Adjustable LO Guides in sheet tips?

[Target]

Gents-

I am looking for a lightweight way to mount an adjustable lead out fence into a sheet tip. I'd like to not have to counter with gobs of weight in the tip box outboard, if I can help it.
I have some of my own thoughts, but I need not re-invent the wheel, and your experience trumps mine I'm sure.

The plane that I am working on is an Umland Magician .35, but lots of older planes have 1/8" sheet tips with gussets, so this has to be fairly common.

Pics appreciated and, they are worth 1,000 words anyhow.

Thanks in advance all.

R,
Target

[Dave Hull]

Have you considered replacing the inboard tip with three layers of balsa? Core layer is cut away for leadout clearance, and sandwiched by a layer on either side, say 3/32" balsa. The guide plate can be glued to the outboard rib. This is a pretty common approach. I'll try to post a picture.

One thing worth mentioning is that it helps to line the inside of the leadout passage with tissue or something similar for a bit of extra durability. If you doped down some silkspan before you glue up the sandwich, then you have fuelproofed and reinforce it at the same time.

This type of tip is pretty lightweight--the adjustable guide might be the heavier piece of the whole arrangement--so you are not going to need gobs of additional tip weight.

Dave

[Bill Morell]

I line mine with 1/64 ply. Holds up better than tissue.

[Dave Hull]

Here's another view during construction. The guide is homemade. It has brass eyelets. I like to use marks on the guide for reference when I use a transparent covering material because you can note where it was and where you moved it to.

I have used 1/64th plywood to line the inside of the tip for durability on some planes--for example a Shoestring used for Formula Unlimited racing. I agree with Bill that it works very well.

Dave

[Target]

I like both of those ideas, gents.
Thanks for the added picture, Dave.

Has anyone tried a laminated strip tip, with gussets added?
Would that be strong enough, and would it be lighter?
 
R,
Target

[Dave Hull]

You could laminate the tip. I am picturing say, three strips wrapped around a tip form, laminated with 50% thinned Titebond. (I have laminated LEs and TEs this way and it works great. Good open time, lots of adhesion and amazing little weight after it dries. If the strips are tall relative to their combined thickness, the height of the tip is going to increase compared to a flat 1/8 tip. So with this design approach, I would chuck the plywood plate leadout device and go to the moveable eyelets, a la Gieseke. If movable eyelets work good enough for a world champ, then....

This approach might save some weight, but it all depends on how you design and build it. I would probably laminate up the gussets as well to give more uniform strength.

Let us know how yours turns out,

Dave

PS--I also made up one tip with the passage lined with carbon vail. Didn't really like it, so I didn't use it. It would have worked ok, but.....

[Steve Helmick]

Having used both style adjustable leadouts, IMO, the eyelet-type is better for a couple of reasons, tho there are also potential problems. If the eyelets come out in flight, things get squirrelly for sure, and you may or may not know where to put them back...unless you use a marker or something to put a dot on the bottom of the tip. Or keep a logbook that tells you where they should be for various conditions. If they get loose, a wee bit of paper towel is the approved way to tighten the eyelets. If the tip/slot/holes aren't properly built, you may have continual problems with this.

The slider-type at first looks more precise, but when buried in the tip like most are, it's really pretty tough to move it to exactly where you want. A track plate made from CF plate seems like a good idea to me, coupled with a slick Delrin slider (or two sliders). The problem with the typical plywood track is that the washers make imprints that prevent movement from one position to another. Heavier, too, requiring more tipweight, so double whammy. If you use this type leadout guide, mount the thing solidly, and not on the 6 lb balsa tip rib! It is NO fun to have a flight with the LO guide broken loose and zigging back & forth as you try to fly, wondering what the devil is going on with your plane!!  Steve

[Gary Dowler]

Here's another view during construction. The guide is homemade. It has brass eyelets. I like to use marks on the guide for reference when I use a transparent covering material because you can note where it was and where you moved it to.

I have used 1/64th plywood to line the inside of the tip for durability on some planes--for example a Shoestring used for Formula Unlimited racing. I agree with Bill that it works very well.

Dave

Dave, great pic.  Can you show how you do the covering over the tip on that set up??

Gary

[Target]

That part is easy, Gary, if you use cable vs the solids. Is that why you are asking?

[Gary Dowler]

That part is easy, Gary, if you use cable vs the solids. Is that why you are asking?

The adjustable guide is well inside the wing, I see well enough how this is set up, but I'm curious how thecovering is done given that the guide is a couple inches back behind the covering.

Gary

[Dave Hull]

If I understand your question correctly, Gary, you are asking how to pull the covering around the tip if the solid leadouts are in the way?

That has been pretty much a non-problem for me. The main panel covering is left long, and tacked down everywhere around the panel perimeter. Then I start heating and stretching the part that is overhanging the tip. Try to do the stretching evenly--some going toward the back and some toward the front. Otherwise you end up with too much stretching required, usually at the LE. (That is because the back looks pretty good right away, so you are tempted to seal it down good, only to realize that the front isn't going to stretch tight with no wrinkles. Been there, done that!) There is always more stretching required at the front due to the thickness of the airfoil there, so don't work just from the back forward.

As you get it worked down, you can slit the covering almost up to the leadout wire, and then start pulling the covering down, perpendicular to the wing. The leadouts are left loose, and with the guide inset pretty far, even the solid .032" leadouts will easily move back and forth and get out of your way. So you will only need one slit. It is not any harder than doing a tip like this than with stranded cable leadouts.

For use with a nylon bellcrank, installing solid leadouts is very easy, and done right, very, very strong.

I hope this is what you were asking.

As far as the plywood guide not being as adjustable as you might imagine because it hangs up in one spot due to compression by the washer, I minimize that by using no-fooling 5-ply birch plywood. Once I have cut and slotted it, I soak both the edges and the faces with thin CyA. The guide needs to be a close sliding fit, but should not hang up anywhere in the useful range. That will give you trouble sliding it back and forth. (Stick, slip, jump, repeat....)  I use a fairly large flat washer, and I install it with the rolled edge in contact with the wood.*  I also resist the temptation to apply ungowa torque to the screw. It doesn't really need it. But all of these versions have worked, so pick one and go for it.

Dave

* --Washers are stamped out in a press using a die and punch. The punch rolls over the top edge where it enters the sheet. Somewhere around 60% of the way thru the sheet, the metal tears and the slug drops out. So one side of a washer is smooth with rounded edges and the other side is sharper, and may even be a bit ragged if you get a cheap commercial batch. There is no reason not to take advantage of this "feature." You can get washers without this manufacturing characteristic. Look for either precision washers or shaft spacers.

Dave

[Target]

With that style slotted tip, and stranded lead outs, I left the leads long, and unterminated, and tucked the bitter ends back into the tip. Then I covered the wing, then cut a slit in the middle of the covering over the slot, and rolled the covering into the slit with a trim iron.
The cables were then fished out and the eyelets wrapped on.
That is both easier and harder than the solids, because they aren't even in the way on covering, but terminating them outside the plane was a bitch for me.
R,
Target

[Target]

Uhh, ungowa, David's got the powah! 

Sorry, I couldn't resist that one!!


Dave-
Are the solids on par weight wise with the cables?

[Gary Dowler]

With that style slotted tip, and stranded lead outs, I left the leads long, and unterminated, and tucked the bitter ends back into the tip. Then I covered the wing, then cut a slit in the middle of the covering over the slot, and rolled the covering into the slit with a trim iron.
The cables were then fished out and the eyelets wrapped on.
That is both easier and harder than the solids, because they aren't even in the way on covering, but terminating them outside the plane was a bitch for me.
R,
Target

That answers my question in a way my brain understood.

Thanks

Gary

[Dave Hull]

You can look at this two ways:

1. Compare .027 1x7 stranded steel cable to .031 solid music wire. The music wire is both bigger, and does not have the voids in it that make cable lighter for a given diameter. For a Nobler-sized plane if you assume you need 33" of wire (including the terminations) the stranded cable weighs 0.14 oz and the solids weigh 0.23 oz. for a set. But for pure tensile loads, the solids are way stronger than the 125 lb yield rating for the cable. So....

2. Reduce the diameter of the solid wire until you attain about the same strength as the cable, and then compare the weight. This gets you to approximately .021" diameter music wire, and the weight for that set of leadouts is about 0.103 oz. So for equivalent tensile load capacity in new condition, and assuming the terminations are adequate to carry full load (ie. the wire breaks before the termination lets go) the reduced diameter solid is actually lighter. This has to do with the fact that true music wire (high carbon 1080 steel) is drawn and work hardened to high strength levels, and the smaller the diameter, the more it is cold worked and the higher the yield strength. Any size in our range is higher than stainless cable strands. (Stainless cables we are using are typically 300-series austenitic steels.)

With the solids, I would go with the larger size (.031" diameter) just for the durability of the part poking out of the wing. Be aware that the highest stresses are actually going to be in the bends around the bellcrank, if everything else is done right. By done right, I mean use teardrop shaped loops on both ends, and do not overheat the wire when soldering. An iron is not a problem, but never use a torch. You will almost inevitably take the metal above the temperature that will anneal it. And now your safety factor is completely gone. I would not go below the .031" diameter without a few calculations and some tests.

The weight penalty of using solids of a robust diameter is just 2.51 grams as compared to the stranded cable for this very typical example....

Hope this info helps,

Dave

[Brent Williams]

Tensile loads aside...Solid leadouts get banged up and bent much easier.  That is reason enough to stay away from them.  Carry on.

[Target]

OK, the solids look a lot bigger in the picture than .032"
Thanks for the explanation, Dave.

Because of my smallish car and the way that my planes get handled, I think I better heed the warning that Brent had, except for maybe 1/2A planes that are smaller and can be more easily transported in smaller cars.

Thanks guys.

R,
Target

[Dave Hull]

This is sort of a high wing/low wing (Cessna/Piper) kind of argument. Guys will have valid reasons why they prefer one over the other.

In terms of bending leadouts from handling, transportation and storage, I always worry a lot more about putting holes in the covering, whether it is silkspan, polyspan, or MonoKote. I suppose adding one more item that could get damaged is a pretty good argument against solid leadouts for those that have that issue. Small cars and jammed storage rooms help that idea along pretty good.

The leadouts in the photos are of a Super Slow Rat racing plane (kind of a Shoestring-like plane) and are actually .039" diameter. They just look big due to the single lighting source and cast shadow from my amateur photography....

Wire it up and geet 'er dun,

Dave

[Akihiro Danjo]

This is my Magician with an independent LO guide from Brodak.

Aki

[Target]

Thanks a lot, Akihiro!

That looks like a good solution. I really like that the LO is closer to the actual tip of the plane. And I think that some folks might not realize that the Magician tip is nearly 4" from the tip rib, it extends quite a way out. However, I also wonder about the strength of not mounting it to the tip rib. That being said, this is more along the lines of what I was thinking about placement wise in the wide tip of the Magician.

Has this plane been flown a lot, so that this method is well tested?
Also, I see that you bridged the top and bottom tip balsa that the guides run through. Do you think that this is absolutely required? It seems like it kind of shortens the full range fore and aft of the LO's.
I guess once the LO position is tuned, one could then add in a bridge between the top and bottom tip outer pieces between the two wires, and start with it open completely for adjustment first. What are your thoughts on that?
Great pics, by the way, thanks again!

R,
Target

[L0U CRANE]

Only difference... I 'face' the surface between the upper and lower "sheet" pieces with 1/32" or 1/64" ply for a better resistance to marring from the lines beyond the guides when the plane is not 'flat' to the lines. That DOES happen, only when we least want it.

Murphy's second  law: Murphy was an optimist.

[Target]

Thanks Lou, that was mentioned earlier, and I will definitely do that.

[Akihiro Danjo]

>Has this plane been flown a lot, so that this method is well tested?

I took these pictures last night and of course my Magician has not flown yet. But, I have already built and flown many models that have the same method, so it is already tested by them.

>Also, I see that you bridged the top and bottom tip balsa that the guides run through. Do you think that this is absolutely required? It seems like it kind of shortens the full range fore and aft of the LO's.

I bridged them because the LO wires would not need to move fully fwd nor aft. I guess the slide range of each separated wires will be enough and , as a result, the wing spar does not need to be cut a slot for wires.

Excuse my bad English, Aki

[Target]

Aki, thank you.
Your English is great, no problem.
I understand that the bridge in the slot is an extension of the spar, that makes good sense.
I appreciate your reply very much. Good luck with your Magician.
Many great flights for you i hope.
Regards,
Target