REFLECTOR: Takeoff roll - fuel burn

Sat May 23 09:15:39 CDT 2009

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
> >>>
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