12" scratch built cat

[NativePaul]

Sorry Dr Jet, I had a senior moment, the wedge under the back will move the CoP back, but it is the opposite of reflex and the CoP will move futher forward with incrased AoA rather than backwards

[Dr. Jet]

Sorry Dr Jet, I had a senior moment, the wedge under the back will move the CoP back, but it is the opposite of reflex and the CoP will move futher forward with incrased AoA rather than backwards

I know what you meant. It's all good and I'm going to employ a "trim tab".

[Dr. Jet]

More Minor Revisions

I put the motor mount and servo mount together today to see how everything fits. The holes for the servo mounting screws were a little too big, so I reduced them to virtually nothing on the plans. Additionally, I neglected to account for the "ribs" on bulkheads E and F so I'll have to trim this motor mount to fit. The final drawings will have my typical locked tab and slot feature.

[Dr. Jet]

Well, I bought some more glue and finished sheeting the bottom of the hull. Since I'm using balsa instead of ply for the sheeting, I put some carbon cloth on the innards to protect against flying batteries and gear.

To seal the wood and apply the cloth, I used my customary LG-285 epoxy. It's pretty thin to start with, about like pancake syrup. I thin it out with denatured alcohol until it is like a thin paint or shellac and paint it on. The thinning allows you to paint a very thin coat which means less weight. Once everything is fully cured, I'll paint the carbon area one more time, let it soak in a bit and wipe off the excess with a paper towel.

[Jesse J]

[Dr. Jet]

Got the hull sheeted. Now, to get all the ride surfaces dead flat.

[Meniscus]

Bill,

I've been watching this thread for a while and wanted to say that I really like this! Once you get to electronics, send me a message. I may have some good suggestions that will save you a lot of time, energy and money. A perfect match for this size might be the little Etti outrunners that they have been running in Europe for 5-years or more.

For durability, you might consider sliding in a piece of Lexan at the inside of the transom. You can always add ride pads/steps later if you want to run in rougher conditions. Have you picked-out hardware yet? I'm not sure if I saw that. If you decide to fabricate some inline hardware, it could really help with holding the bow down and more predictable behavior as the hull airs out.

As a final thought, if you do add ride pads later, you might consider installing them so they are towed-in slightly in the front. That will do wonders for something this size.

[Dr. Jet]

Bill,

I've been watching this thread for a while and wanted to say that I really like this! Once you get to electronics, send me a message. I may have some good suggestions that will save you a lot of time, energy and money. A perfect match for this size might be the little Etti outrunners that they have been running in Europe for 5-years or more.

For durability, you might consider sliding in a piece of Lexan at the inside of the transom. You can always add ride pads/steps later if you want to run in rougher conditions. Have you picked-out hardware yet? I'm not sure if I saw that. If you decide to fabricate some inline hardware, it could really help with holding the bow down and more predictable behavior as the hull airs out.

As a final thought, if you do add ride pads later, you might consider installing them so they are towed-in slightly in the front. That will do wonders for something this size.

I plan to use this strut/rudder assembly: https://www.offshoreelectrics.com/pr...prod=ose-80972 I have a number of outrunners in my motor drawer, but I'm going to start with an Aveox 1005/2Y (Kv=4900) that has a water jacket already installed. The outrunners I have are in a bit lower Kv range, so I suspect they may have quite a bit more torque than the Aveox inrunner and can spin a bigger prop. I'll probably start with a de-tongued X427 and go up from there. The twin version will have long-can outrunners (Kv=3800), and will start with 32mm x 1.6 pitch counter-rotating 3-blade props.

I'm not sure about what you mean by the Lexan and where it would go. The transom on this guy is rock-solid and tied into two bulkheads with 1/16" ply doublers. I will make the first runs without strakes, but I fully plan on adding them to the finished version.

[Meniscus]

Haven't tried that hardware, so I can't really comment. Regarding Lexan, I find that by using it as a doubler, it keeps the nuts and washers from compressing the wood as much. I've used Lexan on 2s setups with soft transoms and it has survived crashes well into the 70s. That includes flips where Speedmaster rudders have bent.

With a model this small, I doubt the mass will ever put much pressure on the transom, but did want to suggest for an option in the future, if nothing else.

Here's a link to the Etti outrunner. It is a little different than the ones of years past, but it is built the same. http://www.etti.com.hk/product_info....pqgim6s4m1vjg6

[Dr. Jet]

Haven't tried that hardware, so I can't really comment. Regarding Lexan, I find that by using it as a doubler, it keeps the nuts and washers from compressing the wood as much. I've used Lexan on 2s setups with soft transoms and it has survived crashes well into the 70s. That includes flips where Speedmaster rudders have bent.

With a model this small, I doubt the mass will ever put much pressure on the transom, but did want to suggest for an option in the future, if nothing else.

Here's a link to the Etti outrunner. It is a little different than the ones of years past, but it is built the same. http://www.etti.com.hk/product_info....pqgim6s4m1vjg6

Structurally, the strut/rudder is mounted to a 1/16" ply box created by the transom, the next bulkhead, and some ply blocking that goes between them (see photo). Additionally, the transom is doubled to 1/8" where the strut/rudder attaches.

[Dr. Jet]

Hardware and Electronics

I think I showed these before, but not mounted

[Dr. Jet]

...........

Here's a link to the Etti outrunner. It is a little different than the ones of years past, but it is built the same. http://www.etti.com.hk/product_info....pqgim6s4m1vjg6

That's really similar to a whole class of readily available Asian-made "450-Sized" helicopter outrunner motors; many of which have built-in fan cooling. I like them for these little hulls as the air-cooling really works; and in reality, these motors aren't working THAT hard in these applications. Our original "Spec" motors for the micro hulls was a 3000Kv, short can, 26mm diameter motor that we ran on a 6-cell NiMh battery. I'm currently using motors that are 28mm in diameter and the same size or longer can than the Etti. My plan for the 16-Inch Cat V2.0 will be to use a pair of these motors: https://www.ebay.com/itm/Detrum-BM28...72.m2749.l2649 I chose this particular motor for its extra-long can (more torque = spin a bigger prop) and usable Kv range.

I mis-stated the Kv of the Aveox motor that will initially power this hull. It is 4900 rpm/V , not the 3900 I initially stated. I originally had it in a 17" MHZ cat hull (See photo). As I recall, I used a de-tongued and cut-down X427 with that motor/battery combo. That's where I'll start with this hull. If I think I need to go bigger in prop size, I may go the outrunner route in this hull.

[Meniscus]

Yeah, what I liked about the Etti outrunners is that they didn't mind being over-propped a little. When I tested others maybe 5 years ago, they didn't survive. That's why I sought the feedback from the guys in Belgium who have done more testing than I could ever imagine. They are the ones who suggested the Etti outrunners. I have a couple that still keep kicking. Also haven't had one fail, so I never sourced any others. I'm sure things have come a long way since then.

[Dr. Jet]

I'm running a real similar motor in my 1/20 scale Atlas Prototype V1.0 With any luck I'll see it go tomorrow. With even more luck, I'll have a video.

Again. a similar motor in my BBY Micro Turbine Hydro.

Lastly, similar motors in my BBY twin Micro Scat Cat.

[Dr. Jet]

Rain day. No boating, no videos.