**8.1 UMGT advantages**

The main advantage of these systems compared to the existing large scale devices resides in the highest power density. Although such systems have an overall efficiency still lower, the produced power for weight unit is the higher than which will be produced by the battery systems. In fact, at the moment, the battery package power density is about 100-150 Wh/kg. Even if an increase of the power density can be presupposed, the power developed by a UMGT is, undoubtedly, higher for weight and volume unit. Also with a lower efficiency the UMGTs have a power density that is, at least, equivalent to that theoretically produced by a lithium battery package It will be noticed, then, as in the field of the same micro turbines, there is a difference, in terms of performances, according to the used fuel: for instance, the combustion of the hydrogen, in fact, concurs to remarkably raise the value of the power density regarding the obtainable result with fuel like propane or kerosene. An ulterior advantage is the operating flexibility that offers such systems: while the battery package, once exhausted theirs energetic potential, need of a period, more or less long, to recharge them, the micro turbines allow the fuel change in a very short period.

### **8.2 UMGT disadvantages**

The main disadvantage, respect fuel cells or the battery package, is the high operational temperature. In fact, to achieve an higher output power is necessary to realize high TIT. Because of the small scale of the machine, this design constraint leads all the system to raise

Ultra Micro Gas Turbines 45

loading of batteries is possible too. At last, 1-5 kW could be used for feeding of exoskeleton :

The UMGT civil applications, as portable power generators, undoubtedly are limited, due to the high system temperature. In fact, in this case the exhaust gas temperature is very high, and the customer safety is a primary objective in the design of the device and its utilization. However, some civil applications can be considered, as battery recharger for mobiles or for

The main application in this field resides in the so-called the MAV (micro aerial vehicles). Their main use is, once again, of military character. The power demanded by the group is lower because the considered vehicle mass is lower than 50 g with cruise speed between the 10 and 20 m/s: in the cruise regime the shaft demanded power is about 2.5 kW, while this doubles during the phase of takeoff and manoeuvres. Due to the high heat exchange during the flight and the low required power, there are not problems regarding the infrared emissions. Such systems have already been used in the Balkans, Afghanistan and Iraq

An unmanned aerial vehicle (UAV) is a machine which functions either by the remote control of a navigator or pilot or autonomously, that is, as a self-directing entity. Their largest use is within military applications. To distinguish UAVs from missiles, a UAV is defined as a powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or non lethal payload". UAVs typically divided in six functional categories (although multi-role airframe platforms are becoming more prevalent):

• Target and decoy – providing ground and aerial gunnery a target that simulates an

• Combat – providing attack capability for high-risk missions (see Unmanned combat air

• Research and development – used to further develop UAV technologies to be integrated

• Civil and Commercial UAVs – UAVs specifically designed for civil and commercial

They can also be categorized in terms of range/altitude and the following has been

• Logistics – UAVs specifically designed for cargo and logistics operation

advanced as relevant at such industry events as Unmanned Systems forum:

these are robotic devices that allow to reduce the payload that weighs on the soldier.

wireless tools. Also as micro cogeneration unit at small scale.

**8.3.1.2 Civil applications** 

during missions of strategic character.

enemy aircraft or missile

into field deployed UAV aircraft

• Handheld 600 m altitude, about 2 km range • Close 1,500 m altitude, up to 10 km range • NATO type 3,000 m altitude, up to 50 km range

vehicle)

applications

• Reconnaissance – providing battlefield intelligence

**8.3.3 Drones and UAV** 

**8.3.2 MAV** 

own average temperature: this produces high infrared radiation emissions, that, especially in military applications, cannot be tolerated. A similar problem is found in the fuel cells in which, a lower value of the operational average temperature is reached. That infrared emissions is not the only problem for the UMGT. The high outlet temperatures of the exhaust gas, can produce problems during the operational life of the machine. To obviate to such disadvantage a regenerator, even built-in would have to be installed inside the device, to cooling the UMGT components using Peltier effect.
