# What are these points in the Propeller Schematic?

If it matters, this is taken from EASA PPL questions.

The graphic appears to be taken from the side point of view, although I've never seen such a round Spinner, unless it's a variable pitch propeller and it's just the ball bearing joint the blade is attached to.

So far my guess is that the points correspond to the following:

1. Angle of Incidence (confirmed)
2. Geometric wing twist (not sure)
3. Angle of Attack (90% sure)
4. Aerodynamic wing twist (not sure)
• C: is Chord line
• D: is Direction of air flow (I think it refers to the Relative Airflow)
• R: is Direction of rotation (I guess clockwise in this case)

2,3,4 could be any of the following "Geometric wing twist", "Angle of Attack" and "Aerodynamic wing twist"

New contributor
GANoob4eva is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
• Do you have any more context, or is the question simple "label these points"? Because that would be a really crummy question... Aug 6 at 2:02
• The gray circle is indeed the joint to which the propeller is attached. The spinner is not shown in this figure. Aug 6 at 5:24
• If my below explanation answers your question, please mark it so. Many thanks! yesterday

## 2 Answers

Like in your last question, you are asking us to label a figure which you have taken from the Aircademy Ltd. PPL question catalog.

In this case, the figure is from Part-FCL Question Bank 80 – Aircraft General Knowledge, Question 65:

So the one label you have been able to "confirm" is the one already marked out in the question catalog.

What you are looking for to label the remaining points is a propeller blade section velocity diagram. A simple one is provided in Figure 5-44 of the excellent FAA Control Flying Handbook, FAA-H-8083-5. More advanced ones are provided in scientific publications, such as Figure 7 in "An Overview of Model Tests and Numerical Predictions for Propeller-Ice Interaction"

Velocity diagram for a propeller blade section, $$\beta$$ is the angle of advance, $$\beta_i$$ is the hydrodynamic pitch angle, $$\phi$$ is the geometric pitch angle, $$\alpha_G$$ is the geometric angle of attack, $$V$$ is the carriage speed, $$V_A$$ is the advance speed, and $$U_A$$ are the tangential and axial induced velocities, and $$P$$ is the pitch at $$0.7R$$.

In short:

point label
1 blade pitch (=angle of incidence)
3 angle of attack (angle between relative wind and chord line)

4 and 2 are velocities which are not mentioned in the main course materials and would not be relevant for the exam.

As a general recommendation, I suggest you purchase the training material (textbooks) by Aircademy Ltd., since you are clearly preparing for your exam using their question catalogs. The expense will be inconsequential compared to the rest of your training cost - but it would enable you to look up these figures without having to resort to StackExchange multiple times.

• Thanks, do you know if the learning materials come in English too? 18 hours ago

None of these are "twist."

If the length R represents the speed of the propeller, then 2 is the "adjacent" side of a triangle, allowing you to calculate the length of D using the Pythagorean formula.

4 represents the forward airspeed of the aircraft in proportion to R, which allows you to calculate 3, the angle of attack.

• "None of these are "twist." Agreed, but they are now, as this is how the questions were translated. 17 hours ago