Modernizing the definition of ultralights thru government regulations is dangerous business. It seems unnecessary when there is so much more that can be done to modernize the ultralight itself into the incredible flying machine that it can be and completely within the limitations of part 103 and A/C 103-7. Other motorsports machines such as motorcycles, all terrain vehicles, jet skis and snowmobiles have blasted past us in terms of high power excitement, maneuverability and strength technology. They have gotten more powerful, stronger, lighter and improved in other ways.
Setting aside the weight issue, many ultralighteers suggest that higher horsepower rated engines can give more reliability, safety, fuel economy and tremendously more fun. All six engine failures that I encountered were while giving ultralight flight instruction in heavier two seat Quicksilver’s powered by Rotax 503s operating at high load. These were maintained by the company that I worked part time for. On the other hand my Brother, Dad and I have never had an engine failure in any single seat using Rotax and Hirth engines and during a much longer total flight time. Of course we are exclusively responsible for our own inspections and maintenance but we have to acknowledge that running the engines under a smaller load percentage to be a major contributor to the significantly increased reliability.
With each large increment of additional engine HP capacity that you can put into the engine means that you can gain features like less engine load percentage, less RPM percentage, dual ignition, water cooling and less fuel consumption per HP. Our Quicksilver Sprint got better fuel economy with an ancient chrome bore DCDI 650cc Hirth than a 447 Rotax. Consider that operating with a newer 65HP 625cc Hirth uses 2.8, 3.8 and 6.5 GPH at 30, 40, and 65 HP respectively. The M7 legal ultralight if equipped with the yet unfinished lightweight float system and using the three cylinder 100 HP Hirth engine would give 2.7, 3.0 and 4.3 GPH at those same three HP levels. Similar results could be expected on an ultralight float equipped M7 ultralight with the Simonini 2 cycle 92, 102 and 110 HP models which weigh just a little more than a Rotax 582. Lighter weight cog belt reductions and in flight adjustable pitch propellers would be used. It was reported in homebuiltairplanes (2-stroke engines section) that a 92 HP Simonini could run on half the fuel of the 65 HP Rotax 582 that was in his Zenair 701. Of course the superior Simonini dual expansion chamber exhaust system was partly responsible. Someone in HBA said that their Rotax 447 could burn 5 GPH at full throttle which I think is only 40 HP while the 100 HP Hirth claims only 3 GPH at 40 HP. Yes the 100 HP Hirth will use 7.8 GPH at 100 HP, but at that burn rate you could jump to 500 feet AGL in 15 seconds and be set to glide 360 degrees and land at the point you launched from. This can be an important safety advantage if emergency landing opportunities are confined to a short runway where landing straight ahead is not a pretty picture. Another improvement to safety is here where the statistical chance of an engine failure in that short 15 second period is more unlikely. Other low power ultralights have to strain at lower altitudes over more neighboring property for a minute to get 500 feet AGL and might have long passed the best places to emergency land. Even at only 4 GPH a 447 would use twice as much fuel to get to 500 feet AGL. With enough power and automatic active speed control at the throttle level, stalls could be unlikely or impossible especially if the angle of attack measurement is factored in to the control too. I disclosed more information about this in www.homebuiltairplanes.com Light Suff, New UL Manufacturer section for defensive publication purposes.
High HP short takeoff roll and healthy climb makes ultralights significantly more versatile, useable and safer from a much greater number of locations. And so much more fun. Why would anyone intentionally select engines that are more closely sized to a weed whacker and more likely to be short lived when the opportunity to use a higher HP engine exists? Well ok if you want to save money, fly less safe, look like an airplane, worry about clearing that obstacle on that hot humid day while packing a few extra pounds around the belly, have less fun and less places to land and takeoff from. I wish the best engines were a lot cheaper too. It seems that ultralight engines can cost close to 100 dollars per 1 HP while the engine prices are much less for the snowmobile and jet ski true motorsports guys who stop at nothing to get the most HP and better technology. Whenever I hear about someone wanting to buy or build an antique airplane style, LSA or ultralight that has to be powered by a weedwacker engine or four stroke engine, I wonder why and think of how many people would go see any powersports competition such as a super cross race if the machines were low power vintage motorcycles or scooters. The answer is none because there would be inadequate interest and excitement and thus no such sport under such low power limitations. Except for those of us mostly aging pilots who deeply appreciate the early machines, they just are not interesting enough or worth paying to watch in competition, sponsor or sell to new people. Engine power is the defining element to any motorsport or aircraft. The absolute best power to weight ratio is more important for an ultralight because of the weight limit and thus should not be subject to compromise.
The 63 MPH ultralight speed limit makes for a wonderful opportunity for ultralights to focus much less on low drag airplane appearance and transfer that weight into more structural strength, maneuverability and more power. Unencumbered by traction and other issues, an ultralight should be a fun flying ATV like machine with more maneuvering power to do simple things like tight corkscrew climbs or follow steep terrain. Ultralights are the most versatile, useable, fun, unencumbered, practical and obtainable flying recreational vehicles. They can be made a lot better if newer concepts are adopted and implemented.
I am doing a lot of work toward the development of a lighter direct drive, vibration free and more powerful broad usage engine of huge displacement that will weigh no more than __ pounds less the propeller. The part 103 weight limit indirectly implies that if you use a 4 stroke, you won’t be taking off from half the places that an equal weight 2 stroke can. We have a lot of small places to fly in and out of here in central east Ohio. While the two strokes have gathered at many places, the four strokes are limited to a fly by.
My favorite engine is the Aaen V4 two stroke 95 pound road racing engine 850cc 200HP@9,250RPM, but Mr. Aaen will not sell them for aviation use, not even for 25K. I would not hesitate for one minute to put such engine on the M7 with some changes already scheduled for the M7. There are a lot of cheap 100+ horsepower snowmobile and jet ski engines out there too with expansion chamber exhaust systems.
Evinrude E-Tec, Mercury and a few others boast of their lines of DFI (direct fuel injection into the combustion chamber during the compression stroke) two stroke engines that get better performance, better fuel economy, outstanding reliability and less pollution than 4 strokes. Two stroke engines are poised to make a big comeback using the new DFI technologies. Unfortunately the automotive and aviation industries will be last to get the message and make the change. Our defense industry uses a lot of two strokes on some very expensive UAV (unmanned aerial vehicles). Hirth is the 2 stroke leader there using technology that is significantly more advanced than that what they share with the ultralight industry or other competing companies. I got to touch and examine the line of Hirth UAV engines which are not shown at Airventure or Sun-N-Fun. DFI was used on some WWII German 4 stroke airplanes and is similar to Diesel engine fuel injection.
New 4 cylinder DFI two strokes are needed for ultralights where the 90 degree combustion spacing (not on the Hirth 4 cylinder or a few others) makes for a super simplistic cross pipe exhaust system that is well tuned at all RPMs. This is unlike bulky expansion chamber tuning where they are often highly tuned only to a very limited RPM range. Four cylinder two strokes have much less vibration than two cylinder in lines.
The Martin jet pack 2000 cc V4 two stroke at 200 HP @ 6000 RPM with a nearly flat torque curve (due to cross pipe exhaust) is very impressive but its 132 lb engine weight does not calculate for a legal fixed wing ultralight even with ultralight weight floats. (An engine like the Martin engine (might be their prototype?) but with the cross pipe exhaust unraveled can be seen on You Tube under 2000cc V4 two-stroke revs to 200 bhp) In the 300+ comments, many of the two stroke guys criticize it for it having too little power compared to the typical high performance engines like the Suzuki 500 cc four cylinder two strokes with between 150 and 200 HP. These guys would laugh at what we call horsepower on our ultralights and LSA.
Note that the Martin jet pack does not need wings to be part 103 legal as per AirVenture 2008 when it was shown. This extreme example should remind us that 100 or even 200 HP should not be considered an impossible ultralight goal. It also suggests yet another way more HP can give legal stall speed with a little less wing span (lower aspect ratios allow more extreme angles of attack)…a little less wing weight required means a little more weight that can be added for more HP and yet a little less wingspan… I was told that 100 HP on an 8 foot diameter wood propeller has demonstrated 600 pounds static thrust. A 120-140 HP 700cc V or radial 4 cylinder 2 stroke (90 degree timed) with cross pipe exhaust, + or - 4:1 cog belt reduction on a 6.5 to 7 foot prop would be a nice M7 ultralight package. This would translate to a 2800cc per prop shaft revolution displacement (only 1400cc on a 4 stroke). A traditional 1000cc 2 cylinder 4 stroke direct drive to a small propeller (500cc per revolution) makes for pitiful static thrust and dependency on the airport. This kind of power is useable for cutting grass in the riding lawn mower so long as the grass is not too deep.
The goal that I think is very possible using a completely different propulsion system is a Part 103 fixed wing ultralight with VTOL capability (where electric power is not yet an option as much as I like it) and without any need to change part 103. We need to get out of the mind set that ultralights must be equipped with low power engines, or represent some classical antique airplane, or be designed solely for MPG or gliding, else ultralight aviation will have a slow future with no powersports excitement. Clinging to the past is a good way to prevent having a future. An ultralight with power is spectacular!
What seems impossible to one does not make it impossible for another. Despite extensive information to the contrary, some still choose traditional misinterpretations and limitations and assert that their perceived limitations applies to everybody or else. Others are free to choose opportunities, creativity and effort toward a really exciting flying machine.
AirVenture can draw more people if they know in advance that they can come and see such new machines, performance, STO, climb, maneuverability and back field versatility and with some resemblance to affordability. This kind of performance can lead to growth and representation/protection in numbers. Many people are drawn or limited toward the absolute lowest cost options. PPGs are a great option that I would like to try someday. However watching someone weed whacking or lawn mowering about in a straight line in a heavily skinned fixed wing machine for MPG or navigating for landmarks is not much a spectator sport or as exciting for the pilot. We do not fly everyday thus our fuel bill is a relatively small part of our flying budget. If I want range, comfort and 24-7 usability, I will use the car.
People pilot for fun. A 15 minute flight with real maneuvering power from a nearby location can better fit our schedules and be more rewarding than a two hour flight. It’s not about miles per gallon, its all about SMILES per mile. That’s what ultralights are about.