# "SkyWing" hybrid wing body ultralight

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#### 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

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• SkyWing v3.3 smaller copy.png
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#### pwood66889

##### Well-Known Member
Welcome aboard, Allen.
And should your rather generously bladed prop ever point NW to 2J0, gimme a shout and I'll buy the coffee!

#### Allen

##### Well-Known Member
Well now I know where 2JO is. [near the glittering metropolis of good old Sopchoppy, home of the internationally reknowned Worm Gruntin Festival] It'll be my first destination when the SkyWing flies. [which will be nice if it happens. I'll rejoin the EAA to use their talented builders' savvy. ;=]

#### Dana

##### Super Moderator
Staff member
Forget about pvc for wing spars or any structural application. No time to write more, use the search function.

#### pwood66889

##### Well-Known Member
Yeah, Allen, that Worm Fest is quite the event around here. Can attest there to as a proud resident of...
But do join the EAA if you can. Some chapters can be standoffish (If you ain't a pilot...). Even hanging out at the local flying field helps.
Hear Marathon Key has a museum and EAA Chapter.

#### Victor Bravo

##### Well-Known Member
Supporting Member
With no disrespect meant at all, and saying this trying to HELP rather than insult, you might want to change the name of the project.

"Sky Wing" sounds just like one of those ridiculous "Chin-glish"names they have for low quality ARF model airplanes made in China. To an experienced airplane person, that name immediately costs you half or 2/3 of the credibility before the conversation even starts.

PVC tube is another huge credibility-killer when you are talking about it in front of anyone who is involved in aviation.

Once again I am NOT trying to make fun of what you are doing or discourage you. I am, however, pointing out things that are doing damage to how knowledgeable people are going to look at your project.

#### Aerowerx

##### Well-Known Member
I was going to say run as far and fast as you can from PVC pipes, but others beat me to it.

In general 'pipe' is a conduit---moves something from one place to another. But 'tube'' is structural.

Since you already mentioned using 2" foam, why not make a spar out of that with fiberglass cloth covered with epoxy, and maybe some carbon fiber rods?

As already mentioned, use the search function on here. All of this has been discussed ad nauseum.

#### Allen

##### Well-Known Member
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. #### Victor Bravo ##### Well-Known Member Supporting Member Multiply that 500 pound gross weight by 6, which will give you a conservative figure for flying through a strong and unexpected gust or turbulence. Then decide if seven pieces of cheap plastic PVC will support 6 times 500 pounds, or 3,000 pounds (that's a small car) with your life at stake. 1) I am sorry to burst any bubble here, but PVC is not a strong enough material. 2) If you are honestly trying to save money, don't forget to add the cost of the hospital and the mortuary in with the cost of your PVC wings. The total cost of those three things (trust me, they all go together) will be higher than the cost of aluminum. #### poormansairforce ##### Well-Known Member Multiply that 500 pound gross weight by 6, which will give you a conservative figure for flying through a strong and unexpected gust or turbulence. Then decide if seven pieces of cheap plastic PVC will support 6 times 500 pounds, or 3,000 pounds (that's a small car) with your life at stake. 1) I am sorry to burst any bubble here, but PVC is not a strong enough material. 2) If you are honestly trying to save money, don't forget to add the cost of the hospital and the mortuary in with the cost of your PVC wings. The total cost of those three things (trust me, they all go together) will be higher than the cost of aluminum. 3) Each of the wing panels on my Minimax weighed about 30 lbs ready to cover. 75 lbs for just the spars is crazy. #### pictsidhe ##### Well-Known Member 6061 tubing is not horribly expensive. If you can't do the required maths to design a plane, that won't work either. Either too heavy, too weak, or most likely, both. There is no room for TLAR engineering in an Ultralight Buy some plans, follow them exactly. Minimax and legal eagle are popular for good reason. #### enderw88 ##### Member Supporting Member TLAR (That Looks About Right) should never be trusted. TLW (That Looks Wrong) should never be ignored. Strength-to-weight of the PVC is not high enough. By the time you get the structure stiff enough to be safe it will be too heavy to fly. So, in a sense this is a self-correcting problem. #### Aerowerx ##### Well-Known Member And PVC will deform easily when under compression. Like in a bolted joint in shear. #### pictsidhe ##### Well-Known Member I'm not too worried about the OP. If he gets this up to flight speed, the wings will snap off at an altitude of 0 feet. The danger is that he make improvements that give a 1.3g ultimate failure strength. #### cblink.007 ##### Well-Known Member Supporting Member I'm not too worried about the OP. If he gets this up to flight speed, the wings will snap off at an altitude of 0 feet. The danger is that he make improvements that give a 1.3g ultimate failure strength. Not defending the OP, but seriously, who would use PVC for a spar? When I was a kid at the tender age of 9, inspired by an article I read in Boys Life, I made a rogallo wing hang glider, using bedsheets and PVC. Worked great running down the small hill, feeling it lift up big time, until I put my sub-100 pound weight into the structure. I heard and felt a big snap, then took a little tumble down that hill....after falling about 10 feet! My first aircraft design... My first 0.1 ... My first unofficial solo... ...ending up scraped up and a little bruised & bloody in a pile of broken PVC and bedsheets. Pride slightly bruised, but devoted more than ever to become an aeronautical engineer and test pilot. @Allen , do not attempt to use PVC on anything structural. You can use a PVC structural foam in a composite sandwich application, but PVC is a no-go for structural! Last edited: #### Sockmonkey ##### Well-Known Member At best a PVC pipe could be used as the internal form for a fiberglass structural tube. As in, wrap the pipe in fiberglass and then remove it. #### WonderousMountain ##### Well-Known Member Last edited: #### Allen ##### Well-Known Member Thanks Victor, yours was the most informative reply I got. Not a high bar, though. Your text sounded like you know how to stress test an airplane. I have seen 3X gross weight used for strength testing wings. Not 6X! It's not an acrobatic design. Look at my photo at top of thread. It is a bi-plane with 1:1 ratio very low aspect sail wings. It is a cigar box frame made from 7 pvc 1 1/2" diameter spars that connect 4 styrofoam ribs. These 7 spars will cost under$100 and weigh 35 total lbs. The 4 ribs cost about $300 and weigh 24 lbs.$400 is most of the 60-pound fuselage/wing cost. Cheap is right! Cheap is good. Otherwise poor people are never gonna fly.
The wing "box" is 15' square. How should I stress test it? How many sandbags, where, and how heavy? Where to put the supporting saw horses.?
What must be understood is that it does NOT have any skinny long cantileverd "wings" to bend and break. Look at the picture closely and understand it better before posting a reply. Keep this board informative and a supportive use of our time and resources.
It is a biplane with sails stretched across the top and bottom of a an external box frame. We're talkin ULTRa lite and ultra Affordable!!
The spars are 1 1/2" SDR-26 PVC pipe. <5 lbs apiece! 35 total lbs for spars. SDR-26 is thinner walled and about half the weight of schedule 40 pipe which is a thick-walled version for 330 psi pressure whereas SDR-26 pipe is only for 120 psi or pressureless drainage use . But it is just as stiff as thick-walled stuff. ;=] This SkyWing design yields a sixty pound bare airframe for four hundred dollars. It is modeled after a sled kite, simple and lite and flys Hi.

<<<<Multiply that 500 pound gross weight by 6, which will give you a conservative figure for flying through a strong and unexpected gust or turbulence.
Then decide if seven pieces of cheap plastic PVC will support 6 times 500 pounds, or 3,000 pounds (that's a small car) with your life at stake.>>>

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#### BBerson

##### Light Plane Philosopher
Supporting Member
The lift is mostly near the leading edge back to 25% chord. Place the sand bags on that first 25% chord. So use 2000 pounds (4X gross). Test to 6X if you want the usual 1.5 ultimate safety factor. (4x1.5= 6)
Aerobatic is 6G limit load and 9G ultimate. (6x1.5=9)

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