REFLECTOR: Takeoff roll - fuel burn

Sat May 23 11:26:56 CDT 2009

Years ago I calculated the effective thrust at GNT on a 90 degree day.
in my STD RG.

Figuring loss of power for density altitude on the engine and prop, plus
loss of power for fixed pitch prop static RPM

I was down to less than 50%!!! of my theoretical 200HP, and my takeoff 
TAS  was  at least 10% higher also!  

I fly a turbo 210 all over the south west, and while density altitude
has less of an effect on it, we use at least twice the runway in the
summer as we do in the winter here at GNT.  We routinely fly near gross
weight and get somewhat lax about that in the winter, but come July I
get down right anal about how much I'm putting on board.  Its not
unusual for us to operate out of 8,000 ft elevation airports and the
density altitude can easily get above 11,000 ft.   You try that real
heavy and it can get really interesting!

Scott

lawrence epstein wrote:
> The effect of density altitude on a wing is the same, whether you are
> taking off or landing. The difference is the engine. Your engine will
> only develop 65% power @ full throttle @ 10000 ft density altitude.
> Therefore, @ higher density altitude, the degradation of takeoff
> performance will be of much greater magnitude than that of landing
> distance. (Unless you are flying behind(in front of) a
> turbo(normalized) engine. In which case the effect will be the same on
> takeoff and landing.)
>
> Larry Epstein
>
> > Date: Sat, 23 May 2009 07:19:16 -0600
> > From: scott at tnstaafl.net
> > To: reflector at tvbf.org
> > Subject: Re: REFLECTOR: Takeoff roll - fuel burn
> >
> > Kill away Dave!
> >
> > Its not the landing distance that varies, its the take off distance.
> > I can tell you for certain that your takeoff distance can easily more
> > than double during the high density summer days here.
> >
> > We have a collection of broken propellers here at GNT, all from summer
> > takeoffs gone bad. I've seen a Cessna FunWifty(150) land in 1000 ft in
> > August, and one hour later use all 7500 ft of runway in a failed
> > attempt to take off. Thats a more than 8 to 1 ratio of landing distance
> > to take off distance. All due to density altitude. In the winter he
> > could have taken off in less than 2000 ft.
> >
> > So my experience tells me that density altitude doesn't effect landing
> > distance nearly as much(if at all) as it does take off distance.
> >
> > Hay Kurt, you operate from a high density altitude, runway challenged
> > airfield. Same experience as me?
> >
> > Scott
> >
> > Dave wrote:
> > > Sorry to be a killjoy, but density altitudes effects are proportional
> > > and in direct relation to the the difference from actual altitude.
> > >
> > > If you can land in half the distance of your takeoff run, your plane
> > > (under same loading) will do that at sea level and at Leadville. The
> > > numbers will vary but the relationship will not.
> > >
> > > Dave
> > >
> > > Scott Derrick wrote:
> > >> Unless I'm very light, just me and little fuel, I can usually land in
> > >> half the distance a take off requires.
> > >>
> > >> Maybe that is because of our high density altitudes.
> > >>
> > >> Scott
> > >>
> > >> Al Gietzen wrote:
> > >>
> > >>> A further comment – For me and my plane the limiting factor is
> landing
> > >>> distance, not takeoff roll. While doing these tests I found I had to
> > >>> brake fairly hard to make the exit at 2400’. Rolling out over the
> > >>> numbers I still carry quite a way in ground effect before the mains
> > >>> touch.
> > >>>
> > >>> Al
> > >>>
> > >>> -----Original Message-----
> > >>> *From:* reflector-bounces at tvbf.org
> [mailto:reflector-bounces at tvbf.org]
> > >>> *On Behalf Of *Al Gietzen
> > >>> *Sent:* Thursday, May 21, 2009 10:47 PM
> > >>> *To:* reflector
> > >>> *Subject:* REFLECTOR: Takeoff roll - fuel burn
> > >>>
> > >>> Here’s a bit of data from today’s measurements.
> > >>>
> > >>> The question came up here awhile back about fuel economy vs CG.
> I did
> > >>> flights today in my SE RG with CG at 120”, total weight about 2060;
> > >>> and at 116”, total weight about 2270. The CG was shifted by adding a
> > >>> person in the right seat. Surprising; within the accuracy of the
> > >>> measurements, both cases were the same: 160 KTAS burning 9.5 gph at
> > >>> 2500 rpm on a fixed pitch prop (rotary 20B, lean cruise). At pattern
> > >>> speed of about 100 KIAS I noted the heavier, forward CG took more
> > >>> power; but I didn’t take any data.
> > >>>
> > >>> Takeoff roll – 85F; 1400’ field elevation, roughly 8-10kt wind
> > >>> component down the runway, fixed pitch cruise prop.
> > >>>
> > >>> Weight – 2100; CG – 120”; about 1630 ft
> > >>>
> > >>> Weight – 2300; CG – 120”; about 1730 ft
> > >>>
> > >>> Weight – 2300; CG – 116”; about 2300 ft
> > >>>
> > >>> These are all single run measurements, taken by spotting relative to
> > >>> taxiway exits and edge lights, and taken from a rolling start –
> > >>> rolling on to the runway, getting it straight and adding power.
> Moving
> > >>> the CG forward made a more dramatic difference than adding
> weight, and
> > >>> I didn’t like the way it handled at pattern speed, or landing.
> > >>>
> > >>> The first case above was repeated using so-called ‘Short field
> > >>> takeoff’ procedure – getting lined up near the end of the
> runway, and
> > >>> applying power while holding brakes; then release. Takeoff roll was
> > >>> the same as the rolling start. My rotary spools up very quickly
> when I
> > >>> push in the throttle; things may be a bit different with a Lyc.
> > >>>
> > >>> Al
> > >>>
> > >>>
> ------------------------------------------------------------------------
> > >>>
> > >>>
> > >>> _______________________________________________
> > >>> To change your email address, visit
> > >>> http://www.tvbf.org/mailman/listinfo/reflector
> > >>>
> > >>> Visit the gallery! www.tvbf.org/gallery
> > >>> user:pw = tvbf:jamaicangoose
> > >>> Check new archives: www.tvbf.org/pipermail
> > >>> Check old archives:
> http://www.tvbf.org/archives/velocity/maillist.html
> > >>>
> > >>
> > >>
> > >>
> ------------------------------------------------------------------------
> > >>
> > >> _______________________________________________
> > >> To change your email address, visit
> > >> http://www.tvbf.org/mailman/listinfo/reflector
> > >>
> > >> Visit the gallery! www.tvbf.org/gallery
> > >> user:pw = tvbf:jamaicangoose
> > >> Check new archives: www.tvbf.org/pipermail
> > >> Check old archives:
> http://www.tvbf.org/archives/velocity/maillist.html
> > >
> > > _______________________________________________
> > > To change your email address, visit
> > > http://www.tvbf.org/mailman/listinfo/reflector
> > >
> > > Visit the gallery! www.tvbf.org/gallery
> > > user:pw = tvbf:jamaicangoose
> > > Check new archives: www.tvbf.org/pipermail
> > > Check old archives:
> http://www.tvbf.org/archives/velocity/maillist.html
> > >
> >
> ------------------------------------------------------------------------
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 260 bytes
Desc: OpenPGP digital signature
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20090523/5b193a62/attachment.pgp>