Chris Kaiser wrote:
> I'd love to fly an airframe that could maintain 99 mph through a max-rate
> turn (how many G's is that at CL 1.5?) and only loose 20 ft of altitude!
> This really doesn't tie in with reality - in practice if you've got the
> height
> (and you ain't going fast if you're low) at least the first 2 turns are
> generally
> split-S'd to maintain speed. This uses up a lot more than 20 ft!
>
Your right on this one and I take back my 20 ft. My error came in extrapolating
CD data at the 600K RN. With the correct drag data, you would loose 70 ft of
altitude.
> I know Joe Wurts has done some calculations and found the best turn
> rate is that which corresponds to max L/D, which I suspect is not at a
> CL of 1.5...
I have read Joe's Senior Project, from up here at Cal Poly, which generated this
theory and I have to disagree. In Joe's report, he uses a starting altitude
before the dive of 500 feet. This means he started out with the constraint of
being altitude limited. Thus you are trying to fly an efficient course. You
stated that you've seen altitudes of 1000ft off of launch. I agree with you on
this and it is definitely possible. So we are starting at twice the altitude of
Joe example, which means you have altitude to burn!
For an RG 15, with about 5 degrees of flap and an RN of 600K, has a max 2D L/D
at a CL of 0.5. This corresponds to a turn duration of about 1.5 second and an
altitude loss of 50 feet (for constant speed). A 0.75 second turn takes a CL of
1 and an altitude loss of 70 feet. So you lose 20 feet more per turn but save
0.75 seconds per turn or 2.25 seconds for the entire course. If you flew a max
2d l/d turn and managed to pull off a 14.07 second speed run you would need to
fly about a 2.5 second leg or 200 feet per second speed. I've flown my share of
speed runs and witnessed quite a bit more and I don't recall seeing any 2.5
second legs even on 14 sec. speed runs. I have scene a fair share of 3.5 second
legs which correspond to a near max CL. In addition, if I can save 2.25 seconds
in the turns and I have the altitude to spare, I don't see the question here:-)
> I'd be real surprised if a model could get to 14 second pace with
> a dive of only 210 ft. You really need to figure drag into this calculation.
> There's also the pull-up into the course to account for.
>
I agree completely with you. This was just a quick estimate. Yes it would take
more than 210 feet. 300 to 400 would be more accurate. In any case you are
burning altitude like it was going out of style.
>
>
> > simulation I ran was a best guess with what I have so there are
> > no guarantees, but it is definitely a lot better than my good friend
> > Mr. Roe's voyage into trigonometry. :-) Anyone care to comment?
>
> I think I have :-)
And you comments were appreciated.
>
> Well, gotta go and put it all into practice. Heading away tomorrow
> for two days of F3B competition. Next time I get to read my email
> there'll be a new (or recrowned...?) World Champ!
Glad to see that F3B exists outside the World Champs. Here in the US, you never
would guess that it does.
>
> Wishing I was at the Worlds... Chris
>
Don't we all.
Thomas Akers
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