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#1 trident58 Nov 26, 2005 09:54 AM

Durex V
I've been thinking about what I want to build next. I just got a copy of the RCM plans for a 135" TD sailplane called the Durex V. This looks like it should be a fun project because there is a lot of shaping and carving to do- just love making complex shapes in balsa!
In looking over the plans, there seem to be a few places that are just begging to get some modern technology:
1) Wing spar- The airfoil section is very thin (about 1") and the main spars are 1/2" x 1/8" spruce. I think these could use some cabon fiber laminations- say about 0.014" top and bottom. The shear webs are 1/4" vertical grain balsa- I might change these to 3/8". Might also wrap the spars with kevlar tow.
2) Poly joints- The plans call for welding rods to be used as spar carry-throughs. There's no other joiner system shown. I think some king of plywood joiner is in order.
3) Wing sheeting- On the outboard panels, the lower leading edge is not sheeted. I think I'll make a true D-tube and sheet that also.
I'm interested to see if anyone else knows anything about this glider. It's not Nostalgia legal, and I doubt it would be very competitive in RES events, but it should be a really nice fun fly plane. The designer states a weight of 56-58 oz, so with a wing area of 1273 sq. inches, it should be a real floater.
Any opinions/suggestions on this project are welcome.

#2 tommyt Nov 26, 2005 10:57 AM


Let me know how it goes. I purchased the plans a few months ago and plan on starting on it next spring. Also KitCutters.com sells the kit or portions of the kit to make our building easier.


#3 trident58 Nov 26, 2005 11:56 AM

Couple other things I've noticed:
The wing rod setup gives me the creeps! It uses 2 7/32" steel rods. These only go about 4" into each wing panel. The size of these rods seems to be limited by the amount of dihedral in the inboard panels (6 degrees on each panel, for a total of 12 degrees on the inboard panels alone).
My planned solution:
1) Decrease inboard panel dihedral to about 4 degrees on each panel. Increase dihedral on tip panels to compensate for this.
2) Place the 2 wing rods on either side of the mainspar, and add an alignment pin near the TE- sort of like what Ray Hayes did on the Skybird.
3) Increase rod diameter to at least 1/4". Also extend them one additional rib bay into the wing.
All this may be overkill, especially as I don't winch launch, but seeing as the plane builds so light, and I normally add ballast, I might as well add the weight in a useful manner (big Rx battery also)

Tommy, I thought about Kitcutters also, but if I'm going to scratchbuild, I'll go all the way.

#4 Esprit2 Nov 28, 2005 09:57 PM

I thought I had some more info on the Durex squirreled away somewhere, but I'm not sure where it is at the moment. However, if you contact the Minnesota RC Soaring Society via their website, you may find some old-timers there who were around back in the 1970's-early 80's when Bob was building the Durex series.

For now I can't add any first hand knowledge of the plane other than to say I used to stop and watch whenever Bob would fly it at the MNRCSS field. It is a graceful floater that you fly up the winch line on launch, rather than the frantic ballistic object so many modern sailplanes become during launch.

It's airfoil and basic layout pretty much "set" what it is, and I don't believe you'll be able to force much of a change upon it's personality with a stronger spar and fully sheeted D-Tube (there's a reason why people don't bother putting jet engines in Piper Cubs). If you want more speed performance and penetration, choose a different plane. If you fly the Durex for what it is, then the spar is strong enough in the same sense that an Aquila Grande's wing is strong enough. Reinforcement you don't need just adds weight to no great advantage.

The launch lasts for seconds. A good flight can last a l-o-n-g time. Don't make the launch the parameter that defines the plane.

Good luck,

#5 schrederman Nov 28, 2005 10:23 PM

Take a look at the Houston Hawk spar system. Doesn't add a lot of weight, but it fears no winch. If you're going to scratch build it anyway, the different spar slots would not be difficult.


Jack Womack

#6 trident58 Nov 28, 2005 10:24 PM

Thanks for the input. You're right not trying to make a plane something that it isn't. I'm not into competition, and while I do enjoy a ballistic launch, I'm more into long, slow flights. My reason for reinforcing the spar/joiner is more for peace of mind than trying to make this thing take a full-pedal, into a 20 mph wind launch.
What you're saying about the Durex being a floater is exactly what I'm looking for. Right now, I'm torn between building the Durex or a Skybench Skybird. I'm leaning towards the Durex because I think it's time I tried scratchbuilding.
Thanks for the info

#7 trident58 Nov 28, 2005 10:27 PM

Last night I was looking at the Houston Hawk build thread and I am thinking about using a similar system- maybe a 1/2" aluminum rod from Hilaunch.com. Looks like it should also be easier to align than the 2-rod setup. It would also fit perfectly between the spars with minimum modification.

#8 schrederman Nov 28, 2005 10:40 PM


I highly recommend the 1/2" rod. It fits inside a 17/32 tube that won't fit in the 1/2" spar without relieving the sides of the box. It isn't hard to do and adds lots of strength. It should make the Durex a sweet model.


#9 MrKie Nov 29, 2005 11:00 AM

Durex V
Was the King of the Minnesota Floaters..Bob got me to sailplanes.Know the airplane well he always bet we..It was one of the best floater in it's day and today will hold it's own Go for it it's a good plane Bob useds drill rod for wing rods .this is a Floater not a Zoomer Still bet all the zoomer in it's day....Craig

#10 MrKie Nov 29, 2005 11:05 AM

Durex V
Photos of Bob and Durex

#11 trident58 Nov 29, 2005 11:21 AM

Thanks for the pix! That's one sweet looking glider. I just finished figuring out the wood I'll need, so I'll order that sometime this week. I'll probably start the build sometime around Christmas, although I've promised my wife I'll redo the flooring in our house first. Oh well....she deserves it, after putting up with both of my insane hobbies (Ironman is the other) :D

#12 trident58 Dec 04, 2005 09:02 PM

Alright- looks like this build is a GO! Just got permission from the wife and I finished up my last building project (electric Eindecker 40), so the workbench is clear- for now. My goal is to keep the outline, airfoil, and moments the same as the original, but I'm going to use a sprinkling of modern construction materials (carbon fiber) to increase durability. I'll post some building pictures, and I welcome any comments or suggestions from those of you who are more well-versed in scratchbuilding than I am.

#13 MrKie Dec 14, 2005 10:18 PM

Durex V
Jon You got me all fire up to make one to..found the plans and a quit look says needs some work in the wing box in the wings...will pass on what i come up with....Have wanted to do this for a long time...looks like now is the time....Craig

#14 trident58 Dec 14, 2005 10:50 PM

Hi Craig,
Guess we're both going to be passing some ideas back and forth. I'm starting my build this weekend (I'm on vacation for the next 3 weeks :D ). I've already got my mods set for the joiner box. I've ordered a 1/2" aluminum joiner rod from hilaunch.com. It'll be mounted inside some 17/32" brass tubes, which will just fit between the spar caps. As per Schrederman's suggestion, I'll box the tubes in with 1/8" ply and wrap the whole assembly with carbon/kevlar tow. I'm also replacing the welding rod poly braces with a 1/4" ply setup- just like what I did in my Laser Arts Majestic. I'm not exactly looking forward to cutting all those wing ribs, but if you're going to scratch build, make it a REAL scratch build!
Good luck with your project!

#15 trident58 Dec 18, 2005 07:00 PM

1 Attachment(s)
Finished cutting out all the ribs today. Brought back horrible memories of my very first balsa kit- a Comet SBD dauntless, with that lovely printwood! Thank God for the Dremel saw. Next step is going to be notching the trailing edges and laminating the C/F on to the spars.

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