Author Topic: Why such low RPMs? (Read 36173 times)

steven yampolsky · « **on:** August 22, 2012, 02:24:14 PM »

I flew a bunch of flights on an OS-52 with UHP venturi but having no prior knowledge of Bob Reeves' setup I set it up a bit differently. The strange thing was: it ran extremely stable, just like the 40VF it replaced. So my question is: has anyone tried setting up Saito's like a piped setup? I have a Saito-56 waiting to go into a new model and would like to know if anyone experemented with Saitos running like a pipe motor.

Here's my setup:
OS-52S
OS F plug
UHP venturi
11.5x4.25 CF prop(Gator or Bolly, same results)
4.5oz uniflow tank
no muffler pressure.
10,100-10,200 launch RPMs

The model was a modern 650sq, 56oz design that had OS 40VF on a pipe. OS-52S was a direct drop-in into VF mounts, that's why I picked it.

proparc · « **Reply #1 on:** August 22, 2012, 02:51:31 PM »

Randy Powell tried it. He blow the rods.

RandySmith · « **Reply #2 on:** August 22, 2012, 03:09:28 PM »

Quote from: proparc on August 22, 2012, 02:51:31 PM

Randy Powell tried it. He blow the rods.

Yep Paul Walker and Gordon DeLany both ran them high RPM, with good results

Randy

Joe Yau · « **Reply #3 on:** August 22, 2012, 03:18:55 PM »

Quote from: RandySmith on August 22, 2012, 03:09:28 PM

Yep Paul Walker and Gordon DeLany both ran them high RPM, with good results

Randy

Just curious if they are using the stock valve train..

or some mods was done like heavier valve springs & stronger push-rods etc.

Brett Buck · « **Reply #4 on:** August 22, 2012, 04:30:47 PM »

Quote from: Steven Yampolsky on August 22, 2012, 02:24:14 PM

I flew a bunch of flights on an OS-52 with UHP venturi but having no prior knowledge of Bob Reeves' setup I set it up a bit differently. The strange thing was: it ran extremely stable, just like the 40VF it replaced. So my question is: has anyone tried setting up Saito's like a piped setup? I have a Saito-56 waiting to go into a new model and would like to know if anyone experemented with Saitos running like a pipe motor.

Here's my setup:
OS-52S
OS F plug
UHP venturi
11.5x4.25 CF prop(Gator or Bolly, same results)
4.5oz uniflow tank
no muffler pressure.
10,100-10,200 launch RPMs

The model was a modern 650sq, 56oz design that had OS 40VF on a pipe. OS-52S was a direct drop-in into VF mounts, that's why I picked it.

   That sort of setup is similar to that used by just about everyone who made a serious effort. In fact I think that the first high-quality runs were Ted and his Enya 46 and maybe a 12-4 Rev-Up back in 1985/6. This type of setup works well enough but it doesn't seem to offer any improvement over the PA/VF or similar.

In fact, I think Jim Aron's Boogaloo was more-or-less exactly as you describe above, and it ran fine. The airplane was a little overweight but the engien runs fine.

   The extremely low rev approach was very rare, in fact, Igor Panchenko was the first person I know that tried it but that was pretty late in the game, when it was obvious that electric was a more fruitful area for development. If I was going to run one now, I would certainly give the low-rev thing a try, using Bob's configuration. The medium rev (10,000/4.5 ish inches) system is already known quantity, with well-known strong points and weak points.

   Brett

Brett Buck · « **Reply #5 on:** August 22, 2012, 04:37:42 PM »

Quote from: Joe Yau on August 22, 2012, 03:18:55 PM

Just curious if they are using the stock valve train.. or some mods was done like heavier valve springs & stronger push-rods etc.

   Everyone I knew doing that had stock engines. They have no significant reliability issues at 10000 rpm or so, and valve float may be a feature rather than a bug.

   Can't say the same for the reliability of the airplanes they were attached to. A fair number of four-stroke airplanes have self-destructed in many interesting and otherwise unheard of ways that we had never seen before in two-strokes - like Paul's Mustang blowing up the fuselage in flight, and Gordan's control horn upright breaking in half. Both of those were large Saito's but that might have been because that's about all anyone was using. And they were all running in the 9500-10500 rpm range with around 4 and a half inches of pitch.

   Brett

Allan Perret · « **Reply #6 on:** August 22, 2012, 05:55:03 PM »

Quote from: Brett Buck on August 22, 2012, 04:30:47 PM

The medium rev (10,000/4.5 ish inches) system is already known quantity, with well-known strong points and weak points.

Hey Brett: What were the weak points of this set-up ?

Allan Perret · « **Reply #7 on:** August 22, 2012, 06:07:50 PM »

Quote from: Steven Yampolsky on August 22, 2012, 02:24:14 PM

I flew a bunch of flights on an OS-52 with UHP venturi but having no prior knowledge of Bob Reeves' setup I set it up a bit differently. The strange thing was: it ran extremely stable, just like the 40VF it replaced. So my question is: has anyone tried setting up Saito's like a piped setup? I have a Saito-56 waiting to go into a new model and would like to know if anyone experemented with Saitos running like a pipe motor.

Here's my setup:
OS-52S
OS F plug
UHP venturi
11.5x4.25 CF prop(Gator or Bolly, same results)
4.5oz uniflow tank
no muffler pressure.
10,100-10,200 launch RPMs

The model was a modern 650sq, 56oz design that had OS 40VF on a pipe. OS-52S was a direct drop-in into VF mounts, that's why I picked it.

Bob Dixon uses the OS-52 and if I remember right from reading his articles on 4-stroke power in Control Line World he uses the higher RPM lower pitch mode. I will dig out some of the back issues and report back if I am wrong about that.

Douglas Ames · « **Reply #8 on:** August 22, 2012, 07:27:36 PM »

I think you guys that tried the high rev/ low pitch setups in the past are missing the point of a 4 stroke, and that is torque, alot wider torque band than a 2 stroke, and one that peaks at a slightly lower RPM.
HP is a mathematical formula but torque is a real number, you just can't compare HP numbers of 2S vs. 4S as the combination of RPM and torque curves for both engines will result in two different HP curves. On a 4 stroke, where the torque peak is - is where you want to prop your engine.

Tuned pipes or even stunt (baffled) 2 stroke type pipes don't work on a 4 stroke. Some backpressure is a good thing but controlling pressure waves with an expansion chamber will achieve nothing on a 4 stroke.

Valve float, next to detonation is probably the most destructive thing in a model 4 stroke. The valves can't close fast enough and the rocker arms are literally pounding the valve stems.

I urge you to try Bob's combo, even on an OS you'd get better results with a higher pitch prop, lower RPM and some 20% nitro.

Chris Wilson · « **Reply #9 on:** August 22, 2012, 08:17:57 PM »

Quote from: Douglas Ames on August 22, 2012, 07:27:36 PM

Valve float, next to detonation is probably the most destructive thing in a model 4 stroke. The valves can't close fast enough and the rocker arms are literally pounding the valve stems.

Hey Doug, would valve bounce be there at something like 10 000rpm considering the minute size and lack of inertia of a model engines valves?

(Or do the push rods add to this.)

Douglas Ames · « **Reply #10 on:** August 22, 2012, 09:49:12 PM »

Quote from: Chris Wilson on August 22, 2012, 08:17:57 PM

Hey Doug, would valve bounce be there at something like 10 000rpm considering the minute size and lack of inertia of a model engines valves?

(Or do the push rods add to this.)

I can't say what rpm a particular engine would float the valves, but consider that these little engines have no dampers or even dual springs like a full scale engine. Spring quality and heat cycles would reduce the spring pressure over time I'd think.

As you know, the rocker arms and pushrods aren't connected, only mated with each other by spring pressure. Bent pushrods are a sure sign of valve float, but unlikely in a properly set up stunt engine.

OS rates their 56a up to 13K! ...but why rev it that high?

Brett Buck · « **Reply #11 on:** August 22, 2012, 09:51:39 PM »

Quote from: Douglas Ames on August 22, 2012, 07:27:36 PM

I think you guys that tried the high rev/ low pitch setups in the past are missing the point of a 4 stroke, and that is torque, alot wider torque band than a 2 stroke, and one that peaks at a slightly lower RPM.
HP is a mathematical formula but torque is a real number, you just can't compare HP numbers of 2S vs. 4S as the combination of RPM and torque curves for both engines will result in two different HP curves. On a 4 stroke, where the torque peak is - is where you want to prop your engine.

   An Saito 56 has *much less* torque at 9000 rpm than a PA61,even a PA61 set up to run ideally at 11,000. We measured it on a dyno. It was something like 50% more. I would guess I could set up a PA61 to have maybe 2x the torque of a Saito 56 at 8000 RPM. At the same RPM, that's also twice the HP.

   Torque and HP are both "real numbers". You get away with the reduced power by running a more efficient prop - more efficient in level flight anyway, where we may be tossing out 30-40% of the shaft HP in level flight with a PA61.

   The reason to run it at low revs is presumably to give it some responsiveness in flight. It doesn't have that if it's already almost topped out. That's also why something like a PA61 has no problem at 11,500 in the air - because there's still plenty of RPM left.

   Brett

steven yampolsky · « **Reply #12 on:** August 22, 2012, 11:03:39 PM »

Quote from: Brett Buck on August 22, 2012, 04:30:47 PM

This type of setup works well enough but it doesn't seem to offer any improvement over the PA/VF or similar.

Exactly the reason I decided that it wasn't worth pursuing 4-strokes at the time. I sold the OS and for 5 years did not pay 4-stroke scene much attention. This spring I was given a Saito 56 and would love to give that motor an honest try but when I looked at this forum, I was surprised that pretty much everyone here talks about low RPM mode only.

I am glad to see that high-RPM mode is used successfully by others. I really like the power delivery of a high RPM/low pitch setup.

Brett Buck · « **Reply #13 on:** August 23, 2012, 12:53:44 AM »

Quote from: Steven Yampolsky on August 22, 2012, 11:03:39 PM

I am glad to see that high-RPM mode is used successfully by others. I really like the power delivery of a high RPM/low pitch setup.

I would certainly try it in low-rev mode as Bob and others are running it, and run it long enough to make an objective evaluation, before drawing any conclusions. To the extent I understand the approach, it does seem to address some of the shortcomings that were found in running at tuned pipe speeds, like the weak overhead performance. With 7" of pitch and some breathing room on the RPM, it's not likely to have a lot of problems penetrating back into the wind, that's for sure! And all 4-strokes definitively avoid the issues you can have with excess corner boost on piped 2-strokes.

Brett

Allan Perret · « **Reply #14 on:** August 23, 2012, 10:58:25 AM »

Quote from: Brett Buck on August 22, 2012, 04:30:47 PM

This type of setup works well enough but it doesn't seem to offer any improvement over the PA/VF or similar.
Brett

No improvements relative to performance, but the cost of a 4-stroke system is half of a piped PA or RO Jett.
And also does the job with nearly half the fuel load.
Bob Reeves has written thats what drove him in the 4-sroke direction.
For me the only negative is the higher vibration level.

proparc · « **Reply #15 on:** August 23, 2012, 11:32:05 AM »

Quote from: Allan Perret on August 23, 2012, 10:58:25 AM

For me the only negative is the higher vibration level.

That's really only a factor with the "big block". And people like myself, and Claudio Chacon, have worked those engineering issues out a long time ago.

Remember, the Beringer's ships, and the Chinese team ships, are all very lightly built stunters.

Allan Perret · « **Reply #16 on:** August 23, 2012, 02:02:08 PM »

Quote from: proparc on August 23, 2012, 11:32:05 AM

That's really only a factor with the "big block". And people like myself, and Claudio Chacon, have worked those engineering issues out a long time ago.

Remember, the Beringer's ships, and the Chinese team ships, are all very lightly built stunters.

How much extra material (weight wise) is needed in the nose structure to handle the vibes from the "Big Block" ?

Brett Buck · « **Reply #17 on:** August 23, 2012, 04:47:21 PM »

Quote from: Allan Perret on August 23, 2012, 10:58:25 AM

No improvements relative to performance, but the cost of a 4-stroke system is half of a piped PA or RO Jett.
And also does the job with nearly half the fuel load.
Bob Reeves has written thats what drove him in the 4-sroke direction.
For me the only negative is the higher vibration level.

It's not half the price of a 40VF and the fuel load is close to the same...

But, I am all for people having options, and to try stuff or at least evaluate what other people have success with. I "went off the reservation", too, looking for a specific type of run and solving specific issues I had, to good effect. So I certainly wouldn't want to stop anyone from trying.

I certainly have learned something useful from Bob's and Igor's low-RPM approach - probably not going to copy it but knowledge is always a good thing.

Brett

Chris Wilson · « **Reply #18 on:** August 24, 2012, 01:51:54 AM »

Am I missing something here?

I thought that the 'idea' of operating Saito's was to place the run revs in the middle of the torque curve so that any added load has the least effect on airspeed.
(Much like my stunt diesels in that respect.)

Why go to a higher place on the power curve if it threatens the stability and constancy of the run?

Joe Yau · « **Reply #19 on:** August 24, 2012, 09:22:01 AM »

Quote from: Brett Buck on August 22, 2012, 04:37:42 PM

They have no significant reliability issues at 10000 rpm or so, and valve float may be a feature rather than a bug.

Hi Brett,

What are the feature of the floating valves? and what rpm do they usually floats at? all I could think of is it could maybe used as a governor, sort of similar to the pipe set up when it lets off at high rpm.

Bob Reeves · « **Reply #20 on:** August 24, 2012, 10:05:01 AM »

"Why such low RPMs?"

Because it works

Brett Buck · « **Reply #21 on:** August 24, 2012, 12:38:36 PM »

Quote from: Joe Yau on August 24, 2012, 09:22:01 AM

all I could think of is it could maybe used as a governor, sort of similar to the pipe set up when it lets off at high rpm.

That's the theory. When 4-strokes were an active area of investigation, people were claiming to intentionally run it to valve float. They also had some evidence of that, including chewed-up cams, bent valves, bent pushrods, and funny smile-shaped spots on the tops of the pistons - after they went too far and the piston hit the valve.

I would be surprised if any of this was important, the power falls off drastically at high revs even without the valves having to float. Near as I can tell the low-rev thing works precisely because it gets further away from the RPM range where breathing goes over the cliff, so it has less regulation. That's probably why it doesn't have the "dead-overhead" problem, at least. I haven't ever seen any sort of analysis from the gurus, so that's my external evaluation for what little it is worth.

Based on limited dyno testing the cutoff revs were a little lower than where we ran the PAs at the time. My PA setup of the time (2002ish) pretty much wouldn't go over 12000 with any prop we dared to start it with (set up for normal flying at a 10000 rpm launch revs with the needle set at a constant launch setting) and as I recall the OS52 was looking like it was running into a brick wall around 10000-10500. That's consistent with needing 4.5" of pitch or so for the 4-stroke and 3 3/4 with the PA. That's just the shape of the curve, of course. The actual power/torque was much less with the 52 at any rpm we tested but that's no surprise. They crossed at about .45 HP at the inflight rpm - also about what you would think given the required power is the same in level flight.

The difference of course was that running at 10,800 in flight with a cutoff at 12000 gives you some breathing room. Running 10000 in flight with a 10500 cutoff means you have nowhere to go to pick up revs. The experience seemed to back this up, hence the weak overheads. Running 8000 in flight with a maybe 10000 cutoff (from reduced venturi size limiting the breathing) gives plenty of headroom, which seems to be the trick of the super-low-rev system. I would expect other less-positive effects but I am sure that those will not be discussed here.

Brett

Douglas Ames · « **Reply #22 on:** August 24, 2012, 03:05:18 PM »

Bob Reeves has posted several hows and whys in regard to his 4 stroke formula including tank setup, but it's important to use the correct nitro % and prop pitch to get the best results. The combo he uses gives a fat torque band to play with.

- Anyone know how the Chinese set up their Saitos?

- I'd like to see the dyno results that Brett was talking about. Not doubting a 2 stroke setup, just would like to see the HP/TQ curves.

Brett Buck · « **Reply #23 on:** August 24, 2012, 05:51:50 PM »

Quote from: Douglas Ames on August 24, 2012, 03:05:18 PM

Bob Reeves has posted several hows and whys in regard to his 4 stroke formula including tank setup, but it's important to use the correct nitro % and prop pitch to get the best results. The combo he uses gives a fat torque band to play with.

- Anyone know how the Chinese set up their Saitos?

- I'd like to see the dyno results that Brett was talking about. Not doubting a 2 stroke setup, just would like to see the HP/TQ curves.

   I posted some of it on SSW but I looked and can't find it in s short search. If you want to look, the context was Brad Walker and I, er, discussion his interesting theories of how 4-strokes didn't have to obey the laws of physics and something about static thrust and "torque flies airplanes" or some such. It was actually three different engines (52 Surpass, 40VF, and PA61) with multiple props. Part of it was proving that at launch settings you have A LOT more static thrust with a 12-4 than you do with a 12-6. Of course anyone who has launched and ST46 airplane and a 40VF airplane back-to-back already knew that.

   I expected to have a lot more torque with the PA at low revs than the 52 but I think we were all surprised at how much more and how well the PA did. Much later it dawned on me that if you are going to run 10800 in the air, the local tuning peak would need to be in the 9500 area, and at 9000 it wasn't going to be far off maximum pipe boost. If you want to try it, put a 14-6 Rev-Up on a 52 or a 56, and see how fast it will turn. The PA was in a rich 2 since we didn't reset the needle from the normal launch position, but it had plenty left.

   Brett

RandySmith · « **Reply #24 on:** August 24, 2012, 07:22:20 PM »

Quote from: Brett Buck on August 24, 2012, 05:51:50 PM

I posted some of it on SSW but I looked and can't find it in s short search. If you want to look, the context was Brad Walker and I, er, discussion his interesting theories of how 4-strokes didn't have to obey the laws of physics and something about static thrust and "torque flies airplanes" or some such. It was actually three different engines (52 Surpass, 40VF, and PA61) with multiple props. Part of it was proving that at launch settings you have A LOT more static thrust with a 12-4 than you do with a 12-6. Of course anyone who has launched and ST46 airplane and a 40VF airplane back-to-back already knew that.

I expected to have a lot more torque with the PA at low revs than the 52 but I think we were all surprised at how much more and how well the PA did. Much later it dawned on me that if you are going to run 10800 in the air, the local tuning peak would need to be in the 9500 area, and at 9000 it wasn't going to be far off maximum pipe boost. If you want to try it, put a 14-6 Rev-Up on a 52 or a 56, and see how fast it will turn. The PA was in a rich 2 since we didn't reset the needle from the normal launch position, but it had plenty left.

Brett

Brett

What Brett said is exactly true, despite what Bob says, the Saito does not come close in HP or torque, much less fails as Bob states, I also have done the graphs and test on over a 100 engines, The PA 51 will put out more HP and Torque that the Saito s that Bob said was so much stronger, If you do the test you will see, or just watch them objectively..or fly them, or launch them, Note this is NOT saying there is anything wrong with 4 Strokes or Saitos, or any knock on 4 Stroke , OS or Saito, but reality needs to set in, instead of just opinion. The PA 65 and Merlin 75 both, will top the PA 51 and put out massive HP, more HP than the 51 or any of the Stunt Saitos, or other strokes people use for stunt.
And truth is the lowly PA 40 will put out huge power, more than the ST60s that people were using at the time. Remember Paul Walker won the NATs in Lubbock TX with a PA40 in 20 mph winds and using a 64 ounce large thick wing airplane in 100 degree heat. He had no power problems or lack of.

Randy

Brett Buck · « **Reply #25 on:** August 24, 2012, 08:27:56 PM »

Quote from: RandySmith on August 24, 2012, 07:22:20 PM

Note this is NOT saying there is anything wrong with 4 Strokes or Saitos, or any knock on 4 Stroke , OS or Saito, but reality needs to set in, instead of just opinion

The missing element in this discussion is the prop efficiency. Running at 8000 rpm in flight and setting the pitch and diameter to get a comparable flight speed, the prop is going to be *much* more efficient than if you were running 11000 and the same airspeed. That's where all the extra shaft HP goes at least in level flight. The slow prop is going to be maybe 80% efficient at turning shaft HP into thrust HP, and the fast prop may be 50-60%. So in level flight the 4-stroke maybe putting out .4 hp at the shaft and the PA might be putting out .5 or more.

Note that the "efficiency" doesn't mean what most people assume, or that "more efficient" = "better". More-or-less you generally want a prop that is very inefficient at level flight speed and count in it gaining efficiency quickly as the speed is perturbed lower, to get better speed recovery/regulation. That's about 75% of the effect on tuned-pipe engines and you can convince yourself that you don't need the pipe at all, just 4" of pitch (until the wind starts blowing).

But with IC engines you can't separate that from the way the engine responds in those conditions, and it's entirely possible that the current 4-strokes work better with less-favorable props and make up the difference by improved run quality at the lower revs. So you just have to try it and see. It's not something I am interested in pursuing but if someone has a 4-stroke I would certainly recommend trying it the way Bob suggests; worst-case, you can go back to a standard setup if you don't like it.

Brett

RandySmith · « **Reply #26 on:** August 24, 2012, 09:14:23 PM »

Quote from: Brett Buck on August 24, 2012, 08:27:56 PM

The missing element in this discussion is the prop efficiency. Running at 8000 rpm in flight and setting the pitch and diameter to get a comparable flight speed, the prop is going to be *much* more efficient than if you were running 11000 and the same airspeed. That's where all the extra shaft HP goes at least in level flight. The slow prop is going to be maybe 80% efficient at turning shaft HP into thrust HP, and the fast prop may be 50-60%. So in level flight the 4-stroke maybe putting out .4 hp at the shaft and the PA might be putting out .5 or more.

Note that the "efficiency" doesn't mean what most people assume, or that "more efficient" = "better". More-or-less you generally want a prop that is very inefficient at level flight speed and count in it gaining efficiency quickly as the speed is perturbed lower, to get better speed recovery/regulation. That's about 75% of the effect on tuned-pipe engines and you can convince yourself that you don't need the pipe at all, just 4" of pitch (until the wind starts blowing).

But with IC engines you can't separate that from the way the engine responds in those conditions, and it's entirely possible that the current 4-strokes work better with less-favorable props and make up the difference by improved run quality at the lower revs. So you just have to try it and see. It's not something I am interested in pursuing but if someone has a 4-stroke I would certainly recommend trying it the way Bob suggests; worst-case, you can go back to a standard setup if you don't like it.

Brett

Agreed, it is most always better to try the proven system and setups that people have developed, Bob did a lot of work and put in much time and energy in his 4 stroke setup, it would not be wise to try to reinvent the wheel until... you tried what was there, then go for another setup if you can make it better. Both High RPM and low RPM setups will work on 4 strokes, you just need to get the "right" If for instance you ever saw Gordy's plane fly at hi RPMs on his Big Block Saito, it did everything very well, including handle winds, and without the normal slowdown at tops of maneuvers. Bob's setup is said to go thru high winds also with the low RPM setup. It looks like you need to go either high or low, and stay AWAY from the middle.

Randy

Paul Smith · « **Reply #27 on:** August 25, 2012, 05:35:23 AM »

Quote from: Douglas Ames on August 22, 2012, 09:49:12 PM

I can't say what rpm a particular engine would float the valves, but consider that these little engines have no dampers or even dual springs like a full scale engine. Spring quality and heat cycles would reduce the spring pressure over time I'd think.

As you know, the rocker arms and pushrods aren't connected, only mated with each other by spring pressure. Bent pushrods are a sure sign of valve float, but unlikely in a properly set up stunt engine.

OS rates their 56a up to 13K! ...but why rev it that high?

Any piston engine burns fuel and makes power with every revolution. If you want more horsepower, turn more revs. Subject, of course, to the structural limitations of the engine. Some users are willing to sacrifice fuel economy and engine longevity for MORE POWER.

ref: Tim Allen

Bob Reeves · « **Reply #28 on:** August 25, 2012, 10:13:30 AM »

The Saito torque curves were posted some time ago and that thread has the same differences of opinions as this one.

http://stunthanger.com/smf/index.php?topic=8479.0

This has been going on every since I first posting that I have a Saito 56 that will fly a 68 ounce Score with authority, no sagging overhead or significant windup in wind. Some seem to think I don't know what I'm talking about and I really don't care. I've been using Saitos for 5 years while slowly making improvements in my setup, with the latest reverse running engines being the best of the best. I've flown against PA's with pipes on several occasions in 15 to 25 MPH winds and came out on top. It works for me and if I can help anyone else that would like to run a Saito 40, 56 or 62 I'll be more than happy to help them as much as I can.

I have zero experience with OS engines or the Saito 72 so can't help or comment as far as they are concerned.

Douglas Ames · « **Reply #29 on:** August 25, 2012, 10:28:34 AM »

A quote from DOUG MOON Feb. 24, 2008.
I agree totally and couldn't add anything so I cut and pasted it here -
________________________________________________________
"I think I can. This just my idea of what might be happening.

As you have pointed out you are operating on the top of the torque curve. The torque is what gets things moving. Like drag car at the start. It is in the lower RPM range for the engine and it blasts off the line. Then once it is moving the HP curve keeps it going. Then it levels off a bit and you shift to the next gear and hit the top of the torque curve and go faster and the hp takes over and pushes it further.

In stunt we operate in a much more narrow rpm range. We also increase and decrease loads on the motor all throughout the flight BUT we need the speeds to be constant, or near constant. We need to utilize the torque curve more than the hp curve to achieve this. Your findings prove this very point. You are setting up the engine through prop load to operate right up on top of the curve. You fly level and it cruises along steady. You point the nose up and the motor has enough torque to keep the prop at or near the requested RPM. But it is loaded enough so it cant over rev either. So you get a nice clean steady paced run throughout the flight.

When you under load it and run the RPM up and get on the HP curve you have no torque left when you dramatically increase the load like a we do in stunt. The motor is running over the curve and nothing is there to keep the prop spinning. The HP curve tries but it doesnt have the booty. The under load lets it rev and it works some but not well and you get erratic runs.

At least that is what it looks like to me." (-Doug Moon)
____________________________________________

4 stroke engines have evolved since your early tests with the OS 52 Surpass. It's an optional powerplant, like electric or diesel.

RandySmith · « **Reply #30 on:** August 25, 2012, 11:50:18 AM »

Quote from: Bob Reeves on August 25, 2012, 10:13:30 AM

The Saito torque curves were posted some time ago and that thread has the same differences of opinions as this one.

http://stunthanger.com/smf/index.php?topic=8479.0

This has been going on every since I first posting that I have a Saito 56 that will fly a 68 ounce Score with authority, no sagging overhead or significant windup in wind. Some seem to think I don't know what I'm talking about and I really don't care. I've been using Saitos for 5 years while slowly making improvements in my setup, with the latest reverse running engines being the best of the best. I've flown against PA's with pipes on several occasions in 15 to 25 MPH winds and came out on top. It works for me and if I can help anyone else that would like to run a Saito 40, 56 or 62 I'll be more than happy to help them as much as I can.

I have zero experience with OS engines or the Saito 72 so can't help or comment as far as they are concerned.

Bob
I have flown against Saitos in winds of 15 and 20 plus, and came out on top, so what, that means nothing in comparing what I said about HP and Torque , The fact still stands and saying It ain't so because you beat someone with a PA is a moot point. They all will work and produce enough power to fly large planes. The PA 40 will fly a 70 ounce large ship, and has on many occasions, The 51 will fly most anything you can find including a 80+ ounce PM, however saying that does not mean anything when it comes to doing actual test plots and making HP and Torque graphs.

Randy

Brett Buck · « **Reply #31 on:** August 25, 2012, 08:44:24 PM »

Quote from: Douglas Ames on August 25, 2012, 10:28:34 AM

4 stroke engines have evolved since your early tests with the OS 52 Surpass. It's an optional powerplant, like electric or diesel.

These were not "early tests" - they were at the height of the 4-stroke popularity and their only demonstrable successes - the WC and the NATs. The engines are, near as I can tell, identical to what they were in 2002 when we did the test. Or about 15 years into the 4-stroke experimentation.

A few people have developed a new setup, which as far as I am concerned is a good thing.

I am not challenging anyone's ideas, I am merely relaying the facts as measured. I am somewhat interested in correcting some very common but dead-wrong interpretations about what torque, HP, etc actually mean, but not hard over about it. It may work dandy but it's not because a Saito 56 has a more torque at low revs than a PA61. Compare the torque (and HP, since that's what matters) curves that Pete Bergstrom thoughtfully provided with the data from Scott Bair's report from ~1984, and you will find it is less than an ST60, as well.

Brett

Bob Reeves · « **Reply #32 on:** August 26, 2012, 11:14:05 AM »

Wow! Maybe we need to start all over as I'm really not sure what point Brett & Randy are trying to make.

My point is simply that a Saito 56 or 62 can power a 60 plus ounce 680 sq/in stunt ship as well as any piped two stroke. I don't care what the charts read my conclusion came from actually flying both power plants and competing against piped engines for a number of years.

I'm pretty sure that neither Randy or Brett have actually flown a 4 stroke set up the way I run them. At least Brett is somewhat giving my opinion the benefit of the doubt. Randy, you seem to be taking this as a personal dig on your PA engines and getting defensive. I for sure have never said the PA's weren't great power plants, I have said I can take a used Saito 56 bought for $100.00 and compete head to head with a piped PA that costs $400.00 plus. That is a fact that I have proven on several occasions.

Maybe we need to revisit the level I fly at as that might effect some opinions. I'm a high Advanced guy with no ambitions of ever competing in open at the NATS. Winning Advanced at Brodaks was the highlight of what I was happy to accomplish and did it with a $100.00 used Saito I bought from an RC guy. If I did have ambitions of competing at the NATS I would for sure need to practice more than ariving at Brodaks two days early so I can shake the cobwebs off.

I really believe a Saito 56/62 in a Legacy size airplane can be competitive at any level with anything presently being used. This is my opinion and I really don't care if anyone doesn't agree. I just don't get how anyone can say that isn't an accurate assumption when you have never flown or seen one of my engines run.

proparc · « **Reply #33 on:** August 26, 2012, 11:40:53 AM »

Bob has weighed in or how he feels about the Saito 56\62. Now its my turn.

Ask me what engine I fear, that I would have to face with my 72. Go ahead!

RandySmith · « **Reply #34 on:** August 26, 2012, 03:16:39 PM »

Quote from: Bob Reeves on August 26, 2012, 11:14:05 AM

Wow! Maybe we need to start all over as I'm really not sure what point Brett & Randy are trying to make.

My point is simply that a Saito 56 or 62 can power a 60 plus ounce 680 sq/in stunt ship as well as any piped two stroke. I don't care what the charts read my conclusion came from actually flying both power plants and competing against piped engines for a number of years.

I'm pretty sure that neither Randy or Brett have actually flown a 4 stroke set up the way I run them. At least Brett is somewhat giving my opinion the benefit of the doubt. Randy, you seem to be taking this as a personal dig on your PA engines and getting defensive. I for sure have never said the PA's weren't great power plants, I have said I can take a used Saito 56 bought for $100.00 and compete head to head with a piped PA that costs $400.00 plus. That is a fact that I have proven on several occasions.

Maybe we need to revisit the level I fly at as that might effect some opinions. I'm a high Advanced guy with no ambitions of ever competing in open at the NATS. Winning Advanced at Brodaks was the highlight of what I was happy to accomplish and did it with a $100.00 used Saito I bought from an RC guy. If I did have ambitions of competing at the NATS I would for sure need to practice more than ariving at Brodaks two days early so I can shake the cobwebs off.

I really believe a Saito 56/62 in a Legacy size airplane can be competitive at any level with anything presently being used. This is my opinion and I really don't care if anyone doesn't agree. I just don't get how anyone can say that isn't an accurate assumption when you have never flown or seen one of my engines run.

Hi Bob

I didn't take anything personal, and my points were very clear, I stated facts about power levels, which are not as you stated, also please note, nowhere did I say the saitos, or 4 strokes would not pull the planes, or they were lacking power to fly the planes. you are The one who brought this on by stating braggadocios things like this quote eluding to the 56 having as much or more power than a PS 65, an how you regularly clean house against the piped stunters because of the massive power of the 56 Saito,

Bob said "Sorry, but I also completely disagree with statement "The 56 never had true 60 power". My first forray into a larger 4 stroke was a 68 ounce Score with a 56 which I flew for two years basically cleaning house at local contests flying Advanced against Piped 60's and 61's in the same size airframes. I was running a 13-7 Rev-Up at around 8 grand. My present stunt ship also has a 56 and it leaves nothing on the table flying against piped 65's, don't tell my 56's they don't have the power of a 60 they sure don't know it yet. "

I simply added some well needed reality to your statements, and they were not personal attacks, just true info for people reading this...note again you cannot show me anywhere that I wrote the 4 strokes had not enough power to fly the planes. and for your info, I have bought tested flown and run almost everything you can think of, Saitos and OS 4 strokes includes plus Magnum YS and Thunder Tigers, and I have flown both hi and low RPM setups with 4 strokes, Using much the same settings as yo do.
So Bob please do not make up things that I said, or think I am bashing 4 Strokes, I am not, I also have sold many many 4 strokes to many people over the years and they have been in my catalogs for many many years, as they are now. Saitos included.
You also cannot point to anywhere that states I am not giving you the benefit of the doubt about how your planes fly well enough to make you very happy and make your planes fly very competitively, I have on many occasions told people to use your type setup if they wanted to use 4 strokes.
It is just me and the facts disagree with some of your power statements, The power of a 56 saito is not more than a OLD ST 60, and it is far from a PA 65, matter of fact a lowly PA 40 will produce more power than either a 56 Saito or a ST 60...note again, this is NOT a knock on the ST 60 or the Saito 56..remember a ST 60 won the WC last cycle.

To your other claim and point from you quote below....no one , not I or anyone else here said the Legacy sized panes didn't or wouldn't fly well with a 56 Saito, and you cannot show me where they did. I think they will fly very well with a properly setup 56, but it still will not have more power than my PA51, nor will it fly any better
"Bob said
I really believe a Saito 56/62 in a Legacy size airplane can be competitive at any level with anything presently being used. This is my opinion and I really don't care if anyone doesn't agree. I just don't get how anyone can say that isn't an accurate assumption when you have never flown or seen one of my engines run. "

You really need to read my post and make sure that you are not misunderstanding what I wrote, and please do not read things into my post, that I didn't say, or mean.

Regards
Randy

Brett Buck · « **Reply #35 on:** August 26, 2012, 09:11:03 PM »

Quote from: Bob Reeves on August 26, 2012, 11:14:05 AM

Wow! Maybe we need to start all over as I'm really not sure what point Brett & Randy are trying to make.

My point is simply that a Saito 56 or 62 can power a 60 plus ounce 680 sq/in stunt ship as well as any piped two stroke. I don't care what the charts read my conclusion came from actually flying both power plants and competing against piped engines for a number of years.

I'm pretty sure that neither Randy or Brett have actually flown a 4 stroke set up the way I run them. At least Brett is somewhat giving my opinion the benefit of the doubt. Randy, you seem to be taking this as a personal dig on your PA engines and getting defensive. I for sure have never said the PA's weren't great power plants, I have said I can take a used Saito 56 bought for $100.00 and compete head to head with a piped PA that costs $400.00 plus. That is a fact that I have proven on several occasions.

I think you are reading far more into my comments than is there. I would say it's more than the benefit of the doubt, I strongly recommend trying it, if nothing else, because we know that the (relatively) high-rev system that everybody was using towards the end didn't offer any tremendous advantage. Maybe yours does and we are just missing something. I doubt it, but I haven't tried it and there's a sure way for anyone to find out.

Anything else was just a little technical analysis of what is likely happening to make it work, or at least make it viable. And correction of some of the items that are clearly factually incorrect (like the relative power and torque curves of various engines that we have accurate test data for) and that are almost certainly incorrect but can't immediately prove (like running at the peaks of the torque curves {which is almost certainly unstable} VICE over the edge of the HP curves) and is definitely not demonstrated by the example cases we have real data for.

I certainly never said anything about any of the commonly-used 4-strokes not being able to fly the airplanes. In fact, I have repeatedly tried to point out that since we found good replacements for the ST46 in about 1985-6, getting enough power to fly the airplane hasn't been an issue. All the systems currently used in competition produce far more than adequate power. It is now entirely a matter of how the power gets applied, how it changes in the maneuvers, and how the props used hook it up

I respect your viewpoints on how your system stacks up against the piped systems you see and compete with. I never said it wasn't competitive since I have seen only a few example of the sort of low-rev system you are talking about. You yourself recognize this is as you own opinion and I wouldn't challenge it. If you are interpreting my comments as some sort of judgement on your capabilities that is certainly not included in anything I said. And even if I was, as you note, why would you care what I thought (or what Randy might think) anyway?

I assure you that I have absolutely no ulterior motive here or any sort of agenda. I don't run 4-strokes, 40VFs, or PAs any more. I may be a 4-stroke "outsider" but nothing is being attacked, so there's no reason to go on defense. I welcome any insights you may have on the topic and, near as I can tell, all I have ever done is encourage you to share what information you can to advance the state of the art. I may not use your system directly but I always try to learn as much as possible about what everyone is doing.

Brett

Bob Reeves · « **Reply #36 on:** August 27, 2012, 12:48:10 PM »

Knew I should have listened to the little voice that said stay out of this when it first started..

Randy, To me and many others the statement "The 56 never had true 60 power" is the same as saying it won't preform in a 60 sized stunter as well as a PA 61 and that I totally disagree with. I should have asked exactly what you meant by that statement because like you say I must have read more into it than you meant to say.

I have seen many posts in the past that said or eluded to numbers and static thrust not meaning anything when it involves a stunt engine, proof is the in-the-air performance. I'm not going to take the time to do the searching but it really wouldn't be a surprise to find something somewhere to that effect written by you.

BTW: The guy that quite often launches my Latency says it pulls just as hard as a PA65 but as we know that doesn't mean anything either and why I haven't mentioned it in the past.

Andrew Tinsley · « **Reply #37 on:** August 27, 2012, 01:14:02 PM »

I have, in the past, asked why people use such large engines (the BIG PAs and Ro Jetts). Brett took the trouble to answer. However I am still a little lost here, because Brett stated that power, as such hasn't been a problem for many years. Basically most engines give out more than enough power to do the job. If this is the case, then it must be the style of power delivery that makes the use of these big engines so popular.
So what is the difference, between a big PA and say a Saito 56, as both have more than enough power to do the job?

Regards,

Andrew.

RandySmith · « **Reply #38 on:** August 27, 2012, 02:02:53 PM »

Bob stated the below in quotes not Randy

"Randy, To me and many others the statement "The 56 never had true 60 power" is the same as saying it won't preform in a 60 sized stunter as well as a PA 61 and that I totally disagree with. I should have asked exactly what you meant by that statement because like you say I must have read more into it than you meant to say."
Bob there you go again, I NEVER made that statement, YOU DID !!! It came from one of your post ,NOT from me
The quote about the 56 not having the power of a 60 came from YOU NOT ME Please get it right see your post below:

"Bob you said this in a post you made, I had nothing to do with that thread and never made any post to it... see below to see what you said.

"Sorry, but I also completely disagree with statement "The 56 never had true 60 power". My first forray into a larger 4 stroke was a 68 ounce Score with a 56 which I flew for two years basically cleaning house at local contests flying Advanced against Piped 60's and 61's in the same size airframes. I was running a 13-7 Rev-Up at around 8 grand. My present stunt ship also has a 56 and it leaves nothing on the table flying against piped 65's, don't tell my 56's they don't have the power of a 60 they sure don't know it yet. "

Had I seen the post you made in another thread earlier I would have told you that NO the 56 does NOT have the power of a PA 61, or even a PA 51.

Randy

Bob Reeves · « **Reply #39 on:** August 27, 2012, 02:33:30 PM »

Ya I know Proparc said it originally in the other thread but you brought it into this thread along with saying "The power of a 56 saito is not more than a OLD ST 60" which put it back on the table.

I give you win, I'm done...

Brett Buck · « **Reply #40 on:** August 27, 2012, 03:09:23 PM »

Quote from: Andrew Tinsley on August 27, 2012, 01:14:02 PM

I have, in the past, asked why people use such large engines (the BIG PAs and Ro Jetts). Brett took the trouble to answer. However I am still a little lost here, because Brett stated that power, as such hasn't been a problem for many years. Basically most engines give out more than enough power to do the job. If this is the case, then it must be the style of power delivery that makes the use of these big engines so popular.
So what is the difference, between a big PA and say a Saito 56, as both have more than enough power to do the job?

Yikes! Trying to get me killed from BOTH directions, eh?

Brett

RandySmith · « **Reply #41 on:** August 27, 2012, 03:17:51 PM »

Quote from: Bob Reeves on August 27, 2012, 02:33:30 PM

Ya I know Proparc said it originally in the other thread but you brought it into this thread along with saying "The power of a 56 saito is not more than a OLD ST 60" which put it back on the table.

I give you win, I'm done...

I am Sorry Bob I am not sure what you expected ,but when you post things that I did not say, or things not accurate about me or my post , I will need to make a reply

Randy

Bob Reeves · « **Reply #42 on:** August 27, 2012, 03:33:38 PM »

Guess I'm not done... Just went back over this thread and found what started this mess...

Quote

What Brett said is exactly true, despite what Bob says, the Saito does not come close in HP or torque, much less fails as Bob states, I also have done the graphs and test on over a 100 engines, If you do the test you will see, or just watch them objectively..or fly them, or launch them, Note this is NOT saying there is anything wrong with 4 Strokes or Saitos, or any knock on 4 Stroke , OS or Saito, but reality needs to set in, instead of just opinion. The PA 65 and Merlin 75 both, will top the PA 51 and put out massive HP, more HP than the 51 or any of the Stunt Saitos, or other strokes people use for stunt.
And truth is the lowly PA 40 will put out huge power, more than the ST60s that people were using at the time. Remember Paul Walker won the NATs in Lubbock TX with a PA40 in 20 mph winds and using a 64 ounce large thick wing airplane in 100 degree heat. He had no power problems or lack of.

Randy

If you were not saying that basically I don't know what I'm talking about and felt a need to defend your PA's, what were you trying to say? Your as guilty as I am about reading stuff into words I did not say, where did you get this from "The PA 51 will put out more HP and Torque that the Saito s that Bob said was so much stronger," Stronger than what? I have never said my 4 strokes are stronger than any PA all I have ever said is they will do the job for allot less money.

Bob Reeves · « **Reply #43 on:** August 27, 2012, 03:59:30 PM »

Quote from: Andrew Tinsley on August 27, 2012, 01:14:02 PM

I have, in the past, asked why people use such large engines (the BIG PAs and Ro Jetts). Brett took the trouble to answer. However I am still a little lost here, because Brett stated that power, as such hasn't been a problem for many years. Basically most engines give out more than enough power to do the job. If this is the case, then it must be the style of power delivery that makes the use of these big engines so popular.
So what is the difference, between a big PA and say a Saito 56, as both have more than enough power to do the job?

Regards,

Andrew.

Cool a legitimate question maybe we can get this thread back on track..

My opinion which is pretty worthless.. The Big PA will fly a bigger airplane but put both in a 62 ounce Legacy tuned to fly that airplane and doubt you would be able to tell much difference other than the sound. You might notice slight differences in flight characteristics as they do deliver power in different ways.

Chris Wilson · « **Reply #44 on:** August 27, 2012, 07:09:29 PM »

Quote from: Andrew Tinsley on August 27, 2012, 01:14:02 PM

I have, in the past, asked why people use such large engines (the BIG PAs and Ro Jetts). Brett took the trouble to answer. However I am still a little lost here, because Brett stated that power, as such hasn't been a problem for many years. Basically most engines give out more than enough power to do the job. If this is the case, then it must be the style of power delivery that makes the use of these big engines so popular.
So what is the difference, between a big PA and say a Saito 56, as both have more than enough power to do the job?

Regards,

Andrew.

Personal preference I suppose.

I know you like diesels for stunt mate, so do I, and there is a smattering of the 'tall poppy' syndrome going on here.

Don't you love putting in a good pattern with something (in theory) that is inferior, cheaper, offbeat, (smelly in the case of diesels) or whatever and gloating over it with the more expensive and popular opposition?

Makes it all worthwhile don't it?

RandySmith · « **Reply #45 on:** August 27, 2012, 07:10:45 PM »

Quote from: Bob Reeves on August 27, 2012, 03:33:38 PM

Guess I'm not done... Just went back over this thread and found what started this mess...

If you were not saying that basically I don't know what I'm talking about and felt a need to defend your PA's, what were you trying to say? Your as guilty as I am about reading stuff into words I did not say, where did you get this from "The PA 51 will put out more HP and Torque that the Saito s that Bob said was so much stronger," Stronger than what? I have never said my 4 strokes are stronger than any PA all I have ever said is they will do the job for allot less money.

Bob

I have a used 159.00 PA 51 in my airplane now it has more power and will do the job just as well as a 62 or 56 that list for over 300.00 and sells for over 250 discount price.. see Bob I can do exactly what you did and twist this to suit what I want to say...just as you did

and if your still wondering where I got this from, in your post above look here, and to start with before I ever made any post you wrote this... see below :

"Bob wote this
My first forray into a larger 4 stroke was a 68 ounce Score with a 56 which I flew for two years basically cleaning house at local contests flying Advanced against Piped 60's and 61's in the same size airframes. I was running a 13-7 Rev-Up at around 8 grand. My present stunt ship also has a 56 and it leaves nothing on the table flying against piped 65's, don't tell my 56's they don't have the power of a 60 they sure don't know it yet. "

It seems clear that you wrote you were "cleaning house" against the piped 61s and you 56 leaves nothing in power to the piped 65s. I am here to tell you that is not true, that is a fact, and can be proven , if you want to keep parsing words and twisting things said we can do that, it was you that started all this with your words, which by the way you have been saying stuff like this for a long while. What I wrote about the true HP and torque is true, even your own chart shows the 56 is near a ST 60 in power, the ST 60 doesn't even come close to the power of a piped 61. If you want to open up the 40, use higher nitro it will put out more power than either the ST60 or the Saito 56, by the way this does not make the Saito bad, or unusable, or unable to fly a Score, it just shows facts about the power of some engines used, by certain persons as comparisons to the 4 strokes in an inferior way, and insinuating they are weaker than 4 strokes.

You will also note, I never said the Saitos are bad weak or downgrade them, in fact go back and read what I actually said, I did say they worked well and had plenty of power to fly the 60 size ships, if you keep confusing that , and try to keep insinuating I said the opposite then we will keep going down this road.

Randy

RandySmith · « **Reply #46 on:** August 27, 2012, 07:31:01 PM »

Quote from: Bob Reeves on August 27, 2012, 03:33:38 PM

Guess I'm not done... Just went back over this thread and found what started this mess...

If you were not saying that basically I don't know what I'm talking about and felt a need to defend your PA's, what were you trying to say? Your as guilty as I am about reading stuff into words I did not say, where did you get this from "The PA 51 will put out more HP and Torque that the Saito s that Bob said was so much stronger," Stronger than what? I have never said my 4 strokes are stronger than any PA all I have ever said is they will do the job for allot less money.

That was not what started this, you need to go back further and look at your post, that is what my reply was to. If you don't remember things you wrote I can go back and cut and paste your quotes from farther back

Randy

RandySmith · « **Reply #47 on:** August 27, 2012, 07:49:27 PM »

Quote from: Andrew Tinsley on August 27, 2012, 01:14:02 PM

I have, in the past, asked why people use such large engines (the BIG PAs and Ro Jetts). Brett took the trouble to answer. However I am still a little lost here, because Brett stated that power, as such hasn't been a problem for many years. Basically most engines give out more than enough power to do the job. If this is the case, then it must be the style of power delivery that makes the use of these big engines so popular.
So what is the difference, between a big PA and say a Saito 56, as both have more than enough power to do the job?

Regards,

Andrew.

Hi Andrew

There are many ways to power a stunt ship, many people use larger engines and "power down"(while keeping a huge power reserve) or prop the engine with a richer needle because they love the high torque and the way the power comes on.
Other use 45 to 60 size engines and run them in a 4 cycle with 2 cycle beeps at the tops of maneuvers, many love this setup and the power delivery, still others use smaller 40s on pipes that they run in a 2 cycle, or wet 2 cycle , and they are flying what use to be ST 60 size planes, they also like the runs they get, and the self imposed top limit.
Others use 4 stokes at either hi or low RPMs, I don't ever see people now using a mid RPM with 4 strokes. Bob's setup uses a lower RPM setup and works very well, It has been used with very good success in many different conditions.
A few people have hi RPM 4 stroke setups they like and I have seen them work very well, Gordan Delany had a Big Block Saito that ran hi RPMs and worked as well as any 4 stroke I have ever seen. His power deliver was very good, and he really liked the run.
Bob Reeves , and many people who have flown with him says his works as good as any 4 cycle out there, and it seem to be a very good setup for the same 60 size ships many use. Bob's lower RPM setup seems to have excellent power delivery and pleases him, and many who have adopted Bob's setup very well.
They too are all please with the power delivery of that setup.
The difference seems to be, for many, how critical, and how your personal performance of level lap speed and power in the maneuvers works for the pilot.
It is sure that all of them will work, but to see for your self , you need to fly many for your self, and do a lot of flying different setups.
Remember The ST 60 that won last years World Champs, had a very happy owner.
Your question has many ,many pages that can be written about and still not cover all of it.

Randy

Brett Buck · « **Reply #48 on:** August 27, 2012, 10:25:56 PM »

Quote from: Bob Reeves on August 27, 2012, 03:59:30 PM

Cool a legitimate question maybe we can get this thread back on track..

My opinion which is pretty worthless.. The Big PA will fly a bigger airplane but put both in a 62 ounce Legacy tuned to fly that airplane and doubt you would be able to tell much difference other than the sound. You might notice slight differences in flight characteristics as they do deliver power in different ways.

A very legitimate question, the only issue is that a frank discussion of the pros and cons has gotten me into so much trouble over the years that even I am hesitant to delve into it.

The other issue is that when discussing it you have to discuss what the word power actually means, not what stunt fliers want it to mean. I gave up on that one in 2002. Also what the prop does. All of that is classic flamebait, for some reason/

Brett

Andrew Tinsley · « **Reply #49 on:** August 28, 2012, 03:13:31 AM »

Thanks Bob, Brett and Randy,
I am not trying to cause trouble with such an innocent sounding question. I am too old, infirm and broke to try out all of the different styles of power plant in stunt. I am not even a particularly good stunt pilot! But I am interested in the science and engineering behind our toy aeroplanes. So I am asking such an apparently simple question to those who know what they are talking about. As Chris Wilson says, I am very happy using a big diesel in stunt, so that puts me beyond salvation.
Seems to me that once you have more than enough power to handle the job in hand (and I mean the scientific definition of power Brett!). The only difference is in how this power is delivered to the end user. Without a description of the power delivery from each solution, it leaves people like me (and I suspect many others) totally in the dark as to which way they should go!
I have tried just about everything apart from the mega sized engines. But I have been unable to experiment at length because of lack of time and finance. I presume that Brett and Randy would go the big engine route and Bob would stick to his Saito. So assuming no lack of power, how would you sum up the run characteristics of your power choice?

Regards,

Andrew.

Author Topic: Why such low RPMs? (Read 36173 times)

steven yampolsky

steven yampolsky