Talk:Mass ratio

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Omitting aircraft stuff from intro

I've never seen a mass ratio used to describe an aircraft, and the inclusion of aircraft in the intro paragraph makes it unnecessarily vague and confusing. If you can cite a use of a mass ratio in the context of an aircraft that's not a rocket, please feel free to re-add the deleted material. --Doradus 03:22, 13 August 2007 (UTC)[reply]

Questions

I've got a couple of questions. They may just be silly questions but bear with me.

You mention that this is a "back-of-the-envelope" calculation: Does this mean it's an approximation (and if so, how good?) or just that it's easy?

It's not clear to me whether this equation takes into account the fact that as you're travelling and using fuel, the wet mass of the rocket will change. Is this under the approximation that the mass is constant, and it's kind of an average velocity? (This may not be relevant here but I thought I'd ask anyway)

Also from what I gather the Tsiolkovsky rocket equation is used in stages. Is the mass ratio also calculated in stages?

One suggestion I have is maybe defining $\Delta v$ early on for the less technically inclined reader (ie, ... the change in velocity, $\Delta v$ ...). Also you've left off a 'v' in math tag in the current last sentence.

This is a well written article btw. Kudos Doradus --JT 02:35, 17 August 2007 (UTC)[reply]

Table Is Completely Wrong

The mass ratios in the table do not count all of the dry mass of the rockets. Is there some reason for that? For Ariane and Space Shuttle, the emtpy mass of the solid boosters is not counted, but their propellant mass is. That is giving wildly exagerated mass ratios. I believe the mass ratio for Ariane is about 7.8, not 39. DonPMitchell (talk) 03:46, 30 July 2010 (UTC)[reply]

I think the table has confused mass ratio and mass fraction. Mass ratio doesn't just use the emtpy mass that reaches the destination, it refers to the ratio that appears in Tsiolkovsky's formula, the total wet mass over total dry mass. DonPMitchell (talk) 06:08, 30 July 2010 (UTC)[reply]

Yep, this is the table from the payload fraction article. Someone misunderstood the concept of mass ratio when they copied that table here. DonPMitchell (talk) 14:00, 31 July 2010 (UTC)[reply]