Motorfloater Storyboard 1

By Mike Sandlin 7 September 2023

My motorfloaters are ultralight airplanes designed to be slow, easy to control, comfortable, and to provide good low speed crash safety. Over the last dozen years I have found them to be fun and satisfying to fly.

Motorfloaters are for recreational local flying, with no emphasis on high speed or range, operating in fair weather with moderate winds. The pilot flies in the open, experiencing the complete flight environment, as in a hang glider, paraglider, or trike, but with more openness, stability and protection, and without the pilot having to run or perform athletics while trying to control the aircraft.

The benefit of slow flight provided by a light wing loading, compared to more heavily loaded airplanes, is a predictable and forgiving mode of flight. Situations develop slowly and give the pilot more time to think and react. This should be favorable to novice pilots and attractive to prospective pilots who want to get their feet off the ground and accumulate some airtime. Maybe there could be a motorfloater training program similar to that of paramotors, focusing on simple flight without the massive curriculum of certificated pilot licensing.

Bloops and Bluebird, biplanes and monoplane, all fly about the same, slow and sedate, real floaters that make ordinary Part 103 ultralights seem fast and heavy by comparison.

Wind turbulence is amplified at lower wing loadings and can be uncomfortable if not alarming. Maybe the question is "can you fly through the bumps and still have fun?".

"Keep it moving and give it some runway".

I like to fly from dirt or grass runways, the paved runway seems hard and slippery. Since my wheels are large in diameter and my airspeed is slow, I can get off the pavement and operate from fields. I may have to dodge tumbleweeds and squirrel holes, but out on the grass (or dirt) I can get a comfortable ground roll and a more relaxed flight experience.

"Traffic, wind, airport (TWA)" works as both a takeoff and landing checklist. "Traffic" means other airplanes in the air, so I look around, especially down wind where someone might be coming straight in on final. "Wind" means mainly stop daydreaming and check the wind direction to see which runway I should be using. "Airport" means look at the runway to see if it's clear and open, without people or cars on it, wandering cattle, dust devils (avoid), or some big new symbol that means "don't".

The air traffic of concern is usually a faster airplane setting up for a landing, which is normally predictable because it will be using the established landing pattern. Fast planes coming straight in on final approach are the most problematic. I avoid doing a long turn as a base leg, instead I turn onto a straight, level base leg so I can take a good look up wind, then turn again onto final (the way it's supposed to be done).

All my flying revolves around the idea that I'm flying so slow that I'm almost a stationary object relative to other traffic. I paint my planes in bright colors and do a lot of maneuvering to make myself visible. The only times I remember having to slow down or hold back for other traffic was when I was mixing with paramotors.

"Look where you want to go and turn with your feet".

My motorized planes use "two axis control", which for an airplane usually means controlling the plane with just the rudder and elevator (a "three axis control" airplane would usually use ailerons in addition).

I enjoy flying an airplane without ailerons, it's a unique flying experience with it's own challenges and rewards. You turn with just your foot pedals, yawing the nose over while the bank angle briefly lags behind. When beginning the turn you feel a shove to the outside, just as you would in a car when making a flat turn, and just as in a car it doesn't matter much so you ignore it.

In steeper turns the plane tends to want to keep banking (airplanes want to stabilize in a spiral dive). To maintain a stable steep turn I hold some outside rudder or step on the rudder as needed, which is effective if not elegant. (I think most pilots would hold a little outside aileron, instead, when they have ailerons). My turns are usually not very steep, I don't think I can usefully bank more than about thirty degrees, and there's not much reason to when the turn radius is really small due to slow flight.

Two axis control precludes the use of slips for crosswind landings, so the landing approach is flown at a crab angle. (True confession: it is likely but not guaranteed that the pilot will notice this). The steering objective for both the approach and ground roll is conventional: keep the plane on course, over and down the runway. My usual touch down procedure is to get slow for the touch down and fly through it at a crab angle, skidding a little sideways on the wheels as I lower the nose to a stable ground rolling attitude. This "wheel dance" is fun after a while but may take some getting used to.

Airplanes that get along without ailerons seem to be mostly small, light, and slow. This kind of airplane might be turning faster without ailerons than it would with them, considering that the adverse yawing effects of ailerons will initially try to turn the nose in the wrong direction and must be overcome by the rudder. Pilots who have flown both two axis and three axis airplanes seem to be overwhelmingly indifferent in their preferences.

Designing a two axis airplane seems to be mainly a matter of providing a big rudder combined with good yaw/roll coupling, particularly with significant but not huge wing dihedral. Many well known conventional airplanes will have a dihedral angle greater than some of my motorfloaters, and I expect that most of them could be steered with just the rudder if they wanted to try.

Two axis flight can contribute to safety. For instance, the procedure for recovery from an incipient stall or spin is: "stick neutral, apply opposite rudder". This means don't use the ailerons, so, for safety reasons, you have just converted your three axis airplane into a two axis airplane.

Two axis turning is not one of my design goals, I use this system mostly because it is simple and convenient. The Bloops and the Bluebird are experiments in low wing loading, to explore the benefits of slow flight, and for those slow flight purposes they could just as well use three axis as two axis control.

"Avoid power lines, deep water, and low turns".

With the engine in back and the wheels at the center of lift, any of my motorfloaters can be stopped either tail down or nose down, at the momentary whim of the pilot. The takeoff is always from the tail down position, because the nose wheel is installed with the brake always on (it is the main ground brake). The nose down stop is important if you have to land in a strong wind. Stopping with the nose down is stable and will allow the pilot to quickly get out.

The required length of your airstrip will be determined by the landing, not the takeoff. Takeoff allows the pilot to choose his start point, wind, and visibility conditions, but perhaps none of these will be as good when he returns for landing. For these and possibly some performance and approach clearance reasons the landing will almost always require a longer runway than the takeoff.

When landing, drag is your friend. Additional aircraft drag works in favor of steeper approaches and short roll-outs. So, could I deliberately increase the drag, and get better landings? Actually, yes, but I would then need a bigger engine to overcome that additional drag to get the same level flying airspeeds as before, so I would have a heavier engine. Larger, heavier engines are dead weight during the landing and require more roll-out distance, so larger engines require larger airports. I favor the small engine, moderate drag trade off.

I try to do the kind of landings that keep me in practice for short runways, rough airstrips and emergency landings. These may not be smooth landings.

Here's Bloop 1, my first motorfloater, a conversion of the Pig glider. It has twin all-flying rudders, flat bottom wings, and a seriously stiff four boom tail structure. Good airframe stiffness has always been provided by the box frame structures of the Bloops and Bluebird.

The nose skid and the protective frame under the pilot are legacy items from the glider days, but served well for the powered version.

Early on I knew little about small engines, this was the beginning of a learning process. I never did come up with any brilliant idea of how to attach the fuel tank, I just tied it on top of the wing and there it stayed.

The twin rudders worked well in the air, but on later designs I used a single rudder to get better steering while rolling slowly on the ground. A central rudder in the propwash will be forceful, especially on takeoff, where you want to stay lined up with your runway from the very beginning. Landing is different, the engine is at idle and there is no propwash at all if you are using a de-clutching propeller. The rudder authority should be reduced by this, but I haven't yet noticed any problem with it.

Control cables are synthetic lines with marine pulleys, the kind used in the running rigging of a sailboat (a very similar application). End connections are made using a series of half hitch knots to fasten the line onto a maillon (steel quick link). The small size line I am using is stiffer and stronger than the 1/16 inch braided steel cable which might have been used otherwise. Synthetic sailboat lines used to have a lot of creep (permanent lengthening after being loaded in flight) but the modern mixed material lines don't do that.

I build and fly experimental prototypes to try out my ideas. Over the years I have built a wide variety of rudder pedals, looking for the stiffest, lightest, easiest to build and most stylish setup. They were all okay, but the prismatic aluminum set was functionally the best. I now favor parts that require minimal precision and don't introduce any new materials or processes to the project, such as those in the photo, except that my latest design doesn't involve much bending of parts (see Bluebird photo). I avoid high precision and exquisite craftsmanship in favor of functional building.

I would rather "buy and fly", getting parts off the shelf rather than making them, and I do that as much as possible.

There are no flight instruments, no airspeed indicator. There is no fuel gage, a fuel check is just a look back at the liquid level in the translucent fuel tank. The panel instruments are for the engine: a tachometer and an exhaust gas temperature gage. In a dozen years of flying I don't think the panel instruments have ever actually been very useful, they are mainly for peace of mind and ground diagnostics.

The elevator control stick is braced against side motion, to resist the wishful thinking of pilots who miss their ailerons. When I was first flying a two axis plane I had some moments of "wing bank brain lock", sudden anxiety in response to a lack of direct roll control. I had to pause and repeat the mantra "steer with your feet" so I could get on course and stop pushing sideways on the stick.

Early on I flew a lot without a pitch trim, and often found myself flying fast because I was nose heavy. Eventually I added a bungee trim, and then also a trim tab on the elevator.

The elastic nose skid shown here works well, it's the same as the tail skid but used up front. Eventually, it turned out to be easier to make a nose skid from a small bicycle wheel. The nose wheel as opposed to the nose skid might also give pilots more confidence that it is okay to roll on the main wheels with the nose level or low, which is good procedure.

When the red plastic cover of the run switch is down, as shown, the switch is "off" and the engine will not run. This is actually a grounding switch that prevents the spark plug from firing when the engine is supposed to be off. To enable the engine to start and run the red cover is flipped up and the toggle under it is switched upward.

Factors favorable to two axis control include wide landing gear, nose down ground roll, nose down stopping, low landing airspeed, and a willingness to land slightly sideways.

The relatively wide track, stiff landing gear that I use on my planes is intended to keep the wing level on the ground, even in a crosswind. By keeping the nose down while rolling I am unloading the wing and putting the weight on the wheels, reducing the lift to help keep the wing level. The wide track landing gear is a major contribution to operating without ailerons.

The Bloop 4 (shown here) and later planes have a free standing center section, so wing panels or other sections can be removed and still leave the plane mostly intact. Also, the wing panels can be adjusted for different trihedral angles just by length changes of the outboard cable rigging.

There is no great allowance for quick transport or loading onto a trailer. To get frequent use I think you have to be at an airport already in one piece, ready to fly quickly. Frequent use is important because to become a skilled pilot you have to get at least one season of substantial airtime, flying often under different conditions. Motorfloaters can teach the basics: pilot discipline and energy management, but you still need that big chunk of airtime to get really competent.

The Bluebird monoplane is an experiment in light wing loading, simple construction, and a small engine. The engine has 16 horsepower, less than 2/3 the power of the Bloop engine. This is marginal power even at sea level, resulting in slow climbs and a need for advance planning to avoid obstacles. It evokes the spirit of the early ultralights, some of which were hang gliders with minimal engines added on. I enjoy flying it, it's gentle and relatively quiet, and the size of the engine doesn't matter much once you reach local touring altitude.

The Bluebird engine has a propeller clutch, so it disengages at idle engine speed. This makes the start easy and safer for bystanders because the propeller is not turning, and when landing the propeller can windmill freely and add drag, contributing to a steeper glide path. If the engine quits while cruising around, however, the added drag will reduce the plane's glide and might limit the emergency landing area selection to a field close by.

Any airplane can be made more energy efficient by reducing drag, but if you are already flying the most efficient plane in the sky, why bother? The Bluebird is a paragon of flight efficiency, it uses about 1.3 gallons of gas per flight hour, as little as any motorized airplane I know of.

The hand deployed emergency parachute is stowed in a commercial paramotor cover container mounted on the right side of the seat. The chute is an ordinary hang glider reserve with a swivel and a long bridle. I have never had to use an emergency chute, but just before a re-pack (about once a year or if it gets wet) I do a practice throw. While seated in the hangar, I pull it out of the cover bag, then toss or drop it onto the floor just to confirm that its ready if needed. My preferred handle is horizontal, as shown, but most cover bags place the handle vertically.

The downward parachute drop is intended to place the canopy in clear air for a reliable opening (there may be a churning mass of collapsed wing above the pilot, so I don't want it to go up). The momentum of the released chute in it's deployment bag should carry it tangentially away from the rotating disabled airframe, providing additional clearance.

The Bloop 4 biplane is probably the best motorfloater of the series. It is practical on the ground and easy to fly. The comparison to the monoplane is not easy because the monoplane has a much less powerful engine, but the biplanes have a shorter wing span in relation to their wheel bases than the monoplane, making them more stable in ground roll (less tendency to tip to the side).

From the beginning I wanted the pilot to be protected from injury in ground slides and low speed crashes. By belting the pilot into the center of an extended airframe a motorfloater should allow the pilot to move as far as possible while the airframe collapses, minimizing the average seat belt forces. This offers protection to the pilot under conditions where an exposed hang glider or paramotor pilot might be injured. The inherently low flying speed of my motorfloaters should make them safer to crash than ordinary ultralights, since those other Part 103 ultralights are mostly fast and heavy airplanes compared to mine.

The goal of crash safety is to turn tragedy into comedy. It's an acceptable outcome to walk away from a destroyed airplane, especially if you got the whole thing on video.

The engine used for my biplanes is a two stroke Vittorazi Moster 185cc, rated at 25 horsepower. Engine and propeller came together and weighed 35 pounds. My normal flight engine speed is full throttle through the take off and departure, reduced throttle for floating around, then low power down to idle for the landing pattern and touch down. Sometimes the engine will quit in idle, and I won't notice it, so I try to stay within gliding distance of the runway throughout the landing pattern.

This is a closed fuel system, pressure compensation is performed by a diaphragm in the carburetor, the only fuel exposure to the atmosphere is the static port, a small hole in the fuel tank cap. The fuel pump is built into the carburetor, it is powered by a vacuum line to the engine body. The fuel pump is needed to suck fuel from a fuel tank below the engine, you might not need it if the fuel tank was mounted above the engine.

Buying, mixing, and loading the fuel/oil mix into the tank is probably the biggest of the flight support efforts, something frequently done. For practical purposes it is important to have good access to the fuel tank. Locating the fuel tank for quick and easy filling from a mixing jug is a non-trivial design goal. It would probably be better for running the engine if the tank was mounted higher, reducing fuel line suction, but that change might make the fuel tank harder to fill.

All of the holes in the fuel tank are up in the top, so it cannot leak. There is no fuel valve other than the check valve in the primer bulb. Most airplanes have a "gascolator", a small reservoir with a drain valve at the low point in the fuel line. Sediment and water can be removed from the fuel by draining from this before each flight. I don't use one. I expect the small amounts of water that are accumulated in the fuel tank to get sucked through the engine without much fuss, and this seems to work for me and the paramotor pilots.

Filling up the fuel tank at the end of the flying day, thus always having a full tank overnight, is a common airplane practice for minimizing water in the fuel, which is assumed to get into the tank by condensing from the air. I took this precaution for many years, then stopped because it wasn't convenient, and I couldn't detect any water in the fuel (by looking through the translucent tank side walls).

My motorfloaters are moved on the ground by picking up the tail and walking them around, usually with the engine off. I don't see any need to taxi a plane that weighs only a little more than I do and which is well balanced on its wheels. My hot engine time and fuel are reserved for flying, not wasted on ground moves.

Every small airplane has to be pushed into or out of its hangar anyway, so why not just keep going? I don't want taxi problems, such as making noise, raising dust, and possibly damaging the plane due to control and visibility limitations. Often the adaptations made for ground movement will add weight and complexity to the aircraft while actually reducing flight qualities, and I want none of it. While in the plane I can power onto or off a runway to keep clear of traffic as needed, and while I admit that ground scooting can be fun, I have gone to some trouble to demonstrate that taxiing is not essential.

My portable aircraft radio is kept in a paraglider chest pack, always on me and not in the airplane, so I can remain in advisory traffic contact as I wheel the plane around.

Go to Motorfloater Storyboard 2

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