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HR2 main longerons

grover

Well Known Member
Harmon drawing shows main longerons are a wee bit longer than stock RV4. 168 v. 172 or something. also don't see longeron bending detail in Harmon dwgs. How are these things sorted?
 
Some weld additional to vans to make longer ones, some buy new material long enough. F1boss Mark has a very old email thread between him and Harry Paine that explains the bending and other fuselage tips. I don't have access to my copy as it's at my summer place. Perhaps F1boss will chime in.......

Russ
 
James,

No welding please. The longeron is no place for that. You can splice in a piece if you must (per AC43.13 techniques), but the best bet is to just go to your local metal distributor and buy 2 brand new pieces that are long enough.

Now, the original HRII longerons were 3/4x3/4", and this size is well proven. However, some stress analysis has shown that the 3/4" size is a bit on the light side. So, upsize it to 1x1" angle if you like.

This will make it MUCH easier to maintain edge distances, particularly when installing the tail. It also reinforces the area just aft of the firewall where the potential weakness shows in cad analysis.

It's possible to mill down the 1x1 to 3/4x3/4 in areas between the tail and forward fuselage if you want to shave weight.

The F4 that I'm building for my personal flying will use 1x1.

YMMV!
 
Bending can be done with a BFH, press, or other technique.

I use a BFH, a stout vise, and pad everything so the it doesn't mar things too much.

I seem to recall someone on the forums making a die set or form block for doing this job.
 
Rocket longerons

Maintaining proper edge distances is difficult even with 1x1 angle. I got 1.25x1.25 angle so that the places where bolts go through the Longeron have plenty of material. I then tapered the rest to save weight. I also used 2024-T3 aluminum extrusion instead of the 6061-T6 Vans supplies; the 2024 is much stronger. I got the material from Tierney in SoCal.

That may have been me mentioning the tooling to make the bend. I made press-brake style tooling to make the initial bend. Then twisted it to get the right offset. All pretty much covered in the RV-4 instructions.

Side note; it was my observation that both ends of these longerons are terminated rather weakly. This was my primary reason for going to the trouble of starting with oversize (1.25x1.25) material. This allowed for a nice staggered bolt pattern at the Firewall end with true edge-distances and similar at the tail end. I also make new Firewall/Longeron Weldments that carry the loads further down the Longeron. Talking with Ken Fowler, he has experienced issues with tail flex/flutter and has beefed up that area (admittedly he is pushing past normal operating parameters). I think it's a good idea not to skimp in these two areas.
 
thanks for the feedback. was wondering if there were differences in the locations/angles of the longeron bends. have found the van's method of BFH a bit primitive, but worked on the -8 ok. .. so, must be adequate for our purposes. other tips welcome. . . some of the harmon dwgs a bit ambiguous (or I've not studied them enough); all advice is welcome.
 
. . . some of the harmon dwgs a bit ambiguous (or I've not studied them enough); all advice is welcome.

Ambiguous? That is a kind description at best. However, if you have your RV-4 plans and a set of HRII plans, it is all there.

Don't forget to visit builder's websites... including mine. (No, I don't get a cent for anything on that site.)

www.vincesrocket.com the first Rocket website on the web, circa 1999, and still a wealth of info, links, and photos.
 
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