CRJ Flex Temp - Takeoff Roll

[downwindabeam]

Hello,

Wondering if anyone has the performance tables or maybe a single airport analysis page of a CRJ-200 page?

I'm trying to figure out if it's a true to say that when reducing the thrust with flex temp and then increasing the V1, Vr correspondingly according to bombardier the airplane rotates at exactly the same point as it would taking off with full thrust in terms of percentage used of the runway model used (0kts->Vlof->Abborted TO Stopping point)?

If anyone has a copy of the performance tables of a CRJ-200, I'd greatly appreciate taking a peek at those.

Unfortunately my company is cheap and keeps a single copy at headquarters and we ofcourse don't get to see but bits of it when they deem it necessary.

Thanks!

-downwindabeam

[barit1]

It will help if you read the FAA Advisory Circular (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/4b385bb9e4e9c4da862569d00076acf7/$FILE/AC25-13.pdf) on reduced thrust ops, particularly what it says about V1, Vr, Vmc etc. - and note that rated thrust be available anytime the crew elects it.

[Mad (Flt) Scientist]

I'm trying to figure out if it's a true to say that when reducing the thrust with flex temp and then increasing the V1, Vr correspondingly according to bombardier the airplane rotates at exactly the same point as it would taking off with full thrust in terms of percentage used of the runway model used (0kts->Vlof->Abborted TO Stopping point)?


Don't have such tables to hand, but it would seem to be impossible to conduct a takeoff with reduced thrust and get to a faster Vr at the same point on the runway. With less thrust, and hence less acceleration, you'll be further down the runway at the same speed.

Unless there's something sneaky in the way the calcs are accounted for...?

[downwindabeam]

Mad flt:

I agree with you. Longer takeoff roll in footage/meters (whichever one you use) - but same point in percentage.

I'm thinking that if a given runway can support a given weight, we'll call that 100% then devide that pie to a blue (run section) and a red (stop section).

Let's assume (just making up numbers here) it's 75% blue and 25% red. I'm asking whether that airplane no matter what thrust setting chosen will achieve Vlof at 75% each time.

At full rated thrust because of the point at which we reach the "true" Vr and subsequently Vlof. And at a FLEX thrust at the "synthetic" Vr and subsequently synthetic Vlof.

Hope that helps clearing my question.

[barit1]

It's the size of the pie that changes.

1) Consider your airplane taking off, rated thrust, at the max permissable OAT (eg 42C) for the weight, r/w length, pr alt, gradient, climb perf. etc. and that the accel to V1 is 75%, stop is 25%.

2) Now consider taking off on a std day, but setting Tflex (Tassumed) to 42C. As a first approximation, the accel/stop will still be 75/25%.

But in reality you'll reach V1 sooner because TAS (i.e. inertial speed) will be less at the lower OAT. Thus greater TO margin. :) That is, the pie is slightly smaller.

3) Now consider takeoff #2, but using rated thrust. You reach V1 in less time and distance, but the stopping distance is nearly unchanged. So the pie looks like (e.g.) 50% accel, 25% stop, 25% unused. Or, considering only the used portion of the runway (a smaller pie) then it's 67/33%.

Please don't take the numbers literally, but I hope this illustrates the point.