The Effects of a Propeller on an Aircraft - Definitive Guide

[@LetsGoAviate]

When to 3-point and when the Wheel land Your Taildragger : kzbin.info/www/bejne/ambGgqucgJJmg68 Understand Airplane Propellers : kzbin.info/www/bejne/nqfFoJxsrJaNb6M Short Takeoff Theory : kzbin.info/www/bejne/l3vHYqt7oseKhbc

[@selwild2050]

Impressive work, thank you.

[@davefoord1259]

Number 2 effect is not shown by the tip path of the prop on that kittihawk. Youre seeing where the prop was at an earlier time. Not a spiraling dlipstream

[@lauriejones3198]

Absolutely right. Much better described than by myself. Cheers. Ps, it worries me that this falacy is in nearly all the pilot theory study books.

[@davefoord1259]

Im thinking that it is a thing as it explains what happens at the top of a stall turn where airspeed is zeeo

[@excellenceinanimation960]

Thank you! your videos are amasing and really helping me an a lot of people!!

[@LetsGoAviate]

Thanks, glad to hear that!

[@txkflier]

Excellent video. Thanks..

[@situbes.972]

Awesome explanation with visual aid!!

[@vib4895]

Thank you sooo much! I love your videos. The animations are great, finally I got this topic and it stuck in my memory. Thanks a lot!

[@gerardoestevao1368]

amazing job!

[@farid7968]

Hi LetsGo Aviate! a billion of billion thanks to you! i dont know if you realize how you are helping people out! i still haven t enrolled to a ppl course but i bought a serious book (same as the one in aviation school ) i am learning by myself every single point (page) before going to school so i will have a good understanding of concepts and wording. But yesterday i got stuck with all these effects ( did not integrated the precession of a top ) . the book does not go into deeper explanation in physics (too bad cause i love maths and physics and cinetics) but then i bumped by accident into your videos .OH MAN I LOVE IT. i do "fucking" understand all these effects very very very well now thanks to YOU. i can sleep well now, yesterday i did not. god bless you brother! Farid :-))

[@FormerFlyer51]

A 70 years old aeodynamics textbook explains the effect of the spiralling slipstream differently (not due to hitting the vertical tail): It sees also the slipstream as a gyro (not only the propeller) which is deflected downwards by the wing's downwash. A clockwise propeller's slipstream is then deflected (turned) clockwise seen from above and the airplane anti-clockwise (action-reaction). Hope I got it right. This explains why multi-engine airplanes yaw even though there's no vertical tail hit by any slipstream. It also explains why I experienced strong left yaw in a turbine C206 standing (!) at the take-off position and why the yaw varied with flap deflection. While P-factor undoubtedly exists (in forward motion) quantifying and telling apart the two effects seems hard. Unfortunately, the book does not go any further into this.

[@the_phaistos_disk_solution]

Fascinating.

[@akbarshoed]

Sir, Question about upcoming video... if it's not too late... would you explain the relationship between thrust and engine power. Sizing our propeller for our chosen applications, especially electric. 😮

[@Rancho-Relaxo]

I built and still fly my 180 HP RV4 after 25 years. The most significant left of runway heading excursion, happens when attempting to bring the tail up too quickly, particularly with a rear seat passenger. As described here, better to pick up speed and raise the tail slowly 👍

[@blackbelt2000]

So do counter rotating props eliminate all these left turning tendencies?

[@LetsGoAviate]

They do yes

[@lauriejones3198]

The spiralling slipstream is completely false. Yes, the tracking of the prop tips DESCRIBE a spiral, however the thrust is moving essentially straight rearwards. It is easy to get proof of this. Do a google image search of Red Bull air race action shots. These aircraft have smoke systems in operation during the events. Smoke is generated by injecting smoke oil into the hot exhaust. The echaust outlet is obviously aft of the prop and completely within the influence of the propellor slipstream. In no image will you see the smoke doing even one spiral completely around the fuselage. It's a bit like everyone assuming a given point on a rolling tire makes a circular motion relative to the road as it driven along. But no. A given point starting at the bottom, for example, is momentarily stationary before it rises, prescribes a half circle accellerating over the top only to come to a halt again at the bottom. The tire as a whole rotates but every given point does nothing of the sort relative to the road surface. The spiralling slipstream is an old fallacy probably born from the first observations of prop tip vorticies. If the slipstream made all those trips around the fuselage there would be no energy left for thrust. Accordingly the airspeed of the thrust would have to be incredibly high. Many many times higher than the aircraft airspeed. It is time this error was removed from pilot study theory books. Cheers

[@davefoord1259]

Good call laurie. I have to agree with you. Flying line astern formation also demonstrates this. Flying echellon and about 1/2 a wingspan out, you get a very strong roll into the lead from the aircraft wake though, and you can clearly see that vortex in smoke

[@davefoord1259]

But at the top of a hammerhead, whats that left yaw? I suspect its slipstream spiralling, at the much lower forward speed

[@lauriejones3198]

@@davefoord1259 if truly vertical its the normal torque effect dominating once airflow over the controls is lost. If not quite vertical its good old P effect. It's for these reasons that aerobatic aircraft normally have a preferred direction of yaw at the top of the stall turn (hammerhead). Some types will happilly go one way, but trying the other way is difficult and/or requires much earlier rudder input before all the non-slipstream airflow is lost. Depends on the type and direction of prop rotation, power available etc.

[@lauriejones3198]

And in formation flying it is absolutely critical to be able to understand, visualise and be ready for the effects of wake and wingtip vortices from other aircraft.

[@davefoord1259]

@@lauriejones3198 its not torque right at the top, thats trying to roll you not yaw you. Aileron position is a good guide to the right time to kick the rudder. and its not p factor as aoa is zero and prop is perpendicular to chord line. I think it is slipstream at that point

[@davefoord1259]

Please make a video explaining why an aircraft that is yawed to the left, but in steady direction flight, with left rudder and right aileron will stall left wing first when aoa is increased to critical angle of attack. You cant say its because the left wing is flying slower. The right wing has the hugher aoa due to dihedral but the ailerons are deflected so that both wings gave the same total lift generated roll moment. And then if you think youve explained it correctly, consider that a plane with zero dihedral still departs to the left even though there is no dihedral effect, I cant answer this and ive challenged every explanation ive seen by youtubers and flight instructors and everyone has conceded their explanation doesnt stand up to scrutiny. Maybe you can explain it as your explanations i find are very good.

[@andytamlyn]

When yawed to the left, but as you say maintaining a steady direction flight - so if I understand your question correctly, the aircraft is flying diagonally forward - ie the 'heading' (the direction the nose is pointing - is a bit left in your example) is different to the 'track' the direction of travel or path of the airplane through the air. The relative airflow is coming from the direction of travel, ie slightly side-on from the right of nose. Easy to visualise with a pen or pencil. So what you have is that the relative airflow to the left wing is being partially obscured by the body of the aircraft whereas the right wing isn't. So in this case the inner part of the left wing, the root and inboard portion of the wing obscured from the relative airflow isn't generating lift because there is no airflow over it, but further out towards the tip, the wing continues to generate lift as the fuselage isn't shielding the wing from the airflow this far out on the span. In contrast, the right wing has clear access to the oncoming relative airflow, so its generating lift across the full span. When AOA (alpha) is increased beyond the critical angle of attack, the tips (OK this is for swept wings) stall first. So in the case of the left wing it is generating no lift at all (its fully stalled), whereas the right wing is still generating lift inboard of the tip. So the right wing is generating lift and the left wing isn't. The resulting moment causes the aircraft to roll to the left.

[@Zilahi-Branyi_Laszlo]

Beyond what the previous wrote, the aoa is higher on the left wing at the area of the aileron due to its deflection, therefore that part of the wing will stall earlier. If there is dehidral so the right wing has higher aoa means aileron should be deflected more to counteract the rolling effect of the different aoa, so at the left wing's aileron aoa will be even higher.

[@davefoord1259]

@@andytamlyn so in my case this still does not hold up. If i yaw left with rudder the aircraft shows a slight roll right. This is a low symmetrical wing with no dihedral. ( this aircraft actually has downturned edges on the inboard edges of the aerobatic spades which are fine tuned to give slight left aileron to negate any coupling between yaw and roll, so in fact i have slight left aileron to hold level) Therefore the assumption that part of the inboard left wing isnt generating lift must be incorrect or there would be a left roll produced. The explanation of the aileron down deflection acting as incrreased angle of attack is also not really satisfactory. Aileron down is increasing the camber and therefore the lift coefficient, just like a down deflected flap should reduce the 1g stall speed as flaps always do at moderate deflections Also per the spades design explanation, there is slight left aileron Further, the tips dont stall first. Its a straight wing and specifically designed with the aft surfaces being dead flat in both directions, as many aerobatic aircraft are, which is done so that the whole wing stalls at the same AOA. The stall when it comes is sudden and very complete. Unless there is yaw, it doesnt tend to drop one wing either upright or inverted Nevertheless my aircraft still departs left. Can you further explain

[@lucab166]

We obviously can't deny the left-turning tendency, but I've always had a problem with P-Factor. It confuses me that we do not apply gyroscopic precession here. Obviously, the downgoing blade creates more lift than the upgoing one. However, this should be considered as a torque on the propeller, and the resulting motion, therefore, must be 90 degrees later, shouldn't it?

[@davefoord1259]

Interesting point.

[@davefoord1259]

Heres my take on that. Every action has an equal and opposite reaction. So if you have a free gyro, sure push on it and it moves as if youve pushed it at a point 90 degrees in the direction of rotation. The gyro feels really rigid to you where youre pushing it. I know this as i repair gyro instruments. However this breaks down if you get gimbal lock on the 90 degree axis and all of a sudden there seems to be no more rigidity whatsoever. Its a really weird sensation, but it is whats commonly referred to as toppling in aircraft gyro instruments or sometimes called gimbal lock An aeroplane makes the prop a non free gyro to some extent. So while there are gyroscopic forces generated its not anything like a free gyro So if you have a high angle between the relative airflow and the crankshaft axis i would expect that the downgoing blade would tend to pull the aircraft forward more than the upgoing blade. In a clockwise from pilots view rotation, ie lycoming/continental/rotax id expect this would also give you some pitch up moment. For a gypsy/russian radial it should also be pitch up. So in my low wing plane, a sudden application of power at a low airspeed should get some pitch up but this would be countered by the prop shaft being above the centre of gravity. It might be different if i do the same from slow inverted flight. Maybe ill give that a try

[@Zilahi-Branyi_Laszlo]

For me it not so obvious that the downgoing blade creates more lift: yes, its cord makes a larger angle with the plane perpendicular to the airflow, but at the same time it goes forward into the airflow means basically it is in a faster stream than the upgoing blade and faster airflow cause less aoa for a same pitched blade rotating with the same speed. In fact the same thing cause the blade's higher pitch angle and its forward movement and if you think about its geometry they should cancel each other.

[@Zilahi-Branyi_Laszlo]

OK. I almost instantly realized that the only false statement is downgoing blade has higher aoa. It has the same as the upgoing blade, because as bigger its angle to the plane perpendicular to the airflow is as faster its forward speed is. But as the downgoing blade goes faster to the airflow it creates more lift despite the same aoa.

[@saurabhsingh7465]

I don't get when wooden props are able to provide thrust enough without breaking

[@davefoord1259]

Perhaps you can explain the effect of the prop that causes left yaw at the top of a hammerhead aerobatic manoeuvre. Its not torque, that would give you roll Its not p factor as aoa is zero Its not gyro as pitch rate is zero So its either spiralling slipstream or something else

[@marcingardyjan6680]

Please create a video telling why planes with wings lifted to up are more stable.

[@Zilahi-Branyi_Laszlo]

Which is more stable: if you try to lift up something by grab at the top and pull, or if you push on the bottom and try to keep it balanced? If you do these by touching the object at a single point, the answer is obvious and although the lift of a plane is a spreaded force, that's just makes the effect less noticable, but not eliminate it.

[@pjccwest]

🙂