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BBerson

Light Plane Philosopher
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Port Townsend WA
The excellent Lazair ultralight used 1" (?) foam ribs capped with with thin aluminum formed channels bonded and strapped around the rib with strapping tape. I suppose they used epoxy or something. I would try the foam that comes in a can at Home Depot and costs $3.84 a can. The foam comes out frothy and weak. But stir the froth and it gets very thick and gooey and sticks to everything. Then wrap with strapping tape.
 

Justin Tien-Smith

New Member
Joined
May 2, 2020
Messages
3
Hello! My name is Justin Tien-Smith, and I’m working to build an ultralight airplane with Flight Club. My peers and I have a few questions about control surfaces after reading a chapter entitled “Miscellaneous Design Notes” from the General Aviation Aircraft Design: Applied Methods and Procedures. We have the preliminary designs for our airplane complete, but we want to make sure the math and physics behind all of our design choices check out before we start construction. Here are our questions:

  1. Control surface hinge moments → The chapter says that in addition to the size of control surfaces, the location of the hinge moment is going to affect our plane’s maneuverability. Prior to reading the chapter, we were planning on doing the “original” configuration as shown below in figure D, however, we were wondering: What exactly are the pros and cons for each configuration? Does anyone have good resources to check out? Our current understanding is that special configurations like Frise ailerons can reduce adverse yaw, but we were wondering if someone could lend an informed perspective on the handling of the other types.

  1. Control surface sizing → Given that control surface size is dependent on many factors, the chapter didn’t have one equation to best determine the control surface dimensions we need. Does anyone have any advice or resources on determining control surface size? We aren’t trying to create a high-performance airplane, but rather, something that feels safe and predictable.
  2. Control system harmony → Another concept that came up in the textbook was control system harmony. The textbook explains it by saying the amount of effort it takes to move the aileron, elevator, rudder is in a ratio that is 1:2:4. It didn’t specify very well what “effort” meant, and since we are using foot pedals to move our rudder, we were a little confused about how to quantify the effort of moving the rudder compared to the aileron and elevator. Is this a familiar concept to anyone? How would the “effort” change based on the different types of control system (pulley or control rod)
  3. Control system jamming → The textbook had a brief section describing the importance of addressing possible scenarios for control system jamming, however, there were no examples. Does anyone have any specific (or common) scenarios we should account for or advice on ways to avoid these scenarios? We’ve already had in-depth discussions on hinge binding earlier in this thread and in our wing thread but there may be some things involving the control system itself that we could be overlooking.

If you have any recommendations on books or research material to better understand any of the concepts above, that would be greatly appreciated. Thank you all so much for the support!
 

Aerowerx

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5,567
Location
Marion, Ohio
IIRC, "effort" refers to the amount of force in pounds required to move the controls, as felt by the pilot.

I don't have them right in front of me, but there are Mil Specs that cover the questions you ask. Perhaps some other member knows what Mil Spec they are.

As far as jamming...There was a case several years ago where Team MiniMax lost a pilot. He went on a test flight in November IIRC. The plane had been stored in a heated hanger. Because it was an ultralight the FCC did not investigate, but conjecture is that some moisture had condensed inside the Teleflex cables, and then froze when he was in the air.

Just did a quick search. I don't know if they will answer your specific questions, but you might want to check out MIL-F-8785c and MIL-STD-1797A .
 

jedi

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Joined
Aug 8, 2009
Messages
2,116
Location
Sahuarita Arizona, Renton Washington, USA
Thank you for all the great insights! Would you be able to provide some photos or drawings of these two methods? I remember reading about them in some other thread but I was still a little confused on how exactly they worked. What would their primary benefits be over the plywood capped foam ribs we're currently planning on using? Also, just to make sure we're both on the same page, could you provide some links to the white and blue foams you're talking about? Thanks again for all for all of the help!
It has taken a while but as I was digging in long term storage and found some old material scraps. I will post photos in multiple posts when I can get them uploaded. Working on it.

Material is a high density styrofoam. If I remember correctly it is 3 pounds per cubic feet.
These samples were cut from a 4 ft by 8 foot by 4 inch block (again from memory).

First photo is a rough surface caused by too high of hot wire cut rate. The second photo is the surface when cut at the proper wire cut rate.

The material was cut 3/8 inch thick as shown in the last photo.

Other cuts in sections as thin as 0.1 inches were made. More photos will follow in additional posts or edits to this post.

E4B80F9E-F831-466E-999D-DD47C2351F5A.jpeg

0851296E-B879-4F92-A05B-8F579D6B7BD3.jpegF8CC0AB7-6AC3-4FC3-B664-6BDD2252CEA6.jpeg

The following photo is the same foam material with a tensile film bonded to the convex surface for bending as for an airfoil leading edge. I used tyvek for my surfaces but this was done with clear packing tape for convenience.

D3C818BF-B788-4534-9633-1179A687BCEF.jpeg
 
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jedi

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Messages
2,116
Location
Sahuarita Arizona, Renton Washington, USA
These photos are of the same material as shown in post # 164 that has been cut to sections 0.1 inch thick.

I would like to try a thin foam sheet covered with Orotex or with a thin single layer of ply wood or glass composite.
 

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Ollie Krause

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Joined
Feb 26, 2020
Messages
96
It has taken a while but as I was digging in long term storage and found some old material scraps. I will post photos in multiple posts when I can get them uploaded. Working on it.

Material is a high density styrofoam. If I remember correctly it is 3 pounds per cubic feet.
These samples were cut from a 4 ft by 8 foot by 4 inch block (again from memory).

First photo is a rough surface caused by too high of hot wire cut rate. The second photo is the surface when cut at the proper wire cut rate.

The material was cut 3/8 inch thick as shown in the last photo.

Other cuts in sections as thin as 0.1 inches were made. More photos will follow in additional posts or edits to this post.

View attachment 98781

View attachment 98782View attachment 98783

The following photo is the same foam material with a tensile film bonded to the convex surface for bending as for an airfoil leading edge. I used tyvek for my surfaces but this was done with clear packing tape for convenience.

View attachment 98786
Wow those cuts are really impressive. That foam looks really flexible though. Did you need to heat it to take that shape or does it naturally bend? I would have major rigidity concerns if it could bend naturally like that. If it is naturally flexible like that, I assume you're covering all surfaces with plywood or some composite material rather than just a cap strip, correct? I'm pretty sure most composite sandwiches utilize a rigid foam core but it would be interesting to see how something more flexible but more durable would hold up. At the moment, we're only considering using a fiberglass cap strip instead of a plywood one since we've already confirmed that a cap strip design will be sufficiently strong for our purposes.
 

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jedi

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Joined
Aug 8, 2009
Messages
2,116
Location
Sahuarita Arizona, Renton Washington, USA
Wow those cuts are really impressive. That foam looks really flexible though. Did you need to heat it to take that shape or does it naturally bend? ............
It is rigid foam like you would get from a big box store. When cut in thin sheets it is of course more flexible but as stiff as a styrofoam model airplane. It is somewhat similar to balsa wood but without the bidirectional properties. It is the same as a foam packing material but is not the bead board although it is the same chemical material.

There is no heat in bending. The trick, if you call it that, is to bond a good tensil strength film to the outside of the bend radius so that the foam yields in compression and takes a permanent set.

I will try to attach some more photos of the wire cuts, etc. The prior photos do show the limit of the acceptable bends.

Self supporting 3/8 inch x 2.5 inch Sheet supported on 12 inch centers.58F1E61D-CAA8-454B-B320-DEA2D65C6ED2.jpeg
 
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jedi

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Joined
Aug 8, 2009
Messages
2,116
Location
Sahuarita Arizona, Renton Washington, USA
Man, calibrated butter sticks. Not quite my favorite spread for foam.
The test weights are recycled at the end of the shift and used to increase the weight of the foam structure of a revolutionary biodegradable material called pop-corn, not to be confused with pop-porn as spell check will occasionally do.

Note: The biodegradable material can be converted while viewing a wide variety of material at the discression of the lead engineer. This post will automatically self destruct as soon as it is discovered by the site administers, I hope!
 

radfordc

Well-Known Member
Joined
Feb 5, 2008
Messages
1,388
Hello! My name is Justin Tien-Smith, and I’m working to build an ultralight airplane with Flight Club. My peers and I have a few questions about control surfaces after reading a chapter entitled “Miscellaneous Design Notes” from the General Aviation Aircraft Design: Applied Methods and Procedures. We have the preliminary designs for our airplane complete, but we want to make sure the math and physics behind all of our design choices check out before we start construction. Here are our questions:

  1. Control surface hinge moments → The chapter says that in addition to the size of control surfaces, the location of the hinge moment is going to affect our plane’s maneuverability. Prior to reading the chapter, we were planning on doing the “original” configuration as shown below in figure D, however, we were wondering: What exactly are the pros and cons for each configuration? Does anyone have good resources to check out? Our current understanding is that special configurations like Frise ailerons can reduce adverse yaw, but we were wondering if someone could lend an informed perspective on the handling of the other types.

  1. Control surface sizing → Given that control surface size is dependent on many factors, the chapter didn’t have one equation to best determine the control surface dimensions we need. Does anyone have any advice or resources on determining control surface size? We aren’t trying to create a high-performance airplane, but rather, something that feels safe and predictable.
  2. Control system harmony → Another concept that came up in the textbook was control system harmony. The textbook explains it by saying the amount of effort it takes to move the aileron, elevator, rudder is in a ratio that is 1:2:4. It didn’t specify very well what “effort” meant, and since we are using foot pedals to move our rudder, we were a little confused about how to quantify the effort of moving the rudder compared to the aileron and elevator. Is this a familiar concept to anyone? How would the “effort” change based on the different types of control system (pulley or control rod)
  3. Control system jamming → The textbook had a brief section describing the importance of addressing possible scenarios for control system jamming, however, there were no examples. Does anyone have any specific (or common) scenarios we should account for or advice on ways to avoid these scenarios? We’ve already had in-depth discussions on hinge binding earlier in this thread and in our wing thread but there may be some things involving the control system itself that we could be overlooking.

If you have any recommendations on books or research material to better understand any of the concepts above, that would be greatly appreciated. Thank you all so much for the support!
Good for you for doing the research and asking valid questions.

First, as a practical matter control hinge moments on an ultralight are generally very small and the simplest method will be more than adequate. If the choice is a simple, lightweight hinge system that isn't optimum as far as hinge moment is concerned or a more complex, heavier system with better numbers, you should always go with the simplest, lightest method. There is a story that Burt Rutan was quoted as saying that when building an aircraft part he would throw it in the air and if it fell back to earth it was still a little bit too heavy.

Control harmony is important to having a plane that "feels" right while flying. Having a control that is too sensitive or not sensitive enough detracts from the overall flying qualities. The numbers quoted have proven to work in many different types of aircraft. "Effort" is the force required to move a surface a given amount. Changing from a pulley system to a push rod should not affect the effort required to move the surface as long as there isn't a lot of drag built into the system.

Control jamming is extremely important. Having a control either lock up or become disconnected is often enough to cause a crash. Examples: where cables bend around a pulley there must be a device that holds the cable in place so that it can't fall off the pulley; ensure that parts of the plane can't shift and bind the controls (this happened to me when the bracket holding the seat back broke and the seat fell against the aileron linkage locking it solid, luckily the ailerons were in neutral when this happened and I flew the plane using rudder to turn); control horns/control surfaces should have stops that prevent them from moving beyond their full throw position and possibly becoming jammed in an overcenter position; all hinge pins and bolts/nuts that are subject to rotation must have cotter pins or safety wire to ensure that they stay in place.
 

TFF

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Joined
Apr 28, 2010
Messages
13,013
Location
Memphis, TN
Ailerons overcentering on early Acroduster Toos was a problem. Lock them solid. No stops were originally designed in for weight savings. Without stops have over stressed rod bearings and other parts in the control system too.

As for the biodegradable weights turned into topping, make sure no one shreds the foam slabs to look similar to your consumable material. Looking similar and even sometimes sounding similar might be the prank corn of the year.
 

Justin Tien-Smith

New Member
Joined
May 2, 2020
Messages
3
Howdy Home Built Airplane Enthusiasts,

First and foremost, thank you all so much for helping out with our project. At the moment, we have a few questions regarding how to best join the tubes on our plane. Here’s some context to our questions:

Based on all of your prior suggestions and some of our initial research, we opted to design a gusseted aluminum truss frame. Over the course of our gusset endeavor, however, we have run into several issues regarding how to come up with appropriate solutions for certain joints, especially the joints on our empennage. A couple months ago, we thought we solved all our gusset problems, but we’ve recently encountered some more, which we can’t seem to find solutions to.

We are struggling with several gussets on our empennage, and below is an example of our upper empennage gusset, it utilizes our double gusset technique, but the rivets are dangerously close to the edge of the gussets on the inside (violating the 2*diameter tearout rule). Since the rivets must be installed normal to the gusset and must be tangent to the circular beam, we are unable to move them further inward. We were originally planning to just use a single gusset on the outside of the tubes like the popular Nieuport replicas but some of our members who participate in FIRST robotics think a single gusset won’t be rigid enough.




Something else to mention is that we attempted analyzing our fuselage truss and were unable to figure out the complex math due to use having many indeterminate structures. Five members of our team watched and took notes on the first 50-60 statics videos from Jeff Hanson, which were super helpful but still weren’t enough to be able to fully solve our frame. We did, however, manage to determine the stress in the most critical beams (eg: empennage longerons, wing spars, etc…). Since we don’t know how to determine the exact stresses in every beam, we have been using many arbitrary dimensions on the gussets we are designing. We don’t know if we need single gussets, double gussets, or how much of each gusset needs to be in contact with the tubing. We also don’t know if filleting our gussets makes sense to save weight or if it will compromise structural integrity. Our gusset design decisions have been based on similar ultralight airplanes that use gussets and on the few stresses that we are certain we know. We want to be certain each of the gussets we are designing meets its necessary strength requirement.

An alternative to a gusseted circular aluminum truss frame would be a welded 4130 steel truss frame like the Legal Eagle uses. We’ve created a comparison between the two, but feel free to let us know if we left anything out:

Gusseted 6061 T6 AluminumWelded 4130 Steel
More home shop friendly in the sense that it doesn’t require a TIG welder or a level welding table. Some people also have an unusually strong aversion to welding for some reason...MUCH quicker to construct (probably about a full week based on what we’ve heard from similar designs)
Potentially lighter since 6061 T6 has a higher strength/weight ratio of 410,260 lbf*in/lb, while 4130 Steel is only 222,180 lbf*in/lbSignificantly cheaper.
If done properly, it will likely be stronger since the 1x0.035” aluminum will have a higher column buckling strength than the ⅝x0.035” 4130 steel. The gussets may also create a more rigid frame. Additionally, we eliminate the risk of all welding related issues, which may compromise the strength of any joint.Significantly simpler. By using a welded frame, we’d remove about a hundred gussets and thousands of rivets from the BOM.
Eliminates complex coping (requires expensive tools to be done precisely). If we had a welded frame, we could easily weld on more safety parts, like tangs, gussets, or other attachment material.
Removes the need to use arbitrary dimensions for the guests and rivets.

We have a professional welding mentor who has offered to help us weld the frame but the average home builder does not.

All that said, what are your thoughts on our current gusset solution? Can anyone think of a better one? Does anyone have thoughts on a single vs. double gusset design? Should we switch from circular aluminum tubing to square aluminum tubing to make putting gussets on easier? Or should we change our truss frame material to 4130 steel so we can weld it more easily?

Thanks,
Flight Club Design and Physics Teams
 

Aerowerx

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Joined
Dec 1, 2011
Messages
5,567
Location
Marion, Ohio
Why do you have that gusset on the inside of the cluster (the one I think you said was the problem)? I don't see the need for it. Isn't the longeron one continuous tube?

Of course others with more expertise than I will probably give their 10 cents worth.

Edit: Never mind I see why, I think.
 

BBerson

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Dec 16, 2007
Messages
13,224
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Port Townsend WA
Looks like a problem getting your pop rivet gun in the inside gusset space to pull a rivet.
I have years trying to find a better system than gussets/welding.
 

radfordc

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Joined
Feb 5, 2008
Messages
1,388
OK, I like the way you're showing off your CAD skills, but there is such a think as "over engineered". Tube and gusset is a very good method of building a small airplane. My Eindecker is a good example of how T&G can be done. Each joint is just a circle of aluminum sheet wrapped around the joint and riveted in place. No need for multiple inside and outside gussets.5503075002_1bc724f742_o.jpg
 

Justin Tien-Smith

New Member
Joined
May 2, 2020
Messages
3
OK, I like the way you're showing off your CAD skills, but there is such a think as "over engineered". Tube and gusset is a very good method of building a small airplane. My Eindecker is a good example of how T&G can be done. Each joint is just a circle of aluminum sheet wrapped around the joint and riveted in place. No need for multiple inside and outside gussets.View attachment 99240
Three questions:
1) What's the thickness of your tubing and the gussets?
2) What alloy is the aluminum you used?
3) What type of rivets did you use?
 
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