Stuka Stunt Main Forum · 93 of 93 known posts recovered
I suppose running on the back side of the torque curve would be one way to do it..
Add nitro. Increase the venturi size, drop the head. Reduce the tip pitch and overall pitch. Never let it break into a 2 cycle. Set the pipe per theoretical for a given RPM.
Add more nitro, repeat...
Over symplification but still true. We have discussed this setup before.
Doug Moon flew at 5.85 at the Nats on the Eather 4 blade at 3.6 pitch. Without a doubt I believe that the tops of his hourglass were unbeatable. Brett uses a very similar setup.
Yes, I guess I am.
The nitro can cause the engine to "not slow down", or in the case of too much pitch cause wind up, even in a solid 4 cycle. So, yes, the the engine will "come on" more, that is why you need to reduce the pitch at the tips slightly.
Same with a 4 cycle.
This may be effective with a constant speed set up such as a 4-cycle when you have power to burn, as, should the plane speed up, the prop at the tips becomes even less effective and it acts like an air brake. But, with that set up, there is no increased thrust going uphill that the original question referred to.
We set the engine up to increase revs going up hill and decrease revs going down hill. That way the engine changes speed, but the maneuver speed remains more constant. Of course, too much kick and it will speed up going up hill and that is not what is desired, either. ("Zippy", as Matthew likes to call it.) There has to be a proper balance here with the engine and the prop. But in our case we are running much lower compression and much lower nitro, and it does have that engine "boost" when going uphill.
Because you are putting the "operating point" further over the hill. It raises the whole torque curve, but you don't need any more for level flight, so it's operating further down the downslope of the curve, making it more responsive to the load.
This entire line of questioning sounds a little strange to me - the "shaping the torque curve"/"making the engine respond to load" question is a fundamental function of stunt for 50 years. I suspect most anyone who flies stunt at any competitive level understands it in functional sense, if not technically.
Brett
As the ideal seems to be constant airspeed in both up & down legs, as well as more power overhead, it seems to me that the only workable variable, that could be tapped, is attitude (model that is, pilot attitude is a different story). The 424 setup relies on the change of attitude affecting fuel flow, classically.
How about this: RC helo gyro, which is a rate gyro, I think, hopefully with a digital output signal ( so that it can be messed with easily), this should be able to detect attitude change. Couple this to a servo & throttle (via the usual electronic tricks) and maybe you get opening throttle uphill, closing downhill. Also maybe, you get more throttle in the overheads, because of the attitude change. Dunno if the centrifugal, sorry centrepital acceleration would mask the gyro output though. Another idea for when I get a round "tuit"
Cheers, Dave
That's the puzzling part. Brian is known to be one of the more technically savvy guys in the event. I think we must be misunderstanding the question.
>As the ideal seems to be constant airspeed in both up & down
>legs, as well as more power overhead, it seems to me that
>the only workable variable, that could be tapped, is
>attitude (model that is, pilot attitude is a different
>story). The 424 setup relies on the change of attitude
>affecting fuel flow, classically.
As a small modification to the load altering the timing and thus the tendency to either 4-stroke or 2-stroke. Many times, the engine breaks into a 2-stroke even as the fuel pressure gets *higher*. Gravity is a very minor part of it.
Brett
I can understand that compared to gravity, the radial force in inside/outside loops is much more significant and is the main consideration when adjusting tank position for equal engine speed (I run pretty constant 4 cycle) inside/outside loops.
Now I've done lost my confidence in Newton!
Cheers, Dave
Of course - but I think this is a pretty small effect compared to the differential loading of the prop by changing airspeed. For instance, when you set the airplane to a 2-stroke on the ground, it frequently goes into a 4-stroke in the air, once it gets up to speed. But, depending on the tank, it either gets less fuel pressure in the air (uniflow) or more (suction). The change in the load on the engine seems to swamp the pressure effects. There's a lot of similar situations - 45 degree dircling flight makes the engine run "leaner"/more tendency to 2-stroke in than in 5 ft circling flight. But the fuel is running downhill into the engine at 45 degrees. My explanation woudl be that the extra induced drag required to keep it at 45 is slowing the airplane, and creating more load on the engine, hence "advancing the timing" or allowing the engine to fire every time on even a marginally rich charge.
It's easy to see this on the test stand, too. Put a 13-6 on your ST46, set to run at exactly the 4-2 break point. Stop it and put on an 8-6, and then start it up with the needle in the same position. Really fast, but dead rich.
The changing pressure certainly affects the run, but it looks like load effects on the engine dominate the characteristics.
Brett
On the climb, it's both pointed up, and the prop is loaded more (since the corner and climb depress the airspeed). So it goes "lean" from both effects. On the descent, the prop is both unloaded and the uniflow vent is above the engine, so it goes "rich" from both effects.
But look at other points in the pattern - like every corner, whether or not the nose is up, down, or horizontal. And in the overhead 8's.
I use the words "rich" and "lean" advisedly - it may or may not be running at a richer mixture, but it acts like it is in the sense that it deeper in a 4-stroke.
I think it's a thermal effect, but not really the way you might be thinking. Consider how a glow engine runs in the first place. You compress the charge, and this heats it up, but not enough to fire all by itself. The thing that puts it over the top and makes it fire is the glowing platinum element in the glow plug. It decides to fire when a combination of the pressure and temperature of charge+temperature induced from the hot engine parts+temperature induced from the heat from the glow plug exceeds the kindling temperature of the charge. Rich charges are harder to set off, meaning it takes longer to get to kindling temperature. Longer means later in the stroke, hence *retarded timing*. Leaner mixtures are easier to set off, hence they fire earlier, hence *advanced timing*. The cylinder temp changes oveer a relatively long period. The short period reaction is a function of the glow plug.
Bog the engine down in rpm, and the plug has longer to transmit heat into the charge, meaning it fires sooner and/or on rich or poorly scavenged charges it wouldn't otherwise fire at all. That's what makes it break in the middle of corners - reduced airspeed => more load on prop => more time to heat up charge => fires slightly rich charges. Note that in the corners, the fuel pressure at the engine is actually driven much higher than in level flight, because of the decelleration of the model due to induced drag. This is another indication of the load effects overriding the pressure.
This is why you can have useful speed control even with constant 4-stroking. The load effects *may* transition the firing from 4 to 2 if the mixture is right on the edge to begin with, but you still get a very similar effect even if it's lean enough to be 2-stroking to begin with, or so rich it's 4-stroking the entire time. Hence "slow 2-fast 2" 'breaks', or "rich 4-lean 4" 'breaks'.
An engine that 2-strokes all the time isn't a "constant speed" run, as many have suggested. If its working right, it still reacts to load and provides regulation.
Funny this topic should come up today. No less than 2 days ago, I saw a certain multiple national champion taking dyno measurements in an effort to acquire quantitive data on the power regulation of load/apparent mixture effects. There's no question the "apparent mixture change" effect is very strong, and maybe it will make a nice article someday soon. All with an essentially constant delivery pressure
Of course, the real answer to the original question is "anything that increases the negative slope of the HP curve at the operating point". Like a tuned pipe tuned to an RPM slower than the desired rpm, a rich mixture, an exhaust throttle that opens whenever the bellcrank is deflected, and on and on. But that can't be the intended question, unless it's intended as a tutorial.
Brett
If this was so, it would also contribute to the "rich downhill" effect, and of course the lean uphill, due to more load, less RPM, less fuel = runs leaner. Kinda interesting, cause this characteristic should be changeable with venturi size, not the relationship, but when it happens. Am I on the right track here?
Cheers, Dave
Hi Dave,
Guess you can see why I use more ears than mouth when I'm out flying with Brett, huh? Seems like his rocket scientist day job just warms him up for the main event...stunt flying. He's definitely a piece of work!
Ted
Crist Rigotti
"A driver trying to be a pilot"
Crist, my brother,
There's a joke that has the punchline: "I'm crazy but I'm not dumb!"...
Aplying it to Ion, it means that Ion has already downloaded this whole thread, so Ion is a keeper!...
Ion
You have this nasty habit: spoiling my "happy ignorance"!
Party pooper... 
Thanks again, Mr. "Rokkit Inginieer"!
God bless you!
Ion
This one has speculative aspects. But the underlying principle is so implicit that I would wager that most everyone has a basic grasp of the concept, whether they can articulate it or not.
Brett
OK, OK, let's just say you have this nasty habit: making me think.
As a matter of fact, I can't agree or disagree with some of your speculations, because I'll have to put my "nonsense generator" (my brain) to work and figure out what you said. Same appies to you, Igor...
I'm going to think about that glow plug - advance - retard- explosion time and let you know where I get.
Maybe there should be created a "free" category in stunt, where people would compete with no restrictions about throtle controls, chips, software, other kinds of pilot generated inputs, like infrared, anything, anything, while keeping the traditional FAI rules untouched.
That would be a CLPA "think tank" . Just imagine...
Ion
My experiences have indicated that to fly well through strong and turbulent winds engine performance above 45 deg. has to be very strong. In fact to overcome gravity and increased drag at these altitudes prop RPM has to be higher than in the manoeuvres below 45 deg.
I do understand the theories being put forward as to why engine torque increases due to load. I agree that engine load has much more effect than fuel head on the engine run. I came to this conclusion after pushing the fuel tank rearwards 4" and inboard and outboard by 1" each way with no obvious change in engine performance.
What I'm looking for is a means of inducing a far greater increase in Prop RPM for manoeuvres above 45 deg. than most of us seem to be achieving at this time.
Some engines/setups seem to have the ability to aproach the desired effect more than others.
There has to be a better way than flying too fast below 45 deg. to achieve the strong performance needed above 45 deg. to push through the strong winds and turbulence experienced at a lot of flying sites in Europe and Australia.
Brian
I knew that we had to be misunderstanding the question!
>What I'm looking for is a means of inducing a far greater
>increase in Prop RPM for manoeuvres above 45 deg. than most
>of us seem to be achieving at this time.
>
>Some engines/setups seem to have the ability to approach the
>desired effect more than others.
I take it that you mean something beyond current passive controls.
Windy used the throttle gadget this way in the Typhoon. Relatively low throttle setting for low maneuvers, and the maximum for the maneuvers above 45. Maximum of course meaning about 60% given that is was a Saito 91!
Given that IR/RF throttles are now, and are likely to be in the future, illegal for FAI, you'd have to sense the altitude somehow. Or use a timer or elevator-actuated switch (like a fuel shutoff, but actuating the throttle instead of pinching the line).
A stabilized platform might be workable but that's an awful lot of mechanism just to get 200 rpm for 45 seconds!
A line tension sensor might be more practical, but the lag would limit the response. I would have to be dead slow to make it stable. Otherwise it would tend to get out of phase and surge back and forth. The throttle could be an exhaust throttle like Scott Bair's - that was the only active throttle system that I ever thought came close to working. The throttle response is *much* better than a carburetor.
I have no idea if any of this could be made practical.
Brett
There must be two stroke designers in existence who have objective research on this. Do we know any? All the stuff I've read however (mostly to do with motorcycles) has tended to be about optimising maximum horsepower rather than the sort of relatively low down torque we are searching for.
I have some thoughts but I must confess they are little more than hunches I'm afraid.
Tim.
The way it's stated, the problem seems to demand some active system.
It's real easy to get a lot of response to load - in fact, with giant high-power-capacity TP engines in 40-sized airplanes, it's easy to get *way too much*. Just think what we are doing - ultra-hot-rod piped 61s in airplane that a lot of people would have thought too small for an (relatively wimpy) ST46 25 years ago. Let's say getting enough ponies is not really an issue. Run a lot of compression, relatively short pipe, large and/or draggy prop, large venturi, and set the pitch to be right on the break point. That'll get you some pop in the corners!
The problem is that it's really hard to fly consistent maneuvers when it feels like the handle is about to get yanked out of your hand halfway through every corner. I've seen and flown set-ups so aggressive that you wouldn't believe it<*1>. It's easy to do - there's so much power capability in a system like this (compared to the requirements) that it's kind of seductive. Feels real macho, but geez!
The problem is how to get overhead improvement without going crazy the rest of the time. The load difference for overhead 8's, for instance, is a lot less than the load difference for hard corners. If you pump up the response to get a significant difference overhead, it tends to be too strong in the corners. So if you are depending strictly on load effects, you have to compromise one for the other.
The best compromise I have found is to run the airplane faster and set the engine up for maximum stability to make the manevuers more controllable. It's really amazing how well the little Skyray/20FP does this. Time it, and it's going like a bat out of hades - 4.7-4.8 second laps. And it doesn't take much time to get through the maneuvers. But the power is so smooth that it's *very* easy to control and keep ahead of. It *feels* and *gives the impression of* being much slower than it really is. Much easier than a lot of other airplanes that fly more slowly, but have a lot more power variation. And at 4.8 seconds laps, overhead line tension is not an issue.
The Paul Walker 40VF setup feels *very similar* - not particularly slow on the clock, but very easy to control, and seems like you have forever in the maneuvers.
This doesn't seem to address the problem as stated, though. In fact, the question is almost the opposite. That's why I thought that it might require an active system of some sort.
Brett
<*1>Note to anyone about to jump down my throat or get offended - again - when I say "aggressive" I don't mean the recommended PA61 setups. The stock system *is* a little too jumpy for *my preferences*, at sea level, in my 46-sized airplane. A little bit.
But there's a whole different time zone of excessive available by just adjusting it differently, and it's hardly unique to the PA series. You can set up a VF to run too aggressively, too. This is what I am talking about.
And no two engines are alike. Matt's two PA engines are set up with different amounts of head shims, while using the same pipe, pipe length, prop, fuel, and venturi, in order to get the same type engine run. (Oh, yes, he mis-measured his pipe length at the Nats which, combined with a change in plugs, explained a bit of his "hastiness" during the first day of qualifying.)
Yup, we need more going up, less coming down, and a little coming out of the corner.
>In all the TP setups I have tried, yes you can set them up
>to produce a lot more power but (seemingly) not in a linear
>response to load. Everything below 45deg. is RELENTLESSLY
>STRONG including the corners even to the point of being
>aggressive as you say. Turn into the wingover and it takes
>off like a rocket and doesn't back off till 1/3rd of the way
>down - YET- at the top of the glass and in the overhead
>eights there is enough but relatively a lot less power than
>elsewhere.
We have experienced this. It is just not set up right.
>Now, tune it for "unjumpy" performance down low and in tough
>conditions the model wants to fall on your head in the
>overheads (unless you fly it really fast) - no penetration
>just when you need it.
When first working with the piped engine that happened with Matt. It actually fell out of the hourglass three times.
>...So what I'm hoping for is MORE of whatever elements make an
>ST46 so approriately responsive but in a 50-60 ABC. Now in
>my opinion that would get us pretty close without the need
>for active overide.
>The active thing is very interesting (and may ultimately be
>the way to go) but if we can get the performance without it
>we are obviously way ahead.
>So I return to my question which asks if we have any 2str
>designers/engineers who know what elements in design produce
>the "ST46 trend" (to give it a name)? I don't think we have
>reached the limit here by any means and I think it is
>correct developmental method to explore this to the limit
>before adding complexity.
>Tim.
Now, interestingly, although you are asking for change, I don't think change is needed. It is there. I mentioned the PA 61 on a pipe falling out of the hourglass above. Yet that same engine, using the same pipe, when finally set up properly (no internal changes except for head shims)--we needed the proper pipe setting, proper prop diamater and pitch--and more at the tips--and the proper venturi and the proper fuel--it works quite well with good overhead tension, a good increase in power going up hill and a decrease in power going down hill. Several people at one contest commented to Matt that it looked like it was in slow motion going down hill in the hourglass. Yet it had a good increase in power going up hill and good overhead tension.
Different people (obviously) like their engines set up differently, and some have just not experienced anything else. Matt has flown other people's planes that he was afraid to take up overhead it had so little tension. The owner was used to it that way and wasn't aware that it could be improved.
Basically there is a lot of trial and error involved. When Matt went out to set up his second engine (and then the rebuilt first one) it was a lot easier to set it up to where he liked it. But each engine is still different and each still takes its individual tune (mostly head shims) to get it to act like what he is seeking.
The TP examples I have outlined above are not how I run my motors. They are to reveal the tendencies at the extremes which I have experienced and witnessed over years of testing (since the first Hunt pipes)and with various engines. (We are no strangers here to head shims, venturis, fuel etc. etc. etc.)
I believe (and am told by those who should know) that I achieve very competitive engine runs - piped and un-piped. I'm happy if yours are even better but this is not the point and hasn't been from the start. The point already made quite clear by Brian is that we are looking for vertical performance better than any of us is achieving at present.
I am trying (usuccessfully it seems) to point to the negative and positive tendencies in engines (piped and unpiped)in order to home in on those elements in engine design which lead to this kind of vertical performance.
You may wish to reconsider my contribution in the light of this.
Tim
This entirely a function of setup, not necessarily an intrinsic function of the engine and exhaust. One of the "double edged sword" features of piped engines is that they are very flexible in their response. You can dial in what you want, or you can dial *out* what you want. There are very stable setups that work the same in most conditions, and very "hair trigger" setups that vary by .2 seconds a lap *even when the sun goes behind a cloud*.
It can be done, you just have to seek it out. The piped engines were a boon for some people, and they were simply a source of frustration for others.
There are known pretty stable sytems for most any popular engine. This is a different thread, but the engines are usually of such high quality that the settings are reasonably transferrable.
I can assure you that my PA61 system is very gentle in low maneuvers, but it's in no danger of falling out of the sky overhead! Neither with the 40VF - although the tension is probably half as much, it's the same all around.
>So what I'm hoping for is MORE of whatever elements make an
>ST46 so approriately responsive but in a 50-60 ABC. Now in
>my opinion that would get us pretty close without the need
>for active overide.
>The active thing is very interesting (and may ultimately be
>the way to go) but if we can get the performance without it
>we are obviously way ahead.
>So I return to my question which asks if we have any 2str
>designers/engineers who know what elements in design produce
>the "ST46 trend" (to give it a name)? I don't think we have
>reached the limit here by any means and I think it is
>correct developmental method to explore this to the limit
>before adding complexity.
It's certainly a different thread of development that we (US fliers) pretty much abandoned the instant we found the 40VF. This was for a variety of reasons, including some that had nothing to do with technicalities. There was (and probably still is) an element that beleives that the ST60's were being discriminated against. As far as I can tell, that's completely wrong, but it's hard to talk people out of delusions.
The best system is the one that helps *you* fly better! You're a lot better off with a properly running 4-2 break system, than a poorly running piped system. The fact that an optimal TP system might work better than an optimal ST60 system is almost irrelevant if you don't have an optimal TP system.
It's not about the engine or airplane - it's about flying them!
Brett
I also saw tests of regulation based on line tension. It was really too slow and worked erratic in figures, probably because of interaction to handle movements.
igor
What did you use as a sensor?
Brett
Now I can implement some amount of positive feedback by software. It means if it feels loaded, it can force system to higher regulated value, and if the system unloaded, it can regulate to lower. It will act exactly as actual pressure / load / nose up 4-2-4 system.
What you think?
igor
I think you would want to use an exhaust throttle, as Brett suggests. Intake throttle response may be too slow. You could easily determine frequency response of both methods. I also think you should change the sign of the feedback.
Maybe, in principle - although I think you want negative feedback! General rule of thumb; you need an odd number of -1's in your control system, or instead of a damper, it's an oscillator.
How fast you can control it depends on the combined lags of the servo and the throttle. I guess that a time constant of about 50 msec would be pretty optimistic. This sets an upper bound on the control bandwidth of maybe 10 hz if you wanted to really push it. Using the "factor of ten rule", you would need to sample this at 100 hz, or .01 secs/sample.
Realistically, you probably couldn't effectively use discrete control. The processing is pretty demanding. These types of applications typically use analog systems.
Unfortunately, a 10 hz (or realistically, lower) system is pretty marginal to recreate the load effects. A corner only takes a few tenths of a second, so a 10 hz system only marginally helps. If you think about it, it's only 40 or so complete engine revolutions.
It would still regulate the *rpm* over the long haul. I threw together a compensator with a bandpass of around 3 hz, proportional + integral, that would do essentially nothing in the corners (to slow), but would keep it at a reasonably constant *rpm* through the maneuvers otherwise. You could let the existing load effect take care of the short-period response.
This still doesn't really address Brian's question. I don't necessarily think RPM is the right thing to regulate.
You could regulate several things:
RPM - constant RPM means variable airspeed based on drag and gravity, limited only by prop thrust vs. velocity characteristics.
Airspeed - regulating the airspeed is maybe a little closer to the desired effect.
Line tension or Y axis acceleration - this creates the desired effect of increasing the airspeed as you get higher overhead to compensate for gravity vector reducing the line tension. This is also BY FAR the most difficult control problem in that there are a BUNCH of oscillatory items whose effects you would have to filter or phase-stabilize out - like the line whip. Use a pot to set the desired line tension, and off you go. But it could do the job. I'd have to dop some simulations to see what happened when you did something like an hourglass - the overhead portion would set the throttle pretty high, and then you dive it at the ground. Might be a bit exciting for a moment or two! The control law would have to be pretty slow, still probably 3 hz. But you might be able to make it work.
This would be competely legal under the AMA rules, and under the proposed FAI rules.
It remains to be seen if this is any better than just fiddling with the pipe.
Brett
Yes!
I'm tired of all these bits and bytes,
this ungainly flipping and flopping.
I need some continuity in my life.
Preston
Brett,
First, on your posting :
"Bog the engine down in rpm, and the plug has longer to transmit heat into the charge, meaning it fires sooner and/or on rich or poorly scavenged charges it wouldn't otherwise fire at all. That's what makes it break in the middle of corners - reduced airspeed => more load on prop => more time to heat up charge => fires slightly rich charges."
Is that a fact? If so, if you have the engine running and you just :pinch the spinner with your thumb and index, giving the engine a "digital load" (literally!) would make the engine break?
About the airspeed business, tests could be done with an airspeed device, something like a fan that would run accordingly to the airspeed, isnt that how it used to be on real planes?. The fan would be monitored by a tachometer, that would transmit the number of revs per minute or second, to a reciever on the ground.
That would give us the real behavoiur of the engine while it does the maneuvers.
For example, a loop:
W rpm on level,
X rpm on the first quarter of the loop,
Y rpm on the top,
Z rpm when coming down.
Same procedures with the square loops, round and square eights, and so on.
Since the pattern is a fixed algorythm a chip would be programmed to regulate the power on all the maneuvers, also using algorythms.
Take off would be at a prefixed rpm, wingovers would be the next algorythm. The software would "know" what's coming next.
Loops: set the revs for level, climbing, and descent. More rpm's on the climb, and les on the way down.
The load would be detected by the airspeed and the optical sensor.
Now, the chip knows the square loops are coming;
Square loops:
1 -Level rpm regime,
2 -more power on the climb,
3 - less on the inverted part, and
4- lower power on the way down,.
5 - back to step 1
outside square loops are expected by the chip;
1 - rpm on the level 45 degree level path before the dive.
2 - Dive, less power.
3- More power after the second corner, the load is higher than on the dive.
4 - More power after the third corner, it's a climb. more load on the engine.
5 - back to step 1 after the fourth corner.
And so on...
It looks complicated, but not impossible. Remember that the chip is not ignorant of what to expect.
'll post this, in order to "keep" it. and edit it later
Ion
That's exactly what happens! Of course, if you do try it (and a lot of us have) I would recommend an .049 instead of a PA61! The larger props at same setting is a lot safer.
Brett
I probably did not write it well, but I really mean POSITIVE feedback to the regulator, which has negative feedback inside. I wrote:
>>> I can make a unit measuring actual rpm and make easy feedback by some small singe chip comp and small nano servo to throttle.<<<
This is typical regulator with negative feedback. It measure actual rpm and regulates it to 10000 for example. The result is constant rpm uphill or down hill.
And now: since the unit regulates rpm by power delivery, the unit also knows the power itself. The prop is not screw and it gets a slippage if more loaded. But we know power, and thus we can also estimate slippage. So why not regulate to 11000 if engine is loaded, and to only 10000 if engine is unloaded. This is that >>>little positive feedback<<< I am speaking about.
>>>I guess that a time constant of about 50 msec would be pretty optimistic. This sets an upper bound on the control bandwidth of maybe 10 hz if you wanted to really push it. Using the "factor of ten rule", you would need to sample this at 100 hz, or .01 secs/sample. <<<
Yes, this is technical problem, but I think solvable. The usual r/c servo is designed to typical frequency 50Hz – it is 0,02s. It needs 2 or 3 impulses to move to CLOSE position. So if I estimate worse case 5 impulses then I get shortest reaction time 0,1s. Such device cannot operate in shorter time.
>>>It would still regulate the *rpm* over the long haul. I threw together a compensator with a bandpass of around 3 hz, proportional + integral, that would do essentially nothing in the corners (to slow), but would keep it at a reasonably constant *rpm* through the maneuvers otherwise.<<<
This is exactly what I am thinking of. I do not think there is any need to react in corners. If I compare drag in corner and mass inertia, it should be enough. I think it is enough if it adds some power for example on top of loops, or in high figures.
>>>You could regulate several things<<<
Yes, that is the question. What is proper think to regulate?
Relative speed to the air? (shall we fly quickly down the wind? Accelerate down the windover?)
Absolute angular speed? (shall we slow down down the wind – just before figure?)
Centrifugal force? (shall we fly quickly overhead?)
… good question … who knows proper answer?
igor
BTW:
>>>This is also BY FAR the most difficult control problem in that there are a BUNCH of oscillatory items whose effects you would have to filter or phase-stabilize out - like the line whip.<<<
It is not a problem I solved it by friction in teflon-coated wire instead of smooth working pushrod. It is clear on picture. It well filtered also moving of handle in corners – it works only if engine shakes, otherwise friction prevents functionality.
That device on picture does not work in full range. It is adjusted to only limited intervention, so it is almost whole time on one or the other side of range. In reality id does exactly what is Brian asking for – it adds power overhead, or prevents from overspeeding in strong wind, nothing else. It is basically regular Jurassic 4-2-4 system from 1985.
Whether or not this is, in any way, useful for detecting "up" and "down" is debateable. You'd need some sort of integrating computer on board that "remembers" the initial attitude, and can calculate the present attitude based on the initial attitude, and the rate and duration of subsequent pitching movements.
Remember, too, that our airplanes don't travel a "great circle route", and for this reason, simple level flight involves a slight pitch component, which introduces error, and might make the integrating attitude recorder think the plane is climbing or diving when it is doing neither. (This, is, of course, more the case at altitude, which fortunately, isn't part of the pattern, except for short segments in the square maneuvers.)
An alternative is to use a pitot tube to sense airspeed. But this will make the airplane behave badly when the wind blows. Going upwind, you want the engine to throttle up. However, if you set it to throttle down on downward legs (when airspeed increases), it'll throttle down going upwind, and throttle up going downwind.
How about a ground based transmitter (radio? audio?) set up at the downwind end of the circle, and receiver which can sense the doppler shift? Kinda like a do-it-yourself GPS.. Limit the range to the downwind hemisphere of the circle. When the plane is moving away from the transmitter (going up, or heading upwind) the engine throttles up. This way it behaves correctly going up and down, as WELL as going up and downwind.
From my tests, the RPM does increase at the break or from a fast to faster 4 stroke - about 800/1000 RPM, in the 4 stroke case, on the climb after the first corner in the hourglass.
The problem with the constant RPM solution is that it (obviously) doesnt produce a constant airspeed in a vertical climb.
That is also the problem with Bretts solution of running the engine to the right of peak (on the torque graph), it has to slow down to produce more torque, this cant produce a constant airspeed without some adjustment to the engine settings(which will speed the engine up again) - probably mixture, it is really only a variation on the 424 setup, with the upper limit assisted by the pipe.
Interesting & fundamental problem,
Dave
They listen to the plane as it flies around,
noting the frequency and the doppler shift.
From these, they can find speed and rpm.
I think Stuart Sherlock (of Supercool Props)
had most of the ideas.
See http://www.supercoolprops.eftel.com/ARTICLES/article_17.htm
and http://www.supercoolprops.eftel.com/ARTICLES/article_18.htm
I copied his ideas (as have several others).
Works like a champ.
Preston
1/ Gravity.
If you point nose up, the lower fuel pressure results in leaner run because of gravity. But our model is not fixed to ground and so gravity does apply to him as well to the whole body. So if it flies rich level, and than it points up, the gravity SLOWS him down, but fuel pressure is still the same. The leaner run is result of more prop thrust, as its AoA after slowing down is higher. It means this effect can work only if we KEEP THE SPEED by some another effect than just fuel pressure.
2/ Centrifugal force out of circle.
I think this is obvious, but we must take care to yaw. Our fuselage flies little nose out 1 to 2 degrees because the fuselage “wants” to point out thanx circular path (it will also do side lift toward the circle if we let him fly perfectly tangent). So this angle and especially on long tank will be enough not to lean in high speed. We (Slovak guys) do a trick. The air vent in uniflow tank does not go to right side of tank. It ends some 10mm before. It allows better centrifugal regulation, or at least does not lean, but it also little accelerates till end of flight when we fly high figures.
3/ Centrifugal force out of radius in maneuver.
Brett, you are right with more load in flight on 45 deg. But there is also another reason to lean. The flight on 45 degrees is in reality large loop. Any maneuver points nose to the center of radius – because of AoA caused by elevator. Every maneuver also creates centrifugal force which is sometimes really strong, so engine gets less pressure in maneuvers than in straight flight (flight at 45 deg is not straight ). This also reason why engine sometimes strongly “jumps on” in corners and “jumps off” in straight segments. Those two effects supports each other.
4/ Change in combustion by load of engine.
Dynamometer can tell us lot, but also single test of two different props clearly shows difference. Anyway, I think that “load” is not the best word. I think the “speed” of combustion does the trick – at least in well lubed thermally stabe engine.
But I wanted to present another trick. We can also “waste” a fraction of power if we do not need it. The trick is easy to see on undercambered props. The trick is, that UCT airfoil can have MORE DRAG at LOWER AoA (see the polar). It means if we load the prop by smaller speed, the prop unloads engine and allows higher rpm and speeding up can load the engine and push him back to lower rpm. It is positive feedback and can sometimes make troubles, but proper amount of camber matched to proper place of torque curve can be very effective.
igor
Although Brett is absolutely correct that load affects things--you can see this just by grabbing the spinner of a running engine on a test stand (another one of those stupid human tricks), and it also becomes evident when flying into and out of the wind--we cannot ignore the affect of gravity (or centrifrugal force, or inertia) when changing the attitude of the nose.
You can see this in its most obvious effect simply by setting a Fox 35 on the ground. The proper setting on that engine is for it to be running 4-cycle when in a level attitude, but breaking into a 2-cycle when pointing the nose up at a 45 degree angle. There is obviously a difference here that has nothing to do with load, as the engine is going 4-2-4 simply as a result of attitude.
Since I do not set up the 35 FP to do a "fox-like" 4-2 break, the difference in sound is not as dramatic. But, if you set up one of my engines properly at a lean 4-cycle before launch and tach it in a level attitude and then point the nose up to a 45 degree angle, there will be a 600-700 rpm increase. Again, there is no change in load, here, but definitely a change in power output.
When the 4-2 engine is "breaking" into a brief 2-cycle at each corner of a square loop, the fuel is sloshing, and the sudden change in direction is the same as gravity working, even when making the downward corner (when the load is certainly not increasing). Matt's pipe 61, when set "properly" (the way we like it) will do that 2-cycle "burp" very nicely in each of the corners of the square loop or eight--even the ones from up above, pointing down. And these, again, are certainly not load related.
His engine will also break at the top of the loops, and anything above 45 degrees. But, as Igor points out, when flying at 45 degrees you are really doing a large loop, not level flying. That loop changes the "gravity" (well, inertia, I guess, would be the proper term) effect on the fuel.
So, there are multiple things working on our engines here, and a lot will depend on how the engine is set up. For some load may be more important. But I still feel that fuel, for most set-ups is the greatest factor. A 4-cycle engine may just go lean and not vary much in rpm through the maneuvers. A 2-cycle engine can break from a 4-cycle to a 2-cycle with very little if any increase in rpm (like the Fox 35) or with a very radical ("zippy") break depending on timing, compression ratios, head shape, and a whole bunch of other things. Just "playing" with compression ratios at the field (or nitro) can make a dramatic effect on how much or how little the engine breaks in relaton to the other forces playing upon it. But everything else also plays its part.
Lew Woolard once made up a bunch of different head buttons for us to test on his Fox 40. We tested these with and without shims so compresson alone was not the sole factor. There was a tremendous difference in how the engine ran and reacted just by changing the shape (and depth) of the chamber. Ironically, although I tested a number of different head shapes with the FP engines, Lew even made me up a head where I could use the Fox head buttons and play with these, I never found a head chamber better suited on the FP than the factory head. You still need to set the height correctly, however. (And that goes for the PAs and Jetts and everything else in between.) And "factory stock" does not mean they are all the same. I have found as much as 17 thousandths difference in the deck height of factory stock OS engines. Commercially built, mass produced, means there are tolerances.
But the way the engine is set up, and load, and gravity (which I still think has the greatest effect during the maneuver) all play a part in how the engine responds to the need for more power in certain parts (and areas) of the pattern.
Len, there IS a load in corner. But you are right that if there is a load (apearing because of excessive drag, and thus lost of speed), then there must be also richening (because of slowing down and thus both fuel pressure alteration and also change in load) in entry to the corner apearing BEFORE that leaning. So there is relative quick richening and leaning. Which is almost ballanced, but really only almost. All those effects work together so the result is, that the entry of corner is little richening (thanx slowing down and unload), fly off is lean (thanks acceleration and load) plus “nose in” leaning while turning tight radius. The result is that it leans somewhre in middle of corner and works lean also little past it.
BTW, the “nose in” centrifugal effect in corner is really important. If AoA in 3,5m corner is 7 degrees and centrifugal acceleration is 18G, than the effect to the run of engine is:
TAN(7) * 18 ~= 0,12 * 18 = 2,6 G !!!
So it can be up to 3 time more effective than vertical pointed nose up.
The same for large loop on 45 deg: AoA is 1,3; acceleration in direction of lift is 8
TAN(1,3) * 8 ~= 0,02 * 8 = 0,16G what is the same as ~9 deg nose elevation in 1G gravity field.
So you see it will probably not be enough to swith from 4 to 2 cycling, and there must be another effect – like loading of prop (without pressure effect to fuel – we do not accelerate in 45 deg fligh). The same is in match with fact that single loop at level makes engine fourcycling on bottom and twocycling ontop, even the AoA on bottom must be higher and thus engine should be leaner than on top. I think we really can not separate all those effects.
igor
Ion
Len, this is what forums like yours are all about. Thanks for making it available. RIP PauleyP.
Ted
Ted,
As the true gentleman you are, it would be really nice if you edited your message and deleted the "RIP PauleyP".
It's not worthy of you to keep an unecessary coment like this one.
I wish PP would get over whatever troubles he has, learned from his mistakes, became a better person and could join th fun.
God bless you!
Ion
It would be really interesting if we could keep the whole shebang mechanical though....and find a way to gear a carbon fiber prop to increase pitch under load rather than try to flatten. This area seems to be the least explored despite earlier attempts get something of this nature to work. Maybe also a means of tuning the engine so that it is one speed and or backs off a little more on the down hill so that the corner would not be so explosive and less responsive to load and fuel head allowing the prop to do its job unassisted by the whims of the engine.
John S.
I am *far* from convinced that they "flatten out" to any significant extent - but I could be wrong.
You could to the Beringer trick prop if you like woodworking - but I don't think it will work correctly from graphite, at least without some trickery. It's greatly washed out at rest. The laminates are such that the bottom/rear face of the prop has the stiff laminations, and the top/front face has more flexible laminations. This allows it to wash in under load as you describe. It's sort of like a spring-loaded variable pitch prop.
To recreate it effectively in graphite you'd have to figure out some way to stiffen the trailing edges and soften the LE. The problem would be to get the LE soft enough.
Otherwise it's a lot like a Rev-Up - which isn't bad but doesn't recreate the original idea.
Brett
My thought was with all this modern metalurgy and composite materials and micro gearing etc. somebody might be able to manufacture a prop that would work well at less pitch.....Berringer prop was highly pitched at the hub and two at the tips. If I remember correctly John said it loaded the engine up pretty good at typical ST60 revs. Maybe this would be a killer prop for the four strokers!!!! Hello!!! Bradley
monster shine! LOL:)
At *rest*. I think the idea was that it washes in (gains pitch at the tips) when loaded. But it seems to depend on the differential stiffness of the laminations. A constant-modulus material like a regular graphite layup probably won't be the same.
Chris Cox and Alan Resinger copied a Berringer prop in carbon. Be interesting to fly them back to back and see if it really works the same.
Brett
That is exactly correct John. I have been aware of this "high root pitch" philosophy for a year or so now. I have been SCREAMING from the rooftops that this is one of the KEY ELEMENTS to achieving the "put put" run on the 4 cycle.
It is absolutely IMPERATIVE the big Saitos be loaded properly. IF not, the "race car" run becomes a stark reality. The racecar sounds like a whining "upshift" to downshift" kind of run. A loaded run sounds like "put put put" (the same everywhere).
This is one my big complaints from the Bolly 14.25 x 6. It is root pitched at 4 and climbs to 6. It would be MUCH better if it were root pitched at 7 and shallowed to 7. The load on the motor would be much more substantial. My biggest problem has been finding carbon props with enough load.
igor
I keep it around just for laughs. How did it change pitch?
On it's own or did you have to do it?
Ion
It'll probably start with something like "Dang! How could I have missed this thread? What a missed opportunity to tell everyone that they're thinking too much!"
In full size applications, sometime during early WWII, they went from manually controlled variable pitch props to "constant speed" props, which I assume used a RPM regulator to set pitch. Nose goes up, RPM drops, pitch is dropped to keep RPM up. The idea was to maximize climb and speed. Don't think that'd help us. We want to opposite to happen - the pitch to steepen going uphill and flatten going downhill.
I dont know where this fits in here but here goes.
You mentioned you wanted more upstairs without the crazzies downstairs.
Here is how I do it and it works best with YOUR props. AWESOME CRAFTSMANSHIP BY THE WAY!!!!
I use a PA 65. I watched others squeeze the head down and add nitro for a cool 4s run. I thought I would join the fun. I eneded up with alot more compression more rpm and shorter pipe length and slower laptimes with excellent line tension all over.
IMHO the slower you are able to go and still have the plane make sharp aggressive corners the better you can get your intersections and bottoms. To me slower is always better no matter what the wind is doing. With enough power it makes wind flying even better.
I lower the head to .011. I set the pipe at 17.25. The venturi is #4. The nitro is 15% and 20% on days above 100degrees. The fuel consumption is 8oz.(full) The prop is your 12" X 3.6" 4 blade. And I make sure those blades stay under 3.6 all the way to THE TIP. I want NO extra tip pitch, NONE. You dont lose power without tip pitch just acceleration. This is also showing to be true on the 4s props Brad is developing.
What I end up with is 10,800 - 11,000 rpms on the ground in a solid 4s. It stays in the 4s all thoughout the flight. From time to time it will come on in the overheads but it cant speed up on you. There is no accelerator(Tip Pitch) The high rpm low pitch setup really yeilds a very steady run. By steady I mean the speed feels steady. Of course mine works just like everyone eleses. I get the same engine reactions as everyone else. It only feels like to me that I have all the time in the world.
Tension? The tension is excellent. Even better than alot planes at the field that run in 5.0-5.3 range of laptime. Overhead the tension is excellent. It makes Hourglasses real snappy but with major controlability.(is that a word)
The cool part is the more nitro the richer you set the needle to get the same rpm with the lower nitro. This lets you get much more rpm before the 2s come into play.
I used to run it much more like Len runs theirs. .26-.30 head shims Props pitched up on the tip significantly to fight the fall away in the maneuvers that he described. Pipes kind of long. It worked, it ran well. However wind could be a mojor factor, with the tips all pitched up it is just waiting to speed up on you. This setup worked well. I got a second place at the Nats Advanced level with it. But it always seemed ready to go and just jump out at any minute. I was taking off at about 9600 rpms. 4 blade prop 4 pitch and 4.5 at the tips.
With the setup I am using now you can keep turing it up and up and it just keeps running steady at whatever rpm you set it. The speed may be faster but the plane doesnt jump at all! No wind up ever.
It was windy in Dallas at our late summer contest and I am flying the 5.8 laptime. Someone comes up to me and says you need a setup that will let you run faster like 5.4-5.3 in the wind. I was like, why? I had as much or more in the wind than anyone there including the .72s. And I was running a good .3 of a sec slower than anyone else. I won that contest by 2 points. RO would have gotten me but he had no app points he was flying Al's Plane. High nitro Big Venturi short pipe Very flat pitches will give you a really high RPM that will penetrate upstairs. It penetrates using power instead of acceleration.
All this is just my opinion. It works for me. Those who I have seen go this route do not go back to the other way.
I think it is truly going back to High RPM low pitch like the 40s were doing a when the pipes first came out. There for a while the 65s around here werent running much faster that D'Ottavios 13yearold ST60. Yep 13years no rebuild and he still gets some of the best sounding st60 runs I have ever heard. By the way he is either 80 or pushing it this year and still gets 200 flights a year! Amazing!
PS one more cool thing about this setup. This year I used only ONE prop all year long at all the different contests, including the nats. In years past with the other setup with the lower 5-10 nitro I always had to have an extra prop for calm days and one for windy days and few for in between days. A real pain to figure out what to do at each site. Had to make test flights and this and that. Worry about shims and plugs and lengths. With this setup I find one prop that works and it seems to work wherever I go, wind who cares. That makes it really fun! Just show up and fly!
Yah. What Doug said.
This may not be the answer you are looking for, as the more I read the thread it appears there may be a more specific answer, but we have found a significant difference in the runs using this setup. One of the real neat advantages is that the engine is always in a "4 cycle" mode which makes the burst in power more "linear". This is especially true when adding nitro for boost. The behavior is more "4 stoke" like and predictable.
We have gone into this explanation before. I would have thought that Doug and Bob G.'s engine runs at the Nats would prove the point. Everyone seems to make good power in Muncie. I would be very intersted to see all of the setups perform in Dallas in 102 degree heat.
And does not need any prolonged period till break back to 4 cycling
"Doug, Your insightful coments are extremly interesting. They remind me of the excitment generated during the early days of pipes. In fact I'm so excited that I'm tempted to try using a piped setup again"
Brian."
Frankly the way I see most people running their large piped motors, 61 65 sizes it really isnt that much of a different run from the old ST60. You can lump me in that group to until recently.
There are numbers that just dont make sense to me out there.
Some will say they take off at 9400 rpms on 3.8 pitch prop and get 5.35 lap times. That doesnt compute to me.
I use Eather props. Cut to his pitch. I neevr repitch his props. I dont touch them. They come ready to go!!
I use a 3.6 pitch and take off at 10800-11000 and get 5.8 laps. i do fly at 69'10" center to center. most I talk with are all the way out also.
So how do these types of statements compute.
Having said all that running a piped engine in the lower RPM like 9500 and down just doesnt really seem to utilize its full potential like running it in high rpm setup with a narrower inflight rpm range.
Only difference between 40 and 60 sizes is the 40 want to it in a 2s and 60s from Randy want to do in a 4s. The 4s is much cooler on the paint on the nose of the plane.
As Doug mentions above, the 4 blade must be turned with total authority at the suggested RPM.
I gave it a go after the nats. The 3 blade I usually run is turning at 10,000 on the ground. On the 4b I had the kind of lap times Doug speaks of and at the RPM he mentions too. I found it to be slow uphill and didn't penetrate well. I think the 65 is what is needed to turn it with enough authority. I tried cutting the diameter to get some load off but was never really satisfied. I do intend to persevere further though. There is potential there. It may work well on BE's shaft retimed PA61 as it would like the higher rpm. I don't think it will work as well as the 65 though. You need the power an torque to SUSTAIN the performance when you go vertical, the torque being the important factor.
My main concern was though that given I was the only person left using a pipe at the nats it started getting back to the comments of the package "seeming too fast". And with having to run an extra 1000 rpm with the 4 blade this "impression" would be worse.
The discussion about the various setups being great below 45 and lacking over 45 is interesting. I experienced this with a different pipe, this gave me a little trouble at the nats and I found myself having to run a bit faster in level flight (200 more on the ground). After the nats I switched back to my old pipe and the problem was solved. So when it comes to pipes I'm now certain there is such a thing as the pipe being too big. It made all the difference to my setup.
I didn't invent the concept, but my idea in pursuing it was to recreate characteristics of the 40/46VF constant 2-stroke run, without the appalling noise. Either way, you avoid the transitions. The key is to put the operating point well away from the 4-2 break point so *it doesn't matter how strong the break might be*, since you're not letting it break anyway. The only downside is the heroic fuel consumption.
The revelation for me (and Ted, I think) was Thursday at one NATs ('99?), when we had been fighting the "jumpies" all week. Everything that worked so well at home had gone very wimpy in Muncie. Then Ted got some 15% SIG at the hobby shop, and it was like a magic elixir.
Avoiding or controlling the "discontinuities" is really the key, I think.
It doesn't work all that well with the smaller engines - because they don't have enough ponies to make running in a 4-stroke viable.
Brett
Howard.. ever see my Dead Macmen T-shirt? Someone was selling them on Usenet circa 1992 (when System 7 came out, to the wild acclaim of Mac users, and to the yawns of Windows users). Guaranteed to offend Macintosh users! It had a dead Dogcow instead of a dead cow. Don't remember exactly what it said on the back, but it was long the lines of..
7 more lines of code to write
7 more bugs to fix
7 times slower than System 6
Could be:
The number of hours to install it,
the number of free calls you could do to microsoft,
the number of floppies you would need,
the number of programs that would be incompatible,
And someone said it could have something to do with the year...
Ion:+
> The revelation for me (and Ted, I think) was Thursday at
>one NATs ('99?), when we had been fighting the "jumpies" all
>week. Everything that worked so well at home had gone very
>wimpy in Muncie. Then Ted got some 15% SIG at the hobby
>shop, and it was like a magic elixir.
>
> Avoiding or controlling the "discontinuities" is really
>the key, I think.
>
> It doesn't work all that well with the smaller engines -
>because they don't have enough ponies to make running in a
>4-stroke viable.
>
>
> Brett
Brett, who or what are the "jumpies"???
The "jumpies" in this regard means that the operating point had been raised (due to greatly reduced power from the hot, humid air) so that we were running across the break point a lot more than before, hence getting a lot of "jumps" in power in the corners. Our engines were set up with too much compression and to much transmission from the prop to work well that way. One solution would have been to reduce the compression to smooth out the break, another would have been to use a less draggy prop. Increasing the nitro lowered the operating point and just dodged the 4-2 break point rather than changing it.
Brett
I have found the same thing to be true.
In a highly compressed motor add nitro and you move the break point further up the RPM range. At least this is how it was working for me.
Why is this? What makes it happen? Does the nitro actually cool the mix? Does it delay the ignition time? Flashpoint is different or what?
The chemistry is mostly a mystery to me. It's simple enough, functionally, though. More nitro raises the power at all revs. Since you still need the same revs to fly the airplane, you can run it richer, and thus further from the breakpoint.
What little I understand the chemistry, nitromethane is an oxygen contributor, and thus is a pretty reasonable compensation for the reduced density altitude that we get when going from CA to IN.
It's not any different with a low compression engine, to first approximation. The only time you will get in trouble is getting a combination of too much nitro and compression, and then it runs ratty or quits from excessively early timing. Most stunt engines are far from getting into this problem, but it does set an upper limit.
You seem to be running *much* more compression than I have ever tried, but sounds like you aren't having any problems. When you say .011 is that gasket thickness, or head clearance (I presume gaskets)?
Brett
The question is how much it brings, and what it does. The nitro we use is mono nitro methane CH3(NO2) but there are also higher grades till C(NO2)4 (explosive).
Unlike the methanol CH3OH that needs 3 molecules of oxygen to produce CO2 and 2x H2O, the nitro methane needs only 1.5 molecules to make CO2 plus 1.5 H2O and one free Nitogen.
The result is, that you need 1.5 more oxygen to burn a methylacohol (in weight), while you need only 0.4 to burn the nitro methane. The amount of energy in one molecule of both is very similar, but nitro methane is heavier (I think 1.5 times more).
The result is, that if you replace a fraction of methanol in fuel by nitro methane in thinner air, you can get very similar run than less amount in colder air, but another truth is, that mono nitro methane does not bring any free oxygen to burn methanol – it needs it to burn itself and more – it still consumes additional oxygen from air.
igor
If you have enough grunt up front with the undercambered props it's not a problem.
Ted
Yeah, Brett has bad musical taste, right?
Accordinga to a certain music (or stunt) expert the sound of a piped VF .40 is bad music! 
BTW, last night I saw a couple of videos from "aeromaniacs" featuring you and David Fitzgerald doing the pattern.
That was good!
Then, I found out that I couldn't save the goods to my hard disk...
That was bad! 
Ion:)
Certainly - the transmission of load variations from the prop seems to be much stronger with lots of camber.
Brett
About 10 years ago I wanted an ST46 but at the time, while they were being used, good ones did not come onto the market.
I was able to obtain a ST29 case and 46 parts and with some setting up help from Herb Hanna, a bit of machining fitted the 46 parts into the 29 case.
After this exercise I discovered the many small changes between the 29/40/46. I have all three.
The passages in the 46 are quite "dirty". In those I have looked at the cylinder transfer window is partially covered by the case casting. The shaft hole is quite small for a 46 based on todays trends.
So, what I feel is that the fuel flow in the 46 is quite turbulent and very suitable for stunt.
The K&B 60 previously mentioned (mine is from about 16 years ago) has suitable shaft hole and transfer passage for a good sport RC engine of about 12000 on a typical 12 * 6 pre APC. Current Topflight 12 * 6
Many of todays engines are designed to go quick. Schnurele ABC big passages. Therefore if they are not run at their top RPM only they can quit and they do in RC models at half throttle.
I once converted an OS 60 BH to spark and petrol. I reduced the shaft hole to about 7/32 The inlet to about 1/8 lowered the exhaust to about 100 deg. It would run at 8500 on a 16*8.
So, engines can be changed. I find that an often quite 0.290 venturie and a standard shaft hole intriguing as I believe that the large hole in the shaft can act as a resivour of fuel.
My experiences may get others thinking differently
Looking forward to reading comments.
John Q