Whiplash Sport 20 FE Build

[LuckyDuc]

Nice pics!

Have those of you who own this boat found the center of gravity to be correct at "14-1/4” from the transom, less fuel" as the manual states?

[Raydee]

The manual was written up for slower nitro boats. I try to get my CG about 1" behind the sponsons and even then with a couple boats in the water running high 50's low 60's its a handfull.

[Scott T]

The manual was written up for slower nitro boats. I try to get my CG about 1" behind the sponsons and even then with a couple boats in the water running high 50's low 60's its a handfull.

I agree with this. The CG given in the manual is way too far back. Brian even runs his nitro versions with the CG about 1" behind the sponsons now.

[Brushless55]

I did forget to mention that I run my Whip with a Neu 1515 1y. 4s2p rocks on this motor. She does get slightly warm tho. 135-140 during the summer with 4 min runs.

This sounds like a fun build..
What speeds are you getting with your Neu 1515 ?

[LuckyDuc]

New location for lipo placement

After the comments regarding a more forward CofG and battery placement I have come up with the following. I will place a 2 cell pack on each side as pictured below.

You will notice that I have a new mock up lipo as well, a Thunder Power Pro Race 40C 5000mAh 2S. The Hyperion G3 5500 35C packs are too long for placement in this location. I will make a mock up for two other batteries as well to test. A XPS 30C 2S1P 5000mAh pack, and a Turnigy 5000mAh 2S 30C Lipo Packs. It's nice to have other more affordable lipo options.

Mods I performed to do this....
I cut out the original solid motor mount location and enlarged the inner sponson frame holes too. I recommend doing this before tacking everything together as it was a major PITA to do after everything was glued together... 2 hours with a die grinder and dremel.

Yet to do...
I will box in the battery compartment area so the packs do not slide around freely in the front/sponson area.
I can take additional pics if anyone is interested.

Dimensions for the Thunder Power Pro Race 5000mah 40C 2S
46.5 x 138 x 23.5mm

[LuckyDuc]

The XPS 2S 5000mAh 30C fit very well also. At $60 each they may be the ones I go with.

Specs...
Size (L/W/H): 6.3" x 1.8" x .66" (160mm x 45.8mm x 16.9mm)
Weight: 9.4oz (265g)
Number of Cells: 2
Rated Capacity: 5000mAh
C Rating: 30C/50C
Balancer Connector: JST
Battery Wires: 10 awg

[LuckyDuc]

Anyone have some suggestions on a retainer/strap setup to hold the lipos in place so they don't move fore and aft? I thought about a velcro strap like I use on my helis, but it doesn't seem like the best choice here.

[crabstick]

looks like a very hard place to get the batts in and out of. I like to pre-heat my lipos before running. most of the whiplash's I have seen run the packs in the area where the Nitro motor would sit.

If you do end up with the cells in there I would box in the area and have a strap at the end so you just release the strap and they slide out, still I think it might be a tight fit and will limit what cells you can run

When I built my whip 20 I built I didnt give a crap about weight as I know at speeds around the 60 + mph, in race water weight is an advantage. (race water - ie racing,which is WAY different than playing around in a pond by yourself )

I laid 2 layers of glass cloth inside the sponsons and the entire tub floor, with a
kb45 and 6s RTR shes about 7.4 lbs cog is 20mm aft of the sponsons.

See Here
http://forums.offshoreelectrics.com/...ead.php?t=8225

[Raydee]

Here is a old pic of my batt placement.

[crabstick]

Cleeeeean Raydee, I like it. Yep thats where most whips i have seen have their cells.

[LuckyDuc]

Thanks for the pics. Did you have to cut the front bulkhead /frame to fit the packs in there like that?

[Raydee]

Yes for sure. Built it with the bulkhead in there and then remove it. Was a pain in the butt but after multiple 60mph flips its still in tact.

[Scott T]

I built mine with the bulkhead also, and cut it out afterwards. I left a small piece across the bottom, just lower than the combined height of the velcro holding the pack in. But this is only for 1P.

[LuckyDuc]

I finished the frame today by gluing the included 1/8”x1/8” spruce “doubling” strips to the bottom gluing surfaces. I then used a sanding flap wheel and dremel to sand them flush and to remove the burnished areas from the laser cut pieces as suggested by Detox (To improve glue absorption and bond.) Be careful not to remove too much material if you use a dremel vs. a sanding block, as you want to keep every thing flat and flush. {First picture below.}

The last step before gluing the bottom sheet on is to tack the included 1/16” template in the nose so it conforms cosmetically. This is supposed to be “tacked” on and removed after the bottom sheet is glued in place. This was a bit tricky. I used thick CA and kicker, but I think that I used too much… I might have trouble removing it when the bottom is glued in place.. I recommend using clamps for this step, as the sides are difficult to bend and hold in place while gluing. Illustrated in the second picture below.

[LuckyDuc]

Next is the test fitting of the bottom sheet.

You will notice that the bottom sheet is larger than the frame, with the exception of the front inside sponson area. The sheet is larger so the builder can cut and sand the edges flush with the outer frames after gluing.

When test fitting the bottom sheet make sure that all sides appear symmetrical and use the “line up” point indicated in the first picture below to gauge the front to back placement. Once you have everything lined up, take a pencil and trace ALL of the frames to the bottom sheet.
I recommend tracing all of the frames for the following reasons…
1. It makes it easier to line up when it comes time to glue.
2. It will allow you to cut off the majority of excess wood before gluing. That way you have less material to remove after everything is glued.
3. It also gives you an outline for laying an epoxy bead. Rather than tacking the bottom in place with CA, I decided to use 2 hour Z-poxy to bond the entire joint surface.
4. If you missed adding a “Doubler” any where it is easier to see where using the outline.