Fairey Huntsman 31

[Chris FellowsParticipant @chrisfellows72943]

You're a braver man than me Ray!

The Fisherman, eeerrr!

I wanted to get my 5 Fairey builds to the painting stage, which I pretty much have now. But then got side-tracked by the Faun, which I was going to build first to get some practise with planking a hull. And I've now got involved in another project, which may be hard to believe, isn't a Fairey! It will be a quicker build though and maybe done in parallel. Trouble is, summer is coming!

Chris

[inonowtParticipant @inonowt]

Hi Chris.

Iv’e read through your account of building the Hunstman 31 today with quite some awe.  I’m quite new to this though I have 3 boats.  Sea Hornet (circa 1970), Arrow and Mowe 2, (both circa 2018).  The reason being is that my grandson wants me to build the Huntsman 31 for him and I was after any build assistance I could find.  Well done by the way, it was all fascinating for me.

I do have a question (only one, he laughed). I am trying to understand the relationship between motors and batteries.  The Arrow has an Etronix Photon 3450Kv motor with 45A ESC powered by a 13S 11.1V battery.  This gives me 38295rpm and the boat performs well.  The Sea Hornet is fitted with a Radient Reaktor 2 4000kv motor  with a 45A ESC and, if I power it with a 7.2V (28800rpm) it only just gets up on a plane, but with an 11.1V it performs well (44400rpm).  Both boat are fitted with 4mm prop shafts.

In reading your posts, in January 2022 you said “The 4mm shaft is rated to 15k. rpm which is more than I will be running it at.”  I didn’t know they were rated.  My question is, to limit the rotational speed to 15000rpm with a 3s 11.1 Lipo, the motor should be only circa 1350kv.  In my (limited) experience, this doesn’t seem ‘big’ enough.  Am I running ridiculously fast motors for the prop shaft?

I’m ready to be educated (if that’s possible).

Also, 1st time on here so apologies if I’ve broken any protocols.

Thanks

Philip

[Chris FellowsParticipant @chrisfellows72943]

Hi Philip

Glad that you are interested in building a Huntsman 31. Sorry that my build is protracted and along with my other Fairey builds it isn’t finished! Also I haven’t touched this build for quite sometime but having just returned to my Huntsman 28 I’m eyeing up the H31 as well as the Swordsman again.

Are you looking to build from one of the kits that SLEC does? As I probably mentioned in my posts I’ve scratch built mine as I wanted one at a scale of 1:12 to match my other builds.

As to the motors, yes you are running ridiculously fast motors! 😁 When I read those RPMs I thought wow! Those sorts of kV are really only needed for race boats and waterjet units with many of the former using flexible drives rather than prop shafts as such. The 1350kV you arrived at is about right for a planing boat where you want about 10k. RPM when running the boat on the plane (around 12k. unloaded). Whilst those RPMs are theoretical given the kV and batteries being used in practise you’ll probably find that the actual figures are much less. Partly because (as per my figures) you tend to get about 80% of the unloaded figure on the water and also because higher kV motors have less torque. At 28800 your Hornet should be going like a bullet! But as it’s not I’m surmising it isn’t getting anywhere near that revs.

You should get all the performance you need with 3S batteries and if you want to replace the motors with something less manic I’m happy to recommend.

As regards the prop shafts, in my planing Faireys I use Raboesch maintenance free prop shafts which are rated to 10k. and 15k. with the latter being fine for the RPMs I want. Some folks use traditional prop shafts with plain bearings and say they are fine at higher revs so it just comes down to choice really.

Anyway, thank you for reawakening interest in my H31 and if you want any further information on the Huntsman 31 and motors etc. then happy to assist as indeed will other forum members.

Chris

 

[Colin BishopModerator @colinbishop34627]

Philip,

If you are building the 1:16 SLEC kit I built the review model for the magazine under designer Dave Milbourn’s advice. I can share info if you want.

Colin

[inonowtParticipant @inonowt]

Just wanted to say thank you Chris and Colin for your replies.  I’ll reply in depth (probably) Monday now.

Thanks

Philip

 

[inonowtParticipant @inonowt]

Good afternoon.

Once again, thanks for your replies.

Yes, the boat will be a SLEC 1/16 kit.  I was putting together a list of the parts required to complete, and bearing in mind my experiences with the other 2 boats, I thought the Overlander 1000Kv motor would not be powerful enough and had thought to buy another Etronix 3450KV motor and ESC.  Until I read Chris’s comment about prop shafts.

The Arrow is fast but I wouldn’t have said it was ‘race’ fast, and the Hornet is not stupid fast either.  There are certainly other boats on the pond that are faster.  I think they look about right, when powered by 3S Lipos. The Arrow has a 40mm screw (which I might reduce to 35mm) and the Hornet 35mm.  Thinking that I’m not getting the RPM as you suggested, I demounted the motors today.  The Radient revolves freely but the Etronix is a bit notchy.  The mounting screws aren’t fouling it.  And there doesn’t feel as though there is any binding in the shafts & tubes.

So, I thought I would buy an Overlander 1000Kv (I’ll need it for the FH31 anyway) and swap them out in turn and see what happens.  If I get the same performance, I can swap them put permanently.

Colin,  I shall be most grateful for any information and advice you can give me.  I haven’t got the kit yet, it’s on my list for next week and start building nexy month.  I’d like to try to enhance the boat with deck planking and such like.  I modified the Arrow at the aft as an homage to the Unowot.

Thank you both for your support

Philip

 

 

 

 

 

 

 

But Of course, I have no point of reference, so maybe they are.

‘m needing huge RPM the results

[Colin BishopModerator @colinbishop34627]

Philip,

My 10 page review of the Huntsman was published in the 2018 Winter Special issue of the magazine. If you have a subscription which includes the Digital; Archives you can see it there otherwise Pocketmags will sell you a download for £5.99.

https://pocketmags.com/model-boats-magazine/winter-special-2018

Colin

[Chris FellowsParticipant @chrisfellows72943]

Hi Philip

I surmised that you might not be getting the revs quoted because of the lower torque of higher kV motors rather than being any issues with the motors or drivetrain etc. but they can happen of course, especially due to binding if not set up correctly i.e. as straight as possible and when you mentioned the size of the props you are using only added to my thoughts that you aren’t attaining the revs stated.

I don’t know the motors you are using and so had to Google them which adds to my thoughts even more! Reason being those are inrunner brushless motors which usually offer less torque than comparable size outrunner motors. Sorry to be the bringer of bad tidings but I think those motors are unsuitable for those boats! Especially the Radient which is only 24mm diameter and in the Hornet with a 35mm prop it’s really going to struggle. The Hornet is a fairly heavy model and really needs a torquey motor with enough kV to get it planing. So an outrunner of around 1200 to 1500kV would be my choice running on 3S and as you say a prop of 35mm.

The Arrow is a sleeker faster boat but you don’t want race boat speeds (unless you really do!) and a similar motor would do the job.

As far as the Huntsman is concerned Colin can tell you what motor is recommended for that, probably a 35mm, but I would suggest going a bit higher than 1000kV, as I said at least 1200kV.

Having said that it might be fine? Reason being that even though I said you usually aim for 10k. RPM on the water my Huntress 23 on 3S gets on the plane quite easily and I doubt at anywhere near 10k. as I have plenty of throttle left. Must try one of those rev counters. (Edit: I see from the SLEC site that an Overlander 2826/18 1000KV motor Tornado Thumper motor is recommended).

I use Overlander motors in most of my builds with my ESCs of choice being HobbyWing Quicruns.

Seeing your Arrow, which is very nice, one of my next projects uses a similar hull, which started off being based on the Arrow/Stiletto hull and with a different superstructure and which really does need a high revving inrunner motor as it’s going to be fitted with a water-jet!

Chris

 

[Colin BishopModerator @colinbishop34627]

Just checked out my boat and it is fitted with a Turnigy 2830 1100kv outrunner. At the moment it is fitted with a 35mm 3 blade brass prop but the plastic two blader supplied with the kit worked well enough.

The Mk 2 Turnigy 2830 is a 1000kv. SLEC’s recommendation is an Overlander 2826/18 1000KV motor Tornado Thumper which appears to be the same motor.

Chris’s suggestion of a slightly larger motor is correct for a model of this size with conventional construction but the SLEC kit is built of Liteply and is VERY lightweight! Some people are a bit suspicious of Liteply but build the kit according to the instructions and you will be fine

With 3S the model is way overpowered and I was concerned about it rolling over. It is more than fast enough on 2S.

As Chris says, Inrunners are not usually recommended for model boats due to their limited torque.

Colin

 

[Len Morris 2Participant @lenmorris2]

Hi Colin,

You mention a Turnigy 2830 1000kV motor.  As kV means a thousand volts, 1000kV would mean a million volts!

I need to come up to speed on this new battery and motor terminology.  Is there a good reference?

Len. 🙂

[Colin BishopModerator @colinbishop34627]

Len,

Yes it is confusing at first but Paul Freshney provided me with the following explanation in my Motors and Props article back in 2021 which explains it.

Colin

A typical Brushless Out-runner may be described as 2822 – 1100KV. To confuse things, some manufacturers may add an oblique after those first 4 digits (as do Turnigy) with another number such as 8, 12, 14 or 17 as in the Mersey Lifeboat motor example, Photo 1. Here, we are only concerned with the first four digits.

The first two digits (28) refer to the case diameter and rather handily this means it will bolt into a standard traditional 360/380 brushed motor mount. Likewise, if the first two digits are ‘35’ this means it will bolt into a 540/550 brushed motor mount but of course be of a larger diameter.

The next two digits ‘22’ refer to the case length, Photo 1. However, what we are really interested in is the KV rating and somewhere within the specification will be listed the motor’s maximum Wattage which is 102 for this particular motor. In this particular motor series, Turnigy offer an identically sized motor Ref: 2822/8 – 2600KV but 260 Watts, a truly remarkable performance from something just over an inch in diameter and barely an inch long. Physically size for size, a brushless motor will be much more powerful than a brushed type.

1100Kv means that the example pictured will produce 1100 revs per volt with no load. So, on a 7.4v two cell LiPo battery this means it will (if it is running at maximum speed) produce 7.4 x 1100 rpm = 8140rpm or on an 11.1v three cell 11.1v LiPo, 12210rpm. Let’s be clear though, you can use ANY battery to power a brushless motor, including a Sealed Lead Acid, NiMH, Dry Cells or whatever. The critical thing is that the volts supplied meet the motor’s minimum needs nor exceed its specification or that of its associated speed controller.

[Len Morris 2Participant @lenmorris2]

Thanks Colin.  The dimensional data is very clear.  Seems the electrical nomenclature kV has been high highjacked to mean revs per volt.  I now understand so once again many thanks.

Len. 🙂

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