Parachute or No Parachute?

Parachute or No Parachute?

Having a "reserve" parachute is generally mandatory for sky diving. It is also recommended for paragliding and paramotoring. 

Emergency parachutes for airplanes are becoming more popular. There is an interesting history.  First, you must learn about a man named Jim Hanbury, a skydiver, hang glider, base jumper, and stunt man who became interested in parachutes for ultralights. In 1977, Jim Hanbury took a Quicksilver Sprint ultralight up and cut the wires supporting one wing, placing the ultralight into a a spinning free fall. He actually had the event filmed with a video produced. Once in free fall, he cast a reserve parachute in the same manner as used for skydiving (except it was mounted to the ultralight and not to the pilot) and the plane crash landed, without injury to the pilot. He later tested a similar concept, except he used a rocket to ballistically launch the parachute with a rocket. (Hanbury later died testing a ballistic parachute for a Cessna 150--the lines became entangled with the plane's tail.) Throwing the parachute resulted in slower deployment, where the ballistic deployment was fast enough function when deployed with less than 100 foot of altitude. Others developed the concept further.

Here is a video showing a two seat Quicksilver E-LSA Trainer with footage showing Hanbury's testing.

Parachute History

Today, ballistic parachutes are available from BRS and Stratos (Magnum).  Stratos began in 1990 in the Czech Republic. BRS began in 1980 in Minnesota, as a result of a hang glider accident suffered by the founder Boris Popov. BRS was actually granted a US Patent: https://patents.google.com/patent/US4607814  A US Patent for an airplane parachute was granted in 1919--so emergency parachutes have been contemplated for a long time. Popov and Hanbury no doubt knew of each other. 

With the advent of UAV drones, there are many examples of saving the UAV using reserve parachutes--the leader being Fruity Chutes with remote ballistic launchers from SkyCat and Harrier.

There is no doubt that these devices do save lives. Success is recorded in video footage for Cirrus and some aerobatic planes. Deploying the device with a front mounted "tractor" propeller seems to work well. Deployment from an ultralight with a high mounted pusher is a bit more problematic as there is risk of entanglement in the prop. To deal with this, most installations shoot the rocket out the side (Aerolite horizontally, Quicksilver out and upward with the bridle routed around the rear bracing and up the wing toward the center anchorage. Hopefully, the prop has stopped, and the ultralight has slowed sufficiently that the bridle avoids getting entangled in the tail or the prop . (Success on the Quicksilver with floats is shown in the above video.) 

These devices seem valuable, but one must carefully weigh risk vs reward.  Unexpected deployment in flight is a remote possibility. Pulling the chute eliminates pilot control and avoidance of dangerous obstacles, like power lines, during the drifting descent. They probably are effective at 200 foot altitude, but only if the pilot reacts fast enough. (The 2018 Quicksilver crash in Maryland was equipped with a chute but it was not pulled.)  My search has not produced any video evidence of successful deployment in an Aerolite 103  with a soft pack and a horizontally sideways launched rocket.  However, at least two reports exists of successful deployment in an Aerolite. The horizontal launch is recommended by Stratos (in their manual) on the side where "the propellers blades move in the upward direction" a to use the effect of prop wash to move the chute upward away from the rudder and elevator and, if the bridle did impact the prop, the drop would tend to drive it upward. (Steel or Kevlar is recommended for the bridle for any length that might impact the prop.) Reasoning is that a vertical launch may allow the momentum of the plane to fly below and in front of the chute, causing the plane to fly up considerably and introduce a significant swinging oscillation. Actually, the manual recommends from zero to 45 degrees up angle---the way the system is recommended for the Quicksilver with a cannister. 

The “factory” install on the Aerolite shoots the rocket out the side horizontally with the bridle nylon zip tied to the rear of the wing. The zip ties hopefully break during deployment or at least after the rocket has fully extended the chute lines and the chute begins to fill (rocket thrust is around 70 pounds and most zip ties break at 50 pounds) with the bridle traveling around outside of rear strut to the center anchoring point on top of the wing in front of the engine. Hopefully the bridle stays in front of prop and avoids a prop strike, but if on the upward side of prop rotation, the bridle would likely be deflected upward.

Stratos-Magnum Manual

Stratos-Magnum Manual II

Galaxy Manual

I did find one first hand "testimony" of a crash a Dragonfly ultralight with a "pusher" engine. Note that the BRS is mounted in front of the wing with the rocket pointed upward. It deployed and did not entangle with the prop even though the pilot failed to kill the engine. 

http://www.ultralightnews.ca/advisories1/dragonflyfailure.htm

Aerolite Crash in Maine

The green Aerolite crash into trees in Maine was with a parachute. The yellow Aerolite crash into a pool enclosure in Florida was without a parachute although it was equipped with one. Often you see or hear of planes equipped with chutes but pilots did not engage them.  Both planes heavily damaged—both pilots walked away! 

The “ideal" reaction to an engine out is to land safely without a parachute. Parachutes should only be used if the pilot has lost control of the plane and control cannot be immediately re-established for stable flight. Invariably, the plane will be dropping like a projectile. (Broken wings, locked/jammed  elevator, rudder or aileron. Fortunately, these types of failures, while notorious, are not as common as many fear and risk can be minimized with good maintenance, and sound flying judgment.) With a chute, the airframe will be heavily damaged--maybe beyond repair. And very good possibility of a prop strike, putting a ? on the engine's condition.  A successful emergency landing in a field will likely only require minor repairs. Fly always with a healthy anticipation of the need to land safely without warning. The story of the red Kolb shown below in a cornfield: 

"The 590th landing, I bent a landing gear leg. I took off from I22 and climbed to about 750 feet agl when the engine dropped to an idle. A split connector for the throttle cable had come unscrewed. I was too low to return to the airport so I elected for a crosswind landing in a cornfield that was close to a house and a main road.

I landed with the cornrows. It did not seem like I hit that hard but the up wind landing gear (right) leg was bent back and up about 4 to 6 inches. There was no damage to the tail feathers."

Hay, wheat and even soybean fields are the most desirable for emergency landings--corn fields can be less forgiving, but always better than trees, overhead wires or fences. Be prepared to compensate the farmer for crop damage. Be careful in pastures as livestock don't stand still.  Roads are a possibility, but traffic and overhead wires often become a hazard. Practice landings with engine at idle and a steep descent so as to learn the best configuration to land over obstacles with a very short field. Properly flown, the Aerolite can land, over a 50 ft obstacle in only 300 feet (100 yards). 

The most compelling justification for a chute is a structural failure or damaged control system. In other words when the plane is no longer flyable. Aerobatic pilots wear chutes and “bail” when the plane’s structure fails or they lose control with no hope of regaining control. Usually they have 1000’ AGL for the chute to open. The whole plane ballistic chutes may work when deployed as low as 200’ AGL.

There are three types of containers used for ballistic parachute--cannister (see Dragonfly above and Zigolo below)---vertical launch (See Dragonfly below) and soft-pack. See Aerolite 103 below. The soft pack is considerably lighter than the 24 pounds allowed by the FAA in Part 103. 

Choice of parachute location may be affected by CG weight and balance. 

Another Option

Aerobatic and glider pilots have been wearing emergency parachutes for years. In fact, aerobatic pilots and passengers are required to wear them when performing aerobatic maneuvers. They "bail out" if/when the plane is no longer flyable.  Wings coming off, unrecoverable spins, loss of elevator or rudder control are reasons to use the chute. If the plane is unable to fly, whether it be a ballistic parachute or a emergency parachute for the pilot, it is time to use the parachute. 

I believe that there are advantages for the ballistic for the plane as it probably deploys faster and there is less loss of altitude during deployment. With an emergency parachute, the pilot must first exit and get clear of the plane. This can be a major issue at low altitude. Unhooking set belts, and moving your body to a safe exit could easily take 2-3 seconds versus pulling a handle---the difference is a loss of 200-300 feet or more. 

What is often underestimated is the descent rate with the parachute deployed. In a perfect scenario, the plane will descend in a stable horizontal attitude and land on it's wheels, impacting at about 10-15 mph. If it is swinging, the impact could be much harder. In many instances, such as a wing failure, the plane would not land in a stable horizontal attitude.  In any case, the impact will probably result in total destruction of the airframe and it is possible that parts of the airframe may strike and injure the pilot. And, the pilot will be subjected to high compression forces in the spinal column and neck. If the plane descends nose first, leg/foot injuries are highly possible. Finally, the pilot is still strapped in at impact, with the possibility of a fire from the fuel stored and fuel lines directly behind the pilot.

There are risks associated with ballistic systems. Inadvertent/accidental activation being one.

Bailing out has another set of risks. As mentioned, more altitude is required. The biggest advantage is the pilot is clear of the plane--no risk of fire or being struck by airplane parts. The pilot is likely to impact the ground at the same 10-15 mph. But, proper body positioning and use of leg muscles will likely result in less injury to the spine and neck.  Even so, for an older pilot, a parachute "landing" is likely to sustain some form of back injury unless he is in extraordinary physical condition--about the same as jumping off an 8 foot step ladder. Another advantage is the risk of inadvertent "launch" of the rocket and parachute is nil. 

Normally, an emergency pilot parachute would only be effective if bailing out about 500'AGL. (Ballistic chutes maybe above 300')  But, here is the testimony of a Christen Eagle aerobatic pilot: "My partner told me later he figures I got out at about 100 feet. I thought he was wrong, due to his maybe being excited, and hanging from his own chute, and being far away, and since I wasn't dead. When I brought my chute to a guy who has a great reputation as a rigger, he figured it was somewhere between 100-200 feet." This pilot did not get the full benefit of the chute--and probably impacted the ground at >20mph=30ft/sec but he did survive and walked away.

It should also be remembered that the "original" parachute use by an ultralight pilot (Handbury) was a "hand thrown" reserve parachute---the kind now used by paramotor "ultralights".  Tandem versions are available rated for 210kg=462lbs or about the same for an ultralight plane with a 208 lb pilot.

US Patent 4445654-Inventor Handbury, 1982

"An ultralight aircraft and/or pilot recovery system includes a parachute having a canopy connected by means of a plurality of shroud lines to a first elongated cable having a length to position the parachute clear of the aircraft engine and propeller with a second cable for connecting the parachute to the frame of the aircraft and including a harness worn by the pilot which includes a pouch for containing the canopy folded within an inner pouch to permit the pilot to grasp and toss the chute clear of the aircraft for deployment for recovery of the aircraft. An alternate embodiment provides for connecting the parachute to the harness worn by the pilot and securing the harness to the aircraft to thereby give the pilot the option to recover the aircraft or cut loose from the aircraft for pilot recovery only."

As a footnote...Handbury died in 1986 while testing a parachute for a Cessna 150. The parachute became entangled in the plane's tail and control was lost at an altitude of 3000 feet. Handbury, wearing an emergency parachute bailed out at about 400 ft above the ground, but there was insufficient time for the chute to open. 

Weight and Weight/Balance

Weight and Weight/Balance

FAA Part 103 limits the empty weights of an ultralight as 254# or 278# with a parachute. A review of history will provide some insight into how the FAA arrived at these figures. 

The Beginning

Federal Register / Vol. 46. No. 143 / Monday. July 27, 1981 / Proposed Rules

Link to NPRM

Link to excellent commentary

In July of 1981, the FAA's Notice for Proposed Rulemaking regarding ultralights aka powered hang gliders was published in the Federal Register. Due to the growing popularity of hang gliders in the 1970's, the FAA had published Advisory Circular 60-10 in 1974 with recommendations for "safe flying" of hang gliders. Hang Gliding activity continued to grow with flights exceeding 500 feet AGL and with the addition of engines and other control surfaces making some powered "hang gliders" approaching the definition and performance of certificated aircraft. There were a few instances of near miss encounters between ultralights and airliners. It is estimated by 1982, there were more than 10,000 ultralights flying in the US.

Given the FAA's mission to protect the safety of air carrier operations and generally the safety of all airspace users, the FAA determined that additional regulations were needed to define an "ultralight vehicle" and differentiate from regulated "aircraft". The result was Part 103. One major definition of an "ultralight vehicle" is it's weight.

Unpowered "hang gliders" were set at 150#. Powered ultralights without an engine and fuel tank weighed more---in the range of 165-168#.

So where did the 254/278# weights come from?  Federal regulators always seek to find examples of successful real life examples that rationalize the regulations. They found their best example in the most popular ultralight at that time: the Quicksilver MX weighed 254# empty and 278# with a BRS Canister Parachute. 

In some countries, ultralight weight limits are defined by maximum takeoff weight. (e.g. UK max weight limit for unregulated microlight is 300kg=660#  which equates to 380# empty weight carrying 250# pilot and 5 gallons of fuel.) The FAA like some countries (e.g. Germany) chose the vehicle's empty weight. (Germany defined an ultralight as 120kg with a rescue parachute. (264#=14# less than the USA weight)  Using maximum takeoff weight makes more sense if the purpose of limiting weight is to limit performance so as to enhance safety.

The 254# Quicksilver was equipped with a Rotax 447 two cylinder engine. The 447 was heavy as two stroke engines go, as it was equipped with fan cooling and had cast iron cylinder liners. More than 15000 Quicksilver "vehicles" have been sold; by far the most popular ultralight. 

Changes

Rotax stopped production of the 447 model, and Quicksilver adapted a highly modified version of the Hirth F23 engine as it's replacement. The F23 allowed the empty weight to be reduced to 250#. Modifications to the engine are not done in the Hirth factory or by Hirth personnel.

The Aerolite 103, aka the Aerolite 120 in Germany was originally designed in 1996 and first flown in 1997. It was more streamlined than the Quicksilver and weighed slightly more with it's dual surface wings, strut rather than wire bracing, front wind screen and compliant flexible "landing gear".  With less drag, safety was enhanced since there was more time for a pilot to react in an engine out situation. With a flexible suspension, airframe is more resistant to "hidden" damage from hard landings with impacts at 4-5fpm.  The Aerolite 103 with a Rotax 503 engine weighed in at 275#. (Weight of the 503 was about 8# more than the 447. The empty weight without engine of the Quicksilver came in at 165-168#. The Aerolite coming in at 173-178#--i.e. abut 8-10# heavier than a engineless Quicksilver.)

Clearly the Aerolite could not meet Part 103 with the Rotax 2 cylinder engines, so "legal" Aerolites were equipped with one cylinder engines in the US and Germany. (e.g. the Hirth F33)

But, with the introduction of more modern "all aluminum" engines with Nikasil cylinders not requiring fan cooling, being more than 20 pounds lighter than the Rotax engines, the Aerolite 103 could meet the 254# limit with a two cylinder. Just as the F23 Hirth replaced the Rotax in the Quicksilver, the MZ201 engine became a viable engine choice for the Aerolite 103. The MZ201 installed is lighter than the Hirth F23. The F23 has horizontally opposed cylinders requiring two mufflers and two carburetors. The MZ201 has inline cylinders requiring only one carb and one muffler. The Kawasaki 440 is slightly heavier than the MZ201 but enough lighter than the Rotax 447 and the F23 that it does meet the 254# limit using a recoil starter. A flight by 14 year old Scott Henry from Virginia to Oshkosh demonstrated this as shown in the video shared in the above “Transition Training” post.

The greatest advantage of the 2 cylinder engines in ultralight vehicles is the climb rate. The Quicksilver with Rotax 447 and the Hirth F23 advertised a climb rate of 850 fpm. The Aerolite 103/120 with a one cylinder engine advertises a climb rate of only 500 fpm. (Less at altitudes above sea level and/or on a hot day)  With the two cylinder, this jumps to over 900 feet per minute. Higher Rate of Climb is important in regards to safety-- faster takeoffs on grass strips, easier to avoid obstacles, better able to recover from downdrafts or stalls, easier to avoid wake turbulence during takeoffs, and less time running engines at full power. On a hot day, at 1000’ MSL, a single cylinder ultralight might only climb at 5 feet per second and would only clear 80 feet on a 1000 ft runway. A twin engine craft would probably clear the 150 foot obstacle with 1000 foot of runway. Although some 1940 vintage general aviation planes climb about the same as a single cylinder ultralight, the planes generally operate with longer runways. An underpowered ultralight flying off a short private field might attempt to clear an obstacle with too steep a climb and risk an unintended stall.

Weight and Balance

It is important to establish a datum for weight and balance--often it is simple to establish this as a component of the vehicle--in this case, the datum will be the center of the tire. The CG can be established as slight behind the tires (empty) and somewhere forward of the tires with fuel and pilot. The Aerolite 103 will lean back on the tail wheel when empty, but will land as a tricycle gear plane using the front tire for steering when pilot over 100 pounds is on board. Pilots weighing below 150# may require some ballast in nose to insure level flight without excess elevator input. (180-220# pilot weight is ideal). Too light load of fuel and pilot will increase risk of unintended stall and would require excess stick/yoke forward position. Too heavy a load may require excess stick/yoke pull interfering in reaching desired climb. Weight on front tire when craft is loaded and pilot on board should be determined before flight. 

Plane should be able to achieve Vne with power off and stick/yoke forward, and stall speed with stick/yoke at max pull. Level flight with little force on stick/yoke is considered ideal--especially for a plane that does not have adjustable trim.

The following video will show a lifting of a Aerolite 120 with a single cylinder engine with the center of gravity being just slightly to the rear of the tires. 

Here are the actual results of my weighing my Blue and Green Aerolite 103 S/N 210713, nickname “BG” on 8/31/2022 with new Accuteck scale. 119#2oz+119#9oz+11#10oz =250#5oz without wheel pants. Almost exactly as expected from data in literature. CG calculations per manual show CG at 75” from datum (nose) full of fuel with 215# pilot—CG moves rearward 1 inch as fuel is depleted.  

Left Side

Tail (level)

Right Side

Angle of Attack and Stall

Maintaining Control at All TImes

It has been said that the essence of flying an airplane is "Control Yaw and Don't Stall". Another way off saying this is "Control Yaw, Angle of Attack AND Speed" at all times.

Pilots are often taught that air speed determines a stall. This is sometimes true, under certain conditions, however it is NOT true under all conditions. Many a pilot has died trying to pull out of dive by pulling back on the stick too far and essentially stalling the wing, even at very high speed. It is hard to remember to only pull the stick back only enough to arrest the descent while avoiding excess angle of attack as well as avoiding excess g forces.

Loss of control often occurs because a lack of awareness that the use of ailerons will often cause the wing with the down aileron to stall and lose all lift because of the increased angle of attack caused by the change in the airfoil's shape with the down aileron. This is the cause of the infamous stall-spin-invert loss of control during "turn to final". 

Angle of Attack AND Airspeed together creates lift, enabling the plane to fly. Too little angle of attack at a given speed and the plane will descend. Too much and the wing/s will stall, lose lift and descend. The pilot's job is to control lift by adjusting speed and the angle of attack---indirectly with the elevator in the case of a traditional three axis airplane, or more directly by tilting the wing on a trike. 

Other than pointing the plane is the direction you want it to go, controlling yaw has to do with keeping the air flowing over the wing perpendicular to the leading edge and minimizing drag. Uncontrolled yaw will cause increased drag and may result in an unanticipated loss in speed. In addition, the rudder that is used to control yaw, also causes one wing to rise and the other to fall.

But Angle of Attack works together with Speed, so uncontrolled Yaw and increased drag, reduces speed and therefore reduces lift.  And adverse yaw (in the opposite direction of travel) creates and need to increase aileron input, increasing the angle of attack on the high wing. 

I fine point often misunderstood, if the concept of "relative wind" over the wing. To illustrate, let's use an example. Assume the plane is flying at 50 mph and the pilot reduces speed by reducing power, and maintains the same nose up/down attitude using elevator--the plane will descend without changing nose up/down attitude--the angle of attack seen by the wing by the relative wind will increase. A high drag ultralight will slow rapidly and in order to avoid too rapid a descent, the pilot may be tempted to pull the stick back---resulting in an further increase in angle of attack to the point of stall. To avoid this, unstable scenario, the descent in an ultralight should always be with sufficient nose down elevator to maintain a safe "margin" of "reserve angle of attack". 

Ultralights are often capable of very steep climb attitudes. When climbing the relative wind tends to decrease the angle of attack. This can create a dangerous situation: 1) With a sudden loss of power; or 2) With a sudden change in wind conditions---as angle of attack could increase suddenly causing a stall. 

Bottom Line---Determine the "safe" nose up attitude for climbs and nose down for descents, devise a way of determining these attitudes and use this to maintain a "reserve angle of attack" for descent, level flight and climb. 

Keep in mind that most planes have a "built in" angle of attack to allow "level" attitude at cruising speed. An increase in power and a change to a nose up attitude will cause the plane to climb. A decrease in power and a change to a nose down attitude will cause the plane to descend. Remember BOTH air speed and nose attitude will determine angle of attack.

 

 

Angle of Incidence + Pitch  =

Angle of Climb + Angle of Attack

For example if Angle of Climb is held constant, a change in pitch equals (created by stick back and reduction in throttle) an exactly equal change in Angle of Attack. 

Another example (with negative pitch and negative climb) If Angle of Climb reduced to descend, then Angle of Pitch must be reduced by same amount with stick forward in order to keep Angle of Attack unchanged. Without moving stick forward to reduce Angle of Pitch, Angle of Attack would increase.

To make planes "safer", most general aviation planes incorporate a feature called "Wing Washout" where the wings have a higher angle of attack (2-3 degrees) near the root than at the tips. This causes the wings to stall "smoothly" with the wing first stalling at the root, allowing the ailerons to still be effective.  

Most ultralights (including the Aerolite 103) do not have any washout. Hence, the stall will occur more suddenly across the entire wing simultaneously, with less "warning" and with the high probability that one wing will drop, with the plane entering a down spiral or spin--especially if the plane's rudder is not perfectly centered.  Hence managing angle of attack and maintaining a "reserve angle of attack" on an ultralight is very important.

Here are two ways to measure AOA without fancy electronics:

The Wright Brothers used a similar method on their first flights.

The Concept of TOP RUDDER 

Whenever an ultralight encounters a situation where a stall does occur and the plane enters an down spiral or spin--remember that abrupt input of top or opposite rudder is the only input that will allow the pilot to regain control. Generally, the best position for the ailerons during this "recovery" is neutral, and of course whenever there is a stall, the stick should be moved forward to increase speed and airflow over the wing.  The use of ailerons when stalled or in slow nose up high angle of attack flight can be ineffective and/or dangerous as they change the angle of attack on each wing differently.

Fuel and Oil for the MZ201 Engine

Fuel and Oil for the MZ201 Engine

Fuel and lubricating oil are important for any engine. For a 2 stroke engine, where the engine is lubricated with a fuel/oil mixture fuel and oil are especially important. And, while fuel and oil are important for 2 stroke outboards, motorbikes and snowmobiles, they are critical for an ultralight.

Engine out failures in an ultralight most often result in emergency landings, so the importance of avoiding engine failures is obvious. 

The most common engine out failures in two stroke engines are the result of detonation, excess deposits of carbon from unburned oil, seizures due to a lack of sufficient lubrication, or dirty contaminated fuel. 

Fuel

Detonation or "ping" is caused by fuel that burns as an explosion rather than a relatively more controlled more gradual pressure increase over time. It is like hitting the piston with a hammer rather an a push. For the sake of simplicity, assuming ignition timing is set correctly, detonation is the result of fuel with insufficient octane rating, excess carbon deposits in the combustion chamber or incorrect air fuel ratio. 

The correct air fuel ratio is usually just a matter of adjusting and/or jetting the carburetor correctly for air density and humidity.

So picking the right fuel becomes a bit of a research project. And, it must be remembered that adding oil to the fuel tends to reduce the octane rating.

Compact Radial Engines and now Fiate, manufacturer of the MZ201 recommend minimum 95 RON Octane gasoline. The engine is advertised to have a 9.6:1 Compression Ratio.

Gasoline sold at automobile service stations generally only share the AKI rating of the fuel. AKI is an average of RON and MON. Generally RON is higher than MON and AKI for the same fuel. e.g. 93 AKI "Supreme" gasoline at most service stations is equal to 98 RON, but it achieves with 10% ethanol. Most ethanol free gasoline at the service station pumps is 90 AKI, with an estimated 91 RON. Since 91 RON is too low and ethanol is not recommended for "aircraft", the only way to use "pump" fuel would be to blend it with Aviation Gasoline 100LL or an unleaded "racing-off road" gasoline. 

100LL Aviation Gasoline has a MON of 100, with an estimated RON of more than 105 (As high as 110). A 50% blend of 90 AKI ethanol free pump gas and 100LL would result in a fuel that exceeds the minimum 95 RON requirement with an estimated RON of 98+. Sunoco 260GTX 98 AKI Racing Fuel has a RON of 103. A blend of 40% pump and 60% Sunoco GTX  would provide an RON of 98 and it would be unleaded.  (Too high an octane is not ideal as higher octane tends to burn more slowly, so there could be incomplete combustion and less power.)  

Another option is Sunoco Optima 95 (what NASCAR Cup uses) which is unleaded and has an RON of 98. The advantage of the blends is that pump gas and Optima have a relatively high vapor pressure compared to 260GTX and 100LL.  As of July 2022: Cost of the 100LL blend would be around $8 per gallon. Cost of the Sunoco blend would be around $12. Cost of the Optima or unblended 260GTX would be $18-20 per gallon including shipping costs. 

It is possible that the MZ201 engine could run better with 103 RON vs 98, depending on ignition timing, so the Sunoco 260GTX might be ideal under certain circumstances. Detonation in an ultralight engine will likely not be detected by an audible "ping" like in an automobile. Signs of detonation will show up in the form of excessive CHT and depressed EGT with some loss of power. When octane is too high or the timing is not advanced enough, the engine will produce less power and will show a lower CHT. All of this complicated by the fact that flame speed is also affected by the fuel air ratio--too lean a mixture can produce the same effect as low octane. Slightly "rich" of peak is usually best. 

Sunoco offers Optima 95 "pre-mixed" with a synthetic 2 stroke oil with a 40:1 ratio. The 2 stroke oil meets JASO FD and API TC Specs. Sunoco does not provide any other tech data on the oil. Since it is advertised as recommended for outboards, it might not be ideal for air cooled engines.

My best judgment will be to run Sunoco 260GTX and experiment with blending it with 90AKI ethanol free pump gas when ambient temps are lower. If 260GTX became unavailable, I would use 100LL blended with 90AKI. While 260GTX is more expensive, the convenience of buying in 5 gal pails, and the logistics of obtaining/transporting 100LL offset the cost.

Oil

The MZ201 Engine Manual specifies Castrol TTS as the desired oil, mixed at 50:1.  Castrol TTS is no longer produced, so something else must be identified.

First let's look at the specs for Castrol TTS (as of 2016):

• Full synthetic 2-stroke motorcycle engine oil
• Creates a tough, heat-reactive layer of protection
• Designed for both oil injection and premix lubrication up to a fuel/oil ratio of 50:1
• Exceeds API TC, JASO FD, and ISO L EGD

API is the American Petroleum Institute, and TC is a very old standard met by almost every 2 cycle oil sold today.

JASO FD is a Japanese more stringent standard requiring lower smoke levels and more detergent.

ISO L EGD, a European standard is essentially the same as JASO FD, but requires a  3 hour test running a Honda engine to document piston cleanliness and detergent effectiveness.

Castrol has introduced "replacements" for TTS,  Castrol Power 1 2T.  Amsoil Dominator is almost the same. Motul produces a similar product, Motul 710 2T. 

Castrol Power 1 2T seems to be in very short supply in the US. Motul 710 is available from multiple sources. The Flash Point of 154C for the Motul is more desirable than the Power 1 2T and Amsoil as is the higher viscosity.  The viscosity of Motul 710 is higher than Power 1, but lower at 100C than Castrol TTS. My opinion is that Motul 710 2T is equivalent and slightly better than the Castrol TTS.  

Another "equivalent" oil would be from Motorex (Switzerland)  Cross Power 2T.  Flashpoint is 110C with Kinematic Viscosity at 40C of 60. This is in between Castrol and Motul 710.

Motorex Power Synt 2T is advertised as designed for “Supersport” motorcycle racing. Similar specs as Cross Power 2T.

Another "possible" oil would be Motul 800 Off Road 2T with Flashpoint of 252C, and Kinematic Viscosities of 120 and 15.

                                                    Flash Point C  Viscosity@40C Viscosity@100C

Castrol TTS                                    89                    43                     22  

Castrol Power 1 2T                        73                  43                      8

Amsoil Dominator                           94                   35                      7

Motorex Cross Power 2T               110                   60                    NA

Motorex Power Synt 2T                  108                50                    9.1

Motul 710 2T                                  154                   70                    11

Maxima 927                                    218                                                                                   155.                 15

Motul 800 OR 2T                            252                   120                  15

Note: Castrol (UK)  Motul (France), Motorex (Switzerland) all comply with JASO FD and ISO L-EGD as well as API TC.  Maxima and Amsoil, both USA companies did not go to expense of testing to meet other than API TC.

The Maxima 927 oil has been around a long time—since the 1970’s and was formulated for racing. Lower viscosity oils were developed to enable flow thru oil injector pumps rather than pre-mix. Maxima 927, like Motul 800 with higher viscosity and flashpoint was for pre-mix only. Maxima 927 is a blend of castor oil and synthetic. Castor oil can provide superior lubricity, but tends to create deposits when run at less than maximum output. Maxima claims to have solved this problem with blending. Pre-mix ratios are changed based on the type of use.

Motul 800 is designed for all out motorcycle racing, lots of full throttle, very high RPM operation. The others are designed for less severe use, less full throttle and lower RPM and are also suitable for chain saws, with intermittent full throttle. Air cooled motorcycle engines and chain saws operate under different conditions than an engine driving a propeller in an aircraft. 

The ultralight aircraft is likely to see full throttle for for one to two minutes during takeoff and climb, and then would be at a lower RPM for cruise. Load for propeller equipped engines is more or less correlated to RPM. (Actually load increases at a faster rate than RPM, but for the range considered, assume it to be linear.)

There is no two stroke engine oil that is expressly designed for ultralights. (Blue Max is one exception that was marketed by the former importer of Hirth engines--but there were no specs provided for that oil--only marketing claims and the fact that it was not a synthetic oil.) In fact, Amsoil will not sell their oil for any "aircraft" application, and all oil manufacturers will be quick to assert that they do not recommend their oils for aircraft operations since they have never been tested for that application. (Amsoil and others probably just wanting to avoid legal suits but demands for oil in ultralights IS different from other applications.)

During that two minutes of climb (red), clearly Motul 800 with a high flash point and density would be a very good oil. But, during cruise (green) it might not vaporize and burn sufficiently to avoid smoke, oil in the muffler, and carbon deposits on the piston. And , during descent (yellow) it would not vaporize and burn sufficiently to avoid smoke, oil in muffler and carbon deposits. 

Most likely the Motul 710 2T would be ideal for both cruise and descent. Feedback from users indicate that 710 is great for "normal" motorcycle operation, with 800 producing a lot of oil in the muffler, called "spooge". 

The fuel/air/oil mixture flows into the crankcase. Being relatively "cool" the mixture directly cools and lubes the crankshaft and conn rod bearing which probably run at a temp below 150C. The mixture also impacts the lower cylinder, probably running at a slightly higher temp. In addition, the mixture also impacts the piston pin and bearing, cooling and lubing it. However, the piston is much hotter, probably running hotter than 150C. Here, a higher flash point can be attractive.

This all focuses on the oil's flash point and to a lesser extent, viscosity. Does the oil vaporize completely during this charging and transfer phase? How much, if any, is the lubrication of the piston pin and bearing affected if the temp is higher than the flashpoint? How much oil remains on cylinder walls?

Reviewing the specs for Castrol TTS, with a flashpoint of only 89C, and MZ201's manufacturer's recommendation, it would appear that a low flashpoint is not too much of an issue. This is confirmed by Aerolite 103 factory and US distributor for the MZ201 who claims Amsoil Dominator at 50:1 is being used with no problems, Motul 710 2T has a significantly higher flashpoint at 154C than Castrol TTS's 89C. And, Motorex’s Supersport racing oil has lower flash point and viscosity than Motul 710. (KTM exclusively uses Motorex, so they raced at “supersport” level with oil with less than 150C flash point, so perhaps higher flashpoint is not necessary. Motorex does recommend 40:1 for supersport racing.

Other than the mess of oil dripping from the muffler onto the ultralight's wings and tail, the another concern about using Motul 800 would be deposits---especially deposits that cause piston ring sticking and damage. Anecdotal evidence does not point toward carbon deposits with Motul 800, perhaps due to detergent efficiency.  And anecdotal evidence with small high RPM motocross racing engines running Motorex (similar to Motul 710) shows more than sufficient lubrication after disassembly and inspection at 50 hours. 

One possible "solution" would be to blend 710 and 800 together to raise the flash point and viscosity. Another would be to increase the ratio for 710 from 50:1 to 40:1 or even 30;1 while insuring a slightly rich above peak air fuel ratio, Another would be to use Motul 800 or Maxima 927 when ambient and cylinder head temps are high, living with the spooge generated during descent. 

It is generally accepted that higher rpm requires a pre mix with more oil, e.g. 40:1 vs 50:1. It must be remembered that the MZ201 is running at half the rpm of racing motorcycles and less than 1/3 the rpm of racing karts.

It appears that whatever oil is chosen, due to the unique loads imposed on ultralight engines, optimum oil and ratio will result in some sponge at low loads encountered during descent. This provides an insight that best operation is to minimize idle and low rpm, using some throttle and higher rpm with lower descent rates during landing pattern. It also indicates that oil with more “solvent” which is used to reduce lower temp viscosity and flash point may be desirable in minimizing carbon deposits. The viscosity of the various oils at 200C “where it matters” are much more comparable than the 100C figures would indicate.

Motul recommendations:

Motul 710--Mixing ratio: from 2% to 4% (from 50:1 to 25:1) according to manufacturers' requirements. Adjust according to your own use.

Motul 800 Mixing ratio: MOTO CROSS GRAND PRIX: 2% (50:1). In normal conditions decrease the percentage by 0.5%. (66:1) Tune according to your own use.

Engine size does affect the decision regarding the "best" oil and mixture. A one cylinder MZ engine will run at 50% higher RPM and likely to be run at maximum load for much longer to climb than a two cylinder MZ201. Another factor to consider is the effect of prop pitch on engine load. With an adjustable pitch prop, one can choose a setting that creates a higher climb rate, reducing the time at full throttle during take off and climb but requiring a higher RPM for cruise. If one planned on long cross country running, choosing a setting for low RPM at cruise would be ideal, overcoming the reduced climb rate by climbing in stages, limiting full throttle to 30-60 seconds at a time. 

Also important to note is that changing oils and ratios probably will require an adjustment to the air/fuel ratio. Oil has as at least 10 times the viscosity of gasoline and higher viscosity oil will require larger (more rich) jetting. (The same vacuum pulling the thicker mixture will produce less flow.) Increasing the oil ratio from 50:1 to 40:1 will also reduce the combustible fuel thru the jetting, requiring more rich settings. In my opinion, an oil with a relatively lower viscosity, if sufficient to support oil film loads, will perform better than a relatively thick oil.

Based on the fact that Motul 710 2T is similar to Castrol TTS and Motorex, but with slightly higher flashpoint, and Motorex recommendation of 40:1 for racing, my best judgment indicates I will run Motul 710 2T at 40:1 (3.2 oz per gal = 2.5%)  in my MZ201, being careful to control (limit) full throttle for extended periods of more than 60 seconds, and limiting off throttle idling on the ground and during descent. I will also run air fuel slightly on the rich side and will monitor CHT closely.

Absent testing, followed by disassembly and inspection, choosing the ideal oil and mixture is not possible. One can only choose a "conservative" strategy with the highest estimate of a good outcome, but having a "safety" factor. And, during operation, make close observations as to smoke, spooge, and CHT. One of the fundamental aspects of “unregulated” flight is personal responsibility—no FAA Reg’s certifying what products and procedures to use..you are responsible for determining what is best.

The Tillotson HR197A Carburetor-Air Fuel Mixture Setting

 The Tillotson HR197A Carburetor Air Fuel Mixture Setting CHT and EGT

In the previous post, it was noted that air fuel ratio needed to be adjusted. In most general aviation planes, the air fuel ratio is cockpit adjustable. The MZ201 engine, equipped with the Tillotson HR197A carburetor does not offer this feature without modifications.

Jack B. Hart's blog provides an excellent illustration of the HR197A. He did make such modification as seen in this link:

Carb Mods

The Tillotson carb has two "mixture" adjustments: Low Speed and High Speed. The Tillotson Manual suggests starting out with "one full turn out" on both. Other anecdotal suggestions from users of the carb on vintage snowmobiles is 3/4 turn out on Low Speed and 1 1/4 turn out on high speed. 

Setting the Low Speed is more or less the same process for setting idle mixture. Turn out--to richen until it stumbles and turn in slightly to smooth it out. 

Setting the High Speed is more complicated as it requires the engine to be run at full speed wide open throttle. One can restrain the ultralight and run on the ground for short periods, but with the lack of air flow from actual flight, there is a risk of overheating. 

Perhaps the most accurate way to determine the ideal setting is the use of the Tillotson Quick Jet tool. (See below) It allows precise and repeatable settings.

Each mark on dial is 1/30th revolution

Take careful notes

During flight, High Speed mixture exists while the plane is in a full power climb for 30 seconds; the CHT and EGT and EGT should be noted. The "ideal" setting would be to find the setting that produces what is generally referred to as 100-150 degrees ROP. (ROP=Rich of Peak EGT). This ROP setting procedure is similar to the system used for GA planes with cockpit adjustable mixture controls.

Four stroke engines can use a air fuel gauge that measures oxygen in the exhaust, but these systems do not work as well in a 2 stroke because of the oil mixed in with the fuel. 

Cylinder Head Temp or CHT should be kept below 380 F. (Fiate suggests a max of 500 F, but engine life at temps above 400 F is seriously reduced.) Anything that makes the air fuel mixture burn faster increases CHT. The fastest burn rate occurs with an air fuel mixture slightly more rich than 14.7 pounds of air per pound of fuel=approximately 50F ROP EGT. Leaner mixtures will have lower CHT and richer mixtures will have lower CHT.

Peak EGT will be at the 14.7:1 ratio referred to as "Stoichiometric". This would be ZERO ROP. Increasing the fuel (turning the High Speed adjuster out) will decrease EGT. Assuming the adjustment is reasonably "close" because the engine is running smoothly, if an increase in fuel causes a increase in EGT, you are on the lean side of peak. If an increase in fuel causes a drop in EGT, you are on the rich side of ZERO ROP. 

Once peak EGT is identified, increasing fuel to richen the mixture will reduce EGT. The ideal would be to be in the 100-150 F ROP or 100-150F below peak EGT. (100 ROP is theoretically maximum power; 150 ROP has a slightly lower CHT for maximum engine life--remembering that 2 stroke engines are cooled by fuel.) Keep in mind that these readings assume you are at maximum power and wide open throttle in climb (46 mph for the Aerolite 103) for long enough time to allow the CHT and EGT to "stabilize".  Having that cockpit adjustment mod like Jack B. Hart's would make this an easy process--without it, would require several repeated flights. 

Prior to actual flight, lean the high speed jet from the "initial reference" setting by one or two 30th marks on the Quick Jet tool and continue if EGT at full throttle run up increases--stop when it approaches max 1250F. (You will also note some "dull" acceleration during a takeoff roll at around 4000-4500 RPM.) Then richen the mixture five (5) 30th marks. Lean the low speed jet until the engine idle speed (set at 1650 rpm) drops, then back one 30th mark. Test the engine during take off roll to verify no "four stroking" in the 3000-4500 RPM range and no "dull" acceleration above 4500 RPM.

Note: Excessively rich LS jet will cause "four stroking" and even engine out during acceleration as engine travels past 3000-3500 RPM---this is because the LS jet has an idle port and an "intermediate" or secondary port that adds considerable fuel in this RPM range during which the HS jet is also "kicking in".  The danger from high EGT will occur during high rpm and high loads, and the engine is likely to have "dull" acceleration if too lean, hence the HS jet should be on the rich side. On the other hand, the LS jet should probably be set as lean as possible to avoid "four stroking" during take off roll. 

This "ideal" performance (prior to first flight during take off roll tests) occurred with settings of 1+6/30 on the HS and 1+3/30 on the LS with Density Altitude of 1200 feet. Best estimate is that engine is set at 150 ROP estimating that each 30th moved EGT down by about 25-30 degrees. (Re-adjustment may be required if Density Altitude changes substantially. ) A final check would be to look at plug condition after a take off roll. (Look for a light tan insulator and a dry electrode.)

Note that all of these adjustments depend on a propeller pitch setting that "governs" RPM during takeoff roll in the 4800-5200 RPM range. If the engine spins above that under load during take off roll, the engine RPM is being limited by the carburetor's maximum air flow and all mixture adjustments will be incorrect (probably too rich) due to excess turbulence in the carb's venturi.

Too much white on insulator is bad-too lean

Medium Setting for 1000-1500 Ft Density Alt

Rich Setting for <500 Ft Density Altitude 

Medium Setting "some four stroking" at 1500 DA; Rich Setting "some four stroking" at 500 DA. Appears 1/30 change is appropriate for High Speed Jet for 1000 Ft change in DA. Since EGT in 4500-4700 RPM "cruise" shows 1225+ EGT with the lower DA "Rich" setting, it may be prudent to run a bit on rich side.

Here is a link to articles about adjusting the mixture.

http://www.iwt.com.au/tillotson.htm

https://resources.savvyaviation.com/understanding-cht-and-egt-2/

In general aviation, running LOP increases fuel economy and mixture must be generally leaned at higher altitudes. Ultralights are generally not flying high enough to require in flight adjustment. Choosing maximum engine life over best fuel economy is a matter of pilot choice. To minimize risk associated with engine outs in an ultralight, I would always choose to maximize engine life. 

The Aerolite 103 nicknamed "BG" for its blue and green colors will be equipped with the Grand Rapids EIS showing CHT and EGT.