# How should I answer this question about measuring airspeed using dynamic pressure?

I have come across a question in the PPL Principle of Flight material which I can't understand how to answer:

Give your opinion on the statement "Measuring dynamic pressure is the way to determine the indicated airspeed of an aircraft".

• Welcome to aviation.SE. You say that you don't understand how to answer that. The question looks like it is coming from a test or similar, so I would expect that you have some material on which you studied to prepare to such a test. In order to answer you, could you let us know what is unclear to you in the material you studied on?
– Federico
Feb 11 '19 at 15:19
• @Federico I think i might have to explain how dynamic pressure works to show IAS at the ASI through the Pitot tube. Then i guess my question would be how does the pitot tube help show IAS and also of the static port is involved. Feb 11 '19 at 15:46
• Welcome to aviation.SE! I edited your question to make it a little clearer but if I got it wrong please edit again or roll back my changes. It looks like you might have translated the question from another language; it might be useful to know which country you're in and see the question in the original language. If you're new to StackExchange, the tour might be helpful. Feb 14 '19 at 2:46

## 2 Answers

You're confused! Great! Confusion is just an opportunity to learn.

In the spirit of education, I won't answer your question, but I will give you some things to consider.

• "Give your argument on the statement" - This usually means you're being asked to support or refute whatever comes next. It will be up to you to decide which is appropriate.
• Measuring dynamic pressure - What is dynamic pressure? Are there other kinds of pressure? Is there something else besides pressure that could be measured instead?
• is - Is it or is it not?
• the way to - the only way? Are there other ways?
• determine the indicated airspeed - Is that what is determined? Is anything else determined? Is indicated airspeed the proper thing to determine or do you need something else?
• of an aircraft. - Is that correct?

If you can answer all of those, you should have no problem putting them together into a solution. If you're having problems with a specific portion, let us know what's unclear.

• I think you missed the most important question of it – what is indicated speed in the first place. Feb 16 '19 at 9:39

This is a slightly more unusual essay question as they are usually multiple choice.

First define dynamic pressure. As its name implies, dynamic pressure is wind pressure as the result of movement of the aircraft. Pressure is measured in units of force (lbf) per area (square inch). How do we measure indicated airspeed with dynamic pressure?

V squared is proportional to dynamic pressure. V = square root of Pdyn

Other types of Pressure? Static pressure, which is dependent on altitude and weather conditions.

Other ways to measure indicated airspeed? How about a tiny windmill attached to a DC generator and measure voltage vs speed. Another way would be to take a pressure transducer (like they have on pocket scales) and place it on a retractable holder (like a nose wheel) to provide a backup airspeed reading in an emergency.

• How do you propose to measure indicated airspeed using GPS? Feb 14 '19 at 9:53
• You would have to add in headwind or subtract tailwind. Might not be as safe. Feb 14 '19 at 15:56
• Let me phrase it differently (it was a rhetorical question): I think they will and should fail you on a PPL test if you mention GPS in the context of indicated airspeed... Feb 14 '19 at 16:02
• Absolutely agree. Appreciate the edit. Feb 14 '19 at 19:24