First post, and sacrilege already

[rv7charlie]

Hi all,
I've had an account here for a while, but I think this is my 1st post, and it will probably be sacrilege to many. Hope you will tolerate it, and possibly even answer the questions.
I'm toying with the idea of building a Cabin Eagle, to have a high wing after-dinner flyer hangar companion for my RV6 traveler/(mild)acro a/c.

Being somewhat lazy and interested in a quicker-build (but still affordable) fuselage, I'm wondering if any of the CNC shops that can do tubing are set up to supply a pre-cut kit of 4130 parts, especially tubing.

Also, as you might guess from my login name, I've got a fair amount of experience working with aluminum (around 99% of an RV7 build). While I also have many years experience working with wood, my *personal* preference for a/c parts is aluminum or 4130. For the true sacrilege: Has anyone built an aluminum (preferably 6061) wing for the Double/Cabin Eagle? Either fabric covered or an all metal wing? I know it 'won't be a Legal Eagle' and will likely be a touch heavier, but if the wing is designed correctly it should fly very much like one. Living in the Humidity Capital of the World (Mississippi), where it rains *inside* hangars during temperature swings, I'll sleep better with 6061 under the skin.
Thanks for any help/info you can offer. 
(Flame suit on...)

[kalazzerx]

I doubt there is anything set up for the Cabin Eagle - I only know of one other built besides the original.  I have the plans and looked at it, thought about doing a CAD layout but never got too far with that.  If you can get a good CAD layout done with correct pipe sizing, there are companies around that can take your CAD layout and (was looking at one at one time) cut/build from there - not sure how much though

[rv7charlie]

I was afraid that would be the case. And when I read about it being done in the past, they usually mention having to 'iterate' at least a little bit before everything fits, so even if I had the CAD chops, it would likely cost more tubing and time for a 'one-off' effort than just doing it the traditional way.

I see a lot of the flat parts already on the website. I could also probably draw the flat stuff up and get it done locally, as well.

[Chuck in Indiana]

^^^^ Yeah a water jet shop can cut out all the flat pieces if you give them a .dxf file cheaply, accurately, and easily. Be aware if you use a laser you will be buying carbide reamers because it will cause localized hardening around the cut edge. Don't ask me how I know this..
Hacksaw and file? Just say no.. 
That said, a well designed aluminum wing will be lighter than an equivalent strength wooden wing. Metal wings suck, though.. they don't ride rough air nearly as well. JMHO.

[Dan_]

Being somewhat lazy and interested in a quicker-build (but still affordable) fuselage, I'm wondering if any of the CNC shops that can do tubing are set up to supply a pre-cut kit of 4130 parts, especially tubing.

Living in the Humidity Capital of the World (Mississippi), where it rains *inside* hangars during temperature swings, I'll sleep better with 6061 under the skin.
(Flame suit on...)

Pre-notched kits are the most useless expenditure of cash ever devised to build an airplane.  It is so easy to do.  It adds thousands of dollars to the project...  There are simple paper patterns to print out for the notches and videos on this forum...

The Ercoupe wing is a beautiful metal design and fabric covered... 

Also there used to be an outfit in Florida that sold (metal spars and ribs) Piper Cub wing kits. 

Also there are extruded spars sold on the internet by the same lady that sells the aluminum streamline lift struts.

Also Ed Fisher designed simple bent sheet aluminum ribs that can be used with regular beam type spars or tube spars, ala Raceair or Zipster ultralights...

[rv7charlie]

Well, I have no frame of reference on CNC'd tubing cost, except that for flat parts, CNC can be very cost effective for the time saved. I've done the paper pattern thing on aluminum (hangar door from 6" irrigation tubing). While it's not hard (if everything's right-angles), it certainly isn't fast and accuracy is highly dependent on the 'operator'. My perspective was that a properly CNC-cut tubing kit could yield a 'snap together' straight fuselage at a price point somewhere between total scratch build and the pre-welded fuselage from the guys in AR. 

I'm aware of the Carlson & D&E extrusions, and that there are fabric covered aluminum (and aluminum skinned) wings for many other a/c. I was just hoping that someone had already mapped out a path to do it with the Double/Cabin Eagle. Simple personal preference for grading material based on alloy number instead of grain count/slope checking, and for dimensional stability/wet climate survivability.

[Dan_]

Let us know what their quote is... I know it will be too rich for my blood.

https://vr3.ca/industries/aviation/

[rv7charlie]

Unfortunately, only the LE & LE XL are listed.

[Dan_]

Send them some home spun cad files or send them them the plans they will make them and put that on the tab.

There are EAA videos on coping the tubes with tin snips and a rat tail file...  The main goal is not so much a perfect fit but that both ends have the coping aligned with the adjacent cluster.  This requires a center line drawn on the tube to clock the cope with.  As long as the gap is not much more than the filler rod and not all the way around you won't have any problems with it.

The printed pattern method allows you to do both ends just suchlike all-the-while allowing you to use paper sheets that you have wrapped around the tube and taped so that you can slip the tube out and slide on the end patterns.  This is all taped in place for the exact perfect fit for perfect cope, perfect clocking of the cope and perfect length...

It took me longer to write this than it would have to mock up the paper tube to slide over a real tube and mark it out.

I dare say if they already had the cad file and you ordered the kit you could have a complete air frame tacked up before they got the kit to you and you would be thousands ahead.

Just an opinion... and perhaps a data point...

Use the search button on the main menu not the search box in the upper right.  There is a YT video on here that shows the method by someone making up an engine mount.

Blue Skies

[rv7charlie]

I do appreciate you trying to help, but as I said, not my 1st experience with hand fitting tubes. In addition to two hangar doors (tube & gusset for them), I did the fit up for a custom/modified motor mount on an RV7 project (alternative engine), welded up by my much more experienced neighbor because I had zero welding experience at the time.

If CNC'd tubing isn't available or available at a reasonable price, then it isn't and I'll move forward with 'traditional' methods.

[Dan_]

 Keep us posted...  

[thseng]

It has occurred to me that a lot of time is spent fixturing the fuselage so that the tubes can be hand-coped to fit.  If the tubes were already precisely coped, it might be possible for the fuselage to largely self-fixture. 

If I remember correctly, a kit with everything except the three longerons could be shipped UPS non-oversize. 

[Brock]

...
If I remember correctly, a kit with everything except the three longerons could be shipped UPS non-oversize.

I recall looking at the VR3 kit and noted the longerons were cut and came with splicing plugs/sleeves.  So perhaps it's no longer oversized.

[BobbyBreadwinner]

Charlie,

I am going out on a limb here to say that I am likely the only one who can answer your question with any experience: I have a CNC router, with a tube cutter, of which I use to cut aircraft tubes. I have written specialized software to perform the coping calculations which result in CNC files. And yes, I am the guy who has cut the tubes for the current builds of Barnaby Wainfan's Facetmobile. Those details are here:

https://worktablecnc.us/projects/facetmobile.html

I have also built a Legal Eagle the traditional way: With two angle grinders, one with a cut-off wheel and one with a grinding wheel, I have cut, ground, ground, ground, and ground until the tubes are all coped perfectly together. I did the welding using TIG, and any gaps left I had to bridge with extra filler. Those details are here:

https://worktablecnc.us/projects/legaleagle.html

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If I had to build a second Legal Eagle...

I would probably use the CNC. It would take more time. I am a builder, that does not bother me. I enjoy building, solving problems, being creative, and ending up with a product which reflects the very best I can do.

If I needed to get it done quickly...

I would cut it by hand just like I did it before, and then blast it with a MIG welder.

---


* There is space enough in this community that either way is the correct way. You do you. *


---

I do have a few additional comments:

+ If you already have a RV-7, then you already have an aircraft with a second seat that most of the time will be empty. If you are looking for a simple after-dinner flying machine then please reconsider the single-seat Legal Eagle. It will be an ultralight, no registration, lots of flying examples, easy-peasy. I have a lot of friends which are RV builders/pilots. A common mantra with those guys is More-Is-Better. Legal Eagle = Less-Is-Better.

+ I previously looked at the VR3 Engineering requirements (for the rest of the group VR3 Engineering is a Canadian company which provides CNC cut tube kits, and they do not exclude aircraft). You can either simply buy one of their kits, or you can send them your own files. However, creating your own files is no small task: You have to take every tube, drawn and coped in 3D, then slit the 3D tube, flatten it, and provide a 2D pattern. I use CAD for a living; this is a mountain of work. Whoever did all of this originally for the Legal Eagle patterns at VR3 deserves a big hug.

+ No, I do not provide CNC services with my router. I only helped out a few of the guys at my local EAA chapter, and Barnaby is now one of them. The time I have spent on their projects I could have completed another aircraft of my own. I have a list of projects I would like to do which exceeds my lifetime, and becoming a tube kit manufacturer is not one of them.


Respectfully,

Robert (BobbyBreadwinner)
Oregon, USA

https://worktablecnc.us