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  • bosh-777
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bosh-777 created the topic: Questions

An increase in Density Altitude what effect does it have on the Vtoss

- a higher TAS but lower IAS
- a higher TAS but same IAS
- the same TAS but lower IAS
- the same TAS but the same IAS
- higher TAS and higher IAS
#1

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bobtait replied the topic: Re: Questions

Vtoss is a fixed IAS which is simply a function of the power-off stalling speed in the take-off configuration. So once it is published it doesn't change, it remains the same regardless of the ambient density. An increase in density altitude means that the ambient air is less dense - same effect as an increase in height. To get the same IAS in the less dense air, a higher TAS will be required.

The second statement is correct.
#2

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Richard replied the topic: Re: Questions

Hi Bosh,

First off, think about what Vtoss is: Take-off safety speed is an indicated airspeed that:

"shall be established for each flap setting for which take-off distance information is to be provided. The take-off safety speed shall be an airspeed not less than 1.2 Vs and at which adequate control is available in the event of a sudden and complete engine failure during the climb following take-off. [CAO 1.1.4.6.6.2]"

Next, consider what effect air density has on the relationship between indicated airspeed (IAS) and true airspeed (TAS). While flying at a constant IAS, your TAS will be higher if you are flying in a higher density altitude compared to your TAS when flying in a lower density altitude.

So, what effect will an increased density altitude have on your Vtoss? Well Vtoss is an indicated airspeed and is declared in the flight manual. When you reach this IAS however, your actual TAS will have increased if you increase the density altitude.

So, your second option is the answer: Higher TAS for the same IAS.

Cheers,

Rich
#3

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Richard replied the topic: Re: Questions

Hehehehe...Bob beat me to it :laugh:
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bobtait replied the topic: Re: Questions

Great minds think alike Rich!!
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  • bosh-777
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bosh-777 replied the topic: Re: Questions

Thanks heaps for that. :) really appreciate your help
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  • bosh-777
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bosh-777 replied the topic: Re: Questions

1. A Echo is loaded at Take Off so that the CoG is loaded on the forward limit of the permitted range.
If fuel is being burnt from the AUX tanks what effect will it have on the CoG?

- if fuel is being burnt from the AUX tanks then the CoG moves forwards because of where the AUX tanks are located. But i had a questions stating if it will move forward and remain in the envelop, or move forward and outside the envelop.


2. In flight which situation is most likely to exceed limit load factors?

- low IAS in severe Turbulence
- IAS above Vne in smooth air
- steep level turn at low IAS
- High IAS in severe turbulence

I went for IAS above Vne in smooth air as i though it is the worst case, anything exceeding this speed is bound for damage.


3. echo 2550KG total moment index 610, whats the minimum that bust be added

-140
-55
-65
-85
#7

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bobtait replied the topic: Re: Questions

Answer to 1. above. The centre of gravity will move forward, but it will stay in the envelope because the forward limit also moves forward, and it moves forward faster than the centre of gravity does. Try it out on the envelope. Pick a point right on the forward limit and then subtract 200kg from the auxiliary tanks. See what happens.


High IAS above VNE will not impose high load factors i.e. 'g' loads. It will impose high shearing loads that may cause structural failure - especially of the tailplane or elevator. I would go for high IAS in severe turbulence. Updrafts in severe turbulence cause sudden large angle of attack increases which produce high load factors.

Answer for 3. above. You cannot use the flow chart to solve a forward limit problem when you are adding weight. Add 100kg to the rear and plot a new point. Join the two points and see where the line crosses the envelope. I reckon it's about 85kg.
#8

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  • bosh-777
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bosh-777 replied the topic: Re: Questions

Thank you so much. I don't know where id be without your help and your questions thank you so much, hope i haven't been a pain in this forum..
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bobtait replied the topic: Re: Questions

You'll never be a pain mate. We all remember what it was like when we started out in aviation. There are no stupid questions.
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