The Low Tech World Beater

The Low Tech World Beater

There Are Only Two Ways-Get Used To It
To be ultimately competitive, you have to be able to go through the pattern at constant speed, without speed up, no matter how bad the conditions.  In my opinion, there are only two ways to run a 2 cycle engine if you want to be competitive at the highest levels of stunt.

One way to successfully run the 2 stroke stunt engine is by using the “cool mode” run.  This is what I call the “stompin 4 cycle”.  Bob Gieseke calls this run “gorilla balls” (he will say this holding his partially clenched hand out in front of him while making a cupping motion) and this type of run has been the standard of his competitive career.  This type of run is achieved when the engine power is set to allow the needle to be set in a very rich and deep 4 cycle.  In this mode the engine will barely change through the pattern, using a growling low 4 cycle to do all of the maneuvers.  If needed, the engine will “8 cycle” if pushed in the wind.  If the engine “8 cycles”, it means it is going to the “cool mode” misfire and further away from the “hot mode” 2 cycle.  The engine is so far into the “cool cycle” that it makes no attempt whatsoever to go leaner.  When the airplane gets pushed by the wind engine just “lays down” and basically sputters rich trying to back off.  Many of the best flyers use this type of engine run.  Some notable flyers include David Fitzgerald, Bob Gieseke, Doug Moon, Brett Buck, Mike Scott, and Frank Williams.

Some typical basic components of this method are high nitro, high compression, a big venturi, and a small diameter or thin propeller with a light load.  All of these things are done to keep the engine in the “cool mode” (this means running in a rich “4 cycle” mode).   While many will argue that their “stompin” engine is making “huge power” chugging along in a 4 cycle, it really *isn’t* compared to the same engine in a full 2 cycle.  This is why it is very common to see “stompers” using small planes or big engines.  This need to run a smaller or lighter plane is due to the fact that an engine running in a deep “4 cycle” is using very little power potential of the engine.  Most of the competitors who use this setup use lighter or smaller airplanes.  It is very common to see a 61/65/75 in traditional .46 sized airplanes right around 650 sq inches or smaller, or lightweight high aspect ratio planes that are low drag.  David Fitzgerald is currently using a PA 75 on a pipe and has just recently reduced his airplane size from 650-660 sq in to 630 sq in an effort to open the performance window and gain penetration in the wind.  Brett Buck’s PA 61 powered “Infinity” uses the wing from Ted Fancher’s “Imitation” that was originally designed for the ST 46.

Another aspect of this setup is that you really need a large fuel tank.  All of the “stompers” mentioned use right around 8 oz of fuel to do a pattern using their Randy Smith PA 61/65/75 engines (all on tuned pipes) while burning 10% to 20% nitro fuel depending on the conditions.  One other downside to this method besides the huge fuel consumption requirement:  if you choose to use this type setup, make sure that you don’t get any trash in your fuel or suck a bug into the venturi.  If you do, the engine will go full lean…if this happens…HANG ON!!!

The other way to successfully run the 2 stroke stunt engine is by using the “hot mode” run.  This is what I call the “east coast run”.  This mode uses the full power of the engine somewhere in the pattern.  For the engine to work in bad conditions the power of the engine has to be limited.  Some typical basic components of this method are low nitro, low compression, a small venturi, or a larger propeller that forces the engine to be nearly fully loaded.  All of these things are done to keep the 2 cycle “hot mode” of the engine controlled.

In this mode the engine will switch rapidly from “4 cycle” to “2 cycle” mode throughout the pattern, even switching rapidly in level flight from upwind to down wind.  This type of run has lots of 2 cycle switching across the tops of maneuvers, even using as much as 10 o’clock to 2 o’clock of 2 cycle across the top of a round loop (or even solid 2 cycle throughout the loops).  Typically, this type of run will have a vertical eight maneuver where the top loop of the eight is completed with the engine in a “full tilt” 2 cycle mode.  If flying in really bad weather, the engine will need to be loaded even more or the power reduced allowing the engine to use even more 2 cycle mode.  At some point the engine simply cannot go any faster no matter how much it is pushed by the wind.  In this sense the engine will need to go *further* into the “hot  mode” to be successful in bad conditions, even up to the point that the engine can be run in 2-2 mode (using a soft 2 cycle into a hard 2 cycle with no 4 cycle mode at all).  My friend Bill Wilson runs many of his engines in a high 4-2 and even a 2-2 mode (soft 2 cycle to hard 2 cycle switching) and he flies his planes in the most horrible conditions.  In fact, many of the best flyers use this type of engine run.  Some notable flyers include Randy Smith, Bill Rich, Curt Contrada, and Derek Berry.  One can also include just about anyone who was a follower of Big Jim Greenaway.

What are some up sides to this method?  Well, for one, it burns substantially less fuel than the “stompin” method.  One other advantage is that the top end is “clipped”.  If the engine sucks up a bug, or runs away during the pattern, the top end is “clipped” so the flyer should be able to complete the pattern albeit at a slightly faster lap time.

What are some down sides of this method?  Well, first of all, the sound…  I know it sucks to say it, but many people simply do not like stunt planes flying around sounding more like combat planes.  Secondly, since there are two distinct “modes” to this run, the user is constantly tweaking both simultaneously.  There is the top end to “2 cycle” mode and there is a bottom end component to the “4 cycle” mode, and both need to be right to work to perform in bad conditions.  With the “stompin” method, the user can always go *deeper* into the 4 cycle mode when things get scary as long as there is adequate power to pull the engine through the pattern.

Finally, I hate to say it, but most everyone else is somewhere in between, which is the last place you want to be.  Unless you have an absolutely *superb* stunt engine that just “knows” when to compensate in the wind, or an inboard mounted tank, you *will* wind up without using one of these methods.

Take the “stompin” mode and get it too lean or get the engine too loaded…ballistic missile.  Take the “east coast” method and make too much top end power…zoomy-zoom-zoom.  It is just that simple.  Both methods fail when the engine simply cannot make enough juice to pull the airplane through bad conditions.

Flipping the Paradigm
The “small plane that looks and performs like a big plane” idea is not a new idea.  Bob Hunt talked about this “small plane” idea in his original Saturn article many years ago.  Randy Smith has been designing these “stealth” smaller planes for years.  Randy’s Staris, Shrike, etc are all based on this larger fuselage/small wing idea, and I think these planes are some of his best examples out there.  Heck, even Dave Fitz is on the band wagon with his latest smaller plane.

The difference here is that I intend to flip the paradigm….and with the new rules change concerning line sizes which start in 2009, I think it is completely appropriate.  Let me explain.

When the tuned pipe came out, Bob Hunt was telling everyone that if they ditched their baffle type ST 60’s and went to the powerful schnuerle 40 coupled to the tuned pipe, they could build a 60 sized plane (supposedly much preferred by judges) and pull it around with a powerful 40.  With the new setup, the pipe would control the windup in the wind.  This tuned pipe was needed due to the fact these original engines had no propensity to “back off” in the wind by design like the older stunt engines.  One of the main advantages that Bob talked about at that time was the rule that allowed those who use engines under .40 cu in. displacement to use .015” cabled lines as opposed to the .018” cabled lines that were required for engines larger than .40 cu in displacement.  Bob touted this as a huge advantage, and I have to somewhat agree.

Small planes lose a tremendous amount of “feel” at the handle with big lines, and they certainly do not penetrate nearly as well in the wind.  For me, the bigger the lines, the more airplane weight and engine power is required to offset the line bow in the lines when the wind starts to blow.  With smaller the lines, less airplane weight and engine power is required at the plane to get the “solid feel” and penetration back (read that “line tension”).  Small lines coupled to a light plane create a much more “big plane” feel.  Many people, including myself, who use .018” cabled lines, tend to use shorter lines even with big planes to control the line drag and bow.  Others use .015” solids to get more solid line tension with their large planes.  While I agree that they are superior, I hate solids.  I am barely able to keep a good set of cables, and I but them in quantity from Tom Morris!

Now, in 2009, that .40 cu in displacement cutoff for line size is out the window!  The new line size rules that will be used in 2009 are based exclusively on weight.
2009 Pull Test and Line Size Requirements

As you can see, .015” cables are allowed for airplanes from 40+ oz to 64 oz (a huge range of 24 oz!).

As you can also see, .018” cables are allowed for airplanes ranging from 64+ oz to 75 oz (a range of 11 oz?  Hmmmm… that’s weird… FYI:  Paul Walker flew his 100+ oz bomber for several years at the highest levels of competition using .018” cables without incident).

With the new rule, pretty much anything from a heavy Ringmaster to an average SV-11 with a PA 75 can be flown on relatively small .015” cabled lines.  Wow!  While I would not want to be a flyer that prefers the Patternmaster and all of its many derivatives, the Strega, or Cardinal due to the restrictive cutoff for line size (even though people have been flying these planes safely for three decades at weights over 75 oz) it is great time to build you’re the low tech “Low Tech World Beater” that will be explained herein.  It is important that this design stay well under 64 oz “ready to fly” for the LIFE of the plane.  Everyone must understand that airplanes will gain weight over time with heavy use, so if a design is close to the cutoff weight, which is bad.

My First Exposure to the Low Tech World Beater
My friend Doug Moon built a plane called the Bear 46.  Basically, it is Bob Geiseke’s oversized high tech Nobler, the “Bear 65” built with the two center ribs removed.  After the modification, the airplane comes out to be about 620 sq inches (I see it as about the size of the bigger Skylark).  It was originally designed for the LA 46, but since it has the full sized Bear fuselage (an important component of the total package) it still looks like a Bear 65.  As built, it came out terribly tail heavy with the lightweight LA 46 because Doug had built the nose like a full sized Bear 65, complete with the short 9” nose and the original tail moment.  On a lark, I gave Doug one of my Big Jim style ST 60’s and restrictive tube muffler to put in the plane.  I had been testing this combination on bigger planes and loved the run but it had only adequate power for a 70 oz plane.  I thought it would be perfect for the smaller plane.

Big Jim Greenaway followers would use the low compression ST engines using unrestricted (and loud) mufflers to get the “big power” needed to pull the very large Patternmasters, Stregas, Cardinals, Spitfires, etc.  Conversely, many of the tube mufflers on the market were developed for the HIGH compression ST 60 engines produced by Randy Smith and Big Art.  Many of these mufflers were also being used for schnuerle engines like the PA, or OS 45 SFR and 46 SF which really like to be restricted on the exhaust side.  These more restrictive tube mufflers have an exit hole closer to .25”, where Big Jim approved tube muffler would have an exit hole from 3/8” to ½”.  This was necessary to make the low compression engine flow the fuel and make the big power.  This Big Jim style low compression head and muffler with the large exit hole has been used in the Northwest for nearly three decades and was also used by Bob Baron to win the 1996 Nats.

With the combination of the low compression head coupled to a restrictive muffler we had a VERY *mild* package that would run very quiet at low RPM (7800 RPM), with a near PERFECT 4-2 break with no real propensity to wind up.  Interestingly, it would complete the entire pattern on 4 ½ oz of fuel.  Imagine the *BEST* ST 46 you ever saw (in your life) that used less fuel than a ST 46.  Once this engine and muffler was placed in the plane we had a plane that “appeared” to be a full sized plane from the side (which is all the judges see) with the airplane/wing drag of a 40-46 sized plane.

Well, in a nutshell, this is one of the BEST “low tech” combinations I have ever, ever, seen…ever.  The judges see a full sized fuselage, the wing is small (so it builds light) and the engine is basically LOAFING to pull the whole package….and oh, the sound was… well… magical.

All total, I think the whole plane is 48-50 oz trimmed with a ST 60 and tube muffler?  That is crazy.

The Time Machine
My friend Steve Fitton flies the Time Machine 60 powered by a Double Star 60 engine.  The Time Machine 60 is basically a 95% Big Jim Greenaway Patternmaster designed by Tom Dixon for Bob Baron.  These airplanes are right around 650 sq inches and typically build between 60 oz and 70 oz (as opposed to the full size Patternmaster that typically builds between 70 oz and 80 oz).  The Double Star 60 engine is a European version of the ST 60 with an ABC piston and sleeve, it has a low compression hemi head based on the Big Jim ST 60, and relatively restrictive muffler (sound familiar?).  This engine was at one time imported by Tom Dixon and was manufactured by the same factory that makes the Brodak 40. Steve has been using this airplane/engine combination for many years, and his setup is based on the setup recommended by Tom Dixon.  This is truly a “low tech” setup and Steve has it mastered.  He can actually hand flip his engine with his finger (like the good old days) without any fear it will rip off his finger.  He even has little marks on the exit hole of the needle valve that looks like a little clock.  After years of constant use, he sets the needle based on this little clock, and he can tell where the needle should be set for any given run or condition.  He can even tell how worn the plug is based on where the needle is set on the clock.  Now that is consistency.

Over the years, Steve has used both of the two modes described previously.  For many years he ran the “stompin 4 cycle” run and recently switched the “east coast run”.  His comments about both were that the “stompin” run was superior for consistency and was  superior in the wind, but lacked the “drive” at the top of the pattern of the hard breaking run.  As explained before, this is due to the fact that the “stompin” run uses only about 2/3 of the total output of the engine in an attempt to keep the engine running very rich.  Keeping the engine running very rich makes it behave in the wind.  Some of this power loss can be made up by using more nitro or reducing the size of the propeller, but only so much can be done before the “sweet” run characteristic of the engine is lost.

Later, Steve switched to a lower compression 4-2 run more indicative of the “east coast run” in an attempt to get more drive.  Ultimately the “hot mode” of any engine is going to produce more peak power than the “cool mode” even when the engine is limited with a drop in compression, smaller venturi, etc.  Steve expressed the wish to look at the Stalker 76 or Double Star 75 (if it ever comes out) for the Time Machine, as these are the closest to the original “classic” baffled stunt engines.  I suggested a completely different route, one similar to the original Time Machine/DS 60 concept developed by Tom Dixon, only more extreme.

Just Crazy Enough to Work
Here is the idea:  Take the smaller plane power to weight ratio to the extreme.  Now that weight is the only factor used for determining line size, we are primed to use large, extremely mild, low tech and (dare I say it) *lower power* engines in even smaller planes than previously thought practical.  It is the next inevitable step in the Tom Dixon Time Machine idea, and is the *flip* of the Bob Hunt sales pitch for the “high tech” tuned pipe of nearly 20 years ago.

Step #1:  Since the goal is to have an engine that can easily function deep in the “cool cycle” if we want it, we will acknowledge that we will need a little extra engine.   We will use a mild .60 sized engine with a muffler.  Consider the PA 61/65, ST 60, Double Star 60, Double Star 60 RE, or the Stalker 61/66 etc.

Step #2:  The engine will not be tuned for big power.  I know… you just did a double take.  Let me explain.  Stunt engines typically run with some kind of limiting factor within the engine.  Something has to “clip” the power of the engine to make it suitable the for relatively low speed use of stunt flying.  Typical limiting factors are the venturi, exhaust back pressure, head compression, internal port timing, port sizes, crank shaft internal diameter, etc.  Most of the best stunt engines use one or more of these factors to “clip” the power.  Use too many of these power limiters at one time and the power is “clipped” too much and the engine is considered a “wimp”.  Consider the Bear 46 example.  We actually took the ST 60 that had been heavily decompressed (originally designed to be used with a wide open muffler) and coupled it to a restrictive muffler.  Now, in its “wimpy” state it would be completely inappropriate for most large .60 sized planes.  However, it is completely appropriate for a .40/.46 sized plane and it runs “prettier” with a great deal more drive than the .40/.46, and would probably last indefinitely.  Note:  One other thing…”wimps” are consistent and typically indifferent to atmospheric conditions compared to their “gorilla balls” brethren.

Step #3:  Fuel consumption will be low relative to the size of the engine.  A low output .60 actually burns less fuel than a smaller engine running at max power, even when running in a “stompin” mode.  The hemi head ST 60 with the restrictive muffler used on the Bear 46 burns 4.5 oz of fuel to complete the pattern using the “east coast run”.  My PA 65 (sans pipe) burns 4 to 4.5 oz of fuel, even on a “stompin” 20% nitro run and appears to run even more indifferent to conditions the more exhaust is restricted at the outlet.  The Double Star 60 as delivered by Tom Dixon burns right at 5 oz of fuel, as does the Stalker 61/66.  Most people do not realize that many of the “classic modern” stunt planes that came out of the 1980’s and 1990’s were designed around the size of the fuel tank.  Most top stunt flyers were using metal stunt tanks of the standard dimensions that held 1 oz per inch.  Many of the top ST 46 ships were designed to carry 7” long metal tanks.  That meant that the nose would need to be 10.5” to 11” long to accommodate the tank and the engine.  Conversely, the tail moment would have to be long enough to turn it.  With the fuel tank limited to 5 oz (or 6 oz for the case of the RC clunk tank) the nose can be limited to 9.5”.

Step #4:  If you have a mild .60 stunt engine and you are only going to use 2/3’s of the power of the engine, then the math goes something like this:  .60 cu in x 2/3 = .40 cu in.  So, the experiment requires a plane that was designed to be used with a typical .40 stunt engine.  There are really few truly modern .40 sized designs out there.  Most true .40 sized designs are classic designs.  In my opinion, the standard for the modern .40 sized design is the Vector 40 by Randy Smith.  The Vector 40 was originally designed to be used with the relatively mild OS Max 40 FP.

Step #5:  Small planes are easier to build light.  If you read my “T-Rex” article in Control Line World a few issues back, you understand that the smaller plane is easier to build “light”.  In other words, the larger the plane, the *harder* it becomes to build the plane the correct weight.  This is due to the fact that surface area is not a linear function. I have a Brodak Vector .40 ARF myself.  My Vector 40 ARF with the obligatory LA 46 with the 5 oz tank weighs in at 44 oz complete ready to fly and these ARF airplanes have not a stick of ultra light contest wood in them.  Again, in my opinion, the *best* flying Vector 40’s are actually a little heavier at 48 oz to 52 oz, and that is in Texas air.  So if we could build a Vector 40 at 52 oz we would be OK.

Step #6:  Low tech is light.  If you add up all of the components used for the typical high tech, three-bladed pipe .65/.75 setup, basically you are looking at a 22 oz drive train (spinner, prop, engine, pipe, coupler, header, zip ties, 8 oz fuel tank).  Now take that and add the 8 oz of fuel consumed to complete the pattern, you have at least 30 oz of weight that you need to haul around before you ever glue two sticks together.  Even if you are light builder, that is lot of stuff to include in your next airplane.  Now compare that to the low tech 60 setup with a 2 blade propeller (spinner, prop, engine, muffler, 6 oz fuel tank) the total is closer to 22 oz fully fueled.  That is a weight loss of 8 oz.  A bushed .60 would be even lighter.

Step #7:  If we retrofit a ST .60/PA 61/65 in the place of the LA .46, we are only going to add a few more ounces than normal to the small airframe.  So, let’s compare the weight gain for substituting the mild ST 60 for an LA 46 in a Vector 40.  I will round up the weights…

•   The ST 60 is a weight gain of 2 oz over the LA 46.
•   The larger tube muffler is a weight gain of 1 oz.
•   The tank is a wash.
•   The nose of a Vector would not be appropriate for a .60 engine.  The nose moment would need to be extended ½” to accommodate the longer ST 60 type engine and the fuselage width would need to be changed to accommodate the wider engine.  I suggest using ½” x ½” maple beams with the large engine instead of the 3/8” x ½” beams normally used for smaller planes.  This is a weight gain of 1.5 oz.
•   The tail moment of the Vector 40 would be too short.  To balance the bigger, heavier engine, the tail moment would need extended to 17” or 17.5”.  This is an extension of about 3” and would result in a weight gain of ½ oz.
•   The stab/elevator *might* be too small.  For the sake of discussion, we will assume it is and add ½ oz to extend the span of the stab elevator 1” on both sides.
•   To make sure the plane “looks” like a big plane, we will add 1 oz for taller fuselage sides.  ½” of height added to the top and bottom of the fuselage sides will make a huge difference in the appearance of the size of the fuselage.  The tail moment will add quite a bit to the larger look.
•   Just to be fair we will assume we will use a larger propeller and spinner.  So, we will add one more ounce just to be sure.
•   So, the total is 7.5 oz…I think that is about it.

So, using my Vector 40 ARF as an example, we will total the weight gain.  My ARF Vector weighs in a 44 oz all up “ready to fly”.  Adding all of the things listed, we have a finished weight of a little less than 52 oz.  Is this too heavy?  Hmmmm?

It is in fact, *not* too heavy.  This equates to wing loading of 13 oz per sq foot.  If you compare wing loadings of larger “world beaters”, most of the 650 sq in airplane crowd build that have wing loading somewhere in the neighborhood of 13-14 oz per sq foot.   This equates to the typical SV-11, Legacy, Trivial Pirsuit, Time Machine, Saturn, etc in the range of 58 oz to 64 oz.  This is a completely normal wing loading for the most successful stunt planes.  In fact, most weigh more, and I think this is going to be apparent when everyone starts weighing their planes before every contest next year.

Let’s say you are stickler for “old school” wing loadings, or worse yet, you want to *paint* your Vector .40/.60.  Oh, no… now it is too heavy.  Well, then do this…change the rib spacing on the Vector approximately .25” to add 2” to each wing bay.  This will result in a increase in wing area of about 40 sq in and will allow 4 more oz to be added for paint, all without any real additional construction weight.

Did I mention we are talking about an ARF, and not a contest wood plane?  I contest wood plane could be built even lighter…think about it.