# Could an airplane takeoff with a very strong tailwind if its propeller blades are set to a negative pitch? [closed]

Would it be possible for an airplane to accelerate and takeoff with a very strong tailwind if its propeller blades are set to a negative pitch?

For example, let's say that a hurricane was approaching an airport in Florida and it had sustained winds of 100 mph and those winds were blowing in parallel with the runway. If an airplane with variable pitch propeller blades was sitting on this runway and the wind was blowing against the airplane as a tailwind, if the pilot were to set the propeller blades to full negative pitch (reverse thrust) and were to then throttle the engine up to full power, would this airplane accelerate very quickly down the runway due to the propelling force that would be generated by a 100 mph tailwind colliding with negative pitch propeller blades?

I believe the airplane would very quickly accelerate from 0 to 60 mph, and once at this speed the pilot could set the propeller blades back to the full positive pitch position, continue to accelerate up to takeoff speed and then takeoff.

I'm not a pilot nor an aeronautical expert, but I believe this kind of takeoff could be possible, at least theoretically.

## closed as unclear what you're asking by Ralph J, Jamiec♦Dec 24 '18 at 19:13

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Pilots do not take off with a tailwind. They would taxi to the other end of the runway, and takeoff with a headwind. – abelenky Dec 23 '18 at 18:13
• According to flightdeckfriend.com/ask-a-captain/aircraft-maximum-wind-limits, the maximum wind speed (Boeing 737) for taxing is 65 knots, and for opening doors the max is 45 knots, so you would never get to that situation. – Eugene Styer Dec 23 '18 at 18:22
• @ abelenky, I understand that pilots always want to take off into a headwind, my question was based on what may be theoretically possible. – HRIATEXP Dec 23 '18 at 19:00
• What makes you think that reverse thrust would be helpful in any way? – Tanner Swett Dec 23 '18 at 19:02
• @ Tanner Swett, well, I'm basically thinking that the negative pitch blades/reverse thrust, would resist the airflow of the 100 mph tailwind and the blades would thus act as a parachute which (theoretically) will pull the airplane down the runway, accelerating it and helping to reach a speed needed for takeoff. – HRIATEXP Dec 23 '18 at 19:31

The all important factor in setting prop pitch is angle of attack to relative wind. The question does have merit as it raises the thought (in this obviously extreme case) of where to set it at 0 mph ground speed and -100 (that's minus) mph airspeed. It is possible that it would be set "finer" than 0mph airspeed.

However, to roll the plane forward, the prop will still be at a positive angle of attack to the relative wind. So, let's compare prop speed to wind speed. A 5 foot prop rotating at 2500 rpm will have a tip speed of: 5 foot x pi/rev x 2500 rev/minute x 1 mile/5280 feet x 60 minutes/hour = around 430 miles/hour.

So theoreticly, there would be slightly less prop pitch with -100mph airspeed (tailwind) at 0 mph groundspeed; and the tailwind would accelerate the plane from 0 mph groundspeed faster, but only up to the point where airspeed = 0 (groundspeed = 100 mph).

Once airspeed was in positive numbers, prop pitch would be as normal for takeoff. So some good thinking there about prop pitch and relative wind, but In reality, attempting this would be extremely dangerous.

• @ Robert DiGiovanni, I would up vote your post if I could but I can't since I'm a new contributor. – HRIATEXP Dec 24 '18 at 0:34

Situation: tail wind, reverse thrust, open throtle.

So what you are doing is moving backward with reverse thrust in tailwind. You are not moving forward.

What you want to achieve when take off is sufficient air speed over the wing. When you have tailwind you need faster forward ground speed in order to reach that sufficient airspeed for taking off. You need more power from your engine in whatever pitch that create forward thrust and allows you to move forward, not the reverse one.

So, likely, you plane will accelerate slowly backward and you may get lucky to takeoff from the tail and flip over and burst in flame. The solution when you have 100 mph wind blowing on the ground: run.

• @ vasin1987, would it make any difference if the pilot was to only throttle the engine up to say 50% engine power? shouldn't the negative pitch propeller blades offer some resistance to the 100 mph tallwind at a particular RPM? – HRIATEXP Dec 23 '18 at 18:58
• No. You don’t takeoff backward so negative pitch doesn’t make sense. You takeoff forward so if your calm wind takeoff speed is 130 mph now you need 230 mph to takeoff. That’s likely exceed your tire speed. You can lower the tailwind and it still would not make sense to try takeoff with negative pitch. – vasin1987 Dec 23 '18 at 19:02
• @ vasin1987, the airplane will takeoff going forward... it will be going forward because the tailwind will be pushing against the propeller blades which will thus push the airplane down the runway and once it reaches 130mph it should take off as designed. Basically, imagine if you hooked up a parachute to the nose of the airplane and the parachute would then pull the airplane down the runway due to the tailwind. – HRIATEXP Dec 23 '18 at 19:40
• Then why don’t you just add a parachute, idle engine and let the plane flies :) btw reverse engine will add drag which works against forward movement. Might not be what you want. – vasin1987 Dec 23 '18 at 19:43
• @HRIATEXP: What you apparently don't realize is that a tailwind will never accelerate a plane to more than the speed of the wind. So the relative wind over the wing will be zero, producing no lift. With engines in reverse thrust, the tailwind accelerates the plane to less than the speed of the wind. – jamesqf Dec 24 '18 at 5:54

No it could not (short answer).

Long answer - if an airplane (e.g. BE200 King Air, etc.) was sitting in hurricane force tailwinds with the power levers moved to beta/reverse range, all this would do is create thrust in the opposite direction that it was designed to fly in. It may generate more reverse thrust as more air is forced through the propeller disks than at low forward speeds. Note as well that beta and reverse power lever positions do not increase the engine power output to its maximum flat rate value, which, while useful in slowing the aircraft during landing ground roll, hamstrings its ability to takeoff.

An airplane like a King Air has a liftoff speed around 100 KIAS. To obtain this airspeed in 100-115 mph tailwinds would require a ground speed of 190-200 knots. Typically, accounting for wheel friction and ground covered during acceleration, this typically requires an increase in ground roll of around 10% for every 2 knots of tailwind over an airport surface*. In this situation, a 100 mph (88 kt) tailwind would increase the ground roll by approximately 440%. This means if the airplane has a ground roll of 1,800 feet in still air, it now needs 9,720 ft to obtain Vr in! Unless you’re departing from at airport with a VERY long runway eg KLAX, KATL, ETC, the airplane will never get airborne, overrun the departure end and impact terrain at a very high speed with a high risk of total destruction and loss of life.

Lifting off from a heavy tailwind is also impossible as the airplane is not structurally nor dynamically stable to fly with a relative wind from behind. It would quickly depart from controlled flight shortly after liftoff and impact terrain. End result is not good here, either. And even if you could, in theory get it to fly in these conditions, you now face the challenge of reversing this condition for forward flight.

Bottom line is, if you were to attempt a takeoff in 100 mph winds (and this, too, is extremely dangerous), you would be advised to taxi to the opposite end of the runway and just attempt a headwind takeoff. The airplane could become airborne very quickly here with a minimum of risk.

*Illustrative purposes only; do not attempt to use for flight operations without consulting manufacturer approved performance tables for airplane in question.

After reexamining my hypothesis which I had drawn out on a piece of paper, I realize now that an airplane with a strong tailwind could not be accelerated by that tailwind with the propeller blades in a full negative pitch position. I realize that with this configuration the negative pitched blades would just create a lot of drag rather than creating additional forward thrust for the airplane.

Sorry for the confusion on my part. I recommend that this thread be closed.

• Don’t be discourage. People can misunderstand things sometime. Your courage to ask clarify your misunderstanding this time. Keep explore and ask question when in doubt. – vasin1987 Dec 24 '18 at 2:05