Best Angle of Climb | What is Vx | Induced Drag vs Parasite Drag

How do we ensure we can clear obstacles off the runway on takeoff? We need the greatest amount of force to allow us to have our best angle of climb, which means we'll gain the most altitude travelling a certain horizontal distance. The aircraft has a speed which will allow us to reach our best angle of climb, and we call it Vx.
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[@jakeh86]

Hands down the best educational aviation resource on KZbin. Thank you.

[@adamconrad1540]

Once again, you explain it better than anyone else. Thank you. It was supremely helpful to understand thrust AND that the total drag curve is adding the two thrusts together.

[@thebadgerpilot]

I no longer watch your videos to learn the basics. I recently decided I want to be a CFI, and your channel gives phenomenal examples of how to break down complex issues to understandable terms. Keep up the great work! I plan on keeping your explanations in my back pocket for the future.

[@shimonfriedman1797]

Literally just had an ATP question on this material today. Thank you.

[@MicahMesser]

Wonderful explanation. Thanks for taking the time to explain these concepts in great detail, it is helping me towards my advanced ground instruction exam I will be taking soon.

[@avfan967]

You do amazing work both in explanation of physic principles and graphical representation. Well done…again!

[@ErickTakada]

Couldn't have a better explanation.

[@741al6]

First time I've seen Vx explained in detail, thanks!

[@sonoftherepublic9792]

Thanks much for explaining the math and physics behind the numbers. Your videos make potentially complex issues easy to understand.

[@nazimhm7780]

Your work is amazing, please keep the videos flowing ! thank you

[@raccoonair]

Perfect, great graphics; thanks for posting.

[@SelinRollan]

This is fantastic. Would love to see something similar on Vy

[@slimgoodman]

Always enjoy learning even if I already know it lol. Making sure it sticks

[@noochification]

Love the explanation! Having made charts like this many times, I might use this to teach some of my co-workers. One small comment, and maybe you just made this to semi-simplify, but induced drag is not the lift vector pointing backwards. I like to think of it as the amount of work you have to do to push the air down to create lift. A bit hard to explain in a comment, but would be very interested in working with you if you wanted to make a video about it.

[@vhscampos1]

Impressive! Thanks for the video

[@simonbussey7530]

Wow your videos are excellent!

[@bluecow10]

Great video as always!

[@jakew9887]

Great Presentation. Thanks

[@utah20gflyer76]

I just recently watched a vlog from social flight where they talked about the risks associated with flying at low altitude while at Vx. It was very thought provoking. To sum it up at low altitude if your engine quits while you are at Vx you are screwed. Best case scenario you walk away from a totaled airplane. Very likely though a worse result. You all ought to watch it.

[@XPLAlN]

Well, I think you have been somewhat misled. The airworthiness requirements, at least those in Europe which are the exact same as the previous FAA part 23 that the vast majority of the GA fleet comply with, require that the plane can be safely landed without exceptional pilot skill if the engine quits. This includes from a max performance take off. The grey area is that Vx can be less than the recommended 50’ speed for a max performance TO. For most airplanes, the recommended Vx (as distinct from the theoretical Vx resulting from excess thrust available) seems to be not less than the 50 ‘ speed. However it is not an explicit requirement. The bottom line is that anytime the Vx specified in the POH is at or above the recommended 50’ speed for a max performance take off, the plane has been shown capable of a safe landing. Therefore I think it is a stretch to say you are screwed if the engine quits at Vx. In general you are not screwed, but you’d better be ready to get the nose down pdq.

[@utah20gflyer76]

@@XPLAlN Maybe but you may want to watch the vlog and consider what they say. All things considered it seems like a Vx climb at low altitude is not a safe practice. Just because the government has bought off on it doesn't make it safe defacto. They can have errors in judgement just like everyone else.

[@cobra646]

Vx is a tool to use to accomplish a certain goal, ie clear a tree line or other obstacle. If you are hanging off the prop at Vx longer than necessary you aren't showing good situational awareness or threat management

[@XPLAlN]

@@cobra646 Exactly right. Vx is there for when you need it, otherwise Vy is literally the best climb speed.

[@XPLAlN]

@@utah20gflyer76 I have seen the same debate more than once. For the avoidance of doubt, I personally use Vy whenever I can, and Vx rarely. But my point to you is that all certified GA singles have demonstrated that they can be landed safely at their recommended short field 50’ speed without exceptional pilot skill, as it has been a requirement since at least 1949. I am not saying that they can all be flared to a safe landing from Vx, since that has never been an explicit requirement. But anytime the Vx is equal or greater than the recommended 50’ speed it follows that the airplane has demonstrated it can be landed safely from that speed. One such airplane is the C-172 and another is the PA-28. Together they make up a sizeable chunk of the GA fleet. So it is not a case of what government believe to be safe in theory, it is a case of performance that has been physically demonstrated by test pilots with skin in the game.

[@ubermenschen3636]

A variable pitch propeller should be able to make Vx = Vg.

[@talreichert]

Something here is rather odd. Lift is always perpendicular to the relative wind and drag is parallel to it. I'm not sure how come in some of the schematics that is not the case (e.g. 2:18 and 4:25).

[@omarijoseph3189]

yeah i always wanted to know what is a good VS to use..at first is was using 3400fpm...but now i use 2000 fpm..

[@XPLAlN]

Hmm. Sorry mate but as good as these videos are I feel the need to be picky here. The lift vector is always normal to the relative airflow (flight path) and the drag vector is always tangential to relative airflow, by definition. There is never a component of the lift vector that contributes to drag. What I am saying is it is wrong to think of the induced drag as the ‘tilting back of the lift vector’. At least, it is wrong by the conventions in use for principles of flight. It is correct to say that drag can be thought of as the rearward component of total reaction though. But not of lift.

[@flightinsight9111]

I've heard this too. Though it makes sense and I've taught it this way, in the end I deferred to the PHAK p.5-8 where it's described that "...the downwash over the top of the airfoil has the same effect as bending the lift vector rearward, therefore the lift is slightly aft of perpendicular to the relative wind." I'll ask my aero students in class next week they know more than I do about this!

[@XPLAlN]

@@flightinsight9111 Thanks for the reply and reference. I see what you are saying and had a look at the PHAK. I understand what they are getting at wrt the downwash changing the relative airflow locally. And now I go looking for it this tilting of the lift vector is not an uncommon way to explain induced drag as you did. But although it is an explanation of how the airflow around each section is modified, a common reference is needed for the airplane performance and the only common reference is freestream. For instance, without using the flight path as RAF, your load factor would cease to become lift divided by weight and your glide ratio would cease to be L/D. But if you define the lift vector normal to the flight path, those things fall right into your lap. According to Aerodynamics for Naval Aviators: “the instantaneous flight path determines the relative wind”. And yet it also makes reference to section lift being inclined aft by the “induced angle of attack”. However, it explicitly states that “the lift and drag must continue to be referred perpendicular and parallel to the remote free stream”. That is my point too. However, I concede that this tilting of the lift vector is a perfectly acceptable way of explaining induced drag. Still, to my mind, when labelling the lift vector of the whole airplane, as opposed to a wing section, the lift vector should be perpendicular to the flight path. Anyway, your videos are probably the best on YT dealing with this stuff and I hope that the above is fair comment.