Airfoils, Ordinates, Fat Wings, Harry Riblett and other musings…

[rv8bldr]

What Jared said...

While this discussion has been educational, we aren't building an SR-71 or an F-104. In fact, our VNE is lower than the stall speed of both of those :-)

Also, keep in mind that many of us are scratch building and are hammering our ribs out over a wooden template: there is no way in, well.... you know, that all of our ribs are *exactly* the same as the kit ribs. I would argue that not all of the ribs in a wing are *exactly* the same, although you probably can't tell that by eye. The kit ribs, however, are as close to perfection as you can get WRT the plans/mylar template.

There are many Bearhawks happily speeding and STOLing around and they couldn't care less about a line width on the plans here or there. The airplanes are wonderful to fly, have great performance, and have no nasty gotchas.

By all means, carry on with the academic discussions (I'll admit my eyes glazed over a bit after a while...I'm a software guy...) but for those that are concerned/confused, don't be. Bob knows what he is doing and designing. The proof is in the flying (both scratch and kit built) and there is a LOT of proof out there....

My $0.02

[stinger]

I did not cut my nose ribs , I wrapped Duck tape around the tip two layers . I think it turned out well. Yes wing ribs may be different however my LAS fly's quite good .I have 21" tires, Cont. 0200 with a top speed of 135 mph at red line of 2750 rpm. Cruise 2450 rpm around 110mph. Stinger

[NCLSA183]

stinger. You are wrapping “duck” tape, nborer is getting attacked by “duck” shoes while I’m having trouble keeping my “ducks” in a row… Maybe we need a new topic. LOL Nice performance numbers on your LSA. I truly enjoyed following your progress. Congrats!!

[NCLSA183]

rv8bldr. Mark, thank you for adding your 2 cents. I’m glad this conversation got you up from that very comfortable looking chair with the beautiful trees in the background.

As someone who has endured some very long coding sessions over the years, I submit that your eyes may likely have been glazed over long before you starting reading this topic. (wink)

I certainly agree with you in regard to the inconsistency of the hammered ribs. But that is an area where we have a bit of control without adding very much to the build time. The airfoil mylar drawing represents the size and shape of the completed wing, cross section. Allowing for rib flange and skin thickness when making the rib form blocks would result in a completed wing that would better match the mylar and, therefore, more likely have the flight characteristics that were originally intended by the designer. And remember, we don’t know the intentions of the Dwg 4 modification.

Based upon the analysis by nborer, a few line widths don’t appear to make any truly noticeable difference, but yet, Bob considered it important enough to make that small change to the Riblett 30-613.5 airfoil without any flight testing to quantify the design or verify and compare the results. A very talented, current builder of a large wing Bearhawk recently told me that his completed wing came in at 0.210 inch thicker than the mylar drawing. Will this person be just as happy flying around with that extra weight, drag and likely loss of performance or will he be wondering “what if” as he questions whether or not to load that trophy moose into the aircraft? To borrow a slogan from the Army, my little LSA wants to “be all you can be” so I’ll be making every effort to assure that. Due to the reasons I wrote in some other posts, I will now be using LSA Dwg 4 as the profile for my build.

Mitch

[nborer]

What Jared said...

While this discussion has been educational, we aren't building an SR-71 or an F-104. In fact, our VNE is lower than the stall speed of both of those :-)

Also, keep in mind that many of us are scratch building and are hammering our ribs out over a wooden template: there is no way in, well.... you know, that all of our ribs are *exactly* the same as the kit ribs. I would argue that not all of the ribs in a wing are *exactly* the same, although you probably can't tell that by eye. The kit ribs, however, are as close to perfection as you can get WRT the plans/mylar template.

There are many Bearhawks happily speeding and STOLing around and they couldn't care less about a line width on the plans here or there. The airplanes are wonderful to fly, have great performance, and have no nasty gotchas.

By all means, carry on with the academic discussions (I'll admit my eyes glazed over a bit after a while...I'm a software guy...) but for those that are concerned/confused, don't be. Bob knows what he is doing and designing. The proof is in the flying (both scratch and kit built) and there is a LOT of proof out there....

My $0.02

Hear, hear. I do NOT want to steer anyone away from the plans. I was about to start forming my aileron spar web prior to my inadvertent shop "closure," and the plans very clearly say "check for fit with rib" right next to the dimensioned spar height. In order to fit my aileron ribs (without joggling - another religious argument that I won't dive into), my aileron spar web needs to be about 0.1" taller than the dimension showed in the plans. Lack of joggling will only account for half of that variation. Yet, when I lay my ribs on my formblock and compare to the Mylar, they look pretty darn close to me. I guess I went a little more to the outside of the line. I'm not sweating it. When my build comes in heavy, this will be one of the 1000 reasons.

But seriously, a software guy? That's where all the problems originate! (*Ducks shoe thrown in my general direction.*)

Nick

[rv8bldr]

Stuff deleted....

But seriously, a software guy? That's where all the problems originate! (*Ducks shoe thrown in my general direction.*)

Nick

At one time them would have been fightin' words.... However, I'm less than 2 years from pulling the plug on working for a living so I find that aspersions don't stick anymore.

[nborer]

Said in jest, of course. My brother is a software engineer, so we've been trading barbs for the last several decades.

[rv8bldr]

And it was taken in jest, Nick :-) No worries....

[NCLSA183]

About 10% of my work over the years has been the design, prototyping and building of custom electronic projects for clients’ niche applications. I would design the hardware and code the software and/or firmware and not once have I ever thrown a shoe, of any kind, at my alter ego. You guys should grow up and stop clowning around before someone loses an eye!! Just learn to get along and play nice!! LOL

Mitch

[Franky139]

Hi guys

I have a question if someone can answer it and maybe somebody already did or talk about it somewhere : The Bearhawk Patrol have a wingspan of 33 feets, 66 inches of chord and 180
square feets of wing area, ( lets put the wing spar out of the equation for the moment) if i take the LSA ribs (60 inches chord) and build a the wings for a 36 foots wingspan wich will also have
180 square feets of wings area, longer flaps and ailerons, wich one will theorically be better?

Franky

[jaredyates]

I'm a builder and not a designer, so for me the best wing is the one drawn on the plans. When it comes to deciding on the wing chord and span, Bob knows how to make each one longer and shorter, but the final design was the optimum. He didn't have the luxury of disregarding the spar, of course.

[kestrel]

( lets put the wing spar out of the equation for the moment)

As Jared points out, Bob didn't disregard the spar. The longer wing will be more efficient in all modes of flight, but it will be heavier for the same strength.

The narrower cord results in a spar that is less "tall". The less tall spar is weaker. ...but because of the larger moment put on it by the longer wing, it needs to be stronger.

The longer wing also won't clear trees on narrow strips as well.

[Franky139]

Everything is a trade off, you win on one side and you loose on the other, i did ask the question because i have a set of beef up spars for a super cub, have a look
below, the main spar is 20 lbs and a bit and the rear spar is 16 lbs, they are supposed to be good for 3500 lbs but if i use them, my limit will be 2500 lbs,
I'm not sure yet if i will use theses spars but i'm exploring the idea.

For the trees, if i dont have at least 20 to 30 feets per side, it's going to be a no-no for me, i will mostly operate on floats.

Thank's for yours opinions, it's highly appreciated.

Franky

[Frank]

How about a clipped wing patrol/supercub? Make it a cruiser and my guess is you can put on any engine and prop and still stol as much as you want. That's my contribution to the fantasy!

[David Swartzendruber]

My fantasy is having my airplane completed and being able to fly it.

[Franky139]

Frank

When you are talking about a clipped wing patrol supercub, i'm guessing about the standard patrol wing at 33 feets, for engine i already have a 150 hp Lycoming 0-320 with 1000 hrs tt, i'm
planning to take it up to 170 or 175 hp by having the cylinders sent to Lycon for a porting job and putting 8.5 to 1 pistons in it,

I'm not sure yet wich direction i will go for the wings, it will definitely be the Riblett GA 30.615.5 profile, for the spars, i will have an aircraft engineer ( university level) to look at it.

David

My fantasy is to be in my garage and building it. i've been a pilot for 46 years.

[Frank]

That's where you'll find me most afternoons. For a while I was getting in 20 hours a week. Lately it's been more like 15. Still requires a lot of imagination to look at the parts so far and see an airplane. Quite enjoyable though. And as I fabricate and assemble I am in increasing awe of the engineering savvy that went into the design (LSA). Not that I understand it.

I look forward to seeing your project when it gets going! Keep us posted!

[Franky139]

Frank

I dont think i will really begin building before the fall, i still fly choppers and i will be busy this summer, after serious negociations with my finances minister (wife) for the project, the deal
is that i will not dig in our bank account for it, i need to get fresh money by working, anyway, yes i will post every once in while somes photos, on the other hand, i can not call this project
a Bearhawk, it will have the wings but that stop there, the end result will be more like a look alike 2 places Aeronca Sedan with a Bearhawk wing so some peoples might say that i dont have
much business putting this project on this forum, i just came to it because of some interest in extending the wingspan of the Bearhawk Patrol, i will see how it goes.

[Nev]

the end result will be more like a look alike 2 places Aeronca Sedan with a Bearhawk wing

Hi Frank. I think most of us here have a real interest in aviation, building, and experimental aspects. I'd be real keen to follow your progress, even if it's not a "classic Bearhawk." There's also a wealth of knowledge lurking in these forums, previous builders, aeronautical designers, career pilots etc. Best of luck with the project. The only advice I can give at this stage is to finish the project with the same finances minister that you started with

[Bcone1381]

I don't think i will really begin building before the fall, i still fly choppers and i will be busy this summer, after serious negociations with my finances minister (wife) for the project....

So, You decided on an airfoil. I think you chose a (the LSA airfoil) good one. What do you think your next step is? If you got a set of LSA plans you would get a full size airfoil printed on mylar, a book that gives broad instructions for fabricating wing and fuselage parts. If you got a set of 4B plans could see the spar web design for a higher loaded wing.

It would also give some ideas for the spar web. Depend on an aeronautical engineer for the spar design though. A longer wing will neeed more strength built into its spar web.

Two sets of plans....an engineer.... I am curious how you satisfy your Minister of Finance to overcome the hurdles this special build might require..... which takes me back to Post #36 and echoing what NEV said in #41. Life is web of interconnections! Btw, when I reserved my N-number our anniversary date was available. That was a good move! It definitely made my wife feel like it our build, not my build.

[Franky139]

I'm not yet decided on the LSA airfoil, i'm looking at it because they would fit better with the spars that i have and i can always cut them down to the standard 33 feets, for the moment, i just want
to find out if a 36 feets wing would have a lower stall speed due to the longer flaps, if it's not worth it, i will probably stay with the standard Bravo wing at 33 feets.

I definitely agree with Post no 36, there's no points in rewriting the book, the thing is that i have that set of spars, they are brand new, and i would like to used them as much as possible, it would be a cost and time saving, they are more than strong enough, it is not a big deal to make the ribs to fit, no change in the cost of materiel, i just need an engineer to check the idea, theses spars were
designed for a fabric wing, there is no doubt that making an all aluminium wing with it, will turn into a much stronger wing, however, i will get it checked,

[Franky139]

Becone 1381

I forgot to say, my best buddy's son is an aeronautical engineer in the Canadian forces, he will look into my stuff for a friend price.

[jaredyates]

Becone 1381

I forgot to say, my best buddy's son is an aeronautical engineer in the Canadian forces, he will look into my stuff for a friend price.

I'm glad to hear you are involving an engineer. You might want to be sure he considers that the fabric covered wing would probably have had drag/anti-drag wires, which yours might not. There is much complexity to these things and the stresses of the spars, ribs, skins, and struts are all related in a system. They are not modular plug and play components.

[N3UW]

I'm not yet decided on the LSA airfoil, i'm looking at it because they would fit better with the spars that i have and i can always cut them down to the standard 33 feets, for the moment, i just want
to find out if a 36 feets wing would have a lower stall speed due to the longer flaps, if it's not worth it, i will probably stay with the standard Bravo wing at 33 feets.

I definitely agree with Post no 36, there's no points in rewriting the book, the thing is that i have that set of spars, they are brand new, and i would like to used them as much as possible, it would be a cost and time saving, they are more than strong enough, it is not a big deal to make the ribs to fit, no change in the cost of materiel, i just need an engineer to check the idea, theses spars were
designed for a fabric wing, there is no doubt that making an all aluminium wing with it, will turn into a much stronger wing, however, i will get it checked,

Just to let you know from the point of view of a person that scratch built the wings, the spars are only about 1-5% of the effort so far. I would think that trying to fit the ribs to a different spar might take more time than simply building the spar. The spar for the Bearhawk was optimized with both weight and strength and most likely any other spar would be some form of compromise.

if you are trying to save time and/or money you should look closely if using your existing spar would actually save you anything.

[kestrel]

This has been my thought... The reason for using the spars is questionable. Just having them seems like the wrong reason.