I don't see much else in the J2 plans, it looks like there are a total of four 20mm x 20mm longerons that go to the nosepiece, plus the skins (which serve as a shear panel between the longerons). The photos of the J-2 show a little fairing in front of the canopy that is above the 'waterline" longeron, and I suppose that might locally deepen and stiffen the nose a bit. Is there additional longitudinal wood or cross-bracing that I missed?
The Janowski Project - Rethinking the J1B/J2/J3
- Thread starter Mohawk750
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Mohawk750
Well-Known Member
Sheet three of the plans shows the foam core to that cockpit structure from the nose back to aft edge of the pylon. It's skinned inside and out to form a composite panel. The floor looks to be single skin but I'd be tempted to make that a sandwich as well with embedded hard-points for the control system, rudder pedals etc.
I love Hepaestus's render above which adds another body line above the longeron with carbon fiber canopy frame and shoulder high crash bar protection. Makes me think if you built it inside out with plywood interior, foam core and wrapped the whole thing in glass/carbon you could make a pretty strong pod.
The only issue I have with that render is the main gear are too far back and the little wheel is on the wrong end!
I love Hepaestus's render above which adds another body line above the longeron with carbon fiber canopy frame and shoulder high crash bar protection. Makes me think if you built it inside out with plywood interior, foam core and wrapped the whole thing in glass/carbon you could make a pretty strong pod.
The only issue I have with that render is the main gear are too far back and the little wheel is on the wrong end!
Thanks, that's a great find. I need to think a bit more about those box keels they have designed and modelled. Each is 60mm high (deep) and 50mm wide. The skins that make up these boxes are 2mm thick aramid reinforced plastic (epoxy, I assume). Inside the box cavity is some supergoo "Theta-6" silicone that is tough and strong (at least for a silicone). As near as I can tell, they are attempting to make the keels "tough" and energy absorbent by including this silicone and using aramid (which certainly does hang together well after it crumples) to make a keel beam that can absorb a lot of energy >when< it crumples. It will be ductile, like a steel tube rather than a stiff. frangible composite component, I guess. And that sounds good. But: Each beam is 197.5cm long, and by my math the aramid epoxy skins weigh 1.2kg (2.6 lbs) each. The silicone density is 1.06g/cm3, and there are 5,088cm in each beam, for a silicone mass of 5.4 kg (11.9 lbs). So, by weight, there's 450% more silicone than composite skin in each keel. Also, aramid is very weak in compression (in some cases, weaker than the epoxy matrix). That could be a problem in this end-loaded column. And, in their modeling these keels do crumple and the occupant safety area is badly compromised (though not as badly as in the "before" case where the glider had no keels/lower longerons at all).
What I'd like to know (and what they didn't model): What if you'd replaced that silicone with light XPS foam or a corrugated CF/epoxy web and used the remaining saved weight to triple the thickness of those walls? And used CF/epoxy to build them? Put a light layer of aramid outside to contain the shards, in case of fracture, but I'd bet there's a good chance that the keels would remain intact and so would the passenger area. Do the energy absorbing with the nose cone, good harnesses, etc. and keep the flail space intact.
Anyway, they have an interesting approach. There are some promising references at the end of the article. I'll try to track them down and see what I probably misinterpreted.
Mark
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Hephaestus
Well-Known Member
Yeah I like that look, and having the structure there. Knocks off a bit of frontal area too. I keep seeing it as tubular structure, need to look through more of those student papers on the carbon monocoque chassis's they build for the solar/offroad/human power challenges. Then struggle through that math tooI love Hepaestus's render above which adds another body line above the longeron with carbon fiber canopy frame and shoulder high crash bar protection. Makes me think if you built it inside out with plywood interior, foam core and wrapped the whole thing in glass/carbon you could make a pretty strong pod.
The only issue I have with that render is the main gear are too far back and the little wheel is on the wrong end!
Gear - had to pick one or the other for a model. Seem to recall something about sales of conventional vs tricycle, ercoupe may have gotten that right
Still think there's a lot that can be done in cockpit crash safety. What can be done at home and keeping a reasonable budget is a whole different question. But there's some great thesis projects on chassis' out there on formula SAE teams and solar car projects to read/mull over.
Was wondering about the carbon/kevlar hybrid fabrics (usually in godawful colors) as the innermost ply rather than straight kevlar inner ply.
Shh I had to find a way to clean up the T-tail. Pretend its a baby dash8 not a tupolev.
Buster the crash test dummy is scaled to 6'6 in this one, room for a helmet too. GRS 3 350 could be fit between engine and seat back.
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Aerowerx
Well-Known Member
I was reacting to your reaction to the graphic rendering which does not show the two longerons in the floor from the nose to the second bulkhead. There are also skins on the inside, and I believe a foam core. Can't read the page number(sheet 2,maybe???) on the plans, and mine are all out of sequence.
And let me buck the crowd and say I think the trigear looks good.
Do you think the narrow front canopy at eye level, the frames, and the high grazing angle of the view through the side panels toward the front will be a problem? It looks good and is probably a good approach from an aerodynamic perspective.
Mohawk750
Well-Known Member
Was thinking about this last night and what about keeping the upper canopy frames parallel and fixed front and back to the bulkheads and hinge the side glass from the top sort of gull wing style. You could make a strong cage that way and with the increase in size entry is still not too bad. You can use a airline style seat foot screwed into each end of your crash bar in the door and a rotary latch to lock it so its part of the cage when closed.
You could also pull the upper nose skins back to the top of the instrument panel to stiffen that area. You can't see past the pedestal through the windscreen so why not close it in and make it strong. You could even add a big Styrofoam crush block in the nose to absorb energy in the event of impact.
This configuration makes the installation of the BRS behind the seat and right above the CG quite convenient but it will compete for fuel tank space which I don't really like behind my head anyway. What were your thoughts of fuel tank location?
Mohawk750
Well-Known Member
I think it looks better from the outside than it will from inside. Too much structure front and center at eye level. I think parallel frames to widen the field of view would be preferable.
Hephaestus
Well-Known Member
Do I have questions about the visibility yes.
But comparing against say an aeronca c2 - It's awesome CGS hawk - you've got a lot less obstruction, And its widening as you go lower, rather than narrowing. A10 has that big bullet proof plate straight ahead.
Eye level for 6'3 me, behind the canopy though, this is the dense glass model, so more reflections given than clear.
I don't know about you but i don't see a massive visibility problem.
But comparing against say an aeronca c2 - It's awesome
CGS hawk - you've got a lot less obstruction, And its widening as you go lower, rather than narrowing. A10 has that big bullet proof plate straight ahead.Eye level for 6'3 me, behind the canopy though, this is the dense glass model, so more reflections given than clear.
I don't know about you but i don't see a massive visibility problem.
It might turn out just fine, I just wanted to mention it.
In the Sonex, the view through the (large) front windscreen is at a very low grazing angle and many folks find the reflections from the internal surfaces very annoying. The solution is to put a very non-reflective cover on the top of the (appropriately named) glarescreen. Work well. But, that won't be an option in the J2 setup because the light will be coming through the opposite side.
Again, maybe it will be okay.
In the Sonex, the view through the (large) front windscreen is at a very low grazing angle and many folks find the reflections from the internal surfaces very annoying. The solution is to put a very non-reflective cover on the top of the (appropriately named) glarescreen. Work well. But, that won't be an option in the J2 setup because the light will be coming through the opposite side.
Again, maybe it will be okay.
Hephaestus
Well-Known Member
Fuel tank, below the wing is still wide open other than the main gear hoop. I've mentioned before I'm leaning towards stub wings and fuel close into CG. Seems to be the prevailing thought in a lot of homebuilts - move it out into the wings. Also permits me a bit more freedom - Since I really do like XPS cores for local availability/cost - keeping the fuel in the wing stubs means less sqft of expensive cores to buy for that section.
Structure wise, I keep mentioning university build a car programs that all seem to use:
This basic 'cage' even if they do make it out of composites. Add another hoop above at the rear triangulation point - that becomes your firewall.
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My unsolicited thoughts on the fuel tank: In a crash, seems like having it inside the very robust safety cage is good. Yes, lash it down securely and build a very strong tank enclosure. But if it is behind me, any foreign object that penetrates it has already penetrated me--no more worries! Keep it higher than the carb, if there is one, and I can avoid the weight of a fuel pump and eliminate one point of failure. No transfer pumps, no fancy valves except a shutoff, and a sight gauge tells me my fuel state.
In the wings--lots of frontal area exposed to the passing trees. A gallon or ten of fuel spilled right outside the canopy is hardly safer than if it were inside the fuselage.
Still, I don't think either approach is worse than the tanks on a lot of certified planes.
In the wings--lots of frontal area exposed to the passing trees. A gallon or ten of fuel spilled right outside the canopy is hardly safer than if it were inside the fuselage.
Still, I don't think either approach is worse than the tanks on a lot of certified planes.
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Mohawk750
Well-Known Member
Fuel in stub wings could work or a big belly tank within the structure with a firewall bulkhead behind seems appropriate, Regardless of where you put the fuel gravity feed to the engine is out of the question so you'll need pumps and if you go fuel injection you need pumps.
What happened to your latest render? It doesn't show up any more
Hephaestus
Well-Known Member
Trade off in compromises. Not aiming for a spectacular unobstructed view - putting more emphasis on being able to build it relatively inexpensively and quickly. 1000$+ for a blown canopy buys a lot of 1/8 acryclic and various coatings to try to reduce glare if it's an issue for you.
Hephaestus
Well-Known Member
HBA seems to be persnickitty this afternoon. Guessing we're having some server upgrade glitches. They're all showing for me.Fuel in stub wings could work or a big belly tank within the structure with a firewall bulkhead behind seems appropriate, Regardless of where you put the fuel gravity feed to the engine is out of the question so you'll need pumps and if you go fuel injection you need pumps.
What happened to your latest render? It doesn't show up any more
The fuel pump thing - so be it, inherent issue with the design - no real option for gravity feed.
Mohawk750
Well-Known Member
Ya, that was kinda my point, there is an added complexity with pumps over gravity feed but with this configuration there's no way around it so it is what it is....inherent to the design.
Images are all back now.
Hephaestus
Well-Known Member
There's another one.
Ballpark VW cowl, YG3 should be able to be a bit narrower. Need to look at what radiator sizes are typical for the YG3.
Pondering through a nose gear option, leaning towards a trailing link, Seeing if I can find an airfoil profile that would fit the LG and wheel - so it's fully faired in with just a single mold
You are morphing towards the Ultrabat:
BJC
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Hephaestus
Well-Known Member
Mohawk750
Well-Known Member
Interesting addition to the rudder trailing edge to increase area in the first link. It ain't pretty but it works!
Much cleaner execution of the configuration in my opinion.I prefer to think I'm morphing into Strojnik's laminar magic
Just goes to show you the influence that the J-series had on the many designs that followed. If you built from tube and gusset you would morph toward the CGS Hawk, Quad City Challenger, Hornet and many others.
While I admire the look of all the composite tadpole like designs these are not very accessible for the homebuilder on a budget. The faceted flat panel composite build up is a little more achievable but there are lots of corners dependent on good bonds to achieve strength.
I'm wondering at this point if its easier, simpler and less expensive to build the fuselage pod with ply skins on the inside of the framework whch carries the load paths, infill the sides of the structure with foam and add some compressive areas in the nose and under the seat. You could then carve to a pleasing shape and wrap with kevlar/carbon for a strong pod structure ala 21st Century KR1/2 and vari eze. Just thinking out loud as to how I could do this in my garage.
