# Why does the Zapata Flyboard Air UL consume so much more fuel/hr than the Mosquito Air?

They are both ultralight and abide by FAA ultralight reg 14 CFR part 103. The Mosquito Air is an ultralight 1 person helicopter whereas the Zapata Air UL is a micro jet turbine powered 1 person ultralight hoverboard. They weigh the same and both only carry 5 gallons of fuel as this is dictated by part 103.

The 5 gallons will last 1 hour of cruise flight time on the Mosquito while only 8 minutes on the Zapata. Granted we are dealing with different technologies here and different fuels (Zapata uses kerosene, Mosquito uses avgas) I was surprised by the fuel burn difference.

The bare physics tells us that equal masses should require the same amount of thrust, thus energy, to hover in place where lift equals weight. Kerosene has similar energy density to avgas. And, a jet turbine is supposed to be much more efficient than a 2-stroke, 2 cylinder gasoline engine.

The Mosquito boasts of a 64hp engine "with the highest power to weight ratio on the market today". The Zapata company seems not so much concerned with the gas guzzling fuel consumption. The 2 companies seem to have different priorities here, so I'm guessing the fuel efficiency of the Zapata could be improved. Still, this is a huge difference that is difficult to understand.

• Powered lift burns a lot of fuel. – acpilot Jul 8 '17 at 2:15
• " Kerosene has greater energy density than avgas". Source please. Everything I can find says the opposite. – Simon Jul 8 '17 at 15:32
• @Simon Gasoline is primarily the 5 carbon hydrocarbon pentane that vaporizes easily and is less dense than the long carbon chain hydrocarbons that make up kerosene. Kerosene, JetA, and diesel are very similar in energy density and composition with less than 1% difference between them. I don't think you are disputing that diesel has a higher energy density than gasoline. Raw pentane is not energy dense enough so the 8 carbon hydrocarbon, octane, is added so we have an octane rating. 100LL is 100 octane rating with Lead compound added, which could be similar energy density to kerosene. – 0tyranny 0poverty Jul 8 '17 at 16:55
• @Simon I will open this topic as a separate question. – 0tyranny 0poverty Jul 8 '17 at 16:57
• @Simon you are correct, my bad, corrected question. – 0tyranny 0poverty Jul 8 '17 at 17:18

It's the difference between jet engines and propellers. It is a lot more efficient to accelerate more air to a low velocity, than it is to accelerate less air to a higher velocity. For fixed wings, the only reason to use jets is if propellers hit their speed limit, when the tips break the speed of sound.

Hovering flight is particularly demanding on fuel consumption. The Mosquito Air burns through its fuel a lot faster than 1 hour when it stays in hover all the time. Cruising in a helicopter makes the fuel consumption a bit more similar to fixed wing: the rotor blades start to act more like wings and can use airspeed to reduce induced drag. Still less efficient than fixed wing cruise, but more efficient than helicopter hover.

The Zapata Air UL is always in a hover, and has no wings, and is a jet. It never gets the increased efficiency effect of forward flight that a rotor gets. And jets are really very inefficient at low speeds!

• It's a pretty cool device though. – Koyovis Jul 8 '17 at 2:40
• the statement about the air velocity clarified my mind fog. E = 0.5mvsq so more air mass at lower velocity is easier than less mass at higher velocity since we are dealing with velocity squared. – 0tyranny 0poverty Jul 8 '17 at 3:04
• Yes, thrust = $\dot{m} \cdot (V_e - V_0)$ – Koyovis Jul 8 '17 at 9:58
• Could you put wings on the Flyboard? – Koyovis Jul 8 '17 at 11:48
• not part of the design – 0tyranny 0poverty Jul 8 '17 at 12:01

First, let's compare apples to apples, and compare the Flyboard to the Mosquito XET, the gas turbine powered version. The Mosquito XET with it's 90hp Solar turboshaft engine consumes around 8.5 gph, while the Flyboard with six small turbojets is more like 38-40gph.

Aside from the greater efficiency of propellers over pure jet exhaust, also consider that the XET has a single gas turbine engine, while the Flyboard has six much smaller gas turbine engines.

Gas turbines are more efficient when they are made larger, which is the primary reason that large twin engine airliners are pushing out four engine airliners for international travel. Far more efficient usage of fuel, now that the larger twins are getting ETOPS certification.

I know this post is a little old, but I happened to find this post while trying to find out what turbines Zapata uses. There seems to be a misperception of how helicopters fly/hover compared to how a turbine engines produce thrust.

Helicopters actually do NOT fly by thrusting/pushing air down, although that is, in part, a result of what is going on. Helicopters create LIFT via the profile of the rotor blades and the angle of attack which varies according to operator input (at least on the bigger boys). As I'm not a helicopter person, I don't know if tiny copters like the Mosquito can actually vary angle of attack, which makes the mechanism quite a bit more complicated.

If you look at a copter blade profile, it's generally the same as an airplane wing. The faster it spins (and therefore moves through the air), the more LIFT is generated, and eventually enough lift is generated to lift/propel the copter.

A turbine engine provides THRUST, and it is the THRUST that lifts/propels things like Zapata's board.

• "I don't know if tiny copters like the Mosquito can actually vary angle of attack" How else would it be controllable? – Bianfable Jul 25 at 13:32