Thorp Air Command - T18.net

Technique only but I normally see the brake lines punch through the firewall not the belly. That way they can line up with the gear better.
Cubes

Cubes thanks for the feedback I agree, I have seen more go via the firewall and it probably does make them line up better with the gear leg. I am still debating with myself the merit of two different approaches.
Having said that the brake lines going through the floor I think initially came from something I read in the news letters. I had hoped that this approach might simplify or reduce part count while making it possible to drop the removable floor and leave all the internal cockpit brake connections intact.
As I have drawn it the brake lines would exit the floor approximately an inch behind and 1/4" inside the gear leg, I hoped that this would still allow the brake line to cleanly fit within the upper gear leg fairing and give enough room to allow some flex in the line as it loops over to the gear leg. Are my assumptions sounding reasonable?

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Stug

Stug,

I would strongly recommend you not make any accessory and fitting holes as part of the CAD assisted cutting and routing. These holes (such as the outlets for the fuel vents and drains) can easily be made with a step-drill after the fuselage is assembled. As to the brake lines, they are more easily accommodated through the firewall.

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Bob Highley
N711SH
SN 835
KLAL

Looks like you considered all the right things on your floor. You might also consider how to attach the close-out for the wing spar. I included a doubler there and nutplates so I can make a flush joint there also. Besides that, I included a small access plate below the rudder cable connections for inspection. Please keep in mind however you do these kind of things, to be careful about collecting exhaust fumes by any amount down there. CO poisoning can sneak up on you.

Les Krumel,
Albuquerque

I wouldn't think it a huge deal, but the gear tend to flex aft during landing. Pop the brake lines out the firewall with a small service loop, not a full 360, just a flair if you will, and they will line up to go directly down the aft side of the gear leg. When you attach them, they need to be able to flex both at the top and bottom.
Cubes

Thanks all. Looks like the brake lines will be moving to the firewall.

Bob can I tease out some more detail from you on your reluctance to pre drill for the accessories. I didn't see it as being a major problem, yes it is easy enough to drill the holes later but the CNC precision will be higher, if I can understand your concerns better it might improve my planning further.

Les I haven't done any planning for the the "close out" I don't recall seeing any reference to in the news letters so it's a bit of an unknown to me at this stage. Is there any chance I could see a photo or picture of your solution to help clarify the approach? For rudder cable inspection I was anticipating providing access via the centre tunnel.

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Stug

FYI I like to run the brake lines on front of the gear legs, I've seen lines pinched from hard landings.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Stug,

My thoughts come after building and maintaining my T-18 for a few decades. I'm also in the process of building another T-18 and I had a hand in building an RV-7A. First and foremost, you have put a tremendous amount of effort in the project so far. It would be a pity if you couldn't make one or several more "kits" due to your "customization" of the accessories. I suppose the additional cutouts could be presented on a CAD layer to be exercised at the desire of the future builder. Secondly, I know from experience that not all accessories are going to come out where you think they will. An example is: The forward tunnel as depicted in the plans leaves no room for brake hoses to pass through. I had to modify my plans built tunnel significantly to accommodate the lines. Another small example is that comm antennas come with either three or four holes in the base plate. You don't want to lock yourself in on small items like that at this time.

As to the spar close out on the bottom of the fuselage, it and the floor pan need to be separately removable. My reasoning here is that the area under the flight controls is a periodic inspection item. You don't want to remove the floor each and every time you pull an inspection. While on the subject of floor panels, this piece is a rather important stress panel in the design of the plane. Randomly cutting large holes in it will substantially weaken this critical piece. Put inspection plates in it with great caution.

Enough rambling. My main point is - do not put a lot of holes in the plane until you see how it all goes together. My two pence.

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Bob Highley
N711SH
SN 835
KLAL

Case in point, note brake line, there has been at least one hard landing some time in the past.
Left gear leg from under the fuselage, there isn't a lot of room to run the brake line through the floor and into the gear leg fairing. The brake lines on this aircraft go through the firewall using a steel AN833 90 deg bulkhead fitting. Large tube running down the front of the gear leg is the crankcase vent.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

I used entirely SS braided Teflon lined race car brake lines ( I think they are Teflon lined ? It has been a while ) and SS fittings. One single line running from the MC to the caliper . Thru the belly (thru a grommet) just aft of the gear leg , attached with 2 adel clamps along the way down the leg . Ran them behind the gear leg as that gave the greatest amount of clearance when the gear fairing was placed on .

RB

Guys thanks for the comments this is all great information. I now have one vote for routing the brake lines out the floor so maybe i have some more to think about. Rich your approach was very similar to what i had in mind if don't mind taking a closer look at the PDF drawing i posted you might be able to confirm if the location of the brake lines seems similar to how you did yours. I expect that the clearance would be very tight. One thing in favor of going out the floor is that it can't pinch the lines as has been shown to occur.

Bob yes the accessories are on a separate drawing layer which can be turned on or off as needed.
I only plan on cutting out those accessory items for which i have confirmed the location and mounting dimensions with a high degree of confidence and have locked myself into. In a few cases i have drawn multiple different accessories just to check adequate clearance and try and understand the implications should an alternative be used. It does get hard when there are so many possible antennas and variations of placement.
The idea of making kits has crossed my mind so I am trying to keep potential production in mind but at the end of the day the drawings are for me mostly about comprehensively thinking through and pre planing as much as I can to improve quality.
Teasing out all these undocumented issues in advance is tricky but if I get it right it could add a lot of "quick build" value to any future use of the drawings or kits derived from them. Now given you mentioned it I will have to go back to the the centre tunnel drawing and look a making more allowance for the brake lines.
Thanks again I appreciate the comments.

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Stug

Stug : I looked at the drawing and your location is approx. where I ran mine thru .

RB

On the Stug drawing, why 2 fuel vents was design on the front skin bottom?
Only one vent is present on the original fuel tank.
I'm tired to scratch my head......with-out good result
Thanks for the answer

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Thierry
French Canadian T-18
C-FPVE #091

One is for the filler area scupper drain in case you overfill the tank.

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Bob Highley
N711SH
SN 835
KLAL

So simple!!!!!
On my T-18 I have a standard gas cap. Same as Cessna or Piper.
I have to eat more bread crust because often I'm behind all of you!
Each day when I read the forum or when I work on my Thorp I learn something new!

Another good leason
Cheers.

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Thierry
French Canadian T-18
C-FPVE #091