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        Discussion Maintaining altitude & speed whilst increasing throttle

#1 rcmaverick Jan 16, 2013 10:11 PM

Maintaining altitude & speed whilst increasing throttle
 
I wonder what the best way to go about this. Almost all my planes want to climb up on applying throttle (worse upwind). So I give it a bit of down elevator to keep it level. In doing this I lose a bit of speed. I am thinking about mixing the elevator with the throttle but it is such a small correction I am not sure if my DX6i is capable of it.

#2 btown2 Jan 16, 2013 10:16 PM

Planes should climb when you apply power. A properly trimmed plane flies straight and level when at a given airspeed. Increasing the throttle (and thus the airspeed) climbs and decreasing the throttle descends.

Why do you want to change this?

#3 E-Challenged Jan 16, 2013 10:17 PM

Use your elevator trim to maintain altitude at various throttle settings. Any airplane will gain altitude as airspeed increases and lose it as airspeed decreases.Full scale pilots use elevator trim a lot.

#4 C₄H₁₀ Jan 16, 2013 10:59 PM

Quote:

Almost all my planes want to climb up on applying throttle (worse upwind). So I give it a bit of down elevator to keep it level. In doing this I lose a bit of speed.
Ummm.... Maybe I'm dense, but does this mean that your planes are fastest at 0% throttle?

#5 rcmaverick Jan 16, 2013 11:08 PM

Quote:

Originally Posted by C₄H₁₀ (Post 23839111)
Ummm.... Maybe I'm dense, but does this mean that your planes are fastest at 0% throttle?

Hmm no..

I can leave the elevator alone at about 50% throttle - the plane flies level - If I now want to speed it up to 80% - 90% it starts going vertical.

Perhaps I need to trim the elevator for a higher throttle position.

#6 C₄H₁₀ Jan 16, 2013 11:13 PM

That's normal. A bit of downthrust can be used to help reduce the nose-up tendency. A throttle-to-elevator mix will accomplish a similar effect.

#7 caseih Jan 16, 2013 11:17 PM

Quote:

Originally Posted by rcmaverick (Post 23839165)
Perhaps I need to trim the elevator for a higher throttle position.

Yes you will have to do this. This is the way all normal airplanes are flown. You trim for the airspeed you want (using a trim tab, changing the entire hstab, or the elevator), and then use throttle to make the plane sink, rise, or fly level.

#8 rcmaverick Jan 16, 2013 11:18 PM

Quote:

Originally Posted by C₄H₁₀ (Post 23839193)
That's normal. A bit of downthrust can be used to help reduce the nose-up tendency. A throttle-to-elevator mix will accomplish a similar effect.

Planning on a race so need to optimise my "speed settings"

#9 Logan4169 Jan 16, 2013 11:26 PM

The DX6i is capable of mixing that, but I think that you would be better served by understanding what is really happening before you do it.

#10 PyroMan Jan 17, 2013 12:28 AM

Instead of mixing I would try a few degrees of down trust. An easy way of adding down thrust is by putting washers behind your motor mount. C4H10 also suggested this above. . .

#11 JetPlaneFlyer Jan 17, 2013 12:40 AM

Personally i'd fine tune the CG before adding downthrust or mixes. Climbing too strongly under power is a often symptom of being nose heavy (CG too far forward). only once you are 100% sure that the CG is in the optimal position should you start adjusting thrust angle.

High wing planes usually need a fair bit of downthrust even once the CG is nailed but on mid and low wing aerobatic types you should be able to get rid of excessive climbing purely by adjusting CG.

#12 solentlife Jan 17, 2013 01:16 AM

Quote:

Originally Posted by rcmaverick (Post 23839224)
Planning on a race so need to optimise my "speed settings"

That is a whole different ball-game to sport flying.

So far I have read standard model sport stuff ... but for racing you should be looking at having plane set-up as neutral as possible at WOT ... that means tailplane angle to main wing ... as little engine downthrust as possible ... all compensations are made in the design and incidence angles of the flying surfaces. We need to minimise induced drag and have power line as straight through model as possible.

A racer will descend when throttle is reduced needing elevator to maintain altitude ... should fly straight and level at WOT.



That's how I set-up my Pylon racing 20's and 40's .....

Nigel

#13 scirocco Jan 17, 2013 01:59 AM

if it wants to pitch up that badly, it's likely to be all 3 of
a) severely overpowered compared to the design assumptions
b) excessively nose heavy cg
c) substantial longitudinal dihedral (sometimes incorrectly called decalage),where the wing is at a signficantly higher incidence angle than the stab.

If it was designed to be speed stable in a narrow range, like most trainers and low speed gliders you're going to have to fight it to go fast level.

Even fast acft need a lot of forward trim at high speed. A real-world example, P-51 based to boot: Reno racing Mustangs require full forward trim and then some stick force to maintain level at their top speed. When the elevator trim assembly failed on Galloping Ghost in 2011 the aircraft pitched up at 17.3g, blacking out the pilot and the acft crashed into the crowd. An earlier similar incident the pilot escaped - fortunately it pitched straight up at only 10g instead of rolling

#14 solentlife Jan 17, 2013 02:16 AM

Quote:

Even fast acft need a lot of forward trim at high speed. A real-world example, P-51 based to boot: Reno racing Mustangs require full forward trim and then some stick force to maintain level at their top speed. When the elevator trim assembly failed on Galloping Ghost in 2011 the aircraft pitched up at 17.3g, blacking out the pilot and the acft crashed into the crowd. An earlier similar incident the pilot escaped - fortunately it pitched straight up at only 10g instead of rolling
Sorry (with deep respect for the Reno Pilots) ..... but a model racer can be set-up to be neutral at WOT - I know from my own model racing.

A model can be altered so easily by spacer under wing mount .... cut and reglue tail .... washers in motor mount ... with no requirement to pass an Aeronautical Official Inspection ....

My RM Racer was reasonably successful and was zero trim at WOT ... I'd LOVE to have that bird again ... but passed it to another guy when I left UK.

Nigel

#15 rcmaverick Jan 17, 2013 04:32 AM

Quote:

Originally Posted by solentlife (Post 23840040)
Sorry (with deep respect for the Reno Pilots) ..... but a model racer can be set-up to be neutral at WOT - I know from my own model racing.
Nigel

Question is where is WOT? My P51 will go bonkers at full throttle and god knows what will happen to the ESC


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