# "SkyWing" hybrid wing body ultralight

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#### Victor Bravo

##### Well-Known Member
HBA Supporter
OK, I'll play.

First, I do NOT know how to stress test your wings, or anyone's wings. There are several people here who know how to do it, some of whom have done it professionally. The mathematics and engineering are way above my level of education.

But I am a world class expert who does know why to test them. I can do that calculation as well as any engineer on this planet, and I can say without a doubt it saves you a lot of money on funeral costs. Remember the guy who had to put Sonny Corleone back together after that toll booth incident, so Don Vito could have an open casket at the funeral? I happen to know how much his services cost, and trust me it's more than you want your family to get the bill for.

And I do happen to have enough experience with experimental airplanes to know when and where cheap is acceptable and is not acceptable. Cheap is always acceptable in a few places on experimental airplanes, it is never acceptable in a few other areas, and it is maybe acceptable in some other places only if you determine each case individually. My point is that one of the areas where it is almost always "never acceptable" is in primary structure.

So it's a bi-plane, you say? Excellent choice. Where are the flying wires that take the shear and bending loads imposed on the aircraft's wings by normal flight loads?

3 times aircraft gross weight applied to the wings themselves may be usable, because when you do a stress test you assume the wings support themselves without applying any bending or shear loads to their own spars. So if you have a 500 pound airplane, and 200 pounds of that are the wings, then you test the wings to 1500 pounds, which is a 7.5G test using the "non-lifting components" as the weight.

Can you tell me how much difference there is in price between 6061-T6 aluminum tube and the SDR-26 PVC tube? Meaning if your design needs a total of X feet of tube for your spars, then that many feet will cost you how much in PVC and how much in 6061-T6 aluminum?

#### Speedboat100

##### Banned
Biplanes are kinda cool. Sleek Streak propeller just doesn't cut it.

#### Speedboat100

##### Banned
I figure that since PVC tubed furniture is made for heavy people to sit on that it should not break under the stress of 500 pounds of ultralight airplane and pilot distributed over seven wing spars of 14 feet long.
That's 75 pounds on each wire-braced spar. I'm searchin for total affordability. Maybe $6,000 with engine. Hirth F-33. I think even electric AC is doable with 6 big ones. #### Allen ##### Well-Known Member Thanks for all the input guys. ;=] I will let you know how the sandbag tests turn out. #### Lendo ##### Well-Known Member I did read somewhere, that some people are determined to kill themselves - at the lowest cost possible. No criticism implied or intended on our Experimental Pilot friends. For myself I try to do everything myself, wherever I can. If this means designing and manufacturing a lot of things I look for the best 'Value for Money' on materials, not always is the most expensive the best. I know I'm preaching to the converted. George #### Allen ##### Well-Known Member This wingless aircraft is an ultralight I'm designing to build with 2" blue styrofoam and 1 1/2" PVC pipe for wing spars. Power will be a 22hp Briggs 4-stroke gas engine. meeceblog.wordpress.com Here is an illustration of how the PVC pipes are arranged into the styrofoam ribs. The outboard ribs have rudders. #### Attachments • 38.8 KB Views: 70 #### Allen ##### Well-Known Member The spars will be covered in shrink-wrap plastic as is used to protect beached boats in winter. Of course there will be braces added to prevent the shrink wrap from bending the pipes. The cockpit module uses doorskin mahogany sheet to provide a rigid center box for the wing base. This looks E Z and affordable. Any POSITIVE ideas? ;=] [Wiseguys stay away from this board please. Go to Twitter and talk to the Dumpster] #### Victor Bravo ##### Well-Known Member HBA Supporter #### jedi ##### Well-Known Member The spars will be covered in shrink-wrap plastic as is used to protect beached boats in winter. ..... The cockpit module uses doorskin mahogany sheet to provide a rigid center box for the wing base. ..... Any POSITIVE ideas? ;=] [Wiseguys stay away from this board please. Go to Twitter and talk to the Dumpster] Yes! Do not give up on your ideas but continue to learn and refine them. Thinking about blue foam and PVC costs nothing but gives concrete ideas a form. Mock ups made of PVC and foam are quick and easy and will show weak areas and deflection under load. Once you have refined the design a hundred times and revised the mock up 20 times replacing a sub par structural pipe with a 6061 T6 tube is a no brainer. #### pwood66889 ##### Well-Known Member "Do not give up on your ideas but continue to learn and refine them." I'm with you, Jedi. Hoever, "Trust, but Verify." #### daveklingler ##### Well-Known Member Allen, I'm assuming that your goal is to put together a design for a cheap, flying airplane that anyone can build with materials available at the local big box store. This goal is held and is discussed daily by a large number of people on this forum. There are hundreds of designs for airplanes that meet your requirements. Begin with Peter Sripol's experiments with foam on Youtube. Also look at the Sky Pup, the Bloop, and the Zing, the KR-2, and the Volksplane as examples of planes that use "cheap" materials. There is a composite material readily available in a different section of your local big box store that's fantastic for airplanes, and really cheap: wood. If you look at the Fisher Flying Products aircraft (or the Zing, or many others), they saw a perfectly good piece of lumber into toothpicks, then carefully reassemble the toothpicks into an airplane. Very little wood is used, so materials can be very cheap. It's covered with Dacron from Joanne Fabrics, and can be painted, should you so desire, with house paint. In the Southwest, where I live, Doug Fir is widely and cheaply available. In Florida, you might look for something else. Regardless, wood is cheap, easy to find in engineering tables, really strong, if used correctly, and easy to cover when you're ready. PVC is good as a foam but it has a poor strength-to-weight ratio and low reliability as a tube. Blue XPS also has a poor strength-to-weight ratio in comparison to PVC foam, but you can make an airplane out of it with fiberglass from the store's paint section. Remember to sand the gloss off it, first. This is where the Peter Sripol videos come in handy. Last edited: #### Allen ##### Well-Known Member PVC TUBE discussion: Thanks designers, now we're talkin construction! I just weighed a 10' tube of 1 1/2" diameter pvc pipe, type SDR-26 thin wall. Three pounds for ten feet!! My wing spars use 105' so that's 32 pounds of weight costing under$100 orderable from my local Ace Hardware. !!!! No shipping or handling fees necessary as in long T6 aluminum tubes which UPS won't handle anyway, they only do six footers or something like that.
[a 1" X 8' alum tube is abt $50 plus shipping so that'd be$700 for 13 pieces plus shipping. Bah]
I HAve to make pvc work through clever structural technique.

#### BJC

##### Well-Known Member
HBA Supporter
I HAve to make pvc work through clever structural technique.
Good luck. (For example, good luck would be that the “spars” fail before you get airborne.)

BJC

#### Allen

##### Well-Known Member
PVC TUBE discussion
Next I'll bend to breaking point some 15 foot lengths which is the wingspan of my sky sled so I can get a feel for their toughness and determine how much reinforcement they will require to fly safely in an airplane. ;=]

#### Aerowerx

##### Well-Known Member
Is there such a thing as PVC tube? All I have seen locally and online is PVC pipe.

Remember "tube" is a structural component, while "pipe" is used for moving fluids (including air).

You say that 13 pieces of 6061 would be $700? How much are funerals in your area? #### Vigilant1 ##### Well-Known Member Lifetime Supporter The clay drainage pipe is stiffer than PVC and comes in even more convenient 2 foot lengths. #### Dana ##### Super Moderator Staff member PVC TUBE discussion: Thanks designers, now we're talkin construction! I just weighed a 10' tube of 1 1/2" diameter pvc pipe, type SDR-26 thin wall. Three pounds for ten feet!! My wing spars use 105' so that's 32 pounds of weight costing under$100 orderable from my local Ace Hardware. !!!! No shipping or handling fees necessary as in long T6 aluminum tubes which UPS won't handle anyway, they only do six footers or something like that.
[a 1" X 8' alum tube is abt $50 plus shipping so that'd be$700 for 13 pieces plus shipping. Bah]
I HAve to make pvc work through clever structural technique.
Allen, you don't HAVE to do anything. Listen carefully (coming from a degreed aerospace engineer): PVC pipe is not a suitable structural material for aircraft. Furthermore, PVC pipe is not a suitable structural material for aircraft. Really.

PVC pipe has a tensile strength of 7450 psi, an elastic modulus of 420,000 psi, and a density of .05 lb/in³.
6061-T6 aluminum has a tensile strength of 45,000 psi, an elastic modulus of 10,000,000 psi, and a density of 0.1 lb/in³.

This means aluminum is 6 times stronger than PVC, size for size, and 3 times stronger for the same weight. But stiffness is also important, and aluminum is 24 times stiffer than PVC for the same weight.

Also, PVC pipe tends to shatter when overloaded, whereas aluminum bends, and breaks at a higher load.

If you want to design an airplane, you need to spend some time studying. You don't need a degree in aerospace engineering, but you have to learn enough to compare structural materials and how they're used. For instance, I don't see a shear web in your second picture. If you don't know what a shear web is and why it's important, you need to study more. Also learn about "design load factor" and "required safety factor." And 1:1 aspect ratio wings will be horribly inefficient, requiring more power, which means more weight, which means more stress on the structure, etc., etc...

PVC pipe used to build furniture is loaded differently, weight isn't a concern, and when it breaks you fall 24 inches to the ground, not hundreds of feet.

#### Allen

##### Well-Known Member
Any help out there on a good lightweight aeronautical way of stiffening PVC pipe so it doesn't bend as much under load? I like the method of criss-crossing it with carbon fiber tape on the outside glued down tight with construction adhesive.
I wonder about stuffing it with a stiff expandable foam of some type? The flimsy yellow foam for filling void is house walls is too soft for that.

<<<So use 2000 pounds (4X gross). Test to 6X if you want the usual 1.5 ultimate safety factor. (4x1.5= 6)>>>
This math seems super cautious which is bad for experimental purposes. First I want to seef it flies well and then over-build it with safety margin strength.
I will use 1.5 X the gross weight of 500 lbs or 750 pounds as the test weight on the wings. I will distribute the weights on the chord at 25% aft of leading edge as u suggested is where the most lift is.
Keep looking up! Cheaply!

#### Allen

##### Well-Known Member
Hiiiii, My design uses 7 spars of 15' length by 1 1/2" diameter. That is 105 total feet of PVC which costs $1 a foot for ten footers at Home Depot. That is$105 for the spars. Aluminum tubing isn't available locally. It has to be ordered and shipped special in 5 or 6' lengths or else it costs $400 special trucking for the ten footers, if locatable. It's not worth it. The cost would be about$10 per foot or $1,050, ten times as much, making it undesirable. My target cost for the airplane is less than$5,000 to first flight. I want everyone to be able to fly, no messing around with conservative mind sets for me. I am the Elon Musk of ultralights. ;=]

<<<Can you tell me how much difference there is in price between 6061-T6 aluminum tube and the SDR-26 PVC tube? Meaning if your design needs a total of X feet of tube for your spars, then that many feet will cost you how much in PVC and how much in 6061-T6 aluminum?>>>>
Ultralight ifting-body Airplane by Somerset Meece, designer and writer - YouTube

#### Allen

##### Well-Known Member
<<<Also, PVC pipe tends to shatter when overloaded, whereas aluminum bends, and breaks at a higher load.>>>
I have sat on a 1 1/2" tube suspended at the ends and it merely folded under me, not shattering at all so that was not an educated engineering statement.
What I am looking for is enthusiasts who solve problems instead of inappropriately practice their Don Rickles insult schtick here on these aviation boards. Only helpful comments please or post elsewhere.