Flap return springs

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Flap return springs

Postby danerazz » Sun Jun 15, 2014 1:31 pm

I have not particularly liked the standard highlander flap return spring setup. I am in the process of building a fixture to wind a custom double-torsion spring that will mount on the center flap hinge using a longer bolt and bushings. The spring will be external to the wing.

I did a quickie hand-wound, single coil spring with no heat treating and it is just about strong enough to work. I had calculated a double coil after heat treating would work, and this pretty much confirms it.

I'll post here when everything is done and tested.
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Re: Flap return springs

Postby danerazz » Thu Jun 19, 2014 10:03 pm

Here is what I have come up with so far. May have to adjust preload to get a nice tight "up" position after covering/paint. Springs are made of .078" music wire, then when fully formed heat treated at 500* for 30 minutes. I will be installing bushings on both sides of the hinge so the spring won't be riding directly on the bolt, and will be retained by washers. The bolt-washer-bushing-hinge stack-bushing-washer group will be tightened as normally intended. I have not yet received the bushing stock. Also, since I don't have the cable attached right now the flap is "reflexed" up quite a bit, the spring/leading edge clearance is fine when the flap is in a normal "up" position, not as tight as what it looks like in the picture.

So far I think it will work great.
Attachments
image.jpg
Winding tool
image.jpg
Spring formed
image.jpg
Flap spring
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Re: Flap return springs

Postby warlev » Fri Jun 20, 2014 2:03 am

Dane: That is very clever. Do you suppose you could supply a set for me? It seems that your solution solves the flap return problem perfectly. Warren
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Re: Flap return springs

Postby danerazz » Fri Jun 20, 2014 12:38 pm

warlev wrote:Dane: That is very clever. Do you suppose you could supply a set for me? It seems that your solution solves the flap return problem perfectly. Warren


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Re: Flap return springs

Postby kenryan » Fri Jun 20, 2014 12:49 pm

The SuperSTOL flap handle has been redesigned to provide for more leverage, presumably because the large flaps require a lot of force to deploy. Will this aggravate that condition?
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Re: Flap return springs

Postby danerazz » Fri Jun 20, 2014 5:13 pm

No, these will only work on the standard highlander and I am pretty sure the escapade. I am not familiar with how the SS flap return works.
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Re: Flap return springs

Postby danerazz » Tue Jun 24, 2014 8:26 pm

Here is the completed installation. Parts are:

4 AN970 washers
2 3/16" x 1/2" bushings (I cut a 3/4" one in half and that is what is in the picture, but they are just a little short and the spring is pinched. Use two bushings and just cut them down)
1 AN3-16A bolt (A -15 bolt is in the picture, but if when I put the longer bushings in it will be too short)
1 nylon lock nut
1 custom spring

It seems to work great, but time will tell.
Attachments
image.jpg
Spring installed
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Re: Flap return springs

Postby Trilander Ted » Tue Jun 24, 2014 8:49 pm

Looks Great; When can we buy a pair??? You already developed the tooling, all we need is the "trick" spring.
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Re: Flap return springs

Postby danerazz » Tue Jun 24, 2014 10:12 pm

I am just finalizing the bushings and making sure they are the right size, and I sent a pair to warelev to evaluate. If all goes well I'll make some up for a (ahem) nominal fee. I'm guessing about $10 a pair to cover the wire, heat treating, packaging and shipping.
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Re: Flap return springs

Postby bluemax » Tue Jun 24, 2014 11:04 pm

danerazz wrote:If all goes well I'll make some up for a (ahem) nominal fee. I'm guessing about $10 a pair to cover the wire, heat treating, packaging and shipping.


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Re: Flap return springs

Postby jak » Wed Jun 25, 2014 5:14 am

I'll take a pair when your up and running with production just let me know how and when to pay. Jak
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Re: Flap return springs

Postby RV6 » Wed Jun 25, 2014 6:41 am

Put me in for a set toooooo!
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Re: Flap return springs

Postby danerazz » Wed Jun 25, 2014 7:25 am

Hmm...I wasn't expecting much of a demand. I may remake part of my fixture to make things a little easier. I really would like to see how they hold up on a flying airplane before I go outfitting everybody with them. I am considering putting bushings, bolts, washers and the springs together as a ready-to-go package, though the price would be a little more. I am looking for the right size bushings so I do t have to cut them.

Playing with the static installation in my shop I have found that if one side of the spring becomes disconnected (as if it broke for some reason) the remaining side will not quite get the flap back up, but only let's the flap droop a bit. This means the plane should still be flyable, though I don't know how likely a break is. They seem pretty durable. Also, I tested by pulling the flap ALL THE WAY down until it was stopped by the bell crank hitting the bottom of the wing (as in a strong gust of wind while parked) which is WAY past any normal flap travel. This did SLIGHTLY deform the spring (I had to remove it and place it next to another one to compare) but didn't seem to affect the operation.

I really want to make sure these will hold up well before I send a bunch of sets out and then later find out they only work ten times or something unforeseen like that. I don't think it will take too much time before I can get to this point (especially if I can get some feedback from early adopters).

Give me a couple of weeks to refine things to a production standard and I'll start making a bunch of them.
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Re: Flap return springs

Postby Trilander Ted » Wed Jun 25, 2014 11:33 am

I plan to install them along with the original coil return spring remaining connected, hoping they will eliminate wind powered "blowdown" when I fold back the wings or set on the ramp. My flaps have always worked properly except for that, so I hope they won't overpower the flap handle.
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Re: Flap return springs

Postby SheepdogRD » Wed Jun 25, 2014 11:40 am

I like this "clothespin" spring idea. I also think significant testing is necessary before it's widely adopted.

One of the issues all along has been gusting winds knocking the flaps down to their maximum travel and overstressing the springs. Gust damage can be avoided when parked by using gust locks, but gusts can still hit when taxiing downwind. After a while, the flaps get droopy because the springs can no longer hold them up; then we need to replace the springs. The system that Steve Dentz installed uses longer springs that can withstanding gust loads because gust overtravel is within the capability of the longer springs. In your design, perhaps more coils would better handle gusting, though more coils might require smaller wire and a longer bolt.

I think your pricing is too low. If your springs are a viable solution, they save a whole lot of installation pain, and they eliminate holes in the wing trailing edges and the flap leading edges. Best of all, they're far easier to replace than the stock springs. Those are significant savings, and worth much more than $10. It might be instructive to go to a spring fabricator and get a quote on 25 and 100 sets of springs.

Any expense beyond the cost of making them just for yourself -- your time and cost to buy material, wind springs, heat treat, ship and administer sales -- should be included in the price. You need to have enough payback in the price that it isn't going to be frustrating to take time away from your build -- or your flying -- to be in the spring business. I'd bet Highlander owners who have replaced their overstretched standard springs would tell you that 25 bucks and 25 minutes is a terrific deal for that job.

Even better, perhaps the factory will test the idea, like it, and make Dane-O-Matic springs the new standard.
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