There are a few really popular planes that have been around for decades and are now considered classics, which were lightweight when they were first published or offered as kits, and now are typically built at 125% to 150% power and wing loading. Everybody seems to be having a good time, so there isn’t any issue that needs to be addressed. That’s all. Have fun!
Well, that would be a short article. How can we make a big deal out of this? (That’s what people usually say. We’re all having fun, so don’t make a big deal out of it!) Most of us tend to watch others and do what they do, and thus a habit is formed. My purpose in writing this is to promote alternate points of view, particularly those that don’t tend to get a lot of attention. I frequently read advice online to build light, and everybody knows it’s a good idea, but a few seconds later the discussion returns to other topics, such as how large of an engine or fuel tank can be crammed into a model, and how much extra reinforcement should be added to the landing gear, engine mount, and wing attachment points to compensate.
Back in the early days of RC everything weighed more. Airplane kits frequently contained hard balsa, planes were covered with fabric and dope, engines were heavier and less powerful than today’s engines, and of course radio gear weighed a ton. Because radio gear was also unreliable, it was a good idea to add reinforcements here and there to strengthen an airplane against an all too likely crash. RC was a hobby pursued by individuals with an unshakable determination to get the plane in the air. A wallowing flight at low altitude around the field was considered a triumph. Those guys knew how to have fun.
As radios and engines became lighter and more reliable in the 1970s, designers embraced the idea of lightening the load. This was the era of the Telemaster, Lazy Ace, Funster, and other similarly efficient designs. Experienced builders in those days had the habit of reducing weight in any way possible, and were rewarded with fine flying models. Today super light radios and engines give us the unprecedented opportunity to build lighter planes than ever, but for some reason it is now surprisingly common to build planes overweight. Instead of enjoying the weight advantage of a light radio, most guys take the opportunity to add extra servos, putting one or two on each aileron and one on each elevator half. Then a bigger battery is needed to feed the servos. And of course now that we can all own dozens of engines, why not use the biggest one that will fit? Instead of enjoying the lightness that is allowed by technology, a lot of people become lackadaisical and add extra weight, just because they can.
Most of us have noticed the trend from glow engines toward gasoline engines. The usual reason given is that gasoline is more widely available and less expensive. A gasoline engine suffers a power penalty compared to a glow engine of similar displacement, so a 20cc gas engine will typically replace a 60 glow. Naturally a larger tank is needed, and more cooling fins, and ignition equipment, firewall reinforcement because of greater vibration, and a heavy muffler to tame the chainsaw sound, so the plane gains three pounds. For a real-world example, consider the Telemaster.
My RCM Senior Telemaster has an OS 70 Surpass engine, and is a little bit overweight because I built it with hard longerons for durability and didn’t take extraordinary measures to keep the structure light, because I don’t want crash damage on the way into the car. It has one cheap servo per aileron, and a 4 cell AA nickel battery. I can fill the 10 ounce tank and fly for half an hour at moderate throttle settings, then land with half a tank of fuel, if I can get it to land at all. It soars like an eagle due to its light wing loading. I have seen Senior Telemasters with 25 and 30 cc gasoline engines. These engines shake like crazy, so the plane needs big slabs of balsa behind the firewall to dampen the vibration. The landing gear mount needs reinforcement. The wing attachment area needs reinforcement. The entire tail section needs bracing to keep it from twisting. That’s a lot of extra effort to make sure the plane doesn’t fall apart. Generally these planes end up weighing 10 pounds or more, and people act like this is normal even though the original spec weight in the RCM article is 6 pounds. How much money are we spending on gasoline to keep all that junk in the air? I don’t see a lot of savings here.
It should be noted that such a plane is fun to fly, and there’s nothing wrong with it. But there is no discernible advantage. Consider the alternative. I can take my Telemaster out for the afternoon, and for about $3 worth of glow fuel I can fly until I’m sick of it. If I had made more of an effort to keep it light I could have used a smaller engine and trimmed that to $2. So money isn’t a big deal. I didn’t even have to buy one of those gasoline engines. But the really interesting point is that it’s a whole different flying experience. Any schmoe can build a heavy plane with a monster engine on it, and they all fly the same. But those who put forth the effort to build extra light are rewarded with an inspiring experience. A light plane really does fly better.
Sometimes I question myself when I start ranting about a topic such as this, because everybody has heard it all before. But then I think about it for a bit and I remember that we are surrounded by overweight, overbuilt, overpowered airplanes. Forget the gasoline engines for a bit and turn your attention to the classic 40 size glow model. Most guys want to use a 46 because well, why not? Now the plane goes faster, so you have to add braces to make sure the tail doesn’t get ripped off, and use better servos to prevent control surface flutter. May as well use a servo on each aileron, right? The 46 may be lighter than its 40 size cousin because it’s just a bored out version of the same engine, but a 46 is always going to have heavy castings with ball bearings and a big muffler. It all starts to add up to an overweight plane. What if you start with a modest sleeve bearing engine and match everything to it? Most guys wouldn’t even consider this, because it just sounds ridiculous. “Hey, try a dinky engine. How about a 40 FP?” The answer will be “Are you crazy? I might as well just throw this plane in the garbage.”
I’ll give you a real world example of how a dinky engine can be an improvement. In my early RC days when I was broke I always wanted a mid size 4 stroke engine, so I saved my nickels and dimes and bought a second hand OS 48 Surpass and put it on a newly built RCM Trainer Jr. It flew well and was a lot of fun. One day the crankpin broke off of the crankshaft, so I replaced the 48 with an OS 40 FP, which was the only suitable replacement I had on hand. The engine itself was considerably lighter, plus I was also able to eliminate the tail ballast which had been necessary to balance the Surpass engine. The plane lost around half a pound, which is pretty impressive for a 5 pound plane. This was a step down in power, but the plane flew so much better I could hardly believe it. Maneuvers were quicker, turning radius was smaller, takeoff was shorter, glide was flatter, climb rate was better. The plane was better in every way, just by fitting a smaller engine that was renowned at the time for being “gutless”.
A guy recently emailed me about modifying the Lazy Ace he is going to build from my kit. The Lazy Ace is a remarkable design. Looking at the plan, it’s obvious that it was conceived as a biplane version of the Senior Telemaster. I fly mine with a Saito 91, which has more power than the 60 engine the plane was originally designed for, but weighs the same as a 60. My Lazy Ace is true to its heritage as a super lightweight, moderately powered, lazy, floaty plane. Flying it is simultaneously entertaining and relaxing.
My correspondent is considering a Saito 180 for his plane. The engine weighs 12.6 oz more than mine and will require a heavier mount, a heavier propeller, a heavier firewall, and considerable firewall reinforcement to dampen vibration. This in itself isn’t a problem, because the Lazy Ace is a big airplane and is capable of carrying a lot of weight. But what about the strength of the airplane itself and all of the hardware, bracing and fixtures? With twice the engine displacement it may be hard to keep the plane slow, so it would probably be a good idea to upgrade the wing struts, add bracing to the tail, add some torsional braces inside the fuselage, and of course upgrade the landing gear to carry all of the add-ons. Can it be said that such a plane would be overpowered? Not really, because now it’s a heavier plane. If somebody were to read me the new specs and ask for an engine recommendation, I would probably consider a Saito 180. Starting with a set of parts for a Lazy Ace you could build it stock, fit a lightweight engine, and fly a light airplane, or you could add a bunch of extras, fit a monster engine, and have a properly powered heavy airplane. They both fly well.
My Lazy Ace building friend also is considering floats, which is always a great idea!
Now I’m going to get into something really controversial. Conventional wisdom says that floats should be accompanied by an extra powerful engine to yank the plane off the water. Because my friend is considering a Saito 180, everything should work out perfectly, especially with all of the recommended upgrades to the wing struts, landing gear, firewall, and fuselage. The plane probably will weigh an extra five pounds, but it should be a load of fun! As I mentioned, this design started super light, so it would take a lot more than that to ruin it.
But consider for a moment what it would be like to put floats on a Saito 91 powered Lazy Ace. It would take considerable distance just to get up on the step, although I’m sure it would get there. I might even be tempted to rock the ailerons a bit to help it come up, which of course is a lot of fun. Then it would have a long, graceful run before lifting off of the water. I don’t know about you, but for me that’s what this is all about. A long water takeoff is a beautiful sight, and a lot prettier than an overpowered float plane simply popping off the water like a bouncing basketball. Because the floats would decease the airspeed, there would be no reason to add any bracing to the 91 powered plane, or strengthen the wing struts, or increase the landing gear size, so the only increase would be the weight of the floats. You can be sure that it wouldn’t be an outstanding aerobatic plane any more, but I fly float planes to see them take off and land, not do hammerheads and figure eights. All things considered, I am quite certain that I would prefer flying the modest airplane instead of the overpowered, overbuilt, overweight one. In fact, I’ve already done this on a much smaller scale when I flew my Guppy on floats with an OS 26 Surpass. Power was ample for flying but marginal for takeoff. If the engine wasn’t tuned perfectly it might not take off at all. But when everything was set right the takeoff run was beautiful. I wish I still had that plane.
I know this is a huge rant, and I apologize. This is a point of view that doesn’t get a lot of support, so I thought it would be good to share it. More power usually requires more strength, which requires more weight, which requires more power, etc. Don’t get sucked into that loop. I have a big collection of lightweight sleeve bearing engines that get a lot of air time because they allow me to build a plane lighter, burn less fuel, and use cheaper servos and smaller batteries, without worrying about structural failures. The result is a superior airplane, rather than one of those crazy rocket bricks I usually see other guys flying. It’s usually not the weight of the balsa that pushes you over the edge. It’s equipment choices. Choose wood with enough strength to withstand handling and transport, then pick a lightweight engine on the small end of the recommended range, and keep the rest of your equipment light to match the engine. Try it and you’ll like it!