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Marat Kulakhmetov.  AS8 AS8.

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Presentation on theme: "Marat Kulakhmetov.  AS8 AS8."— Presentation transcript:

1 Marat Kulakhmetov

2  AS8 AS8

3  Did some rockets tumble?  Did some rockets wobble?  Did some rockets flip over?  Maybe some rockets were unstable

4  l6w l6w

5  Stability refers to how likely an object will return to its initial position or orientation if it is disturbed ◦ Stable – Object returns to initial position ◦ Neutrally Stable – Object does not move ◦ Unstable – Object continues moving away from its initial position

6  Moment describe the object’s tendency to rotate ◦ Moment = Force * Perpendicular Distance  In the example above, the moments generated by the two weights generate 20 N*m and -20 N*m. They are balanced  Moments are usually calculated about their center of gravity (CG)  Unbalanced moments on a rocket will cause the rocket to tumble.

7  Location where the forces will balance  CG = Moment / Total Weight  Example: ◦ Moment = 10 * (0) + 20 * 3 = 60 N * m ◦ Total Weight = = 30 N ◦ CG = Moment / Total Weight = 60 / 30 = 2 m X = 0X = 2 X=3

8 Beer, Russell, Johnston, DeWolf Mechanics of Materials

9 PartLength (cm) Weight (g) Nose Cone510 Parachute sys. 35 Recovery Wadding 11 Launch Lug 32 Engine Mount 515 Rocket Engine 530 Fins53 Rocket Body 1540 X =

10 PartCentroid Formula Distance To Centroid MassMoment Nose Conh/3 =1.675/3 = Parachuteh/2 = = Recovery Wadding h/2= = Launch Lugh/2= = Engine Mount h/2 = =

11 X = PartCentroid Formula Distance To Centroid MassMoment From Above Rocket Engine h/2 = = Rocket Bodyh/2= Total

12 X =  Moment =  Mass = 103  CG = Moment / Mass  = /103 = cm

13  Break it up into a triangle, rectangle and triangle  Area 1 = ½ *b1 * h = 5  Area 2 = b2 * h =5  Area 3 = ½ * b3 * h=5  Total Area = Area 1 + Area 2 + Area 3 = 15  Mass1 = Total Mass * Area 1 / Total Area = 1  Mass2 = Total Mass * Area 2 / Total Area =1  Mass3 = Total Mass * Area 3 / Total Area = B1=2B2=1 B3=2 H=5

14  Part 1 is a triangle  Centroid 1 = b1/3 =.66  Part 2 is a rectangle  Centroid 2 = b2/2 = 0.5  Part 3 is a triangle  Centroid 3 = b3/2 = b1b2 b3 h  Moment Fin = Mass1 * (b1 – Centroid 1) + Mass2 * ( b1 + Centroid 2)  + Mass3 * ( b1 + b2 + Centroid 3)= 7.5  CG Fin = Moment Fin / Total Fin Mass =2.5

15 X =  Moment with fins = (2.5+14)*3  Mass =  CG = Moment / Mass =11.34 cm

16  If : ◦ Rocket has no fins ◦ Thrust is aligned ◦ Rocket pitched a little  Moment = -1*Lift * x  This rocket will keep pitching and fly out of control y x X

17  Little DragLots of Drag

18  If : ◦ Thrust is aligned ◦ Rocket turned a little  Moment = -1* Lift *x + Fin * x1  If Fin * x1 > Lift * x, the rocket will right itself X Fin Force X1

19  Fin force = ◦ Larger Area = More force provided by fins ◦ Larger Velocity = More Force provided by fins  Fin Moment = Fin Force * Distance ◦ Larger Force = Larger Moment ◦ Larger Distance = Larger Moments  For stability, we want large fins as far away from CG as possible.  If fins are too large they create more drag

20  Calculating aerodynamic center will require Computational Fluid Dynamic (CFD) analysis.  We will estimate that the aerodynamic center is at Fin centroid  We calculated that this is at 16.5cm X =

21  Nozzles push on high gasses and accelerate them out the back  In return, the gasses push on the nozzle and accelerates it forward

22  Air wants to go from high pressure to low pressure  Pressure Force ( P1 – P2) * A  Remember that Pressure = Force / Area High Pressure Low Pressure

23  Action-Reacting  If you throw something out one way it will push you the other way  If the rocket nozzle throws gases down, the gasses push the rocket up

24  It is usually easy to study gas flows using control volumes  Forces on the rocket could be calculated by only looking at control surfaces  F pressure =(P e - P a ) A e  Fgas = ρ U e 2 A e

25  Why did rockets filled with water go higher than those filled with just air? Ambient Pressure Constant Exit Pressure Constant Exit Velocity Assumed Constant Changes

26  Rockets usually use converging-diverging nozzles. These could also be called isentropic nozzles  The thrust through the C-D nozzle depends on chamber pressure, ambient pressure, and nozzle shape

27  Upstream of the nozzle, in the combustion chamber, the gas velocity is small  All fluids (water, air, etc.) accelerate through a converging section  The fastest they could get in the converging section is Mach 1

28  If the gases reached Mach 1 in converging section then they will continue accelerating in the diverging section  If the gasses did not reach Mach 1 in the converging section then they will decelerate in the diverging section  This is why our water bottle rockets only had converging section

29  Lets Calculate Rocket Thrust and acceleration  A = F/m = 3050 / 0.5 = 6100 m/s^2 Ambient Conditions: Pa = 101,000 Pa Exit Conditions: Pe = 150,000 Pa Ve = 100 m/s Density = 1.2 kg/m3 Area = 0.05 m^2 Mass = 0.5 kg

30  Pressurized Air ◦ Balloon  Solid Propellant  Liquid Propellant  Nuclear  Electric

31  ISP is used to classify how well a rocket performs  Low ISP = need a lot of fuel to achieve thrust  High ISP =do not need as much fuel to achieve same thrust

32  Propellant is initially in the solid state and it becomes a hot gas during combustion  Pros: ◦ Simple ◦ Cheap ◦ Easy to store ◦ Can be launched quickly  Cons: ◦ ISP only ◦ Cannot turn off after ignition ◦ Cannot throttle during flight

33  Fuel and Oxidizer are both stored separately in liquid form  Pros: ◦ Better performance (ISP )  Cons: ◦ More complex ◦ Requires pumps or pressurized gas tanks ◦ Heavier

34  Nuclear Reactor heats working gas that is accelerated through a nozzle  Pros: ◦ Isp  Cons: ◦ Requires shielding, can be heavy ◦ It’s a NUKE

35  Two types: ◦ Arcjet: Electricity is used to superheat the gases ◦ Ion Thrusters: ionized (charged) atoms are accelerated through an electro-magnetic field  Pros: ◦ ISP ,000  Cons: ◦ Thrust usually <1N  VASMIR


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