# Suitable airframes for industrial engines?

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#### aeronco

##### Member
The Aeronca C2 and C3 have remarkable performance for such low powered machines. I’ve flown several hundred hours in my C3 and have a C2 in the shop. The high aspect ratio wing is very efficient and the Aeronca E113 (or JAP J99 for an Englishman) provides honest horsepower at a sensible propeller speed. It might well only be 36 hp but is efficiently turned into thrust. The higher revving VW doesn’t provide the same efficiency. The suggestion of giving the Headwind a bigger wing is sensible as the original design is only 26 foot span; the Aeronca is 36 foot by comparison.

#### cluttonfred

##### Well-Known Member
HBA Supporter
What about some of the 1920s-1930s designs intended for use with small converted motorcycle engines. In other words, half the designs from the old Flying & Glider Manuals? Aluminum tube-and-gusset construction and other weight savings should really improve performance. I love Les Long's Longsters...no relation. ;-)

#### Bill-Higdon

##### Well-Known Member
What about some of the 1920s-1930s designs intended for use with small converted motorcycle engines. In other words, half the designs from the old Flying & Glider Manuals? Aluminum tube-and-gusset construction and other weight savings should really improve performance. I love Les Long's Longsters...no relation. ;-)

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There was a high wing Longster built as an ultralight & powered by a Carr Twin (1/2 VW)

#### aeronco

##### Member

Lots of inspiration and vintage ultralights in this series. Don’t discount using DOM steel tube, it’s cheap, light and easy to weld with gas, TIG or MIG. The late Robert Hoover wrote an article called ‘Flying On The Cheap’, all about using mild steel DOM instead of expensive 4130. Aluminium tube and gusset construction is OK structurally but always looks like a dogs dinner of nasty sharp edges and pop rivets (just my opinion!).

#### aeronco

##### Member
Having read the article again I think Hoover meant ERW. Certainly ERW is way cheaper than 4130 here in the UK and his argument was that commercial grade steels were suitable for inexpensive non-aerobatic aircraft. Obviously it isn’t as strong but for a flivver, would .049 ERW be OK instead of .035 4130? Very much an individual decision.

#### mullacharjak

##### Well-Known Member
Wayne Ison. Plans?
Aviation Plans Facebook group has got drawings for PDQ.

#### mullacharjak

##### Well-Known Member
Having read the article again I think Hoover meant ERW. Certainly ERW is way cheaper than 4130 here in the UK and his argument was that commercial grade steels were suitable for inexpensive non-aerobatic aircraft. Obviously it isn’t as strong but for a flivver, would .049 ERW be OK instead of .035 4130? Very much an individual decision.
I am also investigating the option of substitution for 4130 which is not available in my country of residence,There is lot of ERW but I think its weak. Someone suggested 201 Stainless steel being a suitable substitute for 4130.The figures on paper look promising but I have to look into it.

#### rv7charlie

##### Well-Known Member
Well, my brain took a vacation the other day when I responded. I hope that Hoover didn't mean DOM *or* ERM tubing should be used for structure. My understanding is that even the old Piper Cub-era planes used seamless tubing, in one or more of the mild steel aloys (1025 for the Cub). I've never seen anyone advocate using welded-seam tubing for aircraft. There was a local legend around my home state of a guy who built an entire a/c out of EMT (electrical conduit) but I don't think he could get the inspector to sign it off.

#### mullacharjak

##### Well-Known Member
Well, my brain took a vacation the other day when I responded. I hope that Hoover didn't mean DOM *or* ERM tubing should be used for structure. My understanding is that even the old Piper Cub-era planes used seamless tubing, in one or more of the mild steel aloys (1025 for the Cub). I've never seen anyone advocate using welded-seam tubing for aircraft. There was a local legend around my home state of a guy who built an entire a/c out of EMT (electrical conduit) but I don't think he could get the inspector to sign it off.
Forget the name now as that information can no longer be accessed on the internet.An australian builder built Early bird jenny.He used ERW 1.2mm tubing.Geo suzuki G10 /Rotax gearbox. It flew fine.

#### rv7charlie

##### Well-Known Member
My understanding is that the issue is not the raw strength of the tubing. It's the relatively uncontrolled process (meaning un-monitored for integrity) of welding the seam on the tubing. Then there's the loading on the welds, once the tubing is in service.

I have no doubt that an airframe could be built using DOM, or ERS, or even EMT, and it would fly 'fine'. Until it doesn't.

#### TFF

##### Well-Known Member
DOM starts out as ERW with one more step in the process. What ERW might do is split in a crash. As for strength, that’s math class.

#### Victor Bravo

##### Well-Known Member
HBA Supporter
The pre-war Taylorcrafts and Cubs used 1020 or 1025 I believe.

The big question is why would you want to save a small handful of money by using electrical conduit or water pipe, when it would cause two large handfuls of risk, worry, failure modes, quality control issues, etc?

#### rv7charlie

##### Well-Known Member
DOM starts out as ERW with one more step in the process. What ERW might do is split in a crash. As for strength, that’s math class.
So...Grade 5 bolts from the hardware store are OK to replace AN hardware? ;-)

#### 12notes

##### Well-Known Member
Log Member
So...Grade 5 bolts from the hardware store are OK to replace AN hardware? ;-)
If you design to use Grade 5 bolts, then yes.

I think some people are confusing ERW tubing with electrical conduit. While conduit is a type of ERW tubing, so is DOM. DOM is a step in the process of making "seamless" tubing.

Pretty much all commonly available tubing is Electric Resistance Welded (ERW) tubing. This can be made with cheap thin steel with little to no QC that is used for electrical conduit. Or it can be made from decent steel to make "normal" ERW tubing. Finally, ERW tubing can be Drawn Over a Mandrell (DOM) to remove the internal welding flashing and cold form to final shape to make DOM tubing. It is called seamless but the seam is still there, just smoothed over.

Aircraft should be engineered to be nowhere near the burst strength of the material in any condition anywhere close to their flight envelope. If it's properly designed for ERW tubing, then it's not going to break up in flight because of any property of the material. For that matter, you could safely design a plane to use electrical conduit, although it would likely be very heavy, as you would need to use a lot of it. In a crash, though, "normal" ERW is more likely to burst at the seam than DOM.

There are tubes that are not ERW at any point and are truly seamless, those are Cold Drawn Seamless (CDS) and Hot Finish Seamless (HFS), but they are not commonly used. It is possible, but I've never heard of it being required for any kind of homebuilt aircraft.

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#### rv7charlie

##### Well-Known Member
*Nothing* is technically 'required' in homebuilts. What is prudent, or what you can get past the inspector for your a/w cert, are different matters.