From: Doug Jones (random@qnet.com)
Date: Mon May 01 2000 - 09:43:46 MDT
Spike Jones wrote:
>
> The reason Im having difficulties with Moller's aircar is a neat
> little estimating technique for the thrust required to maintain straight-
> and-level flight: you need to know the power-off glide ratio. If it is
> 10 forward to 1 down, then it takes a thrust of about 1/10 the weight
> of the aircraft to fly at the power-off glide speed.
>
> The Moller aircar looks like it would power-off glide like a set of
> car keys. What is that little airfoil way back aft for? Just to look
> cool? Glide ratio 10 down for every one forward?
Hey, even a skydiver can do about .8 forward for 1 down- it's fun!
> In any case, it looks
> like you would need to be making power at *almost* the vertical
> takeoff rate just to fly straight and level, and with the numbers they
> call out on the website, with those little tiny rotors, the straight and
> level power requirement looks like in the neighborhood of 800 hp.
> Recall that a typical modern Detroit mobile, ambling down the
> freeway at 100 kph only requires about 30 hp, if I may mix units.
>
> Nowthen, if we want to theorize a really high horizontal speed
> associated with that 800 hp, we are up against the drag-as-square-
> of-velocity problem, and so we still have a voracious fuel appetite.
> Perhaps Doug Jones will weigh in on this, hes more aerominded than
> I am.
>
> I am uncomfortable being in the nay-sayer position, dont like
> doing that. But the Moller aircar as shown on the website
> wont fly in that configuration. spike
I pretty much agree with you- the aspect ratio of their lifting surface
is abysmal, and the frontal area is huge, so they have high induced drag
AND high parasitic drag. This would make a MIG-15 look economical.
Cool idea, lousy product. Sigh.
BTW, we did a bunch of public rocket demos at the Space Access
conference in Scotsdale this weekend, impressing the folks who count.
That engine now has over 800 runs and 30 minutes of run time at main
stage... I plan to do a three minute long run tomorrow just because I
can :)
-- Doug Jones Rocket Plumber, XCOR Aerospace http://www.xcor-aerospace.com
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