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Effect of weight on radius of turn

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Jase88 created the topic: Effect of weight on radius of turn

Hi Bob and Co,

I'm having a bit of difficulty understanding how weight effects the radius and rate of a turn. I can see that in your book it explains that weight has absolutely no effect on Radius or Rate of turn. If weight increases then centripetal force needed increases also, if this is the case wouldn't it mean that you would have to increase power or angle of attack? And if you had to increase power wouldn't that increase airspeed and then your radius would be greater?

Thanks,

Jason
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  • John.Heddles
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John.Heddles replied the topic: Effect of weight on radius of turn

I can see that in your book it explains that weight has absolutely no effect on Radius or Rate of turn.

What this is saying is that weight doesn't come into the equations in isolation, or by itself, if you prefer. Weight is tied up with the lift force to give the load factor.

The useful, basic, equation is

tan (bank angle) = speed^2 / g x turn radius

As you can see, weight doesn't get a look in there at all. The radius of turn is tied up with bank angle and speed.

If weight increases then centripetal force needed increases also

That is to say, we need to increase the lift force. This, in turn, increases the centripetal force.

wouldn't it mean that you would have to increase power or angle of attack?

Increasing pitch is the easiest way to increase the lift force. This will increase drag and you will need more thrust grunt if you want to maintain the rest of the situation. Often/usually thrust will limit, quite severely, turn performance in a light aircraft.

Note that, for the fast jet fraternity, they do their high performance turns either

(a) with burner (just have a look at the tail when watching your next display flight)

for example - www.bing.com/videos/search?q=video+of+f1...B6165D6&&FORM=VDRVSR

(not great video but you can see the burner is on throughout the display. Notice, also, the wingtip smoke angles - this display spends a lot of time at quite high alpha or angle of attack. The display would be pretty lack lustre without burner to increase the thrust available to the pilot)

(b) a significant speed loss (a normal run and break uses a high bank angle with its associated drag, to wash off lots of speed as the aircraft turns crosswind while joining the downwind pattern)

for example - www.bing.com/videos/search?q=aircraft+fa...iew=detail&FORM=VIRE ,

(the break is in the first section of the video. No idea why the missed approaches but all good fun, I guess)

(c) or both.

if you had to increase power wouldn't that increase airspeed and then your radius would be greater?

The main need for a thrust increase is to balance the drag increase and, even then, it is a bit of a battle to maintain speed as the turn performance increases. Unless you back off the bank angle, or have heaps of thrust available, you are not likely to see any speed increase

Engineering specialist in aircraft performance and weight control.
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Jase88 replied the topic: Effect of weight on radius of turn

Hi John,

Thank you very much for the in depth response, i also enjoyed watching those jets.

This clears things up well.

Thanks again :)
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