Randy POwell 4 stroke setup

Could you please explain your tank, venturi, and prop setup?

LAST EDITED ON Sep-12-03 AT 06:21 PM (CDT)
 
'zilla,

Different than yours.

Ok, ok. I'm using a Saito 56 with a .320 venturi. The venturi is my own design and quite different than the Pat Johnston setup. When I get home, I'll upload a picture of it. The current tank is a bent uniflow clunk tank. The uniflow vent is simply run to the center of the tank then bent to the inside. Allows it to be rotated up or down to "adjust" tank height. I use muffler pressure, but it really runs identically with and without the pressure. Just makes it easier to prime the engine and I delude myself that it runs a bit smoother with the pressure, but there really isn't any difference.

The current prop of choice is an Eather 13x4 flat back, 3 blade cut down to 11.5 inches and cleaned up quite a bit. Gives a lot of blade area and reduces tendency toward GP and other unwanted yaw. Ground launch rpm is in the 10,200 to 10,500 range, depending on fuel and conditions. I've run the thing with 10/23 fuel (15% synth/8% castor) for most of 2 years and have been very pleased with the performance. Recently, due mostly to your discussions here, I've been trying YS20/20 fuel (a bit of castor added to bring it up to 23%). At first I didn't see much difference. But as I've continued to use it (I'm on my 3rd gallon of it), I do see some additional power with this mix. The ground launch rpm is closer to the 10,500 mark with it and it seems to have just a bit more juice above 45 degrees. Also seems to run just a little bit smoother.

Anyway, that's it. I'm pretty happy with the setup.

Edit: Oops, forgot to say lap times are in the 5.2 to 5.3 range with this setup. The other prop I use when it's calm is an Eather undercamber 12x4 3 blade also cut down a bit to 11.75. Not as strong as the flat back prop, but slightly better "steerability", particularly above 45 degrees.

Here's the venturi.

You don't happen to make one of these for a Saito 72 do you? Really beautiful and quite innovative work.

Pro,

These were made for my own use. I didn't suspect that anyone else would be interested. I certainly could make one for a 72...if I had a 72. I don't know if the setups that fit the 56 will fit the 72.

I am the one with a Saito 72. Walter Hicks also has a Saito 72. If you would like me to mail you mine, just let me know.

Pro,

Just need to know if the 56 unit will fit on the 72. I know the manifold inlet is bigger, but will the rest of it fit? I'm considering a 72 and may get one myself.

>'zilla,
>
>Different than yours.

Naturally, that is why I asked...

>Ok, ok. I'm using a Saito 56 with a .320 venturi.

I am running a .310 with an OS MAx needle as of late.

I use muffler pressure, but it really
>runs identically with and without the pressure. Just makes
>it easier to prime the engine and I delude myself that it
>runs a bit smoother with the pressure, but there really
>isn't any difference.

This I find very interesting...

'zilla,

With the OS needle, yours should actually be a bit bigger than mine.

I use an ST needle. What's your ground rpm? How about fuel consumption.

Mine runs really well, just wish I could get a plane to last long enough to fly. This has been a tough season for me. At least with the next plane, I won't have to worry so much about getting the set up to run.

>'zilla,
>
>With the OS needle, yours should actually be a bit bigger
>than mine.

LET'S SEE...

'zilla,

Is the stock carb notation for the 72 or the 56?

>'zilla,
>
>Is the stock carb notation for the 72 or the 56?
>
>

Randy Powell

Saito 72. I think the 56 is about the same carb.

>I use an ST needle. What's your ground rpm? How about fuel
>consumption.

My prop is the PW 13 x 5 Bolly 3 blade with the sharpened leading edge.

Fuel consumption is 4.5 to 5 oz, but I am trying to go to 6 oz just for grins.

Ground RPM is always the same, right at 10K. The RPM is a function of the prop not as much the venturi. To get more RPM I THINK I would have to go smaller on the prop. The ground RPM also has little, if nothing to do with the in flight performance.

I read Frank Williams article in PAMPA over and over, and he was the inspiration for some of the new trials. Sadly, I will have to diagree with Frank. The HP available DEFINATELY has something to do with the mixture. The output is definately related to how lean the engine can be run. Getting the engine to run rich and put out the same HP requires some drasticly different numbers, if it possible at all...

Brad,

Frank ran horsepower curves on the same day for both 2 and 4 stroke motors. All tests were run on the same fuel and as indicated a flying setup. Frank has a set of calibrated props that are used to calculate the horsepower curves. I think that the tests are quite accurate given the test conditions.

>Brad,
>
>Frank ran horsepower curves on the same day for both 2 and 4
>stroke motors. All tests were run on the same fuel and as
>indicated a flying setup. Frank has a set of calibrated
>props that are used to calculate the horsepower curves. I
>think that the tests are quite accurate given the test
>conditions.

I have no doubt that the tests were accurate. I hold Frank W. in, literally, THE HIGHEST REGARD. Frank is the smartest guy in stunt, and also one of the nicest, a rare combination. I am only saying that the mixture has a tremendous effect on the peak HP, while in addition, so does the venturi size.

For example, with a small venturi and stoichiometric mixture, output can be tremendously higher than a rich mixture with a venturi of even twice the size. The funny thing is that the torque curves might behave in the same manner and the two runs may use the same propellors and "go over the top" at the same spots in the pattern.

Of course the latter will run much cooler and will sustain power longer.

I do not want to overstate my understanding of torque curves. I am no expert and I have a rudementary understanding of what Frank is trying to say. A lot of what I am saying is a jumbled mix of the practical and scientific. In practical terms, the mixture of a 4 cycle has every bit as much effect on sheer OUTPUT as any 2 cycle. The torque curve is still somewhat of a mystery.

LAST EDITED ON Sep-16-03 AT 00:53 AM (CDT)
 
Godzilla,

I agree, there is a "sweet spot" with the mixture. Strange, I can think I have it on the ground, then it will flatten out under max load in the air. Come down, reset a bit richer and it's great. It seems I need to mess around a bit and fine the absolute peak with a tach, then back off the peak 100 or 150 rpm to hit the right spot. Since going to the 20/20 fuel, I've had less problems with run time. Previously, with the 10/23 fuel, it seemed that every ten degrees of temp made a difference in the run lenght. The same fuel that gave me a 7 minute fight in the cool of the morning, would not be enough for the pattern when the temp went up. This seems less of a problem with the 20/20. Hmm...

I've sure been happy with the setup. While I've had an interesting time this year with plane issues, the power train has been dependable. Only substantial issue I had this summer was flying on really hot days and that just demonstrated that I didn't have adequte cooling in the plane. Re-taught me a lesson I thought I'd learned.

As far as power produced, within reason, the more fuel and air you can stuff in there, the more power the engine will produce. To a point. I spent a good deal of time trying to figure out what that point was. I settled on the .320 as a compromise. At one point I had a some pretty weird setups trying to increase the fuel and air load. But the fuel draw gets pretty suspect after about .330 and is occasionally dicey there.

Surprisingly, there isn't much difference in the the run quality with and without muffler pressure for me. As I noted, it seems a bit smoother overall with pressure, but not a huge difference. At least the way I have it set up. But then, I ran a metal tank most of last year and had pretty good luck with it. I'm using a clunk now and still have pretty good luck.

"As far as power produced, within reason, the more fuel and air you can stuff in there, the more power the engine will produce. To a point."

Maybe you should start designing a little turbocharger Randy

Randy, As I mentioned before, you have apparently found by way of empiral testing,that compromise betweem max power and good fuel draw for the Saito 56. The Chinese stunt team actually set up their Supertigre 60's with this same concept in mind. They operate with somewhat less then max power with the upside of greater fuel draw and consequently more reliable and consistant runs. The downside for them is that they have to build their ships extemely light. The Saito 72 based on my experience seems to have a noticable increase in fuel draw compared to the 56. I am extrapolating when I assume that a .3281, or 21/64 hole will work. The RC carburetor that comes with the 72, full open, is quite big. Your result is quite close to Clementi Cappi's recommendation of approximately 8mm for the 56.

>Surprisingly, there isn't much difference in the the run
>quality with and without muffler pressure for me. As I
>noted, it seems a bit smoother overall with pressure, but
>not a huge difference. At least the way I have it set up.
>But then, I ran a metal tank most of last year and had
>pretty good luck with it. I'm using a clunk now and still
>have pretty good luck.

Maybe the pressure tap for the 56 is not oversized like on the 72.

LAST EDITED ON Sep-16-03 AT 02:57 PM (CDT)
 
Pro,

I'll have to look at my man process sheet. I think the hole is a "P" letter drill. Could have been an "O". I'll look when I get home. It's about .320 (I think it's like .3218, but as I say, I'll have to look). There's also a physical limit. The intake tube is .330 ID. Not much point in going bigger than that unless you could use a bigger intake manifold tube, then punch out the head to accept the bigger tube, increase the head flow and intake valve size. Let's see, that would probably take heavier valve springs and maybe a higher lift cam. And of course, that means a bigger exhaust valve and better lifters and... As I say, .320 is about it for consistency. Nice thing about the 72 is you can take the Ford GT-40 approach. Make an enormous engine and detune it for reliability and still have more torque than anyone else.

Nils,

Hey, I thought about it, sorta. An itty-bitty supercharger. Yea! Saito on forced induction! I seriously considered the YS63 just because of the fuel pump, but DMoon discouraged me.

'Zilla,

The stock pressure tap on the 56 muffler (Old style with the tap at the front of the muffler body) is pretty small. I haven't measured it, but it's pretty small. I suspect the effect would be different if the hole were enlarged.

>'Zilla,
>
>The stock pressure tap on the 56 muffler (Old style with the
>tap at the front of the muffler body) is pretty small. I
>haven't measured it, but it's pretty small. I suspect the
>effect would be different if the hole were enlarged.

There was a definate change in the design when Saito moved the pickup point on the muffler from the front to the rear. My first Saitos (72) were more "charging". They had the small pressure tap toward the front, the new engine, the one I ran at both of the last Nats is the later model with the tap to the rear. The tap is also very large. The power delivery using the over sized pressure is very smooth and allows slightly more pitch without windup. The engine simply refuses to spin up a lot though and requires a larger opening to get the RPM back.

I am still messing with it. I like the new setup better than anything I have yet to try. I like Paul's better at 5 feet, but I am working on that....

Godzilla,

Yesterday you made mention of torque curves and such. I can't help you much here, as I have not yet seen a graphing of the torque curve for either a Saito 56 or 72. In fact, I have no more information today than when I wrote the Bad Boy Stunt column that dealt with the declining torque curve of many (all?) Saito engines.

However, it may help if all of us understand that peak torque--with any engine, regardless of the number of strokes involved in pumping the flammables--is always generated at the point where the engine in question breathes the best. Truly it is that simple. Along with the notation--not for 'Zilla this time, certainly not Howard Rush and a few others--that we are talking about torque, NOT horsepower.

From there it is plain to see that manipulating the point where peak torque kicks in is a matter of fiddling with stuff. As in actual machine work, which is why some of us so readily begin talking about Stunt cams and other cool tricks.

Before anybody misinterprets these comments, yes of course one can increase peak torque by using hotter fuel and a few other tricks. But the absolute peak will still be exactly at the same point in the rev range, because increasing torque is a hugely different matter than moving peak torque up or down the rpm range.

>I read Frank Williams article in PAMPA over and over, and he
>was the inspiration for some of the new trials. Sadly, I
>will have to diagree with Frank. The HP available
>DEFINATELY has something to do with the mixture. The output
>is definately related to how lean the engine can be run.
>Getting the engine to run rich and put out the same HP
>requires some drasticly different numbers, if it possible at
>all...

How can you disagree with Frank? He put the motor on the stand and ran tests and wrote down what he found. Not much to disagree with there.

Besides his findings echo things you have been saying for 2 years. Things such as you want to go faster just open the venturi not screw in the needle like a two stroke. Slower? Just close the venturi but still run it at peak rpm/or in other words max HP for that opening.

The 4s is not nearly as effected by mix as a two cycle is. The 4s doesnt have that extra cycle to get onto like a 2s. A click or two rich or lean is not going to drastically change the HP output like it can on a 2s. It just cant. Especially not in a test stand environment. I think that is exactly what he is saying. There is a sweet spot on each venturi where it can be flown with good results. But the needle settings for each are very similar in characteristics.

The Furias supports his article to the T! I had said Prop that would give me 5.4 laps at 8400rpms on the 72. 56 with the large venturi would spin it 8800-9000, very fast. Mid venturi 8600 rpms 5.1-5.2. Small Venturi 8400 and the 5.4 laptime. Reducing the Venturi reduced the max RPM operating range which in turn reduced the HP. This could not be acheived by just rolling out the needle. Beleive me I would have done it that way if it would have worked.

His article makes sense.

>How can you disagree with Frank? He put the motor on the
>stand and ran tests and wrote down what he found. Not much
>to disagree with there.

I guess it is a matter of degrees. The needle (a couple of clicks) has minimal effect.

>Besides his findings echo things you have been saying for 2
>years. Things such as you want to go faster just open the
>venturi not screw in the needle like a two stroke. Slower?
>Just close the venturi but still run it at peak rpm/or in
>other words max HP for that opening.

Ah, yes, but I can change the lap times almost a full second just by pulling the pressure line on the Saito 72.

I guess what I am saying is the mixture is changing from the static postion with either the non-pressure or pressure setup and it definately effects the output.

I am all about what Frank is saying on the venturi to horsepower relationship. Output is definately directly proportional to the venturi opening---all things equal at a stoichiometric mixture. There also appears to be a lot less detrimental effects to opening the venturi, like you might see on a 2 cycle since there is no 4-2 break to deal with.

Additionally, (IMHO) either side of stoichiometric definately effects the output and the torque peak.

I will call Frank and maybe I can get him to do more tests. I am totally digging what Frank is doing! I would love to see more, it really helps.

Frank was definately the inspiration for the newest tests!

LAST EDITED ON Sep-17-03 AT 10:05 AM (CDT)
 
>Ah, yes, but I can change the lap times almost a full second
>just by pulling the pressure line on the Saito 72.

You are saying you can take a 5.0 laptime setup on pressure and pull the pressure line ONLY, not change any other thing at all, and it will go up to 4.2-4.0 laptime? I haven't seen that.

I have seen increases in your speeds with the pressure off but you are also using much larger Venturis and smaller more efficiant 3 blades than you were old pressure days with large 2 blades and smaller venturis. Remember in the old 2 blades day if it were too fast you had to squeeze down the venturi. Now you are getting the props to give you the speed you want with the RPMs way up almost WOT. The motor is able to use more of its available power in this setup. It is much easier for the motor to fly the plane.

I experimented with pulling the pressure line ONLY on the 26. This was right before you started messing with the PW setups, I mean just a few days before, we talked about it some at the field. Two things happened. One it used more fuel. Two the run was less consistant but seemed to come on during the maneuver and richen up a tiny bit during the level laps. However the lap times stayed very close to the same. NOTHING else was chaned. I had to needle it but the same RPM was gained because the same load was on the motor and the same venturi was being used.

>You are saying you can take a 5.0 laptime setup on pressure
>and pull the pressure line ONLY, not change any other thing
>at all, and it will go up to 4.2-4.0 laptime? I haven't
>seen that.

5.35 TO 4.65. .7 seconds.

I have done it, not back to back though.

Stop busting my balls...

LAST EDITED ON Sep-17-03 AT 11:29 AM (CDT)
 
>5.35 TO 4.65. .7 seconds.

With the same prop???

I thought the lower pitch props were giving you the 5.35? I remember the contest runs and you said those were on 4.8-4.9 pitch giving you the 5.30 laptime??? Then when try PW setup with more pitch like a 5.1 and pulled the pressure line and it went 4.65? Am I following your timeline correctly?? It is hard to keep up.

When you were on pressure and getting a 5.35 lap what was your RPM? Where you on pressure at the contest? When you were getting the 4.65 with the SAME prop off pressure what was your RPM? It must have been a huge jump in RPM to get that much of a speed increase. Or was it different props also?

>Stop busting my balls...

I am not busting your balls. Just trying to get all this info straight. I was not aware that ONLY pulling the pressure line and making NO other changes would jump it .7 of a second on the laptime. I hadnt run into that before. I even ran the Furias off pressure a coupl of time with the 56 and it didnt jump in speeds that drasticlly either, when ONLY removing the pressure line.

Besides someone has to give you a hard time...

LAST EDITED ON Sep-17-03 AT 02:58 PM (CDT)
 
Doug,

I haven't noticed much difference in run with and without pressure, but as Brad noted, the pressure valve on the 56 is considerably smaller and the fuel draw on the 72 is much bigger than the 56.

I worked on getting the 56 to put out as much power as I could without making any mods to engine (changing compression, valve lift, etc). Venturi, pressure, whatever. Tried a lot of stuff. Still am, for that matter. When I got what I felt was all the output I could get out of it while maintaining a consistent run, I started working on what prop layout would give me the lap times I wanted and would harness the available torque generated effectively.

I felt that the first thing was to get the engine to produce it's peak output, then figure out how to harness that output to the best effect.

>I felt that the first thing was to get the engine to produce
>it's peak output, then figure out how to harness that output
>to the best effect.
>
>
>

Randy Powell

This seems to be the path Brad is on now, I think. One thing for sure with the motor using more of it power it runs alot cooler. After the flight the spinner is only warm not hot like the days of old with the smaller venturi opening.

Is your opening as large as the 56 carb opening including the small spigot the 56 uses in its carb?

Doug,

Strangely, the carb opening is about .340 at full throttle. But the intake tube is .330. Hmmm...

It does run cooler, as you noticed.

>I haven't noticed much difference in run with and without
>pressure, but as Brad noted, the pressure valve on the 56 is
>considerably smaller and the fuel draw on the 72 is much
>bigger than the 56.

That is correct. The effect may be more drastic on the Saito 72.

The point being that I think a slightly richer run (slightly) is obtained bu over pressurizing the tank, which conversely allows a much large opening in the venturi, which conversely makes more power, etc. etc.

I will keep working on it.

So far it appears that I have to do some other stoff to run a Bolly at 5 pitch. I can run an Eather at less than 5 pitch but the Bolly takes a tweak more.

Brad,

It just goes to fast for me with a 5 pitch prop. Ground launch is about 10,200 to 10,400, depending on fuel and at that rpm, a 5 pitch gives me 4.8 second laps. I use a 4 pitch for nice, easy 5.2 second laps. Maybe the plane needs more drag.

Again, I think prop choice has a lot to do with the airframe design and the rpm...an preference.

>>I haven't noticed much difference in run with and without
>>pressure, but as Brad noted, the pressure valve on the 56 is
>>considerably smaller and the fuel draw on the 72 is much
>>bigger than the 56.

I have a question. Brad has been speculating that Saito put a larger pressure tap opening on the 72 to make sure the public doesnt overlean the motor and tear it up. Could be true but it is only speculation and without real testing of any sort there is no way to test it out. I read Randy's above post and it just hit me. If the 72 really did have better draw than the 56 it would not need a larger tap. It could go with a standard sized tap and run just fine. Maybe the fuel draw is actually worse on the 72 so the larger tap is needed to keep it running in a nose up attitude. That would make logical sense to me as to why the tap hole is larger. There would need to be a conclusive reason for them to go through the cost of changing to larger tap for the motor.

Could it be that the 72 actually draws worse than the 56?

Just some thoughts.

LAST EDITED ON Sep-18-03 AT 03:43 PM (CDT)
 
>>Could it be that the 72 actually draws worse than the 56?<<

Man, that is a depressing thought. The 56 doesn't draw all that well unless you keep the venturi size down a bit. I got great power from the 56 with increasingly larger venturii, but the run becomes very inconsistent above a certain level. The engine just doesn't provide sufficient fuel draw to use really big intake setups. I've messed with a number of tank configurations to try to increase the pressure in the fuel system to allow a bigger venturi, but nothing really worked very well. Actually, the clunk seems to be the best compromise. Maybe a fuel pump or trying The Dirt's pressure bladder setup would be the ticket.

But I'm sure not interested in using pressure bladders if I can help it. And the truth is, the current setup I'm using delivers plenty of power and a great degree of reliabilty with repeatable, consistent runs. Better than anything else I've tried.

>Could it be that the 72 actually draws worse than the 56?

Yes, I believe that could be the case. I believe the cam in the Saito 72 is much more radical than the 56. Frank Williams' tests showed that the torque peak was far more severe in the 72 than the 56. This would indicate that the valves have less overlap and possibly more lift also.

I know in cars this leads to far less vacuum in the crankcase.

This would explain the large pressure tap in the Saito 72.

Serious, the pressure tap in the Saito 72 may actaully be TOO LARGE. I am not saying the stock setup works the best, but frankly, the slightly rich 4 stroke will pound out power, and very steadily, when the lean running engine takes a big dooky. Specifically when the temperature gets above 100 degrees and the wind feels like sitting inside a blow drier.

Brad,

About rich running. I completely agree. Something I've noticed is that if the 56 is set at peak rpom on the ground, it will go overlean under load. You can hear it go a bit flat and too lean in the overheads and above 45 degrees. Knocking off 150rpm or so on the ground (maybe 1/5 to 1/4 turn rich on the needle) will give the thing some real grunt in those high load situations.

I have had the same experience with my Saito 72. If you set it for peak power on the ground like a 2 stroke, it will crap out on you the second the nose goes up. When you set it for what seems like just a tad too rich, WATCH OUT! The instant that nose points up, the ship is moving! The perception from outside the circle is as if the ship is literally jumping into a corner. What is so nice about this, is that because of the abundance of power in the Saito 72, you can run it below it's maximum and still get PLENTY! of juice for maneuvering.

I am pretty sure the two preceding posts are dealing with a difference in setup--quite likely the tank--rather than stating the case for all four-strokes, even all Saito 56s or 72s. Neither my 56 nor the still new 72 respond in the manner quoted above.

Dan,

That's because you're using a whimpy venturi.

When running the engines (at least the 56) in the 10,200 to 10,500 rpm range, they are pretty much maxed out at the most power available without floating the valves or exceeding the engine's ability to draw fuel, at least in my experience. If the needle is set to absolute peak rpm on the ground, it will unwind slightly in flight and likely go a bit flat and overlean under load. But this is with the sort of setup I use and Brad is experimenting with. When a more modest venturi is used in a lower rpm range, I suspect that this condition doesn't occur.

When a more modest
>venturi is used in a lower rpm range, I suspect that this
>condition doesn't occur.

Actually, that is the heart of everything I have been saying. The behavior described is directly proprtional to the fuel draw, or conversely, the pressure in the tank.

The bigger venturi just has more of everything. Period.

>>Stop busting my balls...
>
>I am not busting your balls. Just trying to get all this
>info straight. I was not aware that ONLY pulling the
>pressure line and making NO other changes would jump it .7
>of a second on the laptime. I hadnt run into that before.
>I even ran the Furias off pressure a coupl of time with the
>56 and it didnt jump in speeds that drasticlly either, when
>ONLY removing the pressure line.

Yup. On the 13 x 5 pitch.
>
>Besides someone has to give you a hard time...

Lucky me...