# Flight Club - Ultralight Build Log

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#### maya.ayoub.32

##### Active Member
Glider Criteria has scheme for load testing ribs....but that alone will not ensure the safety of the wing. To make prototypes of the, tail feathers, wing, landing gear, fuselage etc means essentially just building it and then load testing it, which if you have not calculations could be a frustrating experience. If you have faithfully copied elements of another aircraft as regard to tube size, gusset size, number of rivets, spar cap and depth, wing attach fittings landing gear attach and fittings you might be successful.......you will still have to understand loading of the structure....how much sand where...just to load test it.....As to aerodynamics and tail blocking....that is another can of worms, and again if you have faithfully copied the platform of a successful aircraft and your weight and balance, rigging and power is correct I would think it would fly as well as that other aircraft.
Awesome! Just checked the Glider Criteria and wow it gives a complete in depth explanation of everything we need to do to successfully load test the ribs, thank you for that informative resource. We did not faithfully follow basically any design to be honest, our plane is Frankenstein's monster in terms of bits of other planes. For example, much of the tubing was inaccurate to what we needed as it was steel with the purpose of welding, however ours is aluminum and a gusseted plane. However as you said it will be very worth it to do all the calculations before prototyping or constructing anything, so we’re currently in a physics phase. Now that you mention it, it would be informative to analyze the parent designs and compare it to the numbers we get after all our changes, just for confirmation that we didn’t sabotage our plane while making a multitude of revisions. We’re still pretty new to physics, so if you have any helpful loading resources we’d love to check them out as well! Thanks!

#### Rudy Lee

##### Member
Looking great, but why the fixed gear?
Actually, it isn't fixed gear! If you take a close look at the gusset at the very bottom, there's a slot in which the axle tube fits. We will wrap a bungee around the tube on both sides of the gusset to have suspension. This was inspired by Graham Lee's model.

#### proppastie

##### Well-Known Member
Log Member
Frati "The Glider" and Glider Criteria.....I used Glider Criteria for tail feathers, boom, control surfaces, spoiler....Frati for wing loading......simple platform area method.

#### maya.ayoub.32

##### Active Member
I would like to make a design suggestion for the purpose of reducing risk and being conservative.

The side view of the aircraft shows that the vast majority of the rudder and vertical fin area are above the horizontal stabilizer. At very high angles of attack (in the stall and post-stall range), this creates an increased chance of "blanking out" the vertical tail... meaning that the stabilizer blocks or prevents strong clean airflow to the vertical tail. This can drastically reduce the aircraft natural restorative/corrective force on the yaw axis.

Which in plain English means you could have an airplane that has a lot of trouble recovering from an accidental spin.

Now there are plenty of airplanes that can recover from a spin and still have a "low tail" like yours. That would eventually be determined and verified in flight testing, using a trained test pilot.

So I am not saying that your low tail is a guarantee of unsafe spin characteristics, but I am saying it is very well known that having a larger percentage of fin/rudder/side fuselage area under the tail moves you toward safety in spin resistance/recovery instead of away from it.

So if you have the opportuity to perform a revision of the rear fuselage that puts more vertical side area under the stabilizer/elevator, I would say that's good design practice and worth doing.
Thank you for bringing this to our attention! Although the majority of us are planning on getting our pilot’s license, we won’t have the experience or skills necessary to control an ultralight aircraft with accidental spin characteristics without great stress and fear of crashing.

Following your suggestions is definitely the best way to go for all parties, so we’ll look into how to revise the tail section of our plane! We’ll look into the force and movement necessary of the rudder to determine its optimal size and work on redrafting the empennage accordingly, to place the horizontal stabilizer near the middle of the vertical stabilizers.

We'll post an updated version soon!

#### maya.ayoub.32

##### Active Member
I'm sure other designs use that specific hinge setup but I'm not a huge fan of it. I'd rather see the tabs curl around the tube so that you get a better distribution of loads and your pivoting is happening on the hinge pin and not flexing on the rivet axis at all.
That can be made from a section of 4130 tube with a tab welded to it. Welding thinwall tubing is a great skill to know....look at the beautiful welds of Little Scrapper if you want to see art.
An external, or internal, sleeve, riveted in place and drilled for an I-bolt would be easy.

BJC
Have you gotten into details of how you are going to mount the elevators, rudder, etc...? If so, I'm wondering what you are using for hinges. Is there a good COTS source for control hinges to use on Ultralights? Does anyone know of a supply for something like this that's made to be riveted to a 1" aluminum tube?

We were looking at the EMG-6's aileron hinges, and they use an I-bolt and a fork bolt as their hinge which we were so impressed by! We are going on adapting these for our tail design instead of the current tail hinges in the CAD, but looks like we didn't update it yet. It uses all aerospace grade bolts and is proven to work through their successful flights.
We're also going to look into using this type of attachment for the ailerons as well since it would be quite simple.
Good to know that we should be using a riveted sleeve as well! We're looking into sleeves for the sprar-strut attachment point for extra support, so we will definitely do the calculations for sleeve necessity and sizing on the tail as well.

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#### maya.ayoub.32

##### Active Member
CGS Hawk used a hollow 1" dia fiberglass rod. Easy to replace if damaged and a solid rod was available but with additional weight. You want the landing gear to fail before the primary structure is damaged and repairs should be easy. Others use aluminum. When the aluminum strut yields it would be reversed and the next hard landing bends it back into shape.

I like the glass. Solid rod was replaced free if ever broken. Never had a claim. I thought I would get one free after an elevator control failure. The gear leg was one of the few parts that were undamaged after partially controlled flight into an open field. The gear absorbed much of the crash G load.
What an incredibly strong gear! We'll keep in mind the order of failing for sure. A few of our team mates read through the "Landing gear Design for Light Aircraft" Manual and after strong deliberation between the cub style and whitman style landing gear (with carbon fiber), we stumbled upon the Nuiman plane's landing gear which seemed like a great combination of both. More pictures and information can be found here.
However, we have yet to do the hard core calculations on this design, so we will definitely keep your information about carbon fiber in mind if we end up going back to Whitman style landing gear!

#### maya.ayoub.32

##### Active Member
Flat glass truss/leaf springs are employed on some recumbent cycles and trike aircraft. I recall seeing an ultralight with glass gear struts stung across the bottom with elestic.
That is very interesting! It's almost like a gas spring but adapted for a dampening of the force affect. We will definitely keep it in mind if we have to change our landing gear design. Thank you!

#### maya.ayoub.32

##### Active Member
McMaster-Carr

Structural FRP Fiberglass Round Tubes

5 ft. Lg.10 ft. Lg.
1/8" Wall Thick. (-0.0400" to 0.0400")
ODOD ToleranceIDStraightness
Tolerance
EachEach
1"-0.04" to 0.04"3/4"0.03” per ft.8535K71$18.858535K21$32.70
Thank you for the fiberglass round tubing information! We're thinking of locally sources most of our tubing, however we have yet to do research on carbon fiber vendors so we'll definitely have this in mind if we end up using whitman style landing gear. Thanks again!

#### maya.ayoub.32

##### Active Member
I'm sure other designs use that specific hinge setup but I'm not a huge fan of it. I'd rather see the tabs curl around the tube so that you get a better distribution of loads and your pivoting is happening on the hinge pin and not flexing on the rivet axis at all.
Thanks for whipping something up for us! Sorry for not giving an update on our hinge designs quicker! We did more research on hinges and were thinking of using eye and fork bolts for the tail because it's aerospace grade and proven to work by the EMG-6.
However, many of our attachments are a flat plate attached to our circular tubing, so it would definitely be worth it on some of the biggest weight bearing attachments to implement a circular attachment for more contact spots. We'll keep this as a solution when we inevitably come across an attachment that needs to be stronger! Thank you!

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#### maya.ayoub.32

##### Active Member
Frati "The Glider" and Glider Criteria.....I used Glider Criteria for tail feathers, boom, control surfaces, spoiler....Frati for wing loading......simple platform area method.
Sounds like it's a must read! Thank you for posting the link, it looks like a plathora of useful physics, design, and construction tips that I can't wait to read through and get advice from!

#### Victor Bravo

##### Well-Known Member
If you use the EMG-6 method of eye and fork bolts through the tubes, please remember it is very appropriate to have a block or support inside the tubes, so that tightening the nuts on the eye/forks will not crush the aluminum tubes. You will definitely need to tighten the nuts to some reasonable degree, and those nuts are very capable of crushing the tube. So a wood, plastic, or aluminum block of some sort inside the tube is appropriate.

The other type of welded hinges that were suggested will not require this, and are simply pop-riveted into position. I believe it is worth the extra effort/cost to have a bunch of these little hinges welded. You can CNC cut the bolt lugs, and use a simple chop saw to cut lengths of the tube section, and then run the tube section lengthwise through the band saw, yielding two hinges.

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#### David L. Downey

##### Active Member
HBA Supporter
Sorry for my late reply (I must have missed the notifications on this thread somehow). We are currently planning on using a torque tube to hinge our ailerons and some L shaped pieces of sheet metal to hinge our elevator and rudder. We were cautioned that riveting anything to a circular beam would be difficult but I've seen numerous instances where this L bracket method is successfully employed and it seems pretty simple and more resistant to binding than piano hinges. We'll just have to be extra careful to make sure the hinges are level when we install them.

Note that our current wing design has the torque tube running almost the entire span of the wing which will not be case in the final version. The torque tube will just extend a bit past the ribs adjacent to the ailerons and will be controlled through cables running the length of the wing support struts rather than at the connection point to the cabin.

All of our aileron control questions can be found in the HBA thread Dana linked.

Don't hesitate to let us know if you've got any more questions!

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others have already mentioned the use of eyebolts throught the spar tubes in this applicaiton. Pros: relatively low impact on stresses, simple, robust, durable (especially if the eyebolts are lined with flanged polymer bushings). cons: expensive

#### Mavigogun

##### Well-Known Member
cons: expensive
Polymer bushings aren’t all that expensive, quantity considered- nor bolts -and spar or other related structure already requisite... so, where do you see remarkable cost?

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#### BJC

##### Well-Known Member
HBA Supporter
20 each AN42 bolts would be needed for the ailerons, elevators and rudder. Total cost would be in the $200 to$300 range, depending on the sizes selected.

Edit. Just looking around, it looks like some may be available for about half of the above.

BJC

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#### jedi

##### Well-Known Member
Thank you for bringing this to our attention! Although the majority of us are planning on getting our pilot’s license, we won’t have the experience or skills necessary to control an ultralight aircraft with accidental spin characteristics without great stress and fear of crashing.

Following your suggestions is definitely the best way to go for all parties, so we’ll look into how to revise the tail section of our plane! We’ll look into the force and movement necessary of the rudder to determine its optimal size and work on redrafting the empennage accordingly, to place the horizontal stabilizer near the middle of the vertical stabilizers.

We'll post an updated version soon!
Many ultralights skimp on tail volume and it shows. Please design on the high side of the typical range. It will improve performance and handling and the aircraft will accept growth (increased GW, power, cabin size, etc.) more gracefully.

#### Ollie Krause

##### Well-Known Member
I would like to make a design suggestion for the purpose of reducing risk and being conservative.

The side view of the aircraft shows that the vast majority of the rudder and vertical fin area are above the horizontal stabilizer. At very high angles of attack (in the stall and post-stall range), this creates an increased chance of "blanking out" the vertical tail... meaning that the stabilizer blocks or prevents strong clean airflow to the vertical tail. This can drastically reduce the aircraft natural restorative/corrective force on the yaw axis.

Which in plain English means you could have an airplane that has a lot of trouble recovering from an accidental spin.

Now there are plenty of airplanes that can recover from a spin and still have a "low tail" like yours. That would eventually be determined and verified in flight testing, using a trained test pilot.

So I am not saying that your low tail is a guarantee of unsafe spin characteristics, but I am saying it is very well known that having a larger percentage of fin/rudder/side fuselage area under the tail moves you toward safety in spin resistance/recovery instead of away from it.

So if you have the opportuity to perform a revision of the rear fuselage that puts more vertical side area under the stabilizer/elevator, I would say that's good design practice and worth doing.
Thanks for the insightful advice! We totally didn't take this into consideration. Upon closer inspection, one of our textbooks actually has an entire section on this so I'll go ahead and study that to determine the exact amount of rudder that should be below the horizontal stabilizer.

#### jedi

##### Well-Known Member
Reference Ultralight: Non aircraft methods are required to keep weight and cost down.

Use model aircraft (as in not typical man carrying aircraft) methods. An updated version of the cover hinge or plastic flexible hinge should be attempted. VB help out here. I could see wire ties in a figure eight around the tubes which would require holes in the cover. Replace the wire ties with a heavy cord or leather shoe lace or best use a webbing strap bonded from upper leading surface to lower trailing surface and vice versa. Light strong and no need for a gap seal. Don't forget to make the rear tube slightly larger than the leading tube and the webbing/wire ties make a good vortex generator. Just a suggestion but you can always revise the design as necessary as weight and operations in service require.

Such revisions should not take you out of the Ultralight certification once flying.

#### Ollie Krause

##### Well-Known Member
Reference Ultralight: Non aircraft methods are required to keep weight and cost down.

Use model aircraft (as in not typical man carrying aircraft) methods. An updated version of the cover hinge or plastic flexible hinge should be attempted. VB help out here. I could see wire ties in a figure eight around the tubes which would require holes in the cover. Replace the wire ties with a heavy cord or leather shoe lace or best use a webbing strap bonded from upper leading surface to lower trailing surface and vice versa. Light strong and no need for a gap seal. Don't forget to make the rear tube slightly larger than the leading tube and the webbing/wire ties make a good vortex generator. Just a suggestion but you can always revise the design as necessary as weight and operations in service require.

Such revisions should not take you out of the Ultralight certification once flying.
I'm not quite sure I understand the design you're describing. Do you have any examples you could refer us to (model or full size)?

#### Ollie Krause

##### Well-Known Member
Many ultralights skimp on tail volume and it shows. Please design on the high side of the typical range. It will improve performance and handling and the aircraft will accept growth (increased GW, power, cabin size, etc.) more gracefully.
Yep yep I'll let our physics team know. They've already done some calculations to determine the tail size but we'll go ahead and compare it to some existing ultralights to see where we stand. If needed, we'll scale them up.

#### proppastie

##### Well-Known Member
Log Member
Just remember the camel was a horse designed by committee.....I would not use flexible hinge, wire ties, or leather straps for anything structural (like control surface hinges)....If you look at Glider Criteria the chart on tail loading you will see the larger the tail the larger the proof limit load, so understanding how much tail you need is more than that looks about right.....

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