4 Stroke Thoughts

Hi Folks,

Well, I've been experimenting with a 4 stroke motor for a couple of months. I've figured a few things out. It seems to me that the same principles I applied when I raced at the drags as a kid still hold true. The more fuel and air you can stuff through the thing, the more power you get (to a point). I've tried quite a few combinations of intake and exhaust along with several tank and fuel delivery systems. All of it basically designed to put more fuel and air through the system to create more power to use more blade area. I'm still debating on what I'm going to use. Each move so far has done one thing but taken something else away. Wish I could find an itty-bity B&M blower for then thing. <grin>

Do others have thoughts about 4 Stroke setup? What's working best for you?

Randy,
I can't comment much about the 4S set-up as don't own one yet. But here's one that's related sorta'. If your hoping to turn bigger lumber with the power your going to produce with the 4S, what will you be doing to maintain rate of turn?
Over the last few weekends my fellow flying buds have noted lack of turn as the prop dia. goes up. (We've been testing all the P.Walker trim chart variables as best we can as of late.) Prop diameter has played a major roll in getting Bill's profile P-40 foamy to turn how he likes. Smaller seems to be working, 10" factory Zingers, down from 11" of the same make. He notes, and we see, a big difference in how his plane turns. I would think that as power goes up, and the ability to turn big props comes into play, more tail power will be needed to over come the big prop effect. Is this what we (the stunt community) need to do? May be of no concern if your running large props on a "large prop design"(is there such a thing?). Bigger (prop) is better for line tension and such, but without this in mind during the design stages you could build to small a tail section and hurt the turn rate I should think. I'm thinking you'll need to over come the prop effect, yes? no? Sorry to change the topic somewhat. But getting back to the 4S power question, ...is Crane making lumpy cams for these things yet? Who's doing the new adjustable rate rocker arms for Saito's?

Tony, maybe you should start a new thread on this question. But as to rate of turn, we aren't into the 4-stroke, either, but do like the large props and have not found them to negatively affect the turn. We were using a 12.5 inch diameter prop on a 35 size 570 square inch plane and even flew the same plane with a 53 and a full 13 inch three blade prop. Still had a good turn. Matt's latest pipe powered plane sported a 13.5 inch diameter 3 blade at the end and was turning better than ever. It is just a matter of trim. If your CG is too far forward, yes, it will affect the turn. But if the CG is back far enough, the affect is minor and just a little wider spacing on the handle takes care of it. We aren't using near the full amount of movement available on the controls as is, so it is is not a problem. And this, by the way, is with a faster turning prop. The faster the prop spins, the more affect the prop will have. Most of the people using 4-stroke engines are going to the bigger props and I haven't heard of any problem at all. (There may be a difference, yes, but not a problem.)

Leonard Neumann

Randy:
"Wish I could find an itty-bity B&M blower for then thing. "

OS has, or had, a 4-stroke with a blower. But it is 120 size, so you should have a big plane.
Jyrki

Leonard,
I knew you would comment on this one, and thanks very much. I'm all for bigger in my own mind. State of trim we found out yesterday is a case of moving one variable, then re-adjusting others to retain, or maintain desireable traits, as one variable will possibly effect one or more of the others. We are just getting a "handle" (pun intended) on how trim changes move the balance on all fronts around, very interesting flights. We're learning with each tank of fuel. As we're working with older aircraft, some lacking trim tools, adjustments are limited in some cases. Yesterday morning I cut the wing tip off the latest project, (2ys in build) to remove the non-adjustable tip weight and installed a weight box. By yesterday afternoon I was glad I did. Hinge was evident on the model I was flying. Tip weight is needed, no where (nice) to put it.
Re: Handle spacing, yep did that too. Young fella was given a brand new CG Shoestring and Fox 35 combo two weeks ago from the club members, who had recieved this plane from a retired flyer. Brand new, never flown, 15yrs old. We've been helping him out with first flights. Narrow handle spacing took the lumps out of the solo flight for him yesterday and he's coming along nicely.

Lots to keep in mind while trying to get the best from the airframe. Will re-state/ restart these comments on a new thread if required.

Power is power, props are props. Size and rpm will effect flight trim. Adjustments can be made if the tools are available. Key is having all the tools.

Now, about those Saito cams,...I've got a small block chevy bump stick here that's not being used, ...maybe a re-gring to Saito spec. is in order? We could make four perhaps?

ST,

Well, as I learned at the drags as a kid, at one end of the the scale you have reliability (say, my 3/4 4x4 Ford truck with the giant but detuned 460 V8). At the other we have performance (the drag cars I was once involved with---good for about 20 to 30 minutes overall run time if built well but absolutely the most horsepower that could be had). The tests I've been doing seem to indicate that Saito makes their engines a lot closer to a Ford than a Rail. Reliability is of course great, but I think things could be moved a couple of notches further along the performance curve.

Len,

The prop I've been most happy with so far is a homebrew 3 blade. It's made from 13x5 RevUp extra wide blade props. Pitch is decreased to about 4.75 with the engine turning at about 9800 rpm. Big increase in torque and pulling power in the wind over the Bolly 12x5 3 blade. When I get it right, I may make a mold and try it as a CF prop.

>>If your hoping to turn bigger lumber with the power your going to produce with the 4S, what will you be doing to maintain rate of turn?<<

Well, the way I've been dealing with it using a very long tail moment and a very large stab and elevator. don't know if you've seen the pics of my design "The Heretic", but it's got plenty of turn authority. Despite the sense that high aspect doesn't do well in wind, this plane flies great in the wind. This has been the test bed for my 4 stroke experiments so I probably don't notice any decrease in turn rate.

Back to topic. I've continued to experiment. I just think there's a lot more power to be had for this engine if I can increase the fuel and air load. I'll keep at it.

I have been expeimenting with 4 strokes and have tried the RC carb and a venturi originally made for a smaller engine. This setup improved the needle settings but I agree, it needed more air and fuel. I don't know the exact original venturi size, but I am up to .250 and it is getting much better and stronger. I am running an OS 40 with a 12x5 RevUp releasing at 8700 RPMs. I would like to get the opening a little bit bigger but I have run out of material with the current venturi. It burns about 2.75 ozs for the pattern currently and I am running GMA 5/22. I tried 10% but the 5% again amkes everthing run smoother and more consistantly.

Still learning,
Zuriel

Z2,

Well, I'm working with a Saito 56. Current setup is Powermaster 5% nitro, 20% oil, My own intake port that accepts ST60 venturis (who still sells these?). Right now there is a .330 venturi in it with a trick tank that is designed to keep head pressure up, but I'm planning to try the B-17 setup with a pressure bladder and regulator. Recently I've been using a sort of ram-air system with a piece of tubing facing forward behind the prop and forcing air into the venturi, but it's inconsistent as heck so I'll try something else. Maybe a forced air chamber or something. The prop (today) is a homebrew 13 x 4.75 3 blade made from RevUp 13x5 extra wide blade wood props. I've been running it at about 9800rpm (about all the Saito has with this prop).

If I get brave, I'll tear it down and mess with the intake and exhaust ports to increase flow. I have some other ideas too, but that is all for much later. Right now I just want to get the Saito to put out what it's hiding.

Sure is fun though.

Randy,

The near side radius on the intake port leaves a lot to be desired, in fact it isn't a radius at all. It's two drilled holes that meet and sharp corners result. The flow of the port could be dramatically improved.

Porting and polishing is a thought. I picked up a used Saito a couple of days ago. Some RC guy didn't think it made enough power (?) It has some time on it and may be worth messing with a bit. Worst case...it gets screwed up and I have a parts engine.

How do you think George got started....

Not having one, and not even considering getting one, I would look at running 10% nitro, if not more. A bigger venturi won't help if the head doesn't flow well, so I think you need to build a flow bench and get the ports improved. That said, remember that all this will remove midrange and bottom end torque. A fuel pump of some kind might be useful, but all the ones I'm aware of use crankcase pressure to drive them, and the 4S is not enabled on that score. I learned something about bladder tanks at the Raider Roundup...PW found he had to change tanks after 3 runs, as the tubing developed "aneurisms". When that happens, the engine run is just horrid, I guess there must be more of a pressure variation. I would avoid them like the plague, it makes flying more like work and less like fun. I noticed that Randy was using a 3 blade prop made from wood blades...I don't think this is a real safe thing to do, but know Randy enough to know that he must have a pretty good system figured out. Maybe Randy would start a new thread on the subject or maybe it would be better never to mention it again? Steve

If you're going to run a 4-stroke, just plainly forget everything you know about a 2-stroke; the only common factor about the 2 types of engines is they both have connecting rods. With 4-strokes you can work with tuned intake track (intake manifold length and dim.; the other verable is exhaust tuning, diameter and length of exhaust pipe, straight pipe is the easiest to work with, the next type would be reverse cone magaphone and last, an open exhaust funnel. The easiest to tune is the straight pipe (generally the pipe will be longer than the manufactured length)to dictate where your cam will come in and out. Now your reverse cone megaphone is your best bet for absolute pulling power but will take many configurations to get it right but maybe an advantage in stunt flying. The open cone megaphone give you very good power at high rpm not a way to go in stunt. There's been many formulas written on exhaust tuning and intake tuning, if you can find one there's a book written by Ivar Lloyd entitled "Tuning for Speed", written in England. This book gives you all the basic intake and exhaust tuning formulas for 2-stroke and 4-stroke engines; I've used this book for over 30 years for setting up full scale racing engines. As far as hop-up, lightened rockers, tapered and lightened timing gears, porting and polishing and changing port configuration does not really apply because of the lack of choice of camshafts. So stick with your factory intake length and play with exhaust tuning and different props (not 2-stroke props). 2-strokes rev and 4-strokes have torque. So realistically, a tuned pipe used on a 2-stroke which is meant for very high rpm has no relation to a 4-stroke and as a matter of fact, I see no reason for using one on a 2-stroke engine that you're trying to run on a low 10k rpm engine unless it's in the configuration of a 2-stroke motorcross motorcycle where torque is important.

>>Maybe Randy would start a new thread on the subject or maybe it would be better never to mention it again? Steve <<

I'll say that I don't recommend that anyone use other than a factory prop. That being said, it's pretty easy to make 3 blade props from wood 2 blades if you're reasonably careful and are sure to physically tie the 3 blades together. I've used 2 systems. One is to cut a slot in the center of the blades and use a steal washer. Drill 2 retention holes in each blade through the washer (six holes total) and pin them with 3/32 piano wire. The other is to use a jig and set the blades and glue them together so that the prop is in final configuration. The use a hole saw to cut a round slot in the top and bottom (or back and front, depending on how you look at it) of the hub. Cut two chunks of the correct diameter tubing and epoxy them in the slots. This make a mechanical lock, particularly when the washer and prop nut are torqued down. I favor the second method because one, it's easier overall, two, it's easier to get the blades perfectly aligned and three, you don't have the steal pins verticaly between the thrust washer and prop nut washer possibly keeping you from torquing down the prop.

I've never had one fail that is mechanically locked. 4 blades are even easier since you don't have to cut a prop in half.