Hey guys , I’m just getting back into stunt and trying to learn to be competitive.  Is there a chart that gives info on aircraft size and weight vs. correct engine to use.   I know the basics but what are the pro tips on this so that you don’t overpower or underpower the ship.  I understand that every engine must run at the correct rpm to be in the useable “power band”. For example you would never just richen a .90 for a .60 size ship and i realize you can only under prop it to a certain point.

     As a rule, there's far too much variation in engine power in a particular size range to make such a chart usable. Just look at .15s - anything from a Fox slantplug to a Fora FAI combat engine, or a speed engine. There is no airplane that would be appropriate for any of those.

   Generally, older engines are weaker, as you might expect.

    In fact, people *are* sometimes trying to use a 75/76/88 in a 40-60 sized airplanes, and one of the most successful competitors of all times uses a piped 75 in an 630 square inch airplane, which is smaller than some 35-sized planes. The tuned pipe permits the power to be adjusted to avoid the problem you are concerned about. Try to run it on a muffler alone, then, it definitely gets tricky. The fact that you realize that is a good sign!

     Modern approaches definitely allow you a lot of flexibility that you didn't back in the so-called good old days. For purposes of orientation, a modern fully-competitive IC engine system is a RC schneurle or something like it, running 4" of pitch at around 9500-11,000 rpm, with a tuned pipe. Most competitive airplanes are designed around engines from 40-76, but within that range, while different engines result in different good points or bad points, almost any of them are about equally capable in competition.

     An example would be a OS 40VF ABC (rear-exhaust RC pattern engine from the 80s) with a 11.5-4 graphite propellor and a tuned pipe, launch RPM about 11,000 rpm, in-flight speed around 11,800. A different example is a Precison Aero (PA)75 AAC rear-exhaust engine with a 13.5-4 3-blade graphite propellor and a tuned pipe, launch rpm about 9500 rpm, in-flight speed maybe 10200. PA is a semi-custom AAC engine formerly made by Henry Nelson and Randy Smith (the moderator).

    Competitive airplanes are in the range of about 625 to 700 square inches, and usually weigh around 64 ounces (empty)+- 5-6 ounces. You could build them lighter than that, but the tremendous power increase from the good old days allows (and requires) much harder cornering than possible before, so build it too light and it tends to come apart, in particular, the wing tends to crack or fold.

    They can't get much smaller with these sorts of powertrains, because the hardware alone ends up weighing 22-24 ounces and the wing loading tends to get out of whack any smaller. Although people have certainly done it (smallest reasonably decent flier being something like 585 square inches with various engines up to a PA65 and *72 ounces*). They can't (or at least shouldn't) get much bigger than 700, because the lines can only be 70', and any larger and they just seem awkward like driving a bus around a go-cart track.

    For less-than-full competition, a typical example would be an OS 25LA with a 9-4 propellor, on a smaller former "35-sized" airplane around 400-500 square inches. This gives *much better performance* than could generally have been achieved with an older 35 like a Fox or McCoy. An alternative is a OS 46LA on a larger airplane. You can get away with putting them on rather small airplanes like a Nobler, because the prop (say, an 11.5-4 or 12.25-3.75) will not permit it to go *way* too fast, but that is probably not ideal.

    What is not used much outside of old-time or vintage contests are engines that rely on 6" of pitch and 4-2 break. A lot of the other engines run in various forms of 4-stroke, 2-stroke, or breaking, 6" of pitch is very rare. You give up too much performance in almost all cases to be competitive with the better systems.

     Tell us what engine you are thinking about, and we can give you a better idea what sort of airplane it will fly.

     Brett

What Brett said.  If there was a chart, it'd have to list engines by brand and model (i.e., not just by size and plane weight), and there would be a bunch left off because they're just not suitable.

If you're buying an engine to go with a "full sized" (500-700 square inch) plane and you're not a super-top pilot, get an OS 46LA.  Alternatives include the OS 40FP and Tower 40, and the Magnum XLS if you get a good one.  The 46LA, however, is incredibly flexible, and will work over a wide range of plane sizes and weights.

If you're a former top pilot getting back into the game and you have $$$, contact Randy Smith about getting a whole piped setup -- I've seen everything from PA40's to PA78's work well.  Just spend your money, and enjoy learning the new engine.

Or seriously consider electric.  If you're starting from nothing, it costs about the same to equip yourself with a cheap electric setup with all the trimmings as it does to equip yourself with a 46LA with all the trimmings, and you'll spend about as much money going forward on batteries as you would on fuel.  A super-duper electric setup will cost you about the same as a super-duper PA setup.  So there's no cash advantage, and there's certainly reasons to go electric.

Or seriously consider electric.  If you're starting from nothing, it costs about the same to equip yourself with a cheap electric setup with all the trimmings as it does to equip yourself with a 46LA with all the trimmings, and you'll spend about as much money going forward on batteries as you would on fuel.  A super-duper electric setup will cost you about the same as a super-duper PA setup.  So there's no cash advantage, and there's certainly reasons to go electric.

I made the trip back in 3 years ago and everything said here is right on.  The size does top out at around 700 with a power plant that can probably pull twice that.  I had culture shock over weight at first.  I was used to 30-40oz (dry) ships from the 70's and the thought of 60+ ounces was like..huh?  My best two fliers that I lost this year in a fire were both 65 and 72 ounces.  I started back with IC but soon found that electric offered things that made the switch worth it to me.  As Tim states, cost is about the same but not having the noise, the slime and being able to use just about any finish you can cook up is priceless.  Having a motor that runs the same speed and time every flight lets someone like me who is needle valve setting impaired run with the big dogs.  Give it some thought.

Ken

"Needle valve setting impaired" -- that's me.

My usual response to anything Brett Buck says is "yes, Brett", but he'll tell you that piped engines are super-easy -- then eventually you'll run across a five-paragraph essay on how easy it is to show up at the field and set your needle valve to compensate for the wind and fuel temperature, while you're selecting what mix of nitro to use to compensate for altitude and temperature and humidity and -- I'm going to go with electric now, thanks.

I have been spoiled by only having to remember which side of the plane the little red button is on!

Ken

"Needle valve setting impaired" -- that's me.

My usual response to anything Brett Buck says is "yes, Brett", but he'll tell you that piped engines are super-easy -- then eventually you'll run across a five-paragraph essay on how easy it is to show up at the field and set your needle valve to compensate for the wind and fuel temperature, while you're selecting what mix of nitro to use to compensate for altitude and temperature and humidity and -- I'm going to go with electric now, thanks.

The closest I have come to seeing that was Brett and Fitz taking a density altitude reading on the L Pad on a hot afternoon and then changing props before they attempted a flight (they had just come back out to the field for some late afternoon practice).  I had been out there slogging away at it all day and had ended up chasing nitro and needle in futility.  I doubt they even had to adjust the needle since they had the right prop to start with.
If you only fly one plane and you fly *many hundreds* of flights, motor runs are easy.  If they are not, something is wrong.

Thx guys for all the responses,  as I return to stunt I’m starting with some big planes. I’m building blue max now. I also have a 60” version of the cardinal, thundergazer and trivial pursuit. (Not yet built).  Figured I’d finish the max and get some practice flights and trimming going. Problem is so many power choices these days. I love the sounds and smells of IC. However electric has cleanliness and consistency. I talked with dub Jett so the rojett 61-76 on the pipe is an option, also contacted Igor burger who has some nice carbon props and the axi 2826/13. \

     I run a RO-Jett 61 BSE "Brett" version with a tuned pipe. It would be really good for any of those airplanes. The Jett 76 is a mighty engine but requires a very large prop to get the full effect, which doesn't fit well with my approach. It runs fine on smaller props (like the 12.5-3.75 3-blade I use) but it's reportedly no better than the 61 if you do.

    One of the things you may recall that has changed is the way you extract power. Long ago, getting enough power was always an issue, and the engines were getting pushed to the limits. For older 4-2 break engines the only degree of freedom you have is adding more prop (diameter or blade area) because the power fell off rapidly with RPM, so you really couldn't run it faster with lower pitch.

    The situation is completely different now - even a piped RC schneurle 40 is probably more than you could conceivably use, putting out all it could. You can get a piped *88* now. The problem is no longer how to get more power, but how to control the remarkable power in a favorable way. And you don't need to get it by adding diameter. You can make almost anything work, so now you can use a smaller prop, reduce the pitch, increase the RPM, and get better cornering instead.

    Brett

Indeed .

theres a fair bit of equipment ,, whichever way you go . Glo or Electric .

Setting up for both from scratch , would be the hight of decadance .

The highly technical space age trip , is the ELECTRICAL ONE . This is coming from someone who thinks a side valve may be very good for P.A. .

The S T 60 is the Fred Flintstone approach . Theres Double Star & Stalker CLONES though . So " They have their uses "

Getting up past a few hundred hours flying , if you are aiming ' at the circuits ' would suggest stating with the Flintstone approach , going glow.
Initially .

If you computer savy & can programme things , the electric is usually less smelly . Unless it starts smoking . 

Id browse through the Amped Up freds , the electric stuff will get the wonder wind respose tripe, at the touch of a button .
Plus the planes dont rattle & shake and wear out from vibration and fuel soak .

plenty of used engines about to keep outlay reasonable, at first . if your going glow . Can cost a bundle, either way .
A mint $ 100 ST 60 or any of their clones, is cheap . Likewise the VF 40 & 46s come up , usually $ 150 tho new .

So a $ 50 NiB or as new Super Tigre G 51 isnt to bad a idea, either .

....but even with all that knowledge coming back into stunt with all the changes and new stuff I feel like a beginner.

Been there, done that and you are right on.  One thing I found difficult was walking the line between not knowing anything about the new technology and being a former high level expert flier.   It took time.  I had to choose between piped IC and electric not knowing squat about either one and watching top fliers flying both.  I chose electric because I saw the sport moving that direction.  Still part of me misses flipping the prop!

What I don't miss is flying a plane that was not much more than controlled chaos in wind to one that just goes where you point it.  Both IC and electric will give you that.

Ken

... he is mocking me because he never had to try to do this event at a competitive level with a 4-2 break engine like an ST46...

If I seem to be mocking you, it's certainly not out of any disrespect for your abilities.

And I don't think for a minute that I'd want to try a 4-2 break engine for anything other than curiosity.  When I ripped into the Atlantis my first question was "should I go tuned pipe or 'lectric", and please don't think that I didn't put some thought into the decision.

This is something I discovered myself as I’ve gotten more experience with my piped setups. When I first started flying, and was flying OS’s and Brodak engines, I would just needle it until the right RPM no matter what the conditions were like. With my 75 and 51, I know EXACTLY where the needle should be for my setup and I adjust nitro based on conditions to keep the needle in the same spot. On my 75, if the needle is outside 5-7 o’clock, something is out of whack and I need to make a change. Usually dropping or adding nitro does the trick. Last year I flew anywhere between 5-10% during the year. 10% during the hot Texas summer, 7.5-8.75% in mild conditions and 5% in winter. All year the needle hardly budged more than a needle’s width from 6:00 and the motor run was awesome!

     The most important improvement with these quality engines is that they never just mysteriously "change" for no reason. That is certainly different from before, where you might have everything working fine, and then  it would just change for no obvious reason, and send you scrambling again. When stuff just happens at random, there's no way to make any real conclusions about it, and you don't really learn anything much, you are just continually reacting.

     That almost never happens with these engines, I can think of only one case between David, Ted, and I where this was an issue. Otherwise, it changed for *some* reason, either the conditions or some leak, something loose, etc. With care you can almost eliminate the failure or leak conditions, so all you have to do is react to the air conditions. I am sure the same changes to conditions affected us before, we sort of had and idea what they were, but there was so much "noise" in the system you couldn't take any advantage of that.

    I left the NATS in 2002 with my engine (PA61) running perfectly. When I got home, I started trying to run the RO-Jett and just put the PA in a plastic bag without touching anything except putting in some after-run oil. I ran the RO-Jett with great results until Wednesday at the next NATs, then it had a failed bearing. I pulled out the PA, put it in the airplane, fuel up, flipped, didn't touch the needle, and it started within 100 RPM of my previous year's last flight, run around at 5.4 second laps just like before, and worked exactly like it had the year before.

    That would have been beyond imagination with something like an ST46, it might not run the same way in the same site and same conditions in the afternoon that it did in the morning, and we had LOTS of examples of that.  I have installed a new ring in an ST46, broke it in on the test stand, test flew it 5-6 times tweaking shims and exhaust restriction -  between rounds at a contest!

      Brett