Thorp Air Command - T18.net

Hi all. I have been developing a flat layout of the 580-10 tail fairing. I was interested to know what the current thinking is with respect to removability of the tail fairing and or the addition of small inspection plates I have seen a number of different approaches but not a lot of consistency. I also recall reading a few different approaches in the newsletters. My initial thinking was to attach the whole thing with machine screws into nut plates so that it was fully removable but a lighter option might just be to pop rivet it on with 3/32 or soft rivets and then drill out the rivets to gain access for inspection, if needed.
Any comments? Anyone care to look over my drawing and give it a sanity check?

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Stug

Stug,

Many of us have modified the design slightly, to a 2 or 3 piece assembly, allowing removal of the side pieces for inspection & service without having to remove the rudder & vertical stabilizer. I definitely think nut-plates & screws are the way to go. Use good design practice with doublers & adequate fasteners to maintain structural integrity & strength... it's a critical area. You definitely wouldn't want to use soft or undersized rivets!!

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Mine is made in (3) pieces using floating nut plates and plenty of support for the attachment . Allows me to take off the two small panels for inspection and lubrication of bearings , etc . I've seen one or two that use a hinge on the side pieces . With the hinge your access is reduced slightly . BOOM !

RB

John's comment about "soft" or undersize rivets is sound advice . With my NAS screws and appropriate doublers the 580 piece is a brute !

RB

When I got "Feisty", that area was riveted in, AND painted over!
I had a trim drive failure, during my wife's 2nd lesson in it. So I drilled out the rivets, received my introduction to John Thorp's all flying tailavator, and replaced the driveshaft roll pin.
I reassembled with screws and clip nuts to get back in the air, but I see the posters here feel this should be a sturdy box structure, so I'll probably rivet in some plate nuts at the condition inspection.
I'd like to ad that "Feisty" has a multi piece assembly here, and the 'port side' cover is where I gained access to repair & inspect.

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Scott Emery
EAA Chapter 326
T-18 N18TE

Thanks guys
I kind of already knew that the undersized rivets would be a no go, not sure why I asked that one
I would like to keep the tail light and was hoping to avoid the weight penalty of extra doublers and or nut plates if possible. I was already planning on having inspection/ access panels in the side skins of that bay, would access from below via the side skin access provide adequate access for inspections/ maintenance. Probably not I'm guessing or everyone would have done it that way.
If seeing in from the top is really needed then the attached photo shows one option that appeals to me as it should keep added weight to a minimum. Doesn't give much room to swing a spanner it would be like keyhole surgery one could hope that with 3 points of access there wouldn't be too many occasions when you would need to remove the whole fairing.

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Stug

This is a structural box and should be treated that way. If you look at the Thorp design there are several structural boxes in the design. Spar box, wings, side skins, floor, to name a couple. Make sure when modifing these that you take into consideration you are weakening the structure

Bill I certainly wouldn't want to weaken the structure, for me the simplest and safest option if in doubt is to leave it per plans.
You would assume that those with openings and removability have adequately compensated to retain structural strength. It's also possible that in some cases there may be some over compensation and beefing up of the structure more than is required to compensate but adding unnecessary weight in the process. Do you have an panel in the fairing?

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Stug

The few extra rivets , nut plates/screws and 2 pieces of doubler (to attach the nut plates to) to make the 3 piece 580 weighed next to nothing . When it is all "screwed" together it is a sound structure .

RB

Mine looks very much like yours , Stug. Made it per plans but used 8-32 screws and nut plates. Have 1300 hours on the airframe and no problems.

I would suggest making the side panels removeable as was discussed, but also keep the lower inspection panels. My new airplane has both. It also has lower inspection panels on both sides. Not a big deal structurally as you beef it up as noted. But servicing becomes MUCH easier with that much access.
Cubes

Have updated my flat layout plan to include a small inspection panel, it's minimalist but better than no access. I am still pondering how I would do it if with fully removable hip sections. Sure it would make for easier access but there is some added weight and how often are you really needing to swing a spanner in that area. I have no experience doing annual inspections, I assume it would be a visual inspection, check for any play, adjust if necessary and lubricate, is there more to it more to it than that? On a related note I have seen one T18 where the jack screw nut was changed from aluminium to brass in order to reduce the wear and hence play That apparently worked well for that builder and one would expect that would minimise service demands.

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Stug

Not sure what you are going to really see with that small inspection panel ? You are correct , with the (2) removable sides you will have more access to see all the important areas you need to see and "lube." If you really need to "Swing a Spanner" then it is time to take off the rudder and fin . IMHO there is NO weight penalty installing the 2 side panels . We are talking ounces for a few nut plates/rivets and screws . The time it would take to make your 580 with the small inspection panel you could make a 580 with the 2 side panels .

RB