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Date: Mon, 13 Dec 2004 14:26:54 -0500
From: "canarder@frontiernet.net" <canarder@frontiernet.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Glide distances
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<... best range ... higher speed than best glid ...>
Meant to say "... higher speed than lowest sink rate ..."
Sorry 'bout that ... Jim S.


Quoting "canarder@frontiernet.net" <canarder@frontiernet.net>:

> Actually, it can get complicated with airplanes that common, nominal
> winds amount to 1/3 of glide speed.  Lowest sink rate is NOT best
> range
> glide.  Matter of fact, best range occurs at a measureably higher
> speed
> than best glide.
>
> Best glide speed put out in POH by designer (Vans, Cozy, etc.)is a
> good
> point of departure, but you DO have to depart from there.  If you're
> gliding downwind (in say a 20 kt or > tailwind), you want to be at
> the
> speed that gives you lowest sink rate so as to maximize the
> opportunity
> of the wind to blow you farther downwind.  OTOH, if you're stuck
> gliding
> upwind, if you use best glide range speed (or worse yet, lowest sink
> rate), you'll be pretty much "hovering" and not going much of
> anywhere
> at all.  This can all be quantified, but I don't think any of the
> designers have done it very extensively.
>
> My plan is to use take the recommended best range glide speed put out
> by
> the designer and declare it best no-wind range at that weight - Vo.
> I
> then carefully measure my sink rate at that IAS from maybe 10,000 msl
> to something like 1000-1500 agl (where I can comfortably relight, and
> failing that comfortably dead stick the rest of the way).  Next, I
> repeat the exercise at 5 and 10 (or 5, 7, 9, etc.)kt slower IAS until
> I
> find the lowest sink rate.  With those two airspeeds, I have the no
> wind
> (Vo) and tail wind (Vo-10) glide speeds and can determine the upwind
> best glide airspeed with reasonable accuracy for our purposes by
> declaring it to be Vo+10.  Delta-V can be as much as 10 kt IAS.  Then
> I
> check my sink rate at Vo+10).  I now test again and record sink rates
> at
> Vo+10.
>
> Armed with these numbers and always being acutely aware of the
> difference between my GPS GS and my cruise TAS, I'll have a pretty
> good
> idea of whether I'm dealing with a headwind or tailwind the minute
> the
> engine quits, and can quickly decide whether to go at or 5 or 10 kts
> slower or faster than optimum no wind IAS to wherever I have chosen
> to
> set it down.  With the readily available E6B programs available, and
> knowing your sink rate at optimum glide ground speed (GSo), GSo-10
> and
> GSp+10 you can do some reasonably accurate calculations and tablualte
> some ranges on a spread sheet.
>
> I think it's a safe bet most of us will be more or less astounded by
> the
> difference in range.  Like spittin' distance from double for 30 kt
> headwind v. 30 kt tailwind.
>
> Just a theory ... Jim S.
>
>
>
> Quoting Ed Anderson <eanderson@carolina.rr.com>:
>
> > On my 12 mile engine out glide, I punched up the NRST button on my
> > GPS to find the two closest airfields were both 12 miles away
> > (gulp!).  Since I knew I was going to be gliding around 85 mph that
> > any sort of headwind would considerably shorten the glide.
> > Fortunately I had been paying attention to the wind direction as I
> > was outrunning a cold front, so turned 120 degs for the downwind
> > field.
> >
> >   From 9500 MSL I arrived over the selected airfield with approx
> > 1500-2000 ft AGL.  I had altitude to do a 360 and a couple of hard
> > "S" turns to loose altitude and even then came over the fence at
> 100
> > mph.  This with a stubby wing RV-6A.
> >
> > I did have time in that 8 minute glide to find out that my best
> glide
> > speed (at that weight)  was 87 MPH which produced a 750 fpm rate of
> > descent.  Any slower the rate went up and any faster the rate went
> > up.  Also were I found what airspeeds the prop would stop at as
> well
> > as what it took to get it going again.  So a rather productive 8
> > minutes all things considered {:>).
> >
> > Ed Anderson
> >   ----- Original Message -----
> >   From: Perry Mick
> >   To: Rotary motors in aircraft
> >   Sent: Monday, December 13, 2004 9:29 AM
> >   Subject: [FlyRotary] Re: Glide distances
> >
> >
> >   That's true, if you are flying cross country, and are halfway
> > between two airports, you would want to pick the one that's
> downwind,
> > not necessarily the closest field.
> >   I figure with 1nm per 1000' of altitude, just orbiting the field
> on
> > a test flight, there is plenty of margin built in since I can
> > supposedly glide about 1.65 nm / 1000' with no wind.
> >
> >   Tom wrote:
> >
> > Perry,
> > There always something.  Gotta remember winds.  Being downwind of
> the
> > airport
> > at the distance limit would be a problem.
> >
> > By the way, when flying skydivers I figured out a very easy way to
> > determine
> > winds aloft with a GPS.  Fly a circle keeping your airspeed
> constant.
> >  Your GPS
> > groundspeed will be highest when heading downwind and lowest when
> > heading
> > upwind.  Do the simple math on speeds to determine how much.  I'm
> not
> > suggesting you do this during engine-out, just when you're curious
> > and have a
> > desire to fly in circles.
> >
> > Tom
> >
> > --- Perry Mick <pjmick@viclink.com> wrote:
> >   I've never tested engine out glide, but I also plan with 1000
> > ft/min.
> > And if you assume a 10:1 glide ratio, you can glide 10,000 fpm, or
> > 1.65
> > nm or 1.9 sm per 1000 ft. of altitude. When I do test flights, I
> try
> > to
> > stay within 1 nm of the airport for each 1000 ft of AGL. For
> example,
> > 5000 ft AGL, stay within a 5 nm radius. Easy with GPS.
> >
> >
> >
> >
> >
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> >
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> >
> >
> >
> >
>
>
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