiest to hand start, and never had a vibration issue.

All of my mechanics do it Alaska Style. Horizontal when the engine stops, in case of a forced engine out landing the prop is in its highest clear position without operator input.

akbhm said:

All of my mechanics do it Alaska Style. Horizontal when the engine stops, in case of a forced engine out landing the prop is in its highest clear position without operator input.

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I've never heard that! My prop stops at 10:00/4:00 viewed from the front. Every Cub I know is the same way. The 3-blade on the Cessna stops at different positions every time, but the 12 is always 10 and 4.

Stewart

I would think Alaska style would be where it is easiest to hand start from behind - you guys have more engine failures than battery failures up there? I have had two engine failures, but the number of hand starts I have done are countless.

My real question was about the 180 HP conversion - any of you have such a conversion, with prop indexed as above, for a real reason?

I am going to re-rig the flaps - unless somebody tells me that slack in the cables is a good thing safety wise.

akbhm said:

All of my mechanics do it Alaska Style. Horizontal when the engine stops, in case of a forced engine out landing the prop is in its highest clear position without operator input.

Click to expand...

I have not seen this either. It would make it difficult to prop start from behind and real easy to walk into the tip and get a nice hatchet mark in your forehead.

Jerry

No offense to akbhm, but the last thing I would be worried about on an engine out landing is damaging a prop because it wasn't horizontal. And like Cubflier said, it would make it really difficult to prop start. 10 and 4 is the only only way to go in my opinion.

slightly off topic... univar made some flap latch plates with the notches... but they didn't make them right/long enough, the bent over part at the end was actually part of the flat part... heck i can't say it right... but you physically could not get 50 deg.... too short

that was 10 years ago hopefully it's been fixed or bad batch or not sure what i ran into, wrong part????? just remember lots of head scratching....

I kinda like fabmans idea with taking the slack out, but making the last notch 50... but travel beyond that.... technically legal i think.........

The 180 hp with a constant speed prop is indexed 12 and 6 o'clock via the bushings only allowing the prop to be installed that way. I index the props on O-320s on down so that you can hand prop them and no vibration. I have had a vibration when they were misindexed and re-indexing it took care of the problem. It is in some Cessna manuals but I haven't found it in any Piper information.

I flew an extended wing/extended flap 180 hp Smith Cub the other night. Pulled on the flaps and I was getting a shudder. I played with power and it made no difference. looked back and the flaps were bouncing all over the place. Dumped them and my shudder went away. Got on the ground and found that the cables were way loose. Have to re-rig and fly again to see what happens.

Steve,

That's a Husky thing, reference the prop indexing. And, in fact, it is possible and legal to re-index those props to 10 and 4 as Stewart has described. We did that on the Huskys I flew.

The O-360 engines have some vibration issues--big pistons and not many of them--but the notion that they run smoother with the prop indexed at 12/6 certainly does NOT trump the fact that if you HAVE to hand prop the thing, you definitely want the prop at 10/4.

The Top Cub we have here (O-360, fixed pitch) has the prop indexed at 10/4.

Horizontal prop is "Alaska Style"??? :lol:

I'll take a prop I can spin by hand from behind any day, thank you.

I haven't met one of these things yet (including a new TC) that didn't require that at some point.

MTV

Steve - one more input before I try re-indexing: This engine is a hollow crank model designed to take a C/S prop. It has a fixed Borer on there now. Should I even start? I figure with this big prop way up in the air I will have to rig a crane to catch it when it pops loose - you are on the way to saving me much useless effort.

Mike - it is just as illegal to be less than 48 as it is to be more than 52? I have flown a number of Cubs that seem to have the C-152 flap philosophy - less is better. I subscribe to that only on climbout.

Bob:

I have a hollow crank engine, and when I ran a Borer prop it was indexed at 10 and 4. No problems at all.

Eric