Single motor cat strut/drive

[Les Baldry]

Hi from across the pond here in the UK. I am just about to build my first Cat ,a single motor 34" TFL Cheetah (from OSE).
My question is the position of centre line of the prop /strut hub in relation to the bottom of the hulls when set parallel, both of my fast 30+inch mono's a Pursuit and Hydra (identical to the Dominator ,UK version) the centre of the drive/prop sits between 8 and 10mm above the lowest part of the V or hulls as per Cat...does this measurement work for a single motor Cat??...sorry if this may sound a basic question and may well be answered deep into this forum but i think i may go blind trolling through the masses lol
ps just out of interest im not looking for massive speed as the size of my club puddle dictates anything above 70mph is somewhat butt clenching hence my choice of single motor on parallel 4s.not knowing the water flow between a Cats hull the last thing i need is drag from a wet drive hub.

Look forward to any advise .thanks from Limey Les

[1coopgt]

Here you go. Hope it helps.

[Les Baldry]

A big thanks to you ! that make sence.. cheers limey Les

[Peter A]

Actually I have exactly the same question. I have set up a cheetah on 6s. At this point I have two 6s 5000mah packs in it, so it is probably a bit on the heavy side. I ran it for the first time on Saturday. It was running really wet, but the strut had some negative angle on it which I couldn't sort at the pond. Also the offset rudder brackets are pretty flimsy and move a lot, so I will make a bracket to support it and stop it flexing as that causes quite a bit of steerage issues. They might be ok for zoom zoom, but not for ovals. I have levelled out the strut and it is sitting about 10-12mm up. I might just change it to a 4s setup yet also.

[koen]

set the propshaft horizontal and for starters 5 to 10mm above the sponsons and you have some play how the boat runs with the batteries and keep total weight in check to heavy is not good, for single motor cats prather props work very good(model marine supplies have them)

[Peter A]

set the propshaft horizontal and for starters 5 to 10mm above the sponsons and you have some play how the boat runs with the batteries and keep total weight in check to heavy is not good, for single motor cats prather props work very good(model marine supplies have them)

Thanks for that, sounds like I need to drop the strut a bit from where I set it yesterday. I might change to 4s shortly when I have a new motor get here. I have plenty of props to play with including Prathers.

[koen]

i have 4 cats all single motor for motor choice i have sss tp and lehner ,if you don't want spend much sss will work very good but with lehner that's an other league you can find a perfect advice on there website and for sss just go to tfl-hobby.de

[properchopper]

Some have experienced wet running Cheetahs. Many have been twins and my take is that the combined lift from 2 props can be a contributing factor not to be overlooked. My single 4S2P Cheetah uses a fairly elevated strut (especially with my big-ole 452/2blade for 2-Lap trials pictured). With some CG tuning the boat runs free and just loose enough but will settle when blipped into turns.

I switched from a Neu 1521 1.5D 1890 KV motor to a TP Power 2040KV TP 4060 and haven't looked back since

acheetah1.jpg acheetah2.jpg

https://www.youtube.com/watch?v=Cl5ebHR6wR4

[Peter A]

Some have experienced wet running Cheetahs. Many have been twins and my take is that the combined lift from 2 props can be a contributing factor not to be overlooked. My single 4S2P Cheetah uses a fairly elevated strut (especially with my big-ole 452/2blade for 2-Lap trials pictured). With some CG tuning the boat runs free and just loose enough but will settle when blipped into turns.

I switched from a Neu 1521 1.5D 1890 KV motor to a TP Power 2040KV TP 4060 and haven't looked back since

acheetah1.jpg acheetah2.jpg

https://www.youtube.com/watch?v=Cl5ebHR6wR4

Are you running a skeg strut on that?

[properchopper]

Are you running a skeg strut on that?

Hi Peter,

I set this up for oval heat racing and figured that a skeg strut would help hold the rear end from swapping with the front in aggressive cornering. I utilize the beefy Speedmaster 1/4 inch drive strut stepped down and trim down the rudder some 'tho some extra length helps in bouncy racewater. I've built several for customers this way so there shouldn't ever be a hardware failure in their hands- the RtR Cheetahs I've seen have a teensy offset rudder which has to be a disposable piece the way they'll flex and bend during aerobics.

acheetah4.jpg vance frontview.jpg

[Peter A]

Hi Peter,

I set this up for oval heat racing and figured that a skeg strut would help hold the rear end from swapping with the front in aggressive cornering. I utilize the beefy Speedmaster 1/4 inch drive strut stepped down and trim down the rudder some 'tho some extra length helps in bouncy racewater. I've built several for customers this way so there shouldn't ever be a hardware failure in their hands- the RtR Cheetahs I've seen have a teensy offset rudder which has to be a disposable piece the way they'll flex and bend during aerobics.

acheetah4.jpg vance frontview.jpg

I have that flimsy offset rudder on mine. I have made another bracket back to the transom to support it as it was as flimsy as. I had one of those skeg struts off another boat but sold it
That one had an inline rudder and was no issue turning on the oval, I do wonder why offset rudders are always used and inline ones not on tunnels as there seems to be no real advantages.

[properchopper]

I have that flimsy offset rudder on mine. I have made another bracket back to the transom to support it as it was as flimsy as. I had one of those skeg struts off another boat but sold it
That one had an inline rudder and was no issue turning on the oval, I do wonder why offset rudders are always used and inline ones not on tunnels as there seems to be no real advantages.

Peter,

Here's a tale of two Drifters :

My first Drifter S was set up for NAMBA LSO SAW competition. 2008. With brushed drill motor and round cells it had a correctly sized offset rudder. Set the record first time out. OK, I figured I'd take it to Winter Warmups in Az and race Oval and Offshore. Barrel roll city. Got a good chuckle every time I came out of turn four with a perfect whoopsie, ending on its feet and would keep going. Sold it to a club friend and with an 8XL still would barrel roll if turned with even a little gusto.

Obtained a second Drifter S several years later and went after the NAMBA P-Ltd Cat record with the correct spec motor and an inline strut/rudder. Now close to (and occasionally over) 60mph, I would blast down to the end of the runway, make a U-turn to head up the course and let things settle before going through the lights. Always made the turn without any sign of antics. +1 for the inline strut/rudder 'tho I've been told by several peeps that this shouldn't be the way things should turn out. Love them keyboard warriors

[Peter A]

Peter,

Here's a tale of two Drifters :

My first Drifter S was set up for NAMBA LSO SAW competition. 2008. With brushed drill motor and round cells it had a correctly sized offset rudder. Set the record first time out. OK, I figured I'd take it to Winter Warmups in Az and race Oval and Offshore. Barrel roll city. Got a good chuckle every time I came out of turn four with a perfect whoopsie, ending on its feet and would keep going. Sold it to a club friend and with an 8XL still would barrel roll if turned with even a little gusto.

Obtained a second Drifter S several years later and went after the NAMBA P-Ltd Cat record with the correct spec motor and an inline strut/rudder. Now close to (and occasionally over) 60mph, I would blast down to the end of the runway, make a U-turn to head up the course and let things settle before going through the lights. Always made the turn without any sign of antics. +1 for the inline strut/rudder 'tho I've been told by several peeps that this shouldn't be the way things should turn out. Love them keyboard warriors

HI Tony
I ran it again on Saturday on 4s setup. It still runs really wet, and drags the right hand sponson in the turns. I put some positive strut angle on and moved the batts back a bit, it ran a bit better in the straights but still plowed big time in the turns. I had it set with cg at 11" which I saw you had on on of your posts. I suspect the offset rudder is dragging the sponson so I have bolted it on in line to try and reset the strut with more positive. I am still playing around with props but am way smaller than you run at up to 45mm. On checking the ride pads, the middle pad sits about 1.5mm (1/16") higher than the front and rear ones. Do I need to build this one up as it would seem like it will never ride properly on it and this could be what causes the wet running.
If you have any pics or relevant threads on this that would be much appreciated.
Also apologies to the op if I have hijacked the thread, but I trust these this will be helpful anyway.

20211107_171042.jpg

[properchopper]

Peter,

This is a conversation that went on and on and on right here several years ago as the Cheetah (marketed early on by Ben at Fightercat) gained popularity. Many were twins and almost ALL reported plowing/wet running. I was sent a hull to look into this. As you can see , mine ran fine with some positive strut angle (actually quite a bit) and 11" from the transom CG. Some respectable builders thought I had a different mold pull - that mine was one of the "good ones". I have the same sponsons that you do (&probably same as the earlier ones that ran wet). I don't remember ever blowing over although I have a bit of a "flow interrupter" at the entrance to the tunnel

I race with many gas cats during the FE classes and every gas cat runs really wet in the turns - probably keeps them down on their bottoms.

acheetah7.jpg acheetah6.jpg

cheetah strealth front cropped.jpg

[Peter A]

Thanks Tony
Looking at your pic of the cg and ruler I realised that I have measured 11" from the sponson back not the transom. I will readjust the cg and retry again this weekend.

[properchopper]

Peter,

Funny you mention that - Not long ago a customer of mine told me that I measured his CG the wrong way; that the 33% starting point rule of thumb was measured 1/3 or 33% of the wetted sponson area. Technically CG deals with weight-or gravitational pull if you will ;
thus if 33- 1/3 % " CG " is the amount behind the "CG" point the - entire-boat needs to be used to calculate this. Of course I have heard compelling counterpoint but if there was no differences in opinion there'd be no horse racing

I'm thinking that you may find that your boat loosens up Also going from 6S 5000 x 2 to 4S 5000 x 2 will loosen things up as well. Drop in a TP Power 4060 & prop up

[Peter A]

Peter,

Funny you mention that - Not long ago a customer of mine told me that I measured his CG the wrong way; that the 33% starting point rule of thumb was measured 1/3 or 33% of the wetted sponson area. Technically CG deals with weight-or gravitational pull if you will ;
thus if 33- 1/3 % " CG " is the amount behind the "CG" point the - entire-boat needs to be used to calculate this. Of course I have heard compelling counterpoint but if there was no differences in opinion there'd be no horse racing

I'm thinking that you may find that your boat loosens up Also going from 6S 5000 x 2 to 4S 5000 x 2 will loosen things up as well. Drop in a TP Power 4060 & prop up

It is going to end up with 2 x 4s 3000mah in parallel as our class rules allow for 6000mah max, so I dunno about a 4060 at this point.. I was reworking the cg last night and to get it back to 11" from the transom may require some lead. I will try it as I can with the current batts, the cg goes back to under 10 1/2" with the batts all the way back.

[properchopper]

Peter,

I'm sure you'll find the right combo

Sometimes 'tho it takes a little trial and error - lol

20211108_104351.jpg

[Peter A]

Getting better. Ran on Saturday with cg moved back and it was much better. First run was with an M445, was ok, then I tried a Dr Props 642/3 but changed to a cnc 444 which went really well.
Still really sensitive in the turns with a tendency to hook, as tunnels are prone to do. I have just ordered a speedmaster inline skeg strut rudder. I am preferring the inline rudder. Hope to have the parts and install them for another test in a couple of weeks. Got a few more props to test on it yet to find the "sweet spot".

[properchopper]

Sounds good - will keep looking for the results

[TallyFeli]

Hi....there is next to no fill to do, and I have as of now supported the whole internal body with carbon-kevlar material. Didnt need it yet I love the appearance of the dark/red material and the additional support will be extraordinary with my qd engine, adds weight yes yet I dont race, and the general apperance is wonderful. Besides I have an incredible boat painter to do all the completion work and the custom paint!