Commercial/Multi-Engine Review

Limitation(Seminole)

V speeds

Vso: 55 kts - Low end speed of white arc

Vmc: 56 kts - Red line 

Vs: 57 kts - Low end of green arc

Vsse: 82 kts - Safe intentional one-engine inoperative speed, manufacturer designated

Vxse: 82 kts 

Vx: 82 kts

Vyse: 88 kts - best vertical performance, not always positive, blue line

Vle: 130 kts - Max speed with landing gear extended

Vfe: 111 kts - High end of white arc

Va:  135 kts(3800 lbs), 112 kts(2700 lbs) - Max maneuvering speed

Vno: 169 kts - Max structural cruising speed, high end of green arc

Vne: 202 kts - Never exceed, red line


Vr: 75 kts - Not less than Vmc*1.05, must allow acceleration to V2 at 35' at end of runway

Vlof: 75-77 kts - At least Vmc + 5 kts

V1: Decision Speed - Engine failure below V1 shall abort takeoff, above V1 shall be continued

V2: Takeoff Safety Speed - Approximately Vxse speed, should be maintained until 1000' AGL unless specified otherwise 

Vfs: Final Segment Climb Speed - Best one-engine inoperative rate of climb speed, clean configuration, thrust reduced to MCT(Maximum Continuous) 

Net Take-off Flight Path (NTOFP) For Engine Failure: 4 segments


Weight

Max Ramp Weight: 3816

Max Takeoff Weight: 3800

Max Landing: 3800

Max Baggage: 200

Max Zero Fuel:N/A

Engine

2700 rpm

180 HP

Full Throttle(MP)

Max CHT: 500 

Min CHT: 200 

POH recommends CHT: 350 - 435

Max Oil Temp: 245 

115 PSI(Oil Pressure), 25 PSI minimum

Propeller

74'' Max

72'' Min

Fuel 

Total: 110 Gallon

Usable:108

Unusable: 2 

Minimum Grade: 100, 100LL

Oil 

Max: 8 qts

Minimum(UND): 6 qts

Minimum safe(POH): 2 qts

POH Recommend: 4-8 qts

Electrical

Alternator: Max load on ground: 60 amps, Max in air: 65 amps

Main Battery: 25-32 Volts

Emergency Battery: 20-32V, Minimum for flight: 23.3V

Flight Load

Positive: 3.8G(Flaps up)

Positive: 2.0G(Flaps down)

Negative: -1.5G 


Acronyms

Critical Engine Concept:

PAST
P-factor: Yaw
A-Accelerated Slipstream: Roll
S-Spiraling Slipstream: Yaw  *Only when the right engine fails
T-Torque: Roll 

P-factor Yaw
Descending blades, typically with a higher angle of attack, produce more lift. 
Left engine critical in conventional twins because the right engine has a longer torque arm.
No engine critical in counter-rotating twins. Both torque arms the same length.
             

A-Accelerated Slipstream: Roll
Results from P-factor, higher angle of attack blades produce more prop wash. 
Left engine critical in conventional twins. 
No engine critical in counter-rotating twins.


Spiraling Slipstream: yaw
Slipstream hitting the vertical stabilizer.
In conventional twins:
Left engine prop wash will counteract asymmetrical thrust from right engine failure. 
Right engine prop wash will not do anything.
Left engine critical because left engine failure consequence is more severe, due to no counteract thurst from the left engine. 
In counter-rotating twins:
Both engines help to counteract asymmetrical thrust in an event of engine failure, thus no critical engine in counter-rotating twins. 
 

T-Torque: Roll
Opposite and equal reaction to every action. Newton's Law Law of motion. 
In conventional twins:
Each engine rolls the plane to the left by torque. However, a right engine failure causes the plane to roll right due to accelerated slipstream; a left engine failure causes the plane to roll left more. Thus, the left engine is critical.
In counter-rotating twins:
No engine is critical. Both can offset the accelerated slipstream. 


VMC may not exceed 1.13 Vsr(Reference Stall Speed) provided-
MULTTIOPS
Max Take-off Power
increase Vmc, increase performance

Unfavorable weight(Lighter)_CG
increase Vmc, increase performance

Landing gear up
increase Vmc, increase performance

Take off flaps(Seminole, 0 degrees)
increase Vmc, increase performance

Take off trim
increase Vmc, increase performance

Into operative engine(bank)
decrease Vmc, decrease performance

Out of ground effect
increase Vmc, decrease performance

Prop windmilling
increase Vmc, decrease performance

Standard atmosphere
density altitude decrease:
increase Vmc, increase performance
if density altitude increase:
decrease Vmc, decrease performance

Vmca limitation: 14 CFR § 25.149 paragraph d

-Rudder force must smaller than 150 lbs
-Can't reduce power on operating engine
-Airplane must not assume a dangerous attitude to recover
-Heading change must within 20 degrees without expceptional piloting skill

Engine Failure Steps - 4 Cs:

Control: Vyse, bank towards operative
Configuration: Gear, Flaps, Props
Climb: Airspeed>82 kts
Checklist

3 Control Methods:

Wings Level Method
- Wings held level with ailerons
- Ball centered
Result: sideslip towards inoperative

Aileron Only Method:
- 8-10 degrees of bank
Result: sideslip towards operative

Zero Slip Method:
- bank 2-3 degrees
- inclinometer displaced 1/3 to 1/2
Result: zero sideslip, best rate of climb or least rate of descent if maintaining Vyse

Control vs. Performance

Perfect control(Performance will decrease):
-Pitch Vyse
-Bank 5 degrees towards operative engine

Maximum performance:
- Pitch Vyse
- Establish zero sideslip

Loss of control indications:

- Rudder limit reached
- Aileron limit reached
- Uncontrollable yaw
- First indication of stall


Weight&Balance Jargon

MRTW - Max runway takeoff weight
WETW - Max En Route takeoff weight
MLDW - Max landing weight

System

Differential and Frise Compensates adverse yaw differently:

















Seminole Aileron: Differential Frise 
23 degree up, 17 degree down

Stabilator, anti-servo tab, Elevator down spring(Prevent deep stall), T-tail

Wingspan 38' 6.6'', Semi-tappered

Lycoming O-360-A1H6(Left engine), LO-360-A1H6(Right engine), 4 Cylinders, Aircooled, Naturally aspirated, 180 Brake horsepower, 2700 max rpm.

Prop Forward: Speeder spring tension increase -> Flyweights fall in -> Lowering pilot valve -> Oil goes into the prop hub-> Low pitch - fine pitch - blade angle decrease - high rpm -> Fly weights return to equalibrium -> Raise pilot valve -> Oil flow from oil sump to prop hub stops -> Rpm remain high

Prop Rearward: High pitch - small blade angle - course pitch - low rpm - feather 

Feathering time:
Without accumulator: 6s
With accumulator: 10-17s 

Unfeathering accumulator:
Contain nitrogen and oil pressure(90-100psi)
Assist in unfeathering the propeller without undue stress to start

Seminole POH Section 7 Description/Operation

Basic airframe: aluminum alloy, steel engine mounts, landing gear, fiberglass extremities. 
Fuselage: Semi-monocoque structure. 
Wing: Semi-tapered, with modified laminar flow NACA airfoil section. Spar ends into spar box, located under rear seat. 

Hydraulics
Landing Gear: Hydraulic pressured, electrically powered, reversible hydraulic pump.  Extension:6-8 seconds.
0.020-inch diameter bleed hole









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