Viperjet/Robart strut mods
 

Finally received the Robart 631 struts for my Viperjet on Friday...given that a few of us were waiting for these, I thought I'd post some pics of the mods required to get them to fit. They need to be shortened and as it turns out, a few other mods also need to be made.

First, they need to be completely disassembled. Be careful when removing the E-clips that hold the scissors in place, or yu'll spend some time on your knees looking for them. Use a small screwdriver to pry them off, and hold a rag over them just in case they decide to go flying. :eek:

The strut needs to cut so short that the steel insert that keeps the spring from bottoming out is removed; without limiting scissors movement, the modified strut (with no load) will extend too far to keep the wheel within the wheel well. This will make sense after you cut the strut and spring to the correct length. :D

First, take the scissors and mark the spot where the upper link of the scissors touches the limit stop on the outer strut tube.

Next, drill a 1/16" hole at this spot and thread it with a 2-56 tap. Install a very short 1/8" button head 2-56 screw with the head of the screw inside the scissors. I used some Loctite to keep it in place, though I doubt it can fall out. You could use some CA, as I found it needed to be screwed all the way in anyway.

RE: Viperjet/Robart strut mods
 

Next, you'll need to bend the yoke back about 5/8". To do this, I took two pieces of 3/8"x2"x3" ply and clamped the bottom 2/3rd's of the yoke in a vice and carefully bent the yoke back. Use the outer strut tube for leverage and slide it all the way down the inner strut tube to make sure you don't deform the outer tube. Make sure you bend it in the correct direction - the scissors should point towards the trailing edge of the wing, with the yoke facing inwards towards the bottom of the wheel well. Take your time and check the location of the strut/yoke in the retract well several times. It does take some force to start the bend, but is not as difficult as it seems at first.

After this is done, cut the inner and outer strut tubes and springs to length. For me, this was 2 1/4" for the outer tube, 1 3/4" for the inner tube, and 3" for the spring. FYI, Tam suggested that the spring be cut so that the strut compresses about 1/2 of the total travel when the VJ was sitting level and full of fuel. DISCLAIMER: I have not flown mine yet so the spring length is estimated - Tam suggested shortening the spring by 1/3 of the uncompressed spring length. You can always make it a bit longer and shorten (or shim it up) later if needed.

RE: Viperjet/Robart strut mods
 

Next, reassemble the strut and install it in the retract. Note that you will need to use one of the steel 'inserts' (for adapting the strut to a wire-type retract strut mount) that comes with the Robostrut as a spring spacer.

Retract the strut as much as possible and mark on the wing surface where you need to cut for scissors clearance and carefully use a razor saw to make the cutout. You'll just touch the end of the 1/4" plywood vertical retract mount, so again be patient as you cut downwards. I used a Dremel with a conical steel cutting bit to clean up the bottom of the cut, as it is tough to get a saw in at the angle necessary.

I plan to use some 1/16" balsa to enclose the cutout, just ran out of time to do this tonight. Also, the wheel well molding is not glued in very well, it will pull loose as soon as you put some pressure on it. No big deal, just use some thick CA to glue it back in place. The bottom of the cutout is 7/8" from the wing surface - carefully use an X-Acto knife with a #11 blade to score the thin fiberglass and bend it to remove.

If you use the Robart #530RS main retract units, you'll need to do some cutting and grinding on the mount to clear the screws on the side of the retract unit, as well as cutting/grinding some clearance slots and grooves for the air nipple on the side of the retract unit on the ply retract mount ribs. Do this before you modify the struts. Make it larger than the nipple or you'll nick the air line on installation...makes a nice "hisssss" after you get everything bolted down to test for leaks. [:o]

Here's the finished install, using Tam's suggested Intairco 2 5/8" wheels and brakes.

Can't wait to fly it - maybe next weekend, if the rain clears. Have fun!

RE: Viperjet/Robart strut mods
 

Good Job Barry,
You sure can write better than I can explain.
Thanks for post detail how to do it. This safe me alot time explain to other customer.
Thanks again
Tam

RE: Viperjet/Robart strut mods
 

No problem Tam - thought this would be helpful to everyone, even if the "Mark II" Viperjets won't need to do these mods. "Tamlish" is fun to read but confusing when you are cutting up your $130 struts! :D:)

Hope to see/fly with the Tamjets demo team at BITW in April!

Barry

I love the smell of Jet-A in the morning!

RE: Viperjet/Robart strut mods
 

Barry,
I though I'm the only one the stay up late work on model plane. I guess you're too.
I'll see you soon.
Tam

RE: Viperjet/Robart strut mods
 

Yes, but I have to get up for a business trip in 4 hours. [:o]

I work on my models from 10 Pm to 1 am or so to keep the wife happy - so she thinks they get built only on the weekends.

Seeya! Night - night,

barry

RE: Viperjet/Robart strut mods
 

Barry,
At the time you explained how to do this, I already talked with Sean ( Tam's son) and get a nice a detailed explanation of how to do this....:D
Don't know why....buy I think he'll speak better english than Tam....;)
See you all at FL jets next week.-[&:]
Miguel

RE: Viperjet/Robart strut mods
 

You're killing me.
BTW,
Here is a good news I like to share.
WE only got 4 Viper Jet left
2 at my place and 2 at Cermark.
We sold little over 90 kit in the first 6 months.
Another 100 kit schedule go to be made by June.
This time we offer 4 different color to choose from.
Later,
Tam