Vendor wanted to complete fabrication of a permanent forward landing gear support structure.
Updated 27 June 2020.
Fabrication of the permanent forward landing gear support structure for my Boeing 727 home is well under way, but experienced concrete assistance is needed. Please advise via email if you have an interest in this project.
Very slow tangible work began in earlier years. The framing structure, internal pipe, conduit, and other fabrication work is very roughly 75% complete, and I hope to finish those items by late July. I hope concrete can be poured by 3 August or earlier, before a possible substantial public event on 14 and 15 August 2020.
You can view some year 2019 excavation and internal infrastructure work at images 51 through 60 here, and the more recent image 43 here. And after review of my visitor's information you're welcome to inspect my property and aircraft directly at any daylight time.
● Description of the structure and fabrication details:
The structure consists of a simple rectangular rebar reinforced concrete base pad plus a rebar reinforced cylindrical pillar with a top outward flare and a bowl shaped (concave) top. The pillar diameter is 2.717 M (8.913') and the flare diameter at the outer top rim is 3.1712 M (10.404'). The height from the top of the pad to the outer rim of the flare is very roughly 2.5 M (8.2') (precision figure a bit later). The tires in the images reside at their final height so the center of the structure should just meet them. At a suitable time the tires will be retracted upward by compressing the front landing gear strut with a hand winch to provide working room of very roughly 33 cm (13") above the top of the finished concrete. Rigging for this is already in place. (Alternately the landing gear could be completely retracted to provide much more working room.)
The front landing gear presents a maximum mass of very roughly 9 K Kg (roughly 20 K pounds) so the concrete pillar will yield an immense safety margin. Metakaolin (White) concrete (see "High reactivity Metakaolin" under this) is preferred for better aesthetics and performance.
Multiple sections of pipe, conduit and other materials reside within the concrete.
The framing is fabricated of robust aluminum sheet metal from a freight van. It might be strong enough to resist bursting, but an outer wrap of strap, cable, or heavy rope reinforcement must be added to insure sufficient strength.
I hope to provide precise dimensions for all details, flare construction analysis, plus framing pressure and other analysis here soon.
Clear access for concrete trucks via my neighbors property on my east side, the Denfeld family, with their permission is evidently available except during sensitive nut growth or harvest seasons. However please walk or ATV ride that route with me or a Denfeld family member so you can inspect its practicality directly. There is a short initial section which is steep but otherwise the route's clear and straightforward. Alternately direct access via my private dirt road might be viable.
At a suitable time after this project is complete fabrication of second structure for my left main landing gear should commence. I can provide details for that structure, which will be generally similar except larger in diameter but shorter, whenever you prefer.
Cash stands ready! The major cost should be the concrete since I'll complete most of the preparation work. I'm willing to prepay with tangible assurance the project will be successfully completed.
Please advise via email if you're interested. If so please also suggest a very rough uncommitted price estimate - a figure you don't promise to quote later but suspect is sufficiently in the ball park to enable me to consider the expense.
Many thanks to all prospective fabricators!
The following is legacy information which is no longer significantly relevant.
● These alternate approaches were considered earlier (informal narratives):
Fabricate a conventional reinforced concrete base pad. Then in alternating orientation stack 2" x 4' x 8' Styrofoam insulation panels arranged into an 8' x 8' square onto the pad, in a stack nearly high enough to reach the tires (very roughly 8' high). Then fabricate a bowl shaped reinforced concrete lid on the top to complete the structure.
As a matter of aesthetics cut the outer corners at 45° angles to form an octagon. Or perhaps trim into an oval or even fully circular shape. (That's fast work with a chain or manual tree cutting saw). And perhaps an oval or circular shape would be beneficial structurally since the stack could then be gracefully enclosed by the available aluminum panels.
Or perhaps better: Ovalize or circularize the Styrofoam, then surround it with the aluminum panels but leave a gap of very roughly 15 centimeters (6"), then fill that with rebar and concrete. Then fabricate the top bowl. (Whether before or after the outer perimeter concrete cures is better is uncertain.)
Or perhaps best: The same as just above, but additionally provide a modest diameter reinforced concrete center pillar as well. Perhaps very roughly 30 cm (1') in diameter, or a bit wider. (Inclusive of the central 4" drain and chain housing pipe.)
That last design would be stronger, substantially improve top bowl cracking resistance, and fully enclose the Styrofoam and thus protect it from burrowing insects so long as the concrete remains intact. (A low viscosity polysiloxane coating of the outside surfaces of the Styrofoam would permanently eliminate insect vulnerability but I need to investigate the bulk price of the material to determine whether it's economically tenable.)
The Styrofoam alone is sufficient to support the mass of my nose gear with ample safety margin. At 8' high the cost would be $2.4 K (more if a more moisture resistant grade is utilized). Some very simple vent windows are necessary to allow interior moisture escape. (I suspect the interior will still tend to be damp but doubt that's a serious issue.)
Here's a possible fabrication sequence for that design:
1. Arrange the base pad rebar (including vertical extensions for the central pillar and outer wall), then pour its concrete, then allow it to cure.
2. Fabricate the center pillar rebar.
3. Stack the Styrofoam panels, cutting holes for the center concrete pillar and internal conduits and pipes as the work progresses. The internal 8' long joint line will be alternated 90° with every layer. Smears of low viscosity polysiloxane or vertical insertion of long nails will secure each layer to prevent shifting. This might be reasonably fast work if the conduit and pipe holes are cut rather roughly, which is okay, especially if concrete is poured into the gaps to fill them as the work progresses (perhaps pour concrete into the gaps after every roughly ten layers of Styrofoam are added). For many layers the hole and trim cut locations will be identical so once holes for one panel are cut it can be used as a template to mark the holes for several more panels, enabling swift hole cuts until a conduit or pipe bend is encountered.
4. Ovalize or circularize the outside of the Styrofoam with chain or manual tree saws. Precision isn't necessary so it might be pretty fast work.
5. Fabricate the outer wall rebar structure.
6. Erect the outer concrete retention form from the aluminum panels. This structure is already partly fabricated but I don't know if it's tall enough. It's at least close though, so if necessary a second short cylinder should be fairly easy to fabricate. Lots of bolts and nuts are available on site but addition of an outer wrap of heavy rope, cable, or chain seems wise to insure it doesn't burst.
7. Pour both the inner pillar and outer cylinder wall concrete then allow it to cure.
8. Fabricate the top bowl rebar structure.
9. Pour the top bowl concrete, using a rotating curved wood panel to form the concave top surface shape. That is, pin the inside edge of the wood panel to the center drain pipe then rotate it around several times to form the surface, removing excess concrete or filling shallows as the work progresses. I suspect that'll be reasonably easy.
10. Inspect the cured results. If convincing lower the nose gear onto the structure as the stacked wood supports are removed.
We'll probably need a truck delivery of concrete for the pad, then later the inner pillar and outer cylinder wall concrete pours. But maybe a $200 domestic class mixer would be enough for the conduit and pipe gap fills and possibly the top bowl.
My hope is the structure could be completed for very roughly $4 K, of which about $2.4 K is Styrofoam cost.
Due to mismatched temperature coefficients and age related dimensional changes it might be impossible to maintain well shared support of the top bowl and aircraft by both the Styrofoam and the concrete internal pillar and outer wall structures. So it might be best to isolate the top bowl structure from the internal pillar and outside wall structures so the top bowl is supported only by the Styrofoam. If so the Styrofoam alone will support the mass of the top bowl and aircraft - the inside pillar and outer wall will be disconnected and thus provide no support. The Styrofoam has far more than the necessary compression strength to meet this requirement so long as the top bowl structure provides sufficient spreading of the force from the mass of the aircraft. Polysiloxane can flexibly and permanently seal the junctions between the top bowl and the inner cylinder and outer wall.
However an option is to replace the interior Styrofoam with internal concrete structure. For example several internal reinforced concrete pillars - perhaps very roughly 15 each of 20 cm (8") in diameter, or alternately a few internal hollow cylindrical walls, each roughly 6" thick and each of larger diameter, could completely support the top bowl and aircraft. Perhaps that would be just as strong and enduring as the Styrofoam, possibly cheaper, and perhaps require about the same construction time. However all these structures will require confinement forms (two each for the hollow cylindrical walls) to hold the concrete while it cures, which might add too much fabrication complexity and cost. The Styrofoam automatically provides inside confinement for the outer wall pour, a substantial advantage. But it's not clear to me which design is best.
Copyright 10 May 2019 through 27 June 2020, Howard Bruce Campbell, AirplaneHome.com
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