Question on radials

[David perry 1]

As I approach retirement, like so many before me, i am collecting the toys to keep me amused.  I have long fancied a radial but realistically know that a 120 inch job wont fit my workshop.  Im really in the dark as the pros and cons of petrol vs glow, once past the well known.. Glows eat fuel, petrols idle slower (i think).  I like glow motors, always have.  I like their apparent simplicity over and above stinky petrol.  But how reliable is a three cylinder glow motor?  I guess i could fit on board glow.

 

Whats the question?  Dunno...petrol or glow I guess.  I like the saito 19cc but hear its low on power and high on weight, so the fa120 3 cyl?

 

Thoughts?

 

[Jon H]

I have or have had...7? multi cylinder engines from companies not including laser. With the exception of my dreadful SC400 radial none of them have needed onboard glow and this includes 2 OS 4 cylinders and a saito 450r3. The OS FF240 in my acrowot xl is just a delight and not as thirsty or messy as might be expected. 

 

However. Small radials like the saito 120 are, for want of a better word, pants. A few customers of mine have them and one in particular has commented on how incredibly messy it is, how little power it creates and how awful it sounds due to its very high rpm and small prop (a product of its short bore/stroke ratio). I have recommended he try some different fuel with lower nitro and oil, and a bigger prop than the blurb recommends, but ultimately he is limited by the design of the engine when it comes to its operating rpm band and other issues. Unless he wants to get into shimming liners and adjusting the compression ratio? 

 

This isnt a sales pitch, but if you compared the saito 120r3 to the laser 160 twin, the twin gives you massively more power (probably double), less fuel consumption/mess, better sound (longer stroke, lower revs) and all for similar price. Saito's own 182 twin is also competitive as is the laser 200 in this £600 class of engine. OS are smoking the wacky with their 160 twin at £1500. 

 

Clearly the twins will not cut the mustard if you want a radial, which is fine, but if you are objectively looking for a powerplant first then i would recommend a twin cylinder engine from any brand over a small radial. If you just want the radial because its cool, and that is fair enough, then go in knowing what it is you are getting. 

 

The smallest radial i would entertain personally would be a 300 3 cylinder with long stroke, but then you are looking at 80-90 inch Warbird sort of size model which may or may not suit you, and there no no engines on sale which meet that criteria. 

 

One other thing to remember is that multi cylinder engines, and radials especially, are not flick and forget engines. There are lots of wiggly bits inside flailing around and they do not respond well to over revving, over heating, over cooling, being thrashed from cold, being thrashed at all, prop strikes...etc. They need a lot more care and general mechanical sympathy than a normal single cylinder so bear that in mind as well. 

 

I would also recommend you choose a model first and then find the engine to suit it rather than the other way around. 

 

[Paul De Tourtoulon]

Or maybe just wait, you never know Laser could bring a 3 cylinder radial out by the time you receive your pension,,,🤣

[David perry 1]

Superb answers, thank you.  I almost bought a largeish radial and lysander i saw advertised but even after a good clean up, i have to accept what I already knew...at 120inches the model is too big.  Ive never really got on with huge models, being brought up in an era where a sixty was big.  I think a laser twin 200 will complement my laser 80 and 150 well and sound good in  a lysander, which is what id like. 

 

Thanks again for the very complete answers.  In fact until researching this i hadnt realised that radials were low on power, per their volume.  Lots of internal drag i suppose. The comments on the saito 19cc were particularly illuminating.  I guess theres a reason modern aircraft dont use radials on the whole, and one i know of has troubles with it.  Interesting what you learn.  Thanks again

 

D

[Jon H]

When it comes specifically to something like a lysander 120 inch is not actually that massive. A friend has the Black horse lysander which is 100 inch, and the wings are pretty dinky once removed as they are under 50 inch long. The fuselage is tall with the undercarriage hanging off, but its quite short and stumpy so would easily fit in a small hatchback car. It would be a completely different proposition to a warbird of the same span. So dont be totally put off the idea of the big lysander if that is what you want. 

 

As for the radials, most of the issue with the smaller ones comes from their bore/stroke ratio being borrowed from other engines. In the case of the 120 its effectively 3x 40 4 strokes arranged around the same crank. You would run a 40 4 stroke at..what 9500rpm? 10000rpm? and not even worry. A 120 radial at 10k? not so much. Its just not the right character when its buzzing away like mad. Also if you delve into the murky world of the specs you find that the saito 40 has a bore of 22mm and a stroke of 17.4. Pretty over square. The radial however uses a bore of 22.4 and a stroke of 16.2, even more over square. This is because the engine started life as a 90 (3x30) and had a stroke of 16mm. They bored it out, added .2 to the stroke (likely due to space constraints in the case that was all they could do) and created the 120. In simple terms though, the more over square, the more it wants to rev and less torque it has, especially at low rpm. As we want low rpm from a radial....

 

UMS do use long strokes on their radials, but their smallest one has really tiny cylinders and high cylinder count so things like internal friction do impact the deal, and smaller cylinders can only offer so much grunt anyway. Why have so many cylinders? Well with long stroke the cylinder is very tall, and cowls arent that big, so you have to compromise engine stroke length/cylinder height, which limits bore due to the bore/stroke ratio requirement so you need more cylinders to get the overall capacity up. 

 

Single carb multi cylinder engines also loose power due to their single carb. They are deliberately under size a bit to make the tuning less critical. When you have 3 (or more) cylinders, all slightly different, you need to be conservative with your carb to make sure they all run together. My OS FF240 is very impressive in this regard and although not perfect with the tune on all 4 pots through the whole rev range its really not bad. Laser use twin carbs to get round this issue, but if i ever did a radial it would have to be single carb as you cant get the throttle linkage to 3 without major drama. 

 

I would dearly love a USM 35cc radial just because it looks fantastic, but if it was my £1000 on the table i would have to sacrifice looks and 'cool toy' factor for a day in day out power plant. Others may have a different requirement, and that is totally fine, but for me it is an engine first and i evaluate it on that basis before any other factors. If i win that sweet lottery money though, i will just buy all the toys! 

[Jon H]

3 hours ago, Paul De Tourtoulon said:

Or maybe just wait, you never know Laser could bring a 3 cylinder radial out by the time you receive your pension,,,🤣

 

Might be a while, and it would be too big for the requirement here i suspect. 

[David perry 1]

Thanks Jon.

 

The 120 in Lizzie is too bulky, it would get in the way.  I have to acceot that deep down im a smallish model man -  most fun was a foxjet ha ha.  My xtrawot / laser 150 was perfect, the old Eurobat with the then awful Moki single was absolutely max size for me but the engine was a complete dog.

 

I think a laser twin will do.  The 200 might be too close to the 150 to make a difference so maybe the bigger V.  Im not so keen on the inline because it limits my options I guess (though Ive never cowled the laser...im not owning such beauty and cowling it).  I guess the thinking behind the inline twin is ww2 fighters? (and austers!).  My J1

[Jon H]

Yea the inline was aimed at the scale stuff. Kit built WWII fighters, Tiger Moths and Chipmunks etc. Anything with an inline engine where you want a twin but a V wont fit in the cowl. There's even a dedicated Gipsy edition for DH powered aircraft so the exhaust is on the scale side and cooling is improved and would be ideal for a 1/4 Auster 😉 The flip side is you gotta make it work because mods will be needed to the model to make the engine fit. Ideally the model would be built round the engine from the get go. The FT series were the opposite and intended for ease of use in ARTF models. One tank, bolt it in front, fly. The V's sit in the middle in terms of overall complexity. 

 

When it comes to size though that 120 inch lysander only needs a 200 twin to fly. My friends 100'' BH example uses a 180 singe, massive 19x6 3 blade prop and a whispers around at under half throttle. So if you are thinking of a bigger engine the model will get bigger too. 

 

 

 

 

[Simon Chaddock]

With IC the piston speed tends to dictate the engine rpm and thus the power output. Gas flow characteristics ultimately limit the maximum practical piston speed 

A single cylinder of the same power will thus rev proportionally much slower than a multi so if sound is the characteristic you are after then you would have to choose a multi that had each cylinder as big as an equivalent power single, run at a low power output and suffer the weight penalty.

Just like full size It would likely require a special layout to squeeze it all into a realistic diameter but it would however sound spectacular.

[David perry 1]

Simon, Im almost better off just drinking tea and listening to radials on youtube!

[Simon Chaddock]

David

To my mind about the most disappointing sound big radial is the Bristol Centaurus as on the Sea Fury.

Yes it has a powerful sound but even at speed its exhaust note is remarkably muted due to the slow closing sleeve valves unlike the poppet valves on the big US radials which give a reasonable exhaust beat.

[Chris Walby]

Just an idea, if wingspan and fuselage size are an issue how about a biplane or triplane? Lots of drag for the engine to pull against, nice big cowl to get the radial in and some super low speed passes to listen to as you mooch about. ☺️

 

Ok my DR1 wings are a pain, but I didn't build it that way and in fact 10 screws and that's it assembled is hardly a lot of faff. 

[David perry 1]

 

 

Chris, 

Good idea.

 

I knew asking here would be be bad for my wallet

[paul devereux]

On 24/04/2023 at 09:14, Jon - Laser Engines said:

When it comes specifically to something like a lysander 120 inch is not actually that massive. A friend has the Black horse lysander which is 100 inch, and the wings are pretty dinky once removed as they are under 50 inch long. The fuselage is tall with the undercarriage hanging off, but its quite short and stumpy so would easily fit in a small hatchback car. It would be a completely different proposition to a warbird of the same span. So dont be totally put off the idea of the big lysander if that is what you want. 

 

Pedantic, I know, but some consider the Lysander a warbird: Westland Lysander V9312 (G-CCOM) is the only British-built example of this distinctive warbird in airworthy condition, and one of just a pair still flying in the UK.

Westland Lysander V9312 (aircraftrestorationcompany.com)

Edited April 26, 2023 by paul devereux

[Jon H]

19 hours ago, Simon Chaddock said:

David

To my mind about the most disappointing sound big radial is the Bristol Centaurus as on the Sea Fury.

 

 

Sorry Simon, i cannot agree. 

 

 

 

Paul, yes, splitting hairs a bit there. 

Edited April 26, 2023 by Jon - Laser Engines

[Martin Harris - Moderator]

Music to the ears - but what I'd really love to hear is another sleeve valve engine - the Napier Sabre...preferably in a Tempest.  Unlikely, I know but there is more of a possibility of hearing one in a Tiffie in a few years.

[Jon H]

2 hours ago, Martin Harris - Moderator said:

Music to the ears - but what I'd really love to hear is another sleeve valve engine - the Napier Sabre...preferably in a Tempest.  Unlikely, I know but there is more of a possibility of hearing one in a Tiffie in a few years.

 

A shade off topic but there are 2 Tyhoon's en route to airwothy. One here in the UK and one in Canada. Both intend to use Sabres, and the UK based guys have an inhibited and complete example. the Canadian chaps seem to be attempting to just build a new engine from scratch using a crash damaged and cutaway example as patterns along with blueprints. They have been kinda cagey about their plans, but reading between the lines that seems to be what they intend. Frankly, i think its common sense as a new with modern materials should be more reliable and safe as well as opening up options for Tempest V rebuilds down the line as you can just build another engine. Anyway while they are using original parts in their rebuild  or the airframe they are also being more pragmatic about things and make no effort to hide all of the new parts they are building. There seems to be some beef about this between the Canadian and UK groups, with the UK based mob being a bit on their high horse about theirs being 'genuine' vs the Canadian 'replica'. Seems a bit of a school playground argument as not one single person watching it fly will give a rats if it was actually there in 1944  or you 3d printed it in the shed last week. If it walks like a duck and quacks like a duck....

 

Hopefully both groups succeed and everyone will be happy. 

 

On the Sabre specifically, this video has the best audio of a Sabre running that i have yet found. If this is in any way representative of the sound we can expect at an airshow then it will be quite something. 

 

 

 

While we are at it, this FW190 is a replica made from original plans. Show of hands for those that care.. Oh and crank the speakers lads

 

 

 

[maurice northcott]

190........................... ohhhhhhhhhhhhh it's happened again.............

[Martin Harris - Moderator]

…and it’s got a radial so we’re back on topic. 
 

Hoping to fly mine tomorrow (with its single cylinder radial 🫢)

[David perry 1]

I giess another way of asking is what radial and model combination if i DIDNT want an ARF plastic covered model?

 

A plans built Lysander, i know TN does one.  

 

What does the panel feel is the right modestly sized radial and Lizzy?

[Jon H]

3 hours ago, David perry 1 said:

A plans built Lysander, i know TN does one

 

This model has not been well reviewed. I have never flown or even seen one, but they are fast, heavy and tipstall prone monsters if reports i have seen/heard are to be believed. Some videos on youtube seem to suggest they are a bit of a handful. 

 

The Dennis Bryant one seems to be good, but its a monster of a build and it only needs a 70 or 80 4 stroke so no radial there. 

 

For a radial to really be viable you are going to need a much bigger model than your size constraints allow. The only option i can think of that is even remotely close is the black horse 100 inch artf with a saito 200 or Evo35 radial. But, you are likely to get better overall performance of the model with a saito 182 or laser 200 flat twin, and save a bunch of money in the process. 

[Paul De Tourtoulon]

Maybe this will do the job, the price of the plugs will probably be  the cost of the down payment on a Saito R 90.

[David perry 1]

Why do i see Robbie the Robot???

[john stones 1 - Moderator]

28 minutes ago, Paul De Tourtoulon said:

Maybe this will do the job, the price of the plugs will probably be  the cost of the down payment on a Saito R 90.

 

What is it, Enya ?

[Jon H]

its the Gmark job isnt it?