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Area-51
Joined: 03 May 2021
Posts: 374
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 Posted: Sat Aug 20, 2022 1:55 am Post subject: Density Altitude - Affects Upon Take Off |
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Does anyone wish to share their notes recording performance affects upon T/O at various density altitudes? specifically rolling distances, required to 50', and reduced climb rates... Trying to get a broad picture of how the europa's performance envelope looks taking off at high altitudes.
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 282
Location: Florida USA
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| Posted: Sat Aug 20, 2022 11:41 am Post subject: Density Altitude - Affects Upon Take Off |
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Sorry,
I have a 914 and normally see no appreciable difference other than additional ground speed due to density altitude affecting takeoff and landing for Florida. That is, the affect from the higher DA is the TAS is higher than the IAS or "Q" the aircraft feels and adds more distance than engine power and acceleration and that hotter takeoff/landing speed is going to be noticeable. An extra 25 degrees C on takeoff is putting me at about a 2500 foot density altitude here in Florida so my typical hot-hot day takeoff is about 500 feet longer at full gross than standard day with only 10 degrees of flap. Heat can cause the 914 to cut back the boost slightly (not that I have ever seen it on my boost gauge or computer printout on my 914) but it could happen so, if it is really hot and a high density altitude one should add a bit for the higher temp so I do this in the examples below in the most conservative case.
A normally aspirated 912 or 912S Classic or XS suffers from power loss and as you are well aware, Rotax does not put out data for the density altitudes we have out west. So, I’m no help to those with a 912/912S
I "made up" a simple document for my own checklist TOLD use and has been about right for my old Europa Trigear with XS mods. I gathered the info from my aero books based on the POH and extrapolating data from my sources. Then cross referencing to other similar aircraft with TOLD data published. N12AY's light weight and 914 with Airmaster prop has made calculating takeoff distance not a big deal here in Florida. Medical and aircraft downtime has kept me from flying much this year but from last year when I did the study, this data on the spreadsheet has been fairly accurate for me and my particular aircraft.
The higher density altitude estimates are cross referenced from the CT and Pipistrel aircraft as a comparison for my calculations and some data from my folks flying out of Columbia as a check of my numbers. In Columbia, they operate at a density altitude of 10,000 feet and with a 914 are off in about 1200 feet (400 meters) in a light mono on a 25C day (about 10 degrees above standard).
Landing data at these Columbian altitudes is hard to get as at high density altitude, and the float distance is the serious issue. Slowing slightly on approach helps but from the threshold crossing at 55 KIAS the landing rollout is still about 7-800 meters (2500 feet) as I understand it at a 10,000 feet density altitude on a hot day at about 1300 pounds, so I am assuming once they've touched down, and the roll is about 1200 feet. That tracks with what my calculations approximate. I figure if I do get out west, in mid summer flying out of Reno (7500 foot DA at +30C, I should plan a landing roll out of (1500 for DA plus 15% for Temp for good measure = 1750 foot landing rollout with modest braking but why not let it roll and turn off at 3-4000 feet which is about double what I do in Florida). Takeoff at full 1450 lbs. would be about (3262 feet of takeoff roll for DA + 15% for 30 degrees C added on for extra) or a max of 3750 feet. At 1370 lbs., it would be a lot less at about 2350 feet (interpolating between numbers) which frankly sounds about right for gut planning.
Keep in mind a trigear takes off with less flap than the mono. Eric Trombley would be the best guesser at his performance. Perhaps we can give him a shout to check his data against density altitude, at summer time temperatures.
Let us know what you find out. Graph/chart it out and keep us all honest. The operations out west of a normally aspirated engine can be estimated by comparing the 912S to the Continental O-200 for percentage of power lost at differing density altitudes (or pressure altitude/temperature which I think is how Continental presented their curves). The problem is we all have different propellers on our 912S aircraft. A constant speed prop makes a difference for sure in takeoff and landing.
Best Regards,
Bud Yerly
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Europa_Performance_and_TOLD.pdf |
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61 Time(s) |
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Europa_TOLD_Data.xlsx |
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wdaniell.longport(at)gmai
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| Posted: Sat Aug 20, 2022 12:27 pm Post subject: Density Altitude - Affects Upon Take Off |
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i lived in bogota until 2020
i agree with bud
my turbo xs on a hard runway skgy 8600msl used less runway than a grass strip in south florida 04fa.  the altitude is compensated by lower temperature at least in the morning.
landing is rather easier in my view....float is less because the air is less dense.
i have a turbo 912 and an airmaster.  my plane weighs 920lbs.
weight doesnt appear to have much impact.
William Daniell
+1 786 878 0246
On Sat, Aug 20, 2022, 15:44 Bud Yerly <budyerly(at)msn.com (budyerly(at)msn.com)> wrote:
[quote]Sorry,
I have a 914 and normally see no appreciable difference other than additional ground speed due to density altitude affecting takeoff and landing for Florida. That is, the affect from the higher DA is the TAS is higher than the IAS or "Q" the aircraft feels and adds more distance than engine power and acceleration and that hotter takeoff/landing speed is going to be noticeable. An extra 25 degrees C on takeoff is putting me at about a 2500 foot density altitude here in Florida so my typical hot-hot day takeoff is about 500 feet longer at full gross than standard day with only 10 degrees of flap. Heat can cause the 914 to cut back the boost slightly (not that I have ever seen it on my boost gauge or computer printout on my 914) but it could happen so, if it is really hot and a high density altitude one should add a bit for the higher temp so I do this in the examples below in the most conservative case.
A normally aspirated 912 or 912S Classic or XS suffers from power loss and as you are well aware, Rotax does not put out data for the density altitudes we have out west. So, I’m no help to those with a 912/912S
I "made up" a simple document for my own checklist TOLD use and has been about right for my old Europa Trigear with XS mods. I gathered the info from my aero books based on the POH and extrapolating data from my sources. Then cross referencing to other similar aircraft with TOLD data published. N12AY's light weight and 914 with Airmaster prop has made calculating takeoff distance not a big deal here in Florida. Medical and aircraft downtime has kept me from flying much this year but from last year when I did the study, this data on the spreadsheet has been fairly accurate for me and my particular aircraft.Â
The higher density altitude estimates are cross referenced from the CT and Pipistrel aircraft as a comparison for my calculations and some data from my folks flying out of Columbia as a check of my numbers. In Columbia, they operate at a density altitude of 10,000 feet and with a 914 are off in about 1200 feet (400 meters) in a light mono on a 25C day (about 10 degrees above standard).Â
Landing data at these Columbian altitudes is hard to get as at high density altitude, and the float distance is the serious issue. Slowing slightly on approach helps but from the threshold crossing at 55 KIAS the landing rollout is still about 7-800 meters (2500 feet) as I understand it at a 10,000 feet density altitude on a hot day at about 1300 pounds, so I am assuming once they've touched down, and the roll is about 1200 feet. That tracks with what my calculations approximate.  I figure if I do get out west, in mid summer flying out of Reno (7500 foot DA at +30C, I should plan a landing roll out of (1500 for DA plus 15% for Temp for good measure = 1750 foot landing rollout with modest braking but why not let it roll and turn off at 3-4000 feet which is about double what I do in Florida). Takeoff at full 1450 lbs. would be about (3262 feet of takeoff roll for DA + 15% for 30 degrees C added on for extra) or a max of 3750 feet. At 1370 lbs., it would be a lot less at about 2350 feet (interpolating between numbers) which frankly sounds about right for gut planning.
Keep in mind a trigear takes off with less flap than the mono. Eric Trombley would be the best guesser at his performance. Perhaps we can give him a shout to check his data against density altitude, at summer time temperatures.
Let us know what you find out. Graph/chart it out and keep us all honest. The operations out west of a normally aspirated engine can be estimated by comparing the 912S to the Continental O-200 for percentage of power lost at differing density altitudes (or pressure altitude/temperature which I think is how Continental presented their curves). The problem is we all have different propellers on our 912S aircraft. A constant speed prop makes a difference for sure in takeoff and landing.
Best Regards,
Bud Yerly
--
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Area-51
Joined: 03 May 2021
Posts: 374
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| Posted: Tue Aug 23, 2022 3:55 pm Post subject: Re: Density Altitude - Affects Upon Take Off |
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Thanks for the responses there.. Smart approach using similar aircraft to extrapolate approximate performance curves; great idea thanks!
My interest is more focused on airframe performance than engine performance as engine performance can be easily determined on paper by simply accounting for atmospheric pressure against manifold pressure and then flying at those throttle setting numbers.
William have you noticed any difference in stall characteristics at all? If so what stall speeds have you observed flying around your home field?
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