Building powerchutes for working Americans
There is a common misconception within the powerchute community (those that already own a powerchute and those that are preparing to buy a new or used powerchute) that a 65 horsepower or larger engine is required to lift two people safely.
Nothing could be further from the truth. The good and decent folks that believe this old wives tale have been given inaccurate information by other good and decent people that really don't know what they are talking about.
Thrust, not horsepower, is what enables aircraft of all types to get into the air and to lift a given payload.
Maximum thrust production for an ultralight aircraft can only be achieved with a large (72" or larger) propeller. Adding extra blades (4,5 or 6) to a small prop (anything under 72") only "nibbles" at the edge of the problem.
Here's a good example. Everyone on Earth has seen the "Bigfoot" monster trucks. Most of us have seen "Bigfoot" crush cars and also drive through mud deep enough to drown a grown man. We all know that "Bigfoot's" engine(s) produce thousands of horsepower. But if you replace "Bigfoot's" huge tires with the small tires off of your truck, "Bigfoot" couldn't even make it to the mud pit much less go through it. Why?
Because, those thousands of horsepower have not been efficiently utilized.
Thrust production is really no more than the efficient utilization of horsepower and a large 72" prop does just that.
Which brings us up to the number two culprit that prevents the efficient utilization of horsepower.
Dirty airframe design.
No, I'm not talking about the literal dirt and grim on an airframe, but rather the airframe design itself interfering with proper airflow over the prop.
No powerchute, even those equipped with large, efficient 72" propellers can efficiently utilize horsepower if the airframe itself interferes with proper airflow over the propeller.
Here is a simple example. Most of us own and use a leaf blower. If the air intake of the leaf blower becomes clogged then the output (thrust) of the leaf blower is reduced significantly, sometimes to the point of uselessness.
Remove whatever is impeding the airflow into the leaf blower and your output (thrust) is restored.
Most currently produced powerchute airframes are very dirty in regards to allowing good airflow over the propeller and efficient utilization of horsepower.
If you have a good understanding of how important good, unrestricted airflow over the propeller is, then several glaring design flaws will be visible to even the "guy off the street". I have listed below some of those design flaws and their cure(s).
Design flaw: raised passenger seat. Cure: Lower both seats as much as possible.
Design flaw: radiator required for water cooled engine. Cure: use fan cooled engine
Design flaw: fuel tank shape and location. Cure: use multiple small, smooth shaped tanks properly located
Design flaw: saddle bags. Cure: use storage device that attached behind front seat.
Design flaw: multitude of large diameter braces. Cure: use fewer, stronger, smaller diameter materials
Design flaw: upper fan shroud netting. Cure: proper pilot training
Summary
It appears that the powerchute industry has now decided that the cure for low thrust production is more horsepower. Most manufacturers are now offering 100 horsepower engines on their powerchutes. But these 100 horsepower engines are still being equipped with small, inefficient propellers and mounted to dirty airframes.
Owners of these new 100 horsepower ($30000.00 +) powerchutes report an increase in payload and climb rate, almost equal to a properly designed powerchute utilizing a 65 horsepower engine and 72" propeller (in the $10000.00 price range).
Is that progress or what :)
We are located in Athens Texas (that's 65 miles southeast of Dallas)