Tensile strength of Hoop Pine?

[rgmwa]

It’s not the ‘design by eye’ part that would would worry me. It’s the ‘confirm by test’ bit that would make me think twice about buzzing around at 1,000 feet to find out which part of my design needed improving. 

[kasper]

48 minutes ago, rgmwa said:

It’s not the ‘design by eye’ part that would would worry me. It’s the ‘confirm by test’ bit that would make me think twice about buzzing around at 1,000 feet to find out which part of my design needed improving. 

 

 

 Then for you I  would suggest either factory build or home build from a design you trust.  Your profile lists vans rv-12 so you appear to accept something that's not certified but  but from a designer you trust. 

 

For me I have 1 airframe from a factory that is stock. I have another from a factory that's very not stock. The other three airframes are my design and build. One of those incorporates parts from factory the others are completely mine.  

 

For me it's a mix of maths and test. And as I'm the only person who will EVER fly my airframes I'm ok with accepting my design and the risks. 

 

That's experimental 😃

 

[rgmwa]

Yes, I’m happy to build and fly a plane that I know has been well designed and tested, and to make relatively minor modifications that I know won’t its airworthiness. Nevertheless, even though I’ve spent the last 40 years designing structures for a living, I’d still think twice about tackling an aircraft without doing a lot of homework. Hats off to the true experimenters though.

Edited July 27, 2021 by rgmwa

[duncan_rtfm]

10 hours ago, APenNameAndThatA said:

I’m confused about this. Aren’t you supposed to use maths when you design aircraft? 

Hi,

Plenty of maths involved in the optimal placement of CG, wing articulation (front and optionally also the rear) and so on (in fact I wrote a whole 30-page paper on this), but as kasper says, a lot of the rest draws heavily from existing designs (for example, the HM293 on which the Fleabike is firmly based) and others.

 

As far as the undercarriage is concerned, after some initial thought experiments (quickly shot down by experienced and knowledgeable forum members, both here and elsewhere), it is now essentially the undercarriage of the HM293 prettied up a bit.  Same for the wing masts and braces.

 

Regards,

Duncan

[onetrack]

Rgmwa - Selby Ford of Beverley, W.A. built his "Silver Centenary" experimental in 1929-30 without any blueprints or calculations! But he did study up extensively on aerodynamics (without formal training or without gaining any qualifications) and drew on current designs of the era to build his aeroplane.

He apparently also did draw full-size sketches of the basic design, on the Beverley powerhouse floor! I believe he also had a unique mind that led him to possess excellent practical design skills. I have employed people who possessed similar highly-competent abilities in fabrication.

 

Capt C.H. Nesbitt was the test pilot of the Silver Centenary, and claimed that it flew beautifully. Nesbitt made several flights in the Silver Centenary.

 

However, Selby Ford came unstuck when he went to register the Silver Centenary in 1930, as he couldn't provide any plans, calculations, or even basic drawings to the CAA, to support his registration request!

Strangely enough, no-one has ever found any concerning flaws in Selby Fords aircraft, and it was totally stripped and rebuilt after 76 years of being on display, and it did eventually receive airworthiness certification and permission to fly as an experimental.

 

The most incredible part of the entire Silver Centenary saga, is that Capt C. H. Nesbitt and his two passengers were killed, when the less-than-a-month old De Havilland DH80A Puss Moth Capt Nesbitt was piloting, suffered an in-flight wing separation, and crashed!

The Puss Moth was a fully-engineered aircraft, designed by so-called "highly skilled" aviation designers!! The Puss Moth had a terrible flight record, with the major problem being identified as a major structural weakness at the root of the wing spar!

 

https://aviation-safety.net/wikibase/153451

 

At the end of the day, all single-designer aircraft are only as good as the cleverness and capabilities of the designer, no matter how extensive their written qualifications are.

I've come across qualified mechanical engineers who didn't even understand that mens shavers needed to be regularly emptied.

[rgmwa]

Agreed Onetrack. I've read the Silver Centenary story and also had a good look at it and watched it fly more than once. It's hangared at Serpentine, where I keep my plane.  Ford did a remarkable job - it looks right and in engineering, that's usually a pretty good guide as to whether something is right.  And as you say, just because an aircraft was `professionally' designed doesn't mean that it's going to be any good. There are plenty of examples of professionally engineered flying crocks in the history books.  Nor does having formal engineering qualifications make you a gifted designer, just as having no formal training doesn't mean you can come up with an excellent design. I learned a lot about aircraft construction from assembling (I won't say building) my kit, and am currently one of the mentors helping a bunch of high school kids put together another RV12.  My own preference for a plane that I and others are going to fly in is a kit from a reputable manufacturer, but I'd also be happy to build off plans if I had the time and the right equipment. It's just a lot more work. If I was going to design my own plane, as I said previously, I'd want to make sure I'd done my homework to know what I was doing. In engineering, it's knowing what you don't know that keeps you out of trouble. So far, so good.

 

[spacesailor]

I can,t get over the Dehavaland Comet fiasco.

Bad design ,bad build, then a big cover up. I was certain there were more than just three. After googling, no mention of a pause in the flights. After accusing "  terrorist bombs " taking them out.

The Comit two had a compleat redisign.

Morry Hummel , has done a good job with his designs, AND has taken ideas from his custemers slowly changing his design.

Another is the new  'part 103 '  rules design, not a bad looking all metal aircraft,

 ,.

spacesailor

Edited July 28, 2021 by spacesailor
Missed word

[rgmwa]

Like Morry Hummel, Vans have over time incorporated improvements in the RV-12, and no doubt the other RV models, based on suggestions and modifications made by the early builders and documented on Vans Airforce website. Even yours truly can claim a couple of very modest contributions that have since appeared in the current kit. 

[Geoff_H]

On 28/07/2021 at 12:01 PM, rgmwa said:

Agreed Onetrack. I've read the Silver Centenary story and also had a good look at it and watched it fly more than once. It's hangared at Serpentine, where I keep my plane.  Ford did a remarkable job - it looks right and in engineering, that's usually a pretty good guide as to whether something is right.  And as you say, just because an aircraft was `professionally' designed doesn't mean that it's going to be any good. There are plenty of examples of professionally engineered flying crocks in the history books.  Nor does having formal engineering qualifications make you a gifted designer, just as having no formal training doesn't mean you can come up with an excellent design. I learned a lot about aircraft construction from assembling (I won't say building) my kit, and am currently one of the mentors helping a bunch of high school kids put together another RV12.  My own preference for a plane that I and others are going to fly in is a kit from a reputable manufacturer, but I'd also be happy to build off plans if I had the time and the right equipment. It's just a lot more work. If I was going to design my own plane, as I said previously, I'd want to make sure I'd done my homework to know what I was doing. In engineering, it's knowing what you don't know that keeps you out of trouble. So far, so good.

 

I am about halfway through my own design, aerodynamically it is very similar to an existing design. Before I began I built many test pieces and tested them to destruction.  As it is a composite design I have difficulties getting design values for calculations.  So it is a little heavy.  At one stage some years ago I considered doinfya masters in composite design criteria.  One big problem that I had is what would the shear stress of the main spars.  Assumed that the max shear stress was the max epoxy stress.  The cloth may add extra strength but I went on the side of safety, it now seems a little heavy.  It is ok to use the load test to make sure that things are ok...but... What if your dynamic loads are different to the static loads.  Throughout my career I found that it's not the calculations that bite you in the backside.  99%of the time, it is the incorrect assumptions.  The math will make the aircraft lighter.  I was taught that anyone can build anything, but an engineer should be able to do it for far less cost, math can help.  If you are designing your own design please get someone to do maths on the critical parts.  Even a strut can buckle in compression but be super strong in tension.  Negative G's may buckle a strut. Fibreglass structures are notoriously weak in shear.  Using mathematics can also stop making 6 parts before the final is made, I have done the math and still had to make the part 6 times before the final that works.  However experiment experiment experiment.

I have been using carbon infused nylon and 3d printing.  I have used it in some parts ..I still have reservations, but they are light.  Fantastic for cheaper materials and jigs and alignment tools.