Comment by ahartmetz | Hacker News Reader

Comment by ahartmetz | Hacker News Reader

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I don't think it's completely true. Higher weight increases the speed at which the glide ratio is optimal, and drag (parasitic drag in particular, unrelated to generating lift) increases with the square of speed. Basically, flying faster wastes more energy. That effect is going to dominate at some point, probably about 120 km/h or so with a typical glider. At 200 km/h, the glide ratio is garbage (but it's fun). I have flown gliders.

I'm not sure if simple descriptions of the phenomenon that glide ratio is independent of weight are missing an asterisk or if I'm just wrong...

A decent glider has a ratio of 1:40, an A320 1:17. Is the A320 a "bad plane" or is it optimized for higher speed with the corresponding worse glide ratio? (It also has engines that produce a lot of drag when gliding)

I don't know. On one hand there's your take.

On another hand, there are CFIs, the FAA, books, etc.

I've only found one search result that agrees with you, so far, and at least a dozen that disagree, but the one that agrees with you has no math in it, and the ones that disagree mostly seem to depend on the same source info, so that doesn't feel conclusive in either direction.

The Wikipedia page on lift-to-drag ratio also believes weight does not matter to the ratio.

As a side note, your 200km/h example also sounds like it's just not the correct angle of attack or airspeed for the aircraft, so I'm not sure if that example applies?

As a separate reply, I'll add that I think finding where/if this breaks is pretty academic.

Eg: you wouldn't build a glider out of heavy material that gives you huge speeds but also huge sink rates.

So I think the entire glide ratio conversation mostly fits in the "your plane is fully loaded" vs "your plane is empty" scenario, and the point is that your best glide ratio will be constant, but you'll be gliding at higher speeds if you have more weight.

Gliders utilize Laminar profiles, while airliners use turbulent profiles.

The Laminar profiles perform better, but only when uncontaminated (no bugs or rain). Contaminated turbulent profiles perform better than contaminated Laminar profiles. Since regulations state that you should carry fuel for the worst case scenario, it does not yet make sense to design airliners with Laminar profiles.

Naturally, manufacturers are looking for ways around this.

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