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Leave 5 on the glide
28th May 2008, 17:21
Guys and girls - having just looked at an RTOW chart, I can't quite work out the relationship between the increasing temperature and the V-speeds. For a given RTOW chart and wind condition, can anyone shed some light on the relationship between the temperature and the V-speeds please?

Thanks very much in anticipation,

l5otg

The Real Slim Shady
28th May 2008, 17:35
Without giving you the answer on a plate.......what happens to the air when the temperature rises ?

When the temperature rises and the air " changes " what effect will that have on the engine thrust, lift, TAS and for a given weight the IAS required to generate enough lift to support the weight?

Cl*Half *rho*Vsquared*S??????

Got the answer?

Leave 5 on the glide
28th May 2008, 20:43
The Real Slim Shady - what your saying is that when temperature rises, density decreases, as does your thrust and lift. As far as TAS/IAS goes, as your density decreases your TAS is higher for a given IAS. Correct so far?

According to the sample RTOW chart (A319 w/ IAE2522s) given in the Airbus "Getting to Grips with Aircraft Performance" brochure, for a given wind component:

- V1 decreases with increasing temperature upto the thrust break temperature, where it increases slightly and then decreases again.

- VR behaves in the same way as V1.

- V2 continually decreases as temperature increases.


Can anyone explain this?

Cheers,

l5otg

eckhard
29th May 2008, 20:04
Not familiar with the style of the RTOW chart, but is it maybe a runway and flap-specific one where the temperature increases up the page and the wind component goes across the page? Then for an increase in temperature, the RTOW would decrease, leading to the decrease of V speeds that you mention.

Leave 5 on the glide
29th May 2008, 22:22
eckhard - thanks for the reply. Your exactly right; the RTOW chart is runway / A/c config. (flaps, anit-ice, air-cond. etc.) specific, with wind across the top and tmeperature increasing downward.

It makes sense that when the temperature increases, the RTOW decreases, and so the V-speeds decrease; but the increase and then decrease of the V-speeds around the thrust break temperature is the one I can't quite work out - any ideas?

Cheers,

l5otg

Pugilistic Animus
30th May 2008, 01:55
actually a loaded question due to the many many possibilities---i.e V1, Vr or V2 could be referenced to different fundemental speeds like Vmu, Vs1, Vmc[g,a] as well as other possible factors explained very well by many on this forum---but in reality unless you do the figures yourself it's all guesses and speculations---

PA