Ernie Twells' notebook



Ernie Twells' notebook


A notebook written by Ernie Twells comprising training notes, mostly physics and meteorology theory.





One notebook of 35 pages of handwritten notes

Conforms To


IBCC Digital Archive


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[underlined] F/O TWELLS [/underlined]
NAVAL No. S400
R.A.F. Form 619.
Notebook for use in Schools.
[page break]
[blank page]
[page break]
[underlined] Newtons 3 Laws [/underlined]
[underlined] 1 [/underlined] A force is that [deleted] wich [/deleted] witch [sic] changes or lends to change a [indecipherable word]
[underlined] 2 [/underlined] Rate of change of momentum is proportional to the impressed force
Momentum – WT x Velocity
Momentum given by a force = Force x Time of action
M = W x V
[underlined] 3 [/underlined] Motion and action are equal and opposite
Moment of a force about its point is its twining effect about that point and it is measured by the product:-
FORCE X PERP DIST of lines of action from the point
Work done – force x dist
[symbol] = 3 x 6 ft lbs
= 18 ft lbs
[underlined] Energy cap. for doing work
[page break]
Energy: Potential position
Kinetic – motion 1/2 mass x V2
[underlined] POWER [/underlined] Rate of doing work meas [sic] in ft lbs sec
[formulas] [symbol]
For N of [indecipherable word]
Work done = Force x Dist
[page break]
Work done =
[torque formula]
Power [torque formulas]
[underlined] AIR AND ATMOSPHERE [/underlined]
[page break]
[blank page]
[page break]
[underlined] AIR AND ATMOSPHERE [/underlined]
[underlined] Resource [/underlined] force/units area
[page break]
[underlined] ATMOSPHERE [/underlined] [formulas]
[underlined] Pressure Altitude [/underlined] To the altitude corresponding to any given pressure in the standard atmosphere.
[temperature differentiations]
[page break]
[underlined] MEC EQUIV OF HEAT [/underlined]
I B T U = 778 ft lbs.
[underlined] CALORIFIC VALUE 1lb 100 OCT = 19,000 P.T.U
I.T.E [formula]
B.T.E = [formula]
[page break]
[underlined] AIR FLOW OVER A BODY [/underlined]
[symbols] [formulas]
Force on a body in a relative air flow depends on the square of the Velocity the density of the air & the area or size of the body a constant depends on the shape
[underlined] AIRSPEED [/underlined]
[symbols] [formulas]
[page break]
In the indicator box there will only be pressure P
Different to pressure = K10 V2
Difference in pressure gives an expansion of capsule and this gives a reading on dial. in knots/MPH)
Force on aircraft = [formula]
Pressure pilot head = [formula]
Ratios = [formula]
Position error Error due to constant change of pressure around aircraft on through out [sic] speed of A/C position of pilot static head Speed of the aircraft altitude of aircraft
Static vent can be fitted were [deleted] no [/deleted] position error is most constant
Instrument [indecipherable word] due to manufacturing defects Found by calibration and must not exceed certain figures
Compressibility error [formula]
[page break]
Errors involved are [formulas]
[underlined] TRUE AIR SPEED [/underlined] (T A S or V)
RECTIFIED AIRSPEED (RAS) Position error [indecipherable word] error
EQUIVALENT AIRSOEED (V1) = IAS corrected for pos error instr error and compressibility error
A.S.I calibrated for comp error and with no posit on instr error I.A.S V1
At sea level V = V1
Any altitude [formula]
Aerodynamic force on a body = [formulas]
But K, A [symbol] are constants
Aerodynamic force = const x V,2
For a given V1 [deleted] on a body [/deleted] [inserted] aerodynamic force on a body is the same at any density
[page break]
[page break]
[pressure calculations at different altitudes]
[page break]
Bernoullis Theorem.
Energy of Position + Energy of Pressure –
Energy of Motion
Lift and drag of an aircraft depends on
[underlined] 1 [/underlined] Shape of airfoil and angle of attack
[underlined] 2 [/underlined] Plan area if airfoil (S)
[underlined] 3 [/underlined] Square if the velocity of airflow
4 Density of the air
[formulas] [diagram]
[page break]
[underlined] DRAG CURVE [/underlined]
[page break]
Drag Analis [sic]
Induced drag (Di) +
Parasite drag (Dp) = Total drag
(Then friction + form drag)
Induced drag varies in inverse prop [sic] to the square of the speed
Parasite drag varies in prop [sic] to the square of the speed
[Formula for Parasite Drag]
[Graph plotting induced drag]
[page break]
[Graph plotting parasite drag]
[Graph plotting total drag]
[Insert calculation]
Speed for minimum drag varies as the square root of the weight
[Formula for minimum drag]
[page break]
[inserted in top margin]Calculation[/inserted in top margin]
[Formula for minimum drag]
[Graph plotting minimum drag]
[Page break]
For a given weight and a constant [missing word] and given V1 the drag is constant at all heights
[underlined] Propellors [sic] [/underlined]
Def- Blade angle witch [sic] is the angle between chord of section and plane of rotation
[Diagram of propeller angle 1]
[Diagram of propeller angle 2]
Pitch of a prop [sic] [propeller] is the blade angle 2/3 from the center [sic] of the hub
[Diagram of propellor pitch]
[Page break]
Torque absorbs the power
Thrust gives the forward motion
Ratio for thrust to power absorbed is smaller nearer the hub
[Formulae exploring torque thrust power ratios at different speeds and revs per minute]
Page break]
[Formula for calculation of Thrust Horse power]
[Page break]
[underlined] POWERED FLIGHT [/underlined]
[Formulae for Power, Thrust Horse Power and Drag]
[Graph plotting variables of powered flight
[Page break]
[underlined] Power required for climbing] [/underlined]
[Formula for calculating power for climb]
[Formula for calculating rate of climb]
[line dividing page]
Power in the decent [sic]
[Calculation of power in descent]
[Page break]
[Graph plotting power for climbing]
[Page break]
Power to overcome
[Formula for Induced drag]
[Formula for Parasite drag}
[Graph plotting critical speed]
Supposing that speed is reduced [indecipherable word] from 120 to 100 without chance of power and without change of altitude from the curve can be seen that the power required to fly at 100 is greater than that to fly 120 [sic]. we [sic] can say therefor [sic] that if the aircraft is at all cap[capable] of flying at such low speeds than the reaching of the power curve
[Page break]
[inserted in top margin] numbers [/inserted in top margin]
to the left of the speed of minimum power is compleatly [sic] unstable for the aircraft at these speeds
If we are there for [sic] flying at 140 V. [sic] then a reduction in air speed due to a lump will provide a small excess of power at the lower speed. If we continue to fly level this excess power will tend to accelerate the aircraft back to 140 but the acceleration will be very slow and may take as long as 15 mins [minutes]
Compare rate of airspeed at a higher speed 170 and power and that a lump reduces the speed to 160 the excess power is very much greater and will show it self [sic] in ether [sic] of two ways. One the aircraft will quickly regain speed or two will climb at a noticeable rate of climb
The range of speed at wich [sic] the speed is sensitive to small variations of power is refered [sic] to as the thresh hold [sic] the speed in this range is said to be critical because it
[Page break]
Is not stable for the reason the recomended [sic] for range for an aircraft is some times [ sic] higher than the theory optimum
[underlined] Stability [/underlined]
A body is said to be stable if when there is a small changes [sic].[sic]
Forces are brought into play to return it to its original altitude
[Diagram demonstrating impact of changes on stability]
Zero tail left with slight increases of angle of allack [attack] a proportial [sic] increase of left on the lail [tail] plane will be greater than the increase on the main plane giving a [indecipherable word] affect [sic] from the tail plane to the C of G [sic] [indecipherable word] so restoring aircraft to original altitude
[Page break]
[underline] General Flying Principles [/underline]
[Page break]
[blank page]
[Page break]
[blank page]
[Page break]
[underlined] OBJECT [/underlined]
[underlined]1 [/underlined] To increase safe range of squadrons
[underlined] 2 [/underlined]To obtain reliable data for the caperbilities [sic] of crews and squadrons for use in flight planning.
[Underlined] Conversion Chart [/underlined] .. [sic] Flight Efficiency
Provides the means of [indecipherable word] A.M.P.G [sic] command range combined with and [indecipherable letters] covered [sic] in to [sic] an efficiency % [percentage] afore [sic] or below average. The average curve is constructed from data obtained from M.A.P [sic] [indecipherable word] test It is [indecipherable word] that AMPG [sic] 5% [five percent] below should be obtained from the [indecipherable word] aircraft of that type to allow for [indecipherable word] and [indecipherable word]
[Flight efficiency conversion chart]
AIR RANGE ( [sic] of these potential air Range [sic]
Transport Comand [sic] are required to operate to 75%
[Page break]
Hence any efficiency below average are poor.
[underlined] Cruising Procedure [/underlined]
[underlined] 1 [/underlined] Most ecconomical [sic] cruising condition denoted by the letter E in appropriate columns
[underlined] 2[/underlined] Flights at higher than recomended [sic] I.A.S [sic] denoted by letter F.
[underlined] 3 [/underlined] Flights flown to a schedule denoted by letter S
[underlined] 4[/underlined] Abnormal weather conditions denoted by letter A
Entered in Engineers [sic] Log Aircraft chart and monthly summary
[underlined] Squadron monthly flight efficiency Summary [/underline]
This is a summary to enable squadron to keep a permanent date of Flight Engineers logs Namely A.M.P.G ect [sic]
A copy of the summary are forwarded to Comand [sic] and Group HQ together with engineers logs Were [sic] a thorough analis [analysis] is made and a record of each squadron is kept.
[Page break]
[Blank page]




Ernie Twells, “Ernie Twells' notebook,” IBCC Digital Archive, accessed May 22, 2022,

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