Magnum and KF4 SPAR INSERTS

[EDMO 1078]

Here are copies from the manuals. KF did not have any dimensions,. Sorry, daughter put them upside down. Maybe can be corrected?

Daughter says its a new process, called "print and flip"!!!!

ED in MO

Edited 21 May 2012 by Ed In Missouri

[Av8r_Sed 82]

Here are the attachements flipped and combined

-- Paul S

Avid-KF Spar Inserts.pdf

[dholly 718]

That Magnum stiffener and build manual was from the circa 1500 lb. gross days.

The very early Magnums used a longer Plywood stiffener but shortly afterwards changed to a piece of 1/8" aluminum about 2ft long similar in shape/size as the Flyer plywood type---however two strips of 1/8" x1/2" aluminum were riveted along the Top edge of the aluminum stiffener to form a kind of T--both types of stiffener were held in place by 6 of the lift strut attach bracket rivets---these passed through the bracket and spar and crimped inside the stiffener---just to stop it rolling around inside the spar. When Avid wanted to INCREASE the Gross weight of the Magnum from 1500lbs to 1750lbs (to compete with the Glastar---yep that's right) they offered a Gross weight increase option. This consisted of two x 6ft lengths of extruded Aluminum in the form of an I beam--the lengths were cut into 3ft and 1 piece slipped inside each spar across the Strut attach bracket in place of the Aluminum built up Stiffener---the Magnum from that day forth was advertised as a 1750lb Gross airplane---- We (old) Airdale use this I beam, extrusion in our [Airdale Flyer]wing with the .083" spars as part of our wing improvement to take the gross weight up to 1400lbs. -Steve Winder

[EDMO 1078]

That Magnum stiffener and build manual was from the circa 1500 lb. gross days.

Good info. Randy, if you can buy the newer stiffener, I would go with that.

Thanks Doug.

ED in MO

[Trackwelder 12]

I had contacted Just aircraft about the stiffeners that they use in their Highlander 2 1/2 inch 0.063 spar they would sell their extruded stiffener last year at $80.00 a set. This was about a year ago so prices may have changed.

[Av8r3400 1179]

Just and Kitfox use the same supplier for these.

[dholly 718]

2 1/2 inch 0.063 spar

I'm guessing you really meant to say .065" wall?

[Tree top pilot 13]

OK Now who will sell me 2 pieces of the 4 foot extrusion material ? I think it would be a keen idea to install a 24 inch section in each spar.

[EDMO 1078]

OK Now who will sell me 2 pieces of the 4 foot extrusion material ? I think it would be a keen idea to install a 24 inch section in each spar.

Try Kitfox. But Look at the above post about Just.

Kitfox has been kind enough to sell me parts and supplies even tho they know I am doing a scratchbuilt.

ED in MO

Edited 23 May 2012 by Ed In Missouri

[SuberAvid 617]

Thanks for the great info and help guys. I think I have no choice but to build up my own inserts since I think the HH spars are .083 wall rather than .065 wall as KF and Just currently use.

[EDMO 1078]

Thanks for the great info and help guys. I think I have no choice but to build up my own inserts since I think the HH spars are .083 wall rather than .065 wall as KF and Just currently use.

Randy, Why dont you contact Airdale for your .083 inserts?

OR, slim the ,065 inserts to fit your tube?

Those I-beams look better than the one in my Magnum manual, Never could figure out why they only built up one side,.

ED in MO

Edited 24 May 2012 by Ed In Missouri

[dholly 718]

Thanks for the great info and help guys. I think I have no choice but to build up my own inserts since I think the HH spars are .083 wall rather than .065 wall as KF and Just currently use.

Randy -

Well, I had .083 spars and that's exactly what I decided to do as well. I might have been tempted to pay up for the aluminum stiffeners if I had the .065" spars, but I like knowing I have the heavier spars and it was so cheap and easy to make a set of ply I-beam stiffeners. I would have tried to make up a set of aluminum stiffeners if I had access to a CNC machine, but I think even the larger, reinforced wood stiffeners are plenty strong enough unless you intend to beef the fuselage, replace lift struts, drag tubes and other hardware etc.

There are also several other areas in the HH wing that run out of "stress related" safety factor margin over 1250lbs. These are: The Heim Adjustable rod end, the rod end attach Bolts, the rod end welded screwed thread, the root attach bolt and bushings, the wing attach bolts, the lift strut attach brackets and the carry through tubes. As well as the wing stiffener. Yes, on the Airdale an I beam Alu extrusion was used..same as the Magnum of 1700lbs Gross but the Normal Magnum style spar stiffener, 1/8" Aluminum plywood style, ran out around 1500lbs. The Alum I beam extruded Spar stiffener is no longer available. It was designed to fit .083" Wall Spars. Airdale had some stock over from when Avid went out of business in 2001 but I think they are all gone! or not enough to do whole wing! However, an Aluminum spar stiffener IDENTICAL to original Magnum, (similar shape to Plywood MkIV HH but longer,) works well to over 1400lbs. Also at Higher gross weights, compressive / Drag loads are GREATER so, Airdale wings as per Magnum, ALL Steel Drag tubes needed, with the plywood gussets installed. The Airdale wing also used a Magnum Style Lift Strut Rod end which was stressed in excess of 1700lbs. Regards, Steve

[EDMO 1078]

And, dont forget the extra rivets the Magnum has in the strut attachments.

Now here is a question or suggestion for someone with more experimental engineering knowledge than I have:

WHAT IF; You found a PCV pipe that would fit inside your spars, and used that as an insert?

Of Course, you would want to "V" the ends like the originals to keep from having strain points.

PVC comes in different thicknesses, and you could glue it and/or rivet it in place. Even glue a vertical PVC or aluminum beam inside it?

I just looked at a 2 inch, schedule 40 PVC pipe, and it measured about 2 3/8 inches diameter, about right for the .065 spar, but did not put a micrometer on it. Could be lathe turned down to fit .083 spars.

You can buy flat PVC boards.

OR: Weld a vertical inside an aluminum pipe that fits - split a pipe and reweld it to size? Make your own I-beam insert with top and bottom pieces cut from pipe?

Of course, this would have to be done before riveting the strut attachments to spars.

Just thinking of alternatives. Mine already have the full web. But thinking of putting in another short vertical web insert in addition to it, or one on each side of it.

ED in MO

Edited 25 May 2012 by Ed In Missouri

[SuberAvid 617]

Thanks Doug and Ed; good info. I am planning to upsize the other wing components per your info as well or calculate the strength on the aqttachment bolts to see what they are designed for. I know the heim joint thread in tension/compression and welded nut are probably a lot weaker than the attachment bolts are in double shear but can easily calculate that. I am looking for around 1400 pound capable wing because I think the fusalage is able to take that per Steve W. and I have much heavier duty landing gear with 3 attach points.

Ed, the material strength of PVC is much less than the aluminum or plywood so I dont think a PVC insert would add much strength to the spars.

[EDMO 1078]

Thanks Doug and Ed; good info. I am planning to upsize the other wing components per your info as well or calculate the strength on the aqttachment bolts to see what they are designed for. I know the heim joint thread in tension/compression and welded nut are probably a lot weaker than the attachment bolts are in double shear but can easily calculate that. I am looking for around 1400 pound capable wing because I think the fusalage is able to take that per Steve W. and I have much heavier duty landing gear with 3 attach points.

Ed, the material strength of PVC is much less than the aluminum or plywood so I dont think a PVC insert would add much strength to the spars.

I can almost garantee that sched. 40 PVC pipe is stronger/tougher than plywood - and probably thin aluminum, but it is about 1/4 inch thick, and would be heavier.

If you need the drawing for the Magnum strut rivets, I can post that.

Haven't got the photo of the MAPs yet - will try this weekend.

ED in MO

Edited 26 May 2012 by Ed In Missouri

[akflyer 1427]

I can almost garantee that sched. 40 PVC pipe is stronger/tougher than plywood - and probably thin aluminum, but it is about 1/4 inch thick, and would be heavier.

If you need the drawing for the Magnum strut rivets, I can post that.

Haven't got the photo of the MAPs yet - will try this weekend.

ED in MO

I can 100% garantee that if you take a 4' stick of PVC pipe and you put a 5# weight on the end of it, it will bend a whole boat load more than the plywood or aluminum web.

[EDMO 1078]

I can 100% garantee that if you take a 4' stick of PVC pipe and you put a 5# weight on the end of it, it will bend a whole boat load more than the plywood or aluminum web.

Actually, I have already done that experiment. Try it for yourself with sched 40 pressure pipe.

And, it may bend a little bit more, but dont crack or kink, even with 20 lbs of weight on it, and that was without a center rib.

And at only two feet, barely any give at all.

ED in MO

Edited 26 May 2012 by Ed In Missouri

[Av8r3400 1179]

Ed - What exactly are you proposing? To put a piece of PVC inside your spar tube or to use it in stead of the Aluminum?

[akflyer 1427]

Ed - What exactly are you proposing? To put a piece of PVC inside your spar tube or to use it in stead of the Aluminum?

Ed is talking about using it for the spar stiffener, not for the spar!

[Av8r3400 1179]

Ed is talking about using it for the spar stiffener, not for the spar!

All I have to ask is why?

It won't be as rigid, will be heavier, more difficult to assemble, etc, etc.

Why fix something that ain't broke? Honestly?

[SuberAvid 617]

I can almost garantee that sched. 40 PVC pipe is stronger/tougher than plywood - and probably thin aluminum, but it is about 1/4 inch thick, and would be heavier.

If you need the drawing for the Magnum strut rivets, I can post that.

Haven't got the photo of the MAPs yet - will try this weekend.

ED in MO

Ed, Please post the drawing of the magnum strut rivets when you get a chance. Thanks much!

[EDMO 1078]

All I have to ask is why?

It won't be as rigid, will be heavier, more difficult to assemble, etc, etc.

Why fix something that ain't broke? Honestly?

I was only kicking around some alternatives for making the inserts for the .083 spars, since you cant buy them.

Please note my comments about the aluminum pipe / I beam. I think that would be better, but needs to be welded,

although I guess you could glue the aluminum parts together.

If you can buy factory insterts for the Kitfox .065, then by all means, do that instead of making your own.

I was thinking too, that wood will swell or shrink with age, and PVC and aluminum wont.

Didn't mean to stir up a fuss. Mostly wanted to hear some other alternatives.

Mine has factory full webs, so thinking about adding an insert on each side of original where strut attaches.

ED in MO

Edited 27 May 2012 by Ed In Missouri