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EDF FLYING -- spooling-- increasing response

L Edge

Well-known member
#1
Scenario:
On final for a landing and you are short and near stall--punch the throttle and hope you can go around.
You overshot the field on landing and you need to abort.
You decided to hover and want a vernier change in thrust to hold altitude.

I own a DX9 and one nice feature is the THROTTLE CURVE function.
Typical radio setup which is linear.

P1010001.JPG

When you fly EDF's, as you increase your throttle, there is a lag in time (spooling up) before the thrust matches the position of the throttle. Some pilots on landing, choose idle and continue the approach. Getting into trouble (say, close to stall and crashing), they punch the throttle and it feel like an eternity before the thrust is plentiful. So your talking miliseconds that might get you out of the problem.
Now look at the throttle graph below.

P1010002.JPG

First, I added a few points and now I have an exponential graph (I changed it in the data column) so when the throttle is very low in horizontal direction, you will see a I have a higher in RPM's in a short time. Compare x and y points(now you see why you need Algebra)
Result:
Now, at the low end throttle setting, a SMALL MOVEMENT of throttle drastically changes the RPM's (thrust) in a shorter time and gives you a quicker response.
Might save your $500 jet.

Point to make, yes, I know that you now have to learn to reposition the throttle location to keep the same thrust at the lower end. I always have the throttle open some until I start to stall.

"2 fer 1":
Notice the slope changes from 1/4 to about 2/3 to be shallow. I like to hover my EDF, so with a low slope, now I can use it to have very little change of RPM spooling so the plane doesn't drop out and end up crashing.

So, you can tailor your flying ability so you have a betterand less response (for me, just try the better first) that makes you comfortable. Try it, you might like it!!!!


.
 
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Namactual

Well-known member
#2
If you are approaching stall speeds with a low thrust/weight aircraft you are asking for trouble. The downside of your throttle curve is you lose the ability to maximize your battery life for the flight. EDF's already suck a battery dry faster than Dracula on a bender.

The most important thing to do is understand the airframes natural glide slope. If the airframe is properly balanced and trimmed, it should have a predictable glide slope under no power. The other side of that is not to fight the glide slope rate of decent with elevator. Fight it with throttle.

The second most important thing is if you have to abort, pour on the coals but keep the sticks steady. The worst thing you can do is try to turn or gain altitude really quickly. Throttle up, fly straight and level until you pick up enough airspeed to maneuver.

I notice I tend to bang my throttle stick around alot when I fly my EDF's as well though. I see the point you are trying to make. It would work, but I am not sure I would like the lack of fine throttle manipulation thought the full range of travel.
 

L Edge

Well-known member
#3
If you are approaching stall speeds with a low thrust/weight aircraft you are asking for trouble. The downside of your throttle curve is you lose the ability to maximize your battery life for the flight. EDF's already suck a battery dry faster than Dracula on a bender.

The most important thing to do is understand the airframes natural glide slope. If the airframe is properly balanced and trimmed, it should have a predictable glide slope under no power. The other side of that is not to fight the glide slope rate of decent with elevator. Fight it with throttle.

The second most important thing is if you have to abort, pour on the coals but keep the sticks steady. The worst thing you can do is try to turn or gain altitude really quickly. Throttle up, fly straight and level until you pick up enough airspeed to maneuver.

I notice I tend to bang my throttle stick around alot when I fly my EDF's as well though. I see the point you are trying to make. It would work, but I am not sure I would like the lack of fine throttle manipulation thought the full range of travel.
 

L Edge

Well-known member
#4
Point I am trying to show is that there is an added bonus to reduce the response time of spool up in areas of importance like landing. And the added fact that you can adjust it to your style of flying. It's a chance to explore what can be done.

The throttle curve not only does works with EDF's, why not use it with props?
I did this this video for another set of reasons, but by lowering the slope (flight mode 2- on second graph from about 1/3 throttle to 2/3), I was able to hover it rather easy. By changing the throttle, which gave me smaller increments of +/- thrust, the task was very easy. Notice the flight isn't jerky from takeoff to landing. Once you adopt throttle curves,, the sky is the limit. Now I can dump the candy right on the target.

 

clolsonus

Active member
#5
The way I look at this is slightly different. I believe the spool up time is really about the same between an EDF and a traditional electric motor/prop system. In both cases it is an electric motor and an ESC. I might even guess that the EDF could spool up faster because it's blades have less radius. [queue the ice skater spinning footage ...] Real jet turbines may take longer to spool up, but I've never owned/flown one so I don't know.

The bigger issue [as I see it] is that an EDF is shooting thrust out the back of the plane, so that your control effectiveness is dependent entirely on your airspeed.
With a (tractor) prop plane, if you punch the throttle, you get a burst of extra airflow over your control surfaces which gives you some immediate control while the airplane accelerates back into the flyable range of speeds.

I think what you are referring to as EDF spool up is really, the time it takes for an EDF powered plane to accelerate enough to gain back it's control surface effectiveness. At launch or when recovering from flying too slow, it can feel like an eternity to gain enough airspeed to begin to get control of the airplane (and if something bad happens before you get control, then it shortens the flight.)

With a typical edf (or a pusher prop) it's just harder to power out of trouble because of this

I think the main advantage of your throttle curve tip is that it keeps the motor running at least 50% unless you pull all the way back to full stop and that generally keeps your airspeed up. (But I don't think you are fixing the issue by improving your 'spool up' speeds.) Forcing the throttle to always be 50% or more generally forces your airplane to maintain a healthy airspeed. If this throttle setup helps you or helps other pilots maintain safe flying speed, then maybe it's a great solution. For some setups it might force your airplane to always be flying faster than you are comfortable with, so this is definitely something that needs to be adjusted for each aircraft and each pilot.

For my own personal flying style, I like to adjust the elevator trim for safe power off glide speeds and keep full linear throttle range. Then during approach and landing, I avoid touching the elevator as much as possible. I try to let the airplane itself do as much of the flying as possible. (I try to stay out of the way as much as possible ... the airplane is much better at flying than I am.) :) I find that the natural pitch dynamics of a trimmed airplane generally keep it flying at a safe airspeed. Airplanes really do want to fly if you just let them! But I like big long graceful maneuvers ... I'm not a high energy 3d pilot, so that colors my perspective.

Curt.
 

jfaleo1

Junior Member
#6
For my own personal flying style, I like to adjust the elevator trim for safe power off glide speeds and keep full linear throttle range. Then during approach and landing, I avoid touching the elevator as much as possible. I try to let the airplane itself do as much of the flying as possible. (I try to stay out of the way as much as possible ... the airplane is much better at flying than I am.) :) I find that the natural pitch dynamics of a trimmed airplane generally keep it flying at a safe airspeed. Airplanes really do want to fly if you just let them! But I like big long graceful maneuvers ... I'm not a high energy 3d pilot, so that colors my perspective.
Curt.
This is exactly how full scale aircraft are flown as a rule, especially commercial and corporate jets. Aerobatic aircraft are different certainly, jet powered fighters are different sort of. Your way of trimming is actually the best way to handle most of our aircraft.
As for this EDF power curve change in the program of the transmitter, I see the advantage and disadvantage both. For me it is not what I would use. I feel the need to know how to fly my models how they need to be flown. This is not to say it's bad for others, but I grew up with no expo, no computer radios. D/R even came later. I use D/R but hate anything that takes away my linear control of anything. Just the opinion of the old guy.
 

clolsonus

Active member
#7
This is exactly how full scale aircraft are flown as a rule, especially commercial and corporate jets. Aerobatic aircraft are different certainly, jet powered fighters are different sort of. Your way of trimming is actually the best way to handle most of our aircraft.
As for this EDF power curve change in the program of the transmitter, I see the advantage and disadvantage both. For me it is not what I would use. I feel the need to know how to fly my models how they need to be flown. This is not to say it's bad for others, but I grew up with no expo, no computer radios. D/R even came later. I use D/R but hate anything that takes away my linear control of anything. Just the opinion of the old guy.
Hah, I never setup dual rates because I can never remember which switch switches which axis which way when I'm flying. I always end up the wrong way, landing with high rates, and have to come to a full stop to figure out how to switch it the right way again. And this is probably because I never fly with dual rates so I've never figured out a consistent setup. (Sort of a self fullfilling feedback loop.) The first time I tried expo was on a delta wing that had a very aggressive roll rate. That worked really well in for that situation, but 98% of the rest of the time I just fly with straight linear control too.

We all develop our own strategies for safe flying, so at the end of the day, it comes down to having fun and setting our airplanes up the way works best for our own preferences.
 
#8
Interesting Idea!, so the thrust will become more linear to the throttle position.

I think I will try to do something like this in my next Edf, but mapp the trust against a scale vs throttle position and you should be able to build a linear thrust curve, it should give you a wider operativt range of your throttle.

It might be so that negative expo will do just fine allso.
 

L Edge

Well-known member
#9
The main point of this article is to make you aware that you have a means in the transmitter to assist you in many ways to improve your flying abiliity. Each of us flys different, where sometimes the radio can assist you.

For instance, I use the throttle to move the Tomcat's wing from perpendicular to sweep it back at full open rather than flipping a switch. Much more realistic. So at 3/4 throttle, the wing is back 1/2 way. Looks real cool in flight.