2-stroke radial glow nitro motor 3-5 cylinders 10 ccs supercharged.

[OwenN]

I have seen some pictures of these, and would like to track down a source of a currently made one.

The pictures look quite small capacity, with cox thimble drone or babe bee cylinders and heads. - less that 10ccs for 3

at 0.8 ccs, that would be 2.4 ccs.

The Saito 3 cyl 15 cc 4-stroke is a bit heavy at 890g, but makes quite good thrust. also expensive, at $749 NZ, and out of stock!

My weight budget is around the 500 g mark (2 motor, electric, plus battery.)

Any ideas? 130-150 mm diameter sounds good, too. I estimated the saito at x 6 of the bore at 22 mm?? a typical 15cc 2-strike single is about 3.2 inches
ctr to top, but 10ccs of 2-stroke should be plenty. a 14 x 5 prop at 10,000 rpm does 4.1 kgf thrust, 1.3 hp (988w) - this is just about twice as efficient as
2 x 8 x 4.5 props!

The good thing about electric-quite cheap! - about $250 nz for 2 x motors and battery, plus freight.
That is similar to the price for a 2-stroke 10cc glow single cylinder!

I like the sound of triple radials, though.

Maybe not this build, but maybe the next? Radial front cowl, English Electric Lightning-style wings, close-coupled delta t-top tail and elevator,
short nose. maybe 50 inch span, more then 45 degrees sweep,- what area would that be? - probably less that my twin delta canard. That packs a lot of wing into
the space! Getting the balance point right could be a problem, with a heavy front engine?? Maybe a pusher layout- the engine could be in a better
position?? big scoops needed for engine cooling, though.

I suppose the best way to charge them would be a centrifugal impeller on the propeller side?
You would want to use an electric starter to get a good fuel-air flow going.

 

[OwenN]

Here are some historical examples:

 

[OwenN]

Here is a good picture of a G-mark 0.030 radial-not made anymore.
If I want to build one, I need to find a 0.21 single (3.5cc) with a separate barrel like the cox- either screw-in or bolted flange joint.

Most nowdays have case and barrel one-piece, with drop-in liner.
some of my old diesels had this arrangement. The fins were all on the screw-on head.
I think The DC and the AM had the join line below the exhaust ports - I will check. AM was bolt-down, exhaust ports show in barrel. DC was bolt-down, fins on head, exhaust shows through cast-in crankcase ports, no fins.
All glow engines found so far have fins on the crankcase up to the top of the sleeve. One motor was a 3.5 buggy motor (different driveshaft)

 

[OwenN]

All nz motors seem to be OS, $299-349, with exhaust manifold. (+ nz internal freight)

In Uk, you can get can get NGH, ASP, SH, and various knockoff brands ex amazon, ali express.
.021, 3.5 cc is not a popular rc aircraft size, but 1/8 buggys, cars, trucks use them.
All need to have barrels fabricated to mate to a bolt-up crankcase. Possible if I get a (very) small lathe, and simplify the exhaust port
in the barrel, and cut my own transfer ports? that is a problem-as fins can only start outside the transfer ports.
This woild leave enough material to thread in a manifold adapter.- various taps and dies? buy as required.

I have a small drill press- good for boring bolt holes.
also, transfer ports are milled in from inside the barrel outer. - Dremel-style? I have an Ozito one of those.
The OS engines have very tall heat-sink heads. Possibly a few layers can be chopped off.
OS will sell various engine parts, for a price- usually $60 + each part ...

The knock-off Dynamite brand was $129, + freight. It is a total knockoff of an OS.
Maybe I can advertise for a second-hand small Saito triple-around the 15 cc mark. They seem to only sell a 19cc version
at Horizon Hobby. I will check for a better source.
The cheap saito is the FA-120 R3 glowplug model. I checked saito np, and the new price is $1023nz (76,000 Y) up from $749 in nz!
No luck ebay.com or ebay uk.

 

[slowjo]

Here are some historical examples: View attachment 187957 View attachment 187958 View attachment 187960

I always loved that TD .049 radial !!!

 

[Piotrsko]

As I recall the issue with .049 radials is getting through crankcase flow of air/fuel. So. If you want a 5 cylinder, you need 5 crankshaft journals so all the cylinders go to TDC at the same time. If the .049 cylinders are on a single journal, it will never gain crankcase pressure to force mixtures into the bottom of any cylinder. The only successful single journal radial I ever knew of used a blower to pressurise the crankcase.

 

[OwenN]

Yes, you need a blower of some kind. The G-Mark looks like it has a piston-type blower, maybe reed valve?
A centrifugal blower is OK-that is what the one with the big red pancake at the back has.
You need to spin it up to a minimum speed, though, to get the blower working. 15 psi at full speed is enough.
A centrifugal blower has a similar rpm characteristic to the propeller.

A 3 cylinder is easier to build, and sounds good. Maybe I could just buy enough OE parts from Saito and OS to allow me to finish off an engine? I will check to total price of all the required parts.

I don't need Saito barrels, pistons, and heads, or cam-rings, gears, lifters, pushrod gear etc.
and I only need OS pistons, rings, liners, heads. - match strokes and bores to get the right displacement.
The pistons and/or rods can possibly be bored to match one of the wristpin sizes.

I need to check crank-piston clearance-it may need longer rods?

2-stroke pistons have longer skirts, to cover the exhaust port at the top of the stroke,
and to compensate for the holes in the rear cylinder wall, to give some piston sliding support.

The blower can be pinched off an airhorn compressor? I would need to check rpm, flow rate, pressure.

A 10 cc motor needs a bigger blower? The trick is to pick up the main crank pin end and drive the input of the blower-
The blower needs its own support bearings both sides.
It doesn't need a scroll case, just a ring of flow corrector blades.

I had a good idea on the next plane to suit the motor-a prettied-up FW 190 A, with 50% more chord, older style rounded wing tips,
(Brewster buffalo??) - the old buffalo wasn't a bad plane, just underpowered. It also looks odd from the side.

Trim the wing tips back by 15 %, reduce dihedral by half, more stunt-like wing section, retract undercarriage, but no flaps,
keep a similar tail and elevator profile but increase dimensions by 50%, maybe tail a bit taller in proportion?

I could bring the thrust line slightly more in line with the wing , consistent with having good retract covers.- maybe inner flap covers?

Pretty-up the rear fuselage line, fit a semi-bubble canopy similar to the later American fighters.

I think the ME 262 also has a better canopy, I will check. Both the ME 109 and FW 190 had terrible front screens and forward vision, and the pilot sat too low, compared with Allied planes.

With lower wing loading and tons of thrust, it should be easy to land without flaps,
have a short take-off roll, and make a good stunt plane.

The FW has a nice spinner and cowl line.
<edit>
Now that I look, the Mitsu Zero might be a better starting point. I will print out a few, and compare.
Any ideas on similar layouts for aircraft? The Bearcat really isn't very attractive! The russians, italians, french had a few similar ones.
Any pinterest pages that show several??

 

[OwenN]

Here is a picture of the reworked fw 190. I have shortened the wing slightly, increased area by 20% , changed the wing profile to semi-elliptical,

increased tailplane, vertical tail, reprofiled the fuselage a little, moved the canopy back a little and raised it,

lifted the wing root a bit, reduced dihedral, increased wing thickness in proportion, revise wheel covers.

This would make a good stunt plane, keep wing loading low, keep retract wheels.
This should be good for high angle of attack, slow landings.
The wing blow-over reduces stall, and allows a bit of prop-hanging.
What do you think? It still looks a lot like an fw 109 A ??? Scale = 1:13