REFLECTOR: Takeoff roll - fuel burn

Al Gietzen ALVentures at cox.net
Sat May 23 10:13:27 CDT 2009


Scott;

Your experience is consistent with reality.  Major factors on takeoff roll
are engine power, and prop thrust.  Both are affected by air density,
neither is a factor on landing.  Landing distance would be expected to
increase with density altitude because of higher TAS, but maybe about a
third as much as takeoff roll.

At least that's my take.  And my experience agrees with that as well.

Al 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Saturday, May 23, 2009 5:19 AM
To: Velocity Aircraft Owners and Builders list
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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>>
>>  
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>>
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