2949775330

Comparison of Liąuid Propellant Rocket Engine Feed Systems - 1 - 16

3.7. Materials

It is necessary to dispose both the density and the ma\imum tensile strengh, of the materials employed to manufacture all tanks and the gas generator. For this purpose. the table 6 is presented, where also the oversizing factors chosen for the analysis were included:

Table 3: Proposed materials for the feed Systems manufacturing
Component	Materiał	Density \|kg/mi	UTS IMPal	Oversizing factor
Gas tank	Kcvlar	1700	3300	2.5
Oxidazer tank	Aluminium Alloy	2800	455	2.5
Fueltank	Aluminium Alloy	2800	455	2.5
Gas generator	Hastelloy C	8890	524 (1033K)	2.5
Gas generator	CRES 347	7960	180(1090K)	2.5

Clearly, although there are many other materials options available, they were discarded because both, the materiał itself or the tank manufacturing methods, are quite expensive. From the two options available for the gas generator manufacturing, one may conclude that being not an element that limits the turbo-pumps total mass, whatever be the materiał adoption it will not have major influence. Therefore, all the graphics were madę adopting “Hastelloy C” alloy as the gas generator materiał.

3.7. Motor, Inverter and Batteries

As was mentioned in the introduction brushless DC electric motors are employed. Two merit figures of these motors are relevant for the comparison: the power density and the efficiency. Next, a table with some data examples of these motors is presented:

Table 4: Candidates DC-Brushless Motors
Model	Nominał Power rwi	Power Density IW/kgl	Efficiency	Speed [rpm]	Reference
AXi4120/14	865	2700	85%	29000	ii2i
AXi5320/18	1600	3300	93%	16000	\|121
Hacker A60-14L	2100	2800	-	7100	[15]
Prcdator 37	15000	7890	-	5900	1161
Predator 30	12500	7100	88%	5600	\|161
Himax HC 5030-390	1500	3800		12000	_USL
Hyperion ZS4045-10	3000	4800		10800	IHl
Yuneec Power Drive 60	60000(¹)	2000	92%	2400	_[201_

The power density of an electric motor decreases with power and efficiency but increases with speed. The typical specific mass vs. speed curves for electric motors are depicted below: