Elevator balancing for tube and fabric tail

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Eugene

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What do you mean "approval"?

Billski
I am using pictures to get a feel of what is a good idea to do and what is not a good idea to do. By "approval" I was looking for response like "yes it is a good direction and it's OK to go that way". Some of your messages I have to read 10 times before it makes sense to me. So, I'm using my pictures. And really appreciate any input you can give me. Thank you!
 

Eugene

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I am trying very hard to create mental picture in my head to go with this 2 messages from this morning. Not successful so far. I was thinking about it at work, but without any kind of results. Can someone here help me to understand or provide some kind of picture. Thank you.
 

Eugene

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Sorry, that didn't help. Where is attachment points on my airplane would be? Are we attaching two tubes to the wings after all? And using one on the bottom? So old tail boom will work as bottom tube?
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poormansairforce

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I am trying very hard to create mental picture in my head to go with this 2 messages from this morning. Not successful so far. I was thinking about it at work, but without any kind of results. Can someone here help me to understand or provide some kind of picture. Thank you.
He was referring to something like a Quicksilver Sprint etc.
 

Eugene

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In my mind I was trying to show something similar with my PVC pipes. I was looking for professional opinion, but nobody liked it. Always in the back of my mind I have a little hope to find solution that will work not only for me, but for the rest of Skyboy community . About 100 of them flying around the world. Something relatively easy that anybody can install, like was easy for me to install 2 support cables. But I understand if there is no easy solution, then I need to go to plan B or C. Whatever it takes.
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Eugene

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I am learning that better way to do mass balancing is inside the fuselage internal or external just like on picture below. This way you don't have any twisting moments on fabric elevator.

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wsimpso1

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I am trying very hard to create mental picture in my head to go with this 2 messages from this morning. Not successful so far. I was thinking about it at work, but without any kind of results. Can someone here help me to understand or provide some kind of picture. Thank you.
So was I...

I was trying to show how both the sheet metal aft fuselage with some longerons and the fabric covered tube fuselage can be transformed into an open three tube fuselage. You showed us one that actually struck me as the right way to solve your problem of needing a light and stiff way to support the a tail having more tail volume than you currently have without shifting CG aft a bunch. It has the additional advantage of requiring little in the way of new education to analyze and check as you iterate the design.

The trouble I have with your illustration of a couple PVC pipes laid on your current airplane is that two tubes are most likely too small and one tube is massively oversize for their respective jobs. It is a three tube, just an awful one.

Most likely, the bottom tube must be a little bigger than the two upper ones, but much smaller and lighter than the current one. The lightest way is likely to include a triad of jury struts tying all three together at mid length. The lowest drag way may be a slightly larger set of tubes with no jury struts, or it may include the jury strut set. You will only know by doing a little bit of self educating with help from us, then setting up the analysis and iterating each of the designs until they are both strong enough and stiff enough.

Billski
 

Eugene

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So was I...
It is a three tube, just an awful one.



Billski
Thank you for not giving up on me.

From what I understand general direction is good?

- I do understand that upper tubes diameter will need to be determined. That will change with tail arm I will decide to go with as well. Calculations, if I ever learn how to do that, will show us what kind of tubes I will need to use.

- about existing tail pipe that is oversized and too heavy. Inside of this tail boom is push - pool elevator control rod. It is supported inside in few places with special rollers. It's already there and tail surfaces attached to it. I can make old tail boom lighter by drilling many openings. This is only idea.

- some kind of aft fiberglass cowling will needs to be made anyway to prevent flow separation and cleanup air that's feeding horizontal tail. Thank you very similar to my form right now. So, old tail boom with many drilled holes will be covered anyway.

Not really trying to talk my way out of doing anything. Just wanna make sure that there is not easy and elegant solution to this Aircraft before I spend a lot of time and money to get maybe only 5 miles an hour faster. This project is really not about speed at all.

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wsimpso1

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Sorry, that didn't help. Where is attachment points on my airplane would be? Are we attaching two tubes to the wings after all? And using one on the bottom? So old tail boom will work as bottom tube?
Attachment points would likely be underneath the engine for one tube and either the main spars or the drag spars for the other two. For the as-built design, the current tube is both heavy and not long enough and not stiff enough. For any new design it is grossly oversize and high drag and not long enough. Yes, I would deign a new scheme that eventually removes the existing tube from under the engine on aft.

The photo is a very nice example of a traditional tube fuselage without a cover. Not a bad starting point, remarkably light but with the tubes spread out to your proportions (wing drag spar attachement and beneath the engine) and the prop blowing through it all, it will be kind of draggy. The low drag way is likely to be somewhat larger longerons and removing all but three brace tubes running between longerons. Miholland came up with a remarkably simple fun little bird.

Billski
 

wsimpso1

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I am learning that better way to do mass balancing is inside the fuselage internal or external just like on picture below. This way you don't have any twisting moments on fabric elevator.

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I do not like any of these very much.

"External mass balance" is also an aerobalance horn, very useful if the control feel was too heavy. This does allow you to put the balance mass on the middle (spanwise) of the control surface if the surface is not strong enough (and/or stiff enough) to hang the mass at the end. This is also rather high drag;

"Weights ahead of hinge line is done, but since the arms are short, masses added to balance must be high. An additional down side is that control surface travel must be kept small the keep the mass inside the surrounding structure;

"Mass balance inside the fuselage or fin" is used as Pops said in the Cherokees. You have to set aside room inside for this, and it must clear all of the strucure, control runs, etc. It becomes a bit of balancing act to fit it all inside. The longer the arm, the less it can weigh. This could be great if you go the long hard expensive way of educating your engineer in composites, tooling up a new aft fuselage, and building it. It will be a poor way to go if you come up with an open three tube aft fuselage because you will have no "inside" to put the mass.

Frankly, imitating the previous horizontal tail design, and maybe bumping the tubing one size for the added area and prop blast, sounds like the way to go. If you get concerned about drag, making a simple foam and fiberglass fairing that attaches to the stabilizer and puts the balance horn in its wind shadow is easy and light. Look at any elevator equipped Cessna... It is simple, light, works great.

Billski


Weights ahead of the hinge line
 

wsimpso1

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I am not sure what you are illustrating here. A couple possibilities occur to me. One is a triangular cross section (three longerons with intercostals and diagonals, sort of like that Legal Eagle), the other is is just is just a big tube above and smaller one below with intercostals and diagonals.

First, any design that leaves that big heavy tube that is too flexible and not long enough or strong enough just plain offends this engineer's sense of good...

Make it a three longeron steel tube or aluminum tube fuselage ( and remove the big tube) and it can work. Problem is where to hang the two bottom tubes. The top one would attach under the engine, but you may have very little distance vertically and horizontally between the big tube and the others, making the loads pretty high in the other two tubes and driving their size and weight up. The further apart the three attach points, the lighter it can be.

Now if you are illustrating a new lower longeron under a longeron in place of the current big tube it will likely be too soft and weak to side loads from the vertical tail. If instead, you leave the current big tube and just add this underneath it, you can make the tail stiffer and stronger, but you will shift weight aft significantly, and we really do not want to move the CG much if you can avoid it.

All sorts of downsides can come in to things when you make CG changes, then sweep the wings more to compensate. Dihedral effect, roll behaviour, roll stability, stall speed, roll-yaw coupling (Dutch Roll), the list goes on and on. The best solution is bigger tail surfaces a little further aft, stiffly supported, without gaining weight and without shifting CG. Which is why I keep going back to that instead of the elegant but time consuming, flight time losing, and expensive new composite back end.

Billski
 

wsimpso1

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Thank you for not giving up on me.
I am hoping someone else can benefit from this as well.

From what I understand general direction is good?
Which scheme are you talking about? Three tube aft fuselage looks worthy of a little educating and iterating to see what it would take.

- I do understand that upper tubes diameter will need to be determined. That will change with tail arm I will decide to go with as well. Calculations, if I ever learn how to do that, will show us what kind of tubes I will need to use.
I doubt it. I STRONGLY suspect that you can make the tail arm longer and keep weight down simultaneously with the mounting points spread apart.

- about existing tail pipe that is oversized and too heavy. Inside of this tail boom is push - pool elevator control rod. It is supported inside in few places with special rollers. It's already there and tail surfaces attached to it. I can make old tail boom lighter by drilling many openings. This is only idea.
With an open truss, you have several possible schemes for the control puss-pull rod - keep in mind that extending the tail a little means doing this bit of engineering again as the lengths will be longer. You will need to work out the rod loads with the bigger elevator:
  • You can use the same size tube (or maybe the next one up will be needed) and same location rollers by putting a jury strut set between the longerons at those locations, and hang the roller sets on the jury struts. Kind of ugly and draggy;
  • You can work out a one piece pushrod at that new push load. Might be kind of big but it is aerodynamically cleaner;
  • You can support the one pushrod with rollers at midspan (within a jury strut set at midlength) or actually break the tube into two pieces with an idler at midlength, both allowing some reduction n tube size over one long tube supported at each end only.
- some kind of aft fiberglass cowling will needs to be made anyway to prevent flow separation and cleanup air that's feeding horizontal tail.
I doubt it. The current one is likely fine with a little attention to making sure the whole prop disc is "wetted" with flow.

So, old tail boom with many drilled holes will be covered anyway.
I was hoping to remove it from the airplane....

Not really trying to talk my way out of doing anything. Just wanna make sure that there is not easy and elegant solution to this Aircraft before I spend a lot of time and money to get maybe only 5 miles an hour faster. This project is really not about speed at all.
There are easy ways and elegant ways, rarely simultaneously. I think the three tube truss is the least inelegant way of doing it easy. Other reasons to investigate the designs of an open three tube truss and a new boom steel tube boom is these can be modest cost and minimum interruption of flying... The composite solution will interrupt flying for a long time and may be costly indeed.

Billski
 

Eugene

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I was talking to designer of this airplane in Russia. He was telling me that 3- tube structure is turned out to be pretty flimsy. On top of everything else they end up using many cables to stop tail from side-to-side motions. He was telling me this is not very good idea to go this way. He claims that aircraft turns into very draggy machine because of that and he call it "flying farm".

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