Need some info re: JAE21 build

[John MacLean]

I've been building a couple of boats this winter, a redtail kneeler hydro and a JAE21 FE. The kneeler is complete and saw her maiden run two weeks ago. I'm pretty excited about that. I am in the final stages of the JAE21 build based on the public domain plans. This is only the second scratch boat I've built so I have a lot to learn. Unfortunately these plans seem to lack some improtant details that I need to complete the build.

FE Specs. .

ESC -- Turnigy Marine 120

Motor -- Turnigy 3665 1900 KV

Batteries - 4s 5000 mah

Servo -- Hitec

Prop 1450

Strut and rudder --- HK

Flex shaft --- 3/16 (Zippkits)

Collet --- Kintec Racing

I purchased the recommended prop from Zippkits --- the 1450 along with a 3/16 flex cable, drive dog and cowl. The collet came from Kintec racing.

My questions:

1. What is the recommended distance from the transom to the drive dog or prop. There is no mention of this at all in the plans or of the correct cg placement. The Zippkits cable is 18 inches long and will need to be cut but I don't want to cut it too short.

2. I've also seen mention in a number of discussions re: the JA21 of the 1450 needing to be modified. Does anyone know if the Zippits version has the modficiations already done to them? Zippkits recommends the UL-1 motor and ESC as a good match up for this hull. I have the same set up in my supervee 27 but run a smaller prop. I am assuming that the difference is in the way a hydro runs as opposed to a mono.

3. My cg right now is close to the trailing edge of the turnfin. I've read about a 60/40 rule for estabishing the cg but am ot sure as to how to achieve that. I have an electronic kitchen scale that I can use but need some suggestions as to how to get that done.

Would appreciate any help and positive feedback you can offer. Thanks for looking.

John

 

[gil sonsino]

John I'm finishing a JAE Fe with different motor/esc/battery(check it at my site) and I see that your motor is placed too forward from the original plans so I don't know how is your cg ie the rule of 60/40%.If you choose the Zipp strut you will have the right position of your drivedog/prop from the ransom..The 1450 Zipp will work with your motor.In the FE forum you can have good info about this boat.

Gill

wwww.grsboats.com.br

 

[John MacLean]

Thanks for the input. I did check out your site. The main difference I see between your build and my own is that you are building from a JAE kit which I am assuming has a complete layout for all components. My plans include the overall dimensions of the rigger and any other information had to be gotten from taking dimensions off the scale plans which I did. There were some discrepancies between a couple of the pages, almost as though the paages were a compilation from two different sets of plans. That led me to wonder about the cg and do some further checking.

I found the dimensions for the z strut and did the math re: the length of my shaft assuming that my cg is approximately where it should be. I've read posts that suggest starting out with a cg equal to approximately 50% of the hull length which would put it pretty much where it is right now with all hardware, electronics, batteries and cowl installed. The rear boom tube on my JAE is just behind the turnfin and that's the pivot point right now with the boat ready for the water.

 

[John MacLean]

Cut the flex shaft, installed prop, receiver, speed control and pushrod and met up with a couple of boating friends at the river today. Made a couple of first runs that highlighted a couple of issues that need to be addressed.

Steering: the boat kept wanting to go to the left and was reluctant to turn right at speed. It took a few laps to isolate the problem. . . a loose servo mount. On closer examination we found that the epoxy was still a little tacky. I think the rudder was dragging enough to prevent the boat from getting up on the ski. On the last attempt of the day it did hook up for a short burst before the rudder mount pulled away from the hul all together. Didn't get much in the way of a video but looking forward to getting it wet again real soon.

It seemed like day for steering trouble with hydros. One of the guys tunell went through three clevices before he finally called it a day. Similar issues with the Redtail kneeler I built this winter. The thing ran beautifully in a straight line but if I got off the steering would pull left and eventually refused to turn right. Checked it out and found a loose setscrew that fastened the pushrod at the steering horn. Once we got that sorted out it was a lot of fun to watch it run. Still some work to do to get it dialed in but its getting there. . . I think.