The Janowski Project - Rethinking the J1B/J2/J3

[Marc W]

Anton Cvjetkovic wrote an article on a simplified method for designing wooden spars for Sport Aviation. No calculus. It was published around 1970 maybe? If you search the SA archives it should come up. He designed the CA-61 and CA-65 wooden airplanes.

 

[Hephaestus]

Anton Cvjetkovic wrote an article on a simplified method for designing wooden spars for Sport Aviation. No calculus. It was published around 1970 maybe? If you search the SA archives it should come up. He designed the CA-61 and CA-65 wooden airplanes.

So it's easily found...

Thanks, I'll sit down with it and some coffee in the morning

 

[Michael Silvius]

Michael wasn't there a fatal crash where the builder didn't follow Alejandro's suggestions?

Yes that is correct. Juan Terron was a friend of Alejandro's who built his own J-1B. He installed a Rotax 583 with a three blade prop. I don't know how high the thrust line was on this example but it looked to be considerably higher than whats prescribed in the plans. He encountered the same inability to rotate out of ground effect on his first flight and contacted Alejandro who promised a visit the next day to review the plane. Juan got impatient before Alejandro arrived the next day. He re-pitched the prop blades for more thrust and attempted to fly the plane. Unable to rotate out of ground effect a crosswind blew the plane off center-line, through a barbed wire fence at the side of the runway, impacted a berm which tore the landing gear and nose off and left Juan with the plane attached to his back and nothing in front. He met his demise when he crashed into a semi-trailer in a lot next to and about 3 meters below the runway level. Alejandro was the first person on scene.

 

[Hephaestus]

Almost at virtual sit in it and make putt putt noises stage

Putting engineering math aside for now, should probably take some more looks at aerodynamics, sort out W&B for a sasquatch (definitely doesn't balance with me in it). And take a better look at whether the tail obviously needs tweaks or not.

 

[Mohawk750]

Putting engineering math aside for now, should probably take some more looks at aerodynamics, sort out W&B for a sasquatch (definitely doesn't balance with me in it). And take a better look at whether the tail obviously needs tweaks or not.

Very impressed with your progress so far drawing up the J2. I think the world would benefit from this design puffed up to "sasquatch" size, a little longer and a little wider is good for everyone and if you are a standard size pilot you could take a little more fuel or baggage along.

 

[Hephaestus]

Very impressed with your progress so far drawing up the J2. I think the world would benefit from this design puffed up to "sasquatch" size, a little longer and a little wider is good for everyone and if you are a standard size pilot you could take a little more fuel or baggage along.

I think baggage compartment will always be coming up short on this one...

On the practical size, it would stretch / widen just like a kr2. Those are pretty well documented. About the only real thing that makes you think harder is the wing root spars would have to tweak to match.

But W/B becomes an issue...


To answer my own earlier dimensional question. That ?160? mm notation looks like it should be about 128mm

 

[Mohawk750]

On the practical size, it would stretch / widen just like a kr2. Those are pretty well documented. About the only real thing that makes you think harder is the wing root spars would have to tweak to match.

I was thinking about this and yhe loads would have to be worked out if you made changes to the attach pin locations ie. lengthened the stub spar but what if you left that the same and just moved the root rib outboard to accomodate the wider fuselage? The leading edge attachment then becomes an issue. Again, a case of one change trigering a dozen more.....

 

[Hephaestus]

Not sure I agree. If you think of the bolt closest to the root rib as a pivot, once you've passed the 2nd bolt it's dead - just acting as spacer / material to endure the bolt doesnt rip out. Spreading the bolts farther apart - isn't going to increase any stresses.

 

[Mohawk750]

Not sure I agree. If you think of the bolt closest to the root rib as a pivot, once you've passed the 2nd bolt it's dead - just acting as spacer / material to endure the bolt doesn't rip out. Spreading the bolts farther apart - isn't going to increase any stresses.

If moving the pivot bolt outboard makes little difference then what difference does lengthening the spar stub? Just wondering if one is preferred over the other? Will moving the two attach points further apart to accomodate the wider fuselage have any negative effects. Assuming you keep the spar dimensions the same tip to root and just taper over a longer distance can the existing spar design tolerate the change without further modification?

 

[Hephaestus]

No, if you widened the fuselage, The wing attachments would stay - widened down the centerline so only change really is distance between the 2 bolts. Maybe I'm thinking of it all wrong but I'm struggling to see that as any real load change.



I'm always open to hearing I'm wrong. I'm very good at being wrong

 

[Mohawk750]

Not to worry, folks will be along shortly to sort us out I'm sure. I'm sure the numbers change if the distance between the pins changes (arm for the bending loads) Question would be, is it enough to make a difference?

 

[Vigilant1]

Hepaestus,
Out of curiosity (and not to pin you down), what is your goal for all this really nice work you are doing?
1) Create a set of unambiguous, correct, legible digital drawings for the original J-2?
2) Create a set of digital drawing of a new plane derived from the J-2 (a bit wider, higher gross weight, a little more fuel, taildragger)?
3) Same as #2, but using other construction materials instead of wood in some places.

Any/all of these are great and worthwhile objectives. At my current (low) state of knowledge, if I wanted to do #2 or #3, I'd probably start with a good look at the J-2 structure to understand the loads and how they are reacted in that original before going my own way. I think that is what you are doing now with the number crunching.

On the wing loads and attachment pins with a wider fuselage, do they change? In my uninformed view the answer likely depends on where we consider the wing shear load ("upward force") as terminating. If we are working with the assumption that the shear ends at the first pin it encounters (and the distance from that pin to the wingtip is unchanged by the fuselage widening), then no change to the spar calcs is required, and any lengthening of the distance to the second pin will only reduce the (downward) force on that pin. OTOH, if we are working on the assumption that the terminus of the wing shear is at some point between the two pins, then the spar length does change if we increase the distance between the pins. My caveman view is that there will be an "up' force on the first pin and a 'down" force on the second pin, so the actual end of the wing shear forces (zero up or down force) is somewhere between them. If that is right, then increasing the distance between the pins changes the effective spar loaded length and the calculated loads. But, it would be WAY better to get the opinion of someone who knows what he/she is talking about

The renderings are great, thanks.
Mark

 

[Hephaestus]

what is your goal for all this really nice work you are doing?
1) Create a set of unambiguous, correct, legible digital drawings for the original J-2?
2) Create a set of digital drawing of a new plane derived from the J-2 (a bit wider, higher gross weight, a little more fuel, taildragger)?
3) Same as #2, but using other construction materials instead of wood in some places.

#1 Goal right now is to keep myself from getting further covid crazy Even being a loner - lack of options and things to do is driving me insane... This at least puts the mind on something different. Will I give the model / drawings out - not sure today. Partly why I'm looking at loads - Understand the structure better, not about to release anything to the wild without at least a MTOW that I'm confident isn't copied/pasted from a different design.

#2/3 Been slowly progressing that way for years. Yes my fat butt wants/needs a design that doesn't exist, and isn't apparently marketable. That long promised PAV/personal air vehicle, Something very fast, with a solid 3+hr range that fits me myself and I. Maybe a backpack with a change of clothes. (BD5 was supposed to be this, Quickie was there but no range and definitely no big scottish butts - notice this was 2 aircraft that sold a lot of plans/kits).

200+mph, single seat, room for a backpack with a change of clothes and 3+ hours range. Easiest way to go fast, reduce wetted area to the absolute minimum, throw a big engine on it. This configuration still keeps all the major loads very close together so structurally efficent.

Yes I'd prefer composite. Ideally CNC cut cores, mostly tab in slot self-jigging assembly. Rutan 1.5 style - so mostly vacuum bagged wet layups. Majority of the parts being flat-ish profiles to keep the end finish sanding fairly quick and easy (with a nice 6' sanding block) Canopy like this out of flat stock drops another 1000$ or so off the cost.

If it's eventually considered like the quickie a throw-away/disposable plane, so be it. If the construction hours/costs can be kept inline - I don't see an issue with it getting that title.



So, currently this is the configuration. looks like 325lbs is max pilot size. (Might be good post covid) Wings do taper and have a little forward sweep. Tail is pushed back about 2' (yes the H&V stabs are making me crazy to get them to look right) It'll get a T tail. Laminar airfoil, nearly full span flaperons - Leaning towards stub wings in this iteration (allows more fuel/range with less CG movement - and safety wise puts it outside the fuselage) Working around Yamaha Nitro 3cyl turbo, And a little bit more room for a prop. In theory it makes the numbers I'm looking for - with a phazer 2cyl 50-80hp (so would also fit a VW for the aircooled folks) and less pilot weight still does respectable #'s.

 

[Vigilant1]

Hephaestus,
Thanks for the insight. Your little project there would be a go-er, and a natural for VW power.

An aside: Just for grins, I've been comparing the J1 and J2 specs to the (prospective, speculative) numbers for that twin-industrial engine MicroMaster idea I've been fixated on. The wingspan and wing area dimensions weren't much different, and the installed HP (56-60 HP with both engines running and 28 HP with one dead) are very similar to the J-series aircraft (with their biggest engines and the smallest ones). The performance of the J-birds on 23-30 HP give some support to the single-engine climb numbers I'd figured for the MicroMaster (even after making allowance for the stopped prop drag and the higher weight that airplane would have). So, that's encouraging news.

Any word on your hopped-up B&S engine project? Ya know, it could power a light J-2. Just sayin . . .

 

[Hephaestus]

B&S, Well it's on a very back burner - I keep saying I should build the lazy bee to use it. But honestly - I don't need it... I'm not thinking I'll get use out of it if I do.

Whereas an fast single, that's an easy 2-3x a week use, and fuel / hours saved on the mooney make it a quick ROI.

The B&S is still being worked on but it's a very back burner project - kind of loosing interest in it honestly. Builder and I have talked a few times about possibly letting it go to one of his other customers when it's finished...

 

[Hephaestus]

Speaking of size, Probably should have done this sooner.

That's a rather scrawny 5'2" design tool.

Direct xyz scaling up to 6'3, full face helmet, steel toes and removable shoulders seem necessary

Canadians are going to have to put up with flashbacks to their childhood

 

[Vigilant1]

View attachment 107071

Speaking of size, Probably should have done this sooner.

That's a rather scrawny 5'2" design tool.

Direct xyz scaling up to 6'3, full face helmet, steel toes and removable shoulders seem necessary

Canadians are going to have to put up with flashbacks to their childhood

Looking at that frame, and at the risk of sounding like Ralph Nader, the area from the seat back to the rudder pedals of this craft could do with some beefy structure to keep the trees and rocks out, and maybe a little honeycomb or EPS forward of that to slow the decelleration of our pudgy pinkness a little bit if we hit something solid. It can't be an F1 crash cage, but something akin to what the glider guys now have seems appropriate and practical, at least if using composites.

 

[Hephaestus]

It can't be an F1 crash cage, but something akint towhat the glider guys now have seems appropriate and practical, at least if using composites.

Mclaren, so a little high end. But notice the F1 crash cage left.

I may have borrowed a few lines / structural cues. based off of it. The big beam in the canopy wasn't a aesthetic choice.

https://journals.sfu.ca/ts/index.php/ts/article/viewFile/529/500 Interesting read

 

[Aerowerx]

Looking at that frame, and at the risk of sounding like Ralph Nader, the area from the seat back to the rudder pedals of this craft could do with some beefy structure to keep the trees and rocks out, and maybe a little honeycomb or EPS forward of that to slow the decelleration of our pudgy pinkness a little bit if we hit something solid. It can't be an F1 crash cage, but something akin to what the glider guys now have seems appropriate and practical, at least if using composites.

There is more structure there, in the floor and sides, not shown in his rendering.

 

[Vigilant1]

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