Back again.
If an engine, well the OS Max .90 to 1.08 engine to be specific, is recommended by the manufacturer, I assume the numbers refer to displacement in inches. How would I translate that to a radial engine size? Or is it whatever fits when dealing with a radial? Thanks.

Why would you want to substitute that size with a radial? Usually it is the addition of all cylinders to make up the total displacement. Not sure anyone even makes one that small.

Thanks Tom, to answer the first, scale. Scale sound, scale looks. I'm building a Zero and the only thing about this hobby that interests me is how close to the original I can make it look. If I had the cash I'd probably build a real one. Guess it's a good thing I don't have the money.
I might have been remiss in not stating scale, the engine will be for a 1/5 scale a/c. I'm thinking Evolution has one that may fit the bill at 35-77 cc. If it fits the cowling that is.

I don't think it's a good idea. 1200 bucks just to sink into an engine? I wouldn't be able to. But a .90 to 1.08 engine, much more probable. I do like the Zero as a subject though. Good luck.

Displacement is displacement whether it's a single opposed or radial clyender arrangement. Power out put will probably differ.

A 1.08 c.i. engine equates to about 17cc's........obviously a 77cc engine would be a little much. Usually the manufacturers recommended engine sizes are only a guideline. I usually figure out what the weight of the recommended engine is and start there....I go with the highest displacement for the given weight range....unless you're going to have to add a bunch of nose wieght anyway....then I'll go bigger.....much better to add engine displacement than lead....you can always throttle back.

A 77cc radial would fit well into a 50cc sized warbird. Power would be comparable but it would weigh a bit more. The Top Flight 1/5 scale Zero is a 50cc sized aircraft so if that is what it is going in...you should be fine. If they recommend a .90-1.08.....these are way too small for that sized aircraft.

CB

Two stroke, glow engines are the easiest & cheapest way to get a lot of power in the most compact, lightest package.
As a result any 4 stroke engine, particularly multi cylinder 4 strokes, would require larger displacement to get the same
horsepower. With multi cylinder engines the drag of all those mechanical bits whirring around eat into the horsepower
being developed.

Two buts. Generally model engines deliver more power the faster they rev, the only way to achieve this is with a smaller
propeller. A four stroke engine will swing a bigger diameter propeller, exactly what you need in front of a big radial cowl.

Weight. Compared to model 2 stroke engines full size radial engines have a lousy power to weight ratio so the full size aircraft
had short noses. Most model Zeros finish up with a heap of lead in the nose to get them to balance. Or a nice radial engine!

If I was making the choice I would fit the biggest radial that would fit in the cowl. Power is like money, it's better to be looking
at it than looking for it!

Sounds like a great project.

John.

Just so I understand what your saying, you'd go with the biggest glow radial that will fit under the hood (maybe the 77 cc). I'd like to be swinging a three bladed prop and I'm not looking to win any races, from what I understand flying slower has a more of a scale appearance.

For the 1/5th scale Zero (recommended 50cc-60cc engine), I think the 77cc Evolution would be a good fit IF it fits under the cowl. This engine is 9.1 inches wide so if your cowl is more than that...you should be good. If you compare the specs from this engine and a DA-50...they're pretty close except for weight....the radial weighs almost twice as much.....but this may be of no consequence....if you need to add weight to the front anyway....which I would think you would need to do. This airplane was probably designed with a Zenoah G-62 in mind....which is comparable in weight to the Evolution.
DA-50: 2.7 Lbs (without muffler) 5+ HP
Evolution 77cc Glow Radial: 5.7 Lb, 4.7HP
Zenoah G-62: 5.1 Lb, ~ 5HP

If performance is the goal....definitely consider a modern GAS 2 stroke engine such as the DA-60, DLE 55, Etc. If scale is what you desire and you have the means to afford the radial....go for it!

CB

Not me. For a kit that size I'd go gasoline for certain They are MUCH cheaper to run and are easy to tune and maintain. Don't know what a four-stroke glow of multiple cylinders takes to keep happy.

Problem with smaller radials is that you need multiples of the peripherals - which add weight - so five .25 cylinders might give you the displacement of one 1.25 size single cylinder but you will have a penalty in weight to get airborne. But, as CastleBravo noted - you'll likely need nose weight of one kind or another, anyway. You may come up with something like an Evolution seven cylinder 4-stroke glow that will give a good sound and have plenty of power for a 30 lb model. A glow engine won't sound or behave like a supercharged Nakajima Sakea 14 cylinder no matter what you do. Anything "model size will have higher rpm and fewer cylinders. The 1,130 Hp version took off at 2,200 rpm. Compare that to about 6,000 rpm for a small multi-cylinder four stroke.

http://pwencycl.kgbudge.com/S/a/Saka...aft_engine.htm

http://www.horizonhobby.com/7-cylind...engine-evoe777

You want a speed of 65 mph to be "scale" to the top speed of a Zero. That's pretty zippy. But they didn't maneuver so well flat out and were harsh to control; so probably 275/5 = 55 mph.

A one cylinder glow is just as radial as a seven. It's just that it has fewer cylinders. ;-)

Yes!

A larger engine working easy will sound better & last longer anyway.

As an example I had a Gypsy Moth designed for a 40 4 stroke engine but I fitted an 80 size 4 stroke
because I had one & it fitted under the cowl. Yes, it had enough power to aerobat like a Pitts Special
but it spent all it's life chugging around at less than half throttle sounding just like the full size.

Sure, there are cheaper ways to fly a Zero but is that what you really want?

John.

I know that if I don't put a radial in this Zero I'll not be satisfied. I've learned after 56 years that I have a retentive personality, it must be as close to scale as allowed by market availability. In fact, being a gear head I'm not sure if its the plane or the engine that has my imagination fired up. I kid, but the war in the Pacific influenced me to join the Marine Corps to get to the Pacific region to scout out some wrecks. The best laid plans of mice and men, mingled with the optimism of youth. So this plane will represent a dream once dreamt by a very naïve youngster, finding a Zero and bringing it home. Naïve isn't the word is it.
Getting back on subject, the question of cowling fitment comes to mind. I know the engine needs airflow around it to keep it from over heating. How much clearance is necessary? I don't want to cut holes in the cowling, as I saw someone do to fit a radial. I suppose I should have stated that this plane will be built from a Platt short kit. I read where a person put a Saito 5 cylinder 1.70 in a Platt Zero. But it would appear that Saito makes the 1.70 in 3 cylinder only now a days.
I appreciate all who have answered, whatever side they're on.

Anyone see the youtube video of the 1/4 Zero with the working cockpit and pilot that turns his head? Looks real nice with the cockpit lights on and so forth.

Clearance around the engine?

As close as possible to nil. The air has to go THROUGH the engine, not round it.
The critical issue will be getting the warm air out. To do this you may have to modify
the cowl to have the cowl flaps in the open position & possibly a hole at the bottom/rear
of the cowl.

John.

Hey, there's a Mitsubishi A6M5 Reisen (Zero Fighter) Model 52 ZEKE at the Smithsonian National Air and Space Museum in D.C. I've always liked the subject since I built a fairly successful No-Cal free flight model of it and my interest in WWII aircraft. One of the Senior members would always kid me, "that plane is nothing". It's a great subject for a scale model.

THe moving pilot is an easy to do mod. I have done them with a servo directly under the pilot dedicated just for the pilot but a lot of others use the rudder servo. I think the how to was in MAN and I'm not sure but I think John Buckner here on RCU has shown how to do it. Just the head is easy but I have seen the head and arms moving also.