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Re: [Paparazzi-devel] fixed wing angle of attack and cruise speed

From: Reto Büttner
Subject: Re: [Paparazzi-devel] fixed wing angle of attack and cruise speed
Date: Wed, 20 Nov 2013 09:12:37 +0100

Hi Chris
To optimize efficiency you can display an efficiency indicator on the 2D map using papgets. An easy efficiency indicator would be "Speed per Percent Throttle". Better efficiency indicators are "Speed per Fuel Flow" or "Distance per Litre Fuel", but this needs a fuel flow measurement. For electric planes it would be "Speed per Amps" or "Distance per Ah". The simple math needed for these indicators (one division) can be done directly in the papget. Then choose a calm day (no wind), fly large circles and manually play around with the throttle setting (using pitch neutral as described) until you get maximum efficiency. We have done so successfully with our long distance small electric planes (>125km, 140cm wingspan, 2kg weight).

2013/11/19 Chris <address@hidden>
Got it, thank you very much for your help.
I think i will try to increase pitch with the "pitch_neutral_default" and see what happens.
Btw i am always learning, i didn't knew the cruise throttle setting behavior as you described it, thank you again.

On 11/19/2013 08:20 PM, Loic Drumettaz wrote:


If you want to reduce speed without using an airspeed sensor, the easiest is to set nominal pitch using pitch_neutral_default in the airframe configuration.
This will offset the measured pitch.
You can tune pitch_neutral in flight by adding settings/estimation/ins_neutrals.xml in paparazzi center.
Constant airspeed in level flight is then obtained with accurate (no static error) attitude pitch loop.

nominal_cruise_ throttle is a preset of thrust which is corrected by auto throttle loop. Reduce it will only increase the airplane altitude error, but won't help to reduce speed ( at least in steady flight)


Le 19 nov. 2013 16:41, "Chris" <address@hidden> a écrit :
I was thiniking that if i want to make an airplane to go slower could i use a higher angle of attack during flight thus increasing lift (within the lowest drag envelope of course)?
If i am right what settings other than minimum cruise throttle do i need or is possible to adjust?
I am asking because i have an airplane (the huge Cessna) that can fly more than safely with 80km/h
and have significantly reduced drag but the autopilot gives it a cruising speed of 110km/h even with low throttle (40%) and at 3 degrees wing pitch during flight.
I am searching for those last bits that can decrease fuel consumption to a minimum :-D

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