Starting Landing Gear

8/22/2009

Too Bloody Hot

It's been a while since my last update. There are two reasons for this, i) waiting for gear legs, ii) we've had triple digit temperatures for 50 + days here in central Texas. Working in a convection oven like a steel hangar is not fun when it's 106 degrees outside :-| .

RV/Wittman Style Landing gear

Recap...

I had been looking at the possibility of using spring steel (SS) landing gear (Wittman Tailwind and RV's) as opposed to the traditional bungee gear, or the Groves aluminium gear. My reasons for this deviation is i) sleek modern look (which is the look I desire) ii) less under-wing turbulance iii) less drag. However, the penalty is potentially more weight compared to bungee gear. So, one has to compare the trade-off between looks/heavy/but streamlined versus traditional/lighter/bulky.

I initially had a spare RV7 leg that someone loaned me for mocking-up. I was kind of hoping this leg would be darn close to my geometry, but as half expected, that was too good to be true, but it did get me close regarding visualization. I then discovered two significant leads...i) the EAA website has a design spreadsheet with formulae dedicated to this type of gear design and ii) I discovered the contact# for the company that make the spring gear for RV's - and they do custom sizes (Harmann Lange).

Moving On...

I decided to go ahead with the SS gear. Without help from a knowledgeable friend (Markus Goetting - multi RV/F1 Rocket fabricator) I wouldn't be doing this modification. I ordered the custom sized gear from Lange Machining, and they arrived 5 weeks later. They came out at $600 for the pair. On the scales, the legs weigh 16 pounds each.

According to the spreadsheet, the proposed spring gear was to be heavier and slightly thicker/longer than the RV7 leg, and will have 1.5" axle dia, like the RV10. Currently, it seems the SS gear is less in weight compared to the alum groves type gear when comparing apples. Here are the weight breakdowns;

Grove

00.30 - 0.90 4130 various small fillers (ballpark)

39.00 - alum gear (for 1800GW)

00.92 - tube 4130 3/4x0.49x30"

00.60 - tube 4130 3/4x0.35x27"

00.21 - tube 4130 7/8x0.49x6"

00.85 - tube 4130 3/4x1.88x9"

01.30 - support channel 4130 2.5x10x0.90 2 of

00.86 - clamp plate 4130 1.75x7x0.375 2 of

00.65 - bolt nut washer AN6-42A 4 of

02.56 - grove axle 2 of

00.48 - alum bearing block 1x1x1.25 4 of

00.24 - alum radius plates 1.5x7x.250 4 of

n/a - brake linings (gun drilled)

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47.97

Spring round tapered steel (RV/Wittman style)

32.00 - legs 2 of (custom made for Skybolt S 1800GW)

03.60 - sockets 1.750x.188x11" 2 of (reamed up to fit leg O.D.)

00.25 - bolt nut washer 4 of (ballpark)

00.30 - 0.90 'possible' 4130 gussets

00.50 minimum - horizontal socket connector tube (attributes yet unknown)

??.?? - brace tubes (attributes yet unknown)

(??.??) - less cut-out engine mount material (attributes yet unknown)

02.00 - fairings & wood (competition balsa) dampers

00.30 - brake linings (best guess)

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38.95+

Bungee Gear

34.00 - legs 2 of

01.00 - fuselage leg attach points

??.?? - gear truss

00.33 - center block

??.?? - bungee cords

00.30 - brake linings (best guess)

??.?? - fairings

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If anyone feels like getting me numbers for the bungee gear, that would be cool, for a comparison.

To Do

Next, will be getting the leg sockets reamed up to fit the SS leg O.D. So I am now sourcing a drill bit to get me 'close', adjustable reamer, and maybe a cylinder hone for good measure.

Fuselage Rotisserie

I made up a fuselage rotisserie. Those who have built with and without one know the easier route :0). I purchased a sacrificial engine mount from Harbor Freight for around $35. I needed to raise the mount so it's center point matched the center point running through the fuselage and alter the mount angle to 90 degrees (they come angled, slightly). So I chopped the upright in half and hammered in some 2x4 lumber on each end, then bolted on a pair of 1/8 steel angled plates to bring it back to vertical. The tail stand is from 2x4s studs.

The rotisserie is now ready, but I cannot use it yet because I have the fuselage inverted and clamped solid to a wood frame complete with concrete bags as ballast, while I mess around with a jig for the SS landing gear.