Author Topic: Interesting Experiment using the E-Primary Force (Read 2447 times)

Crist Rigotti · « **on:** October 19, 2008, 09:29:22 AM »

Yesterday I did some experimenting to see what effect weight has on an airplane e-system. I took the EPF and flew it in its standard weight and then added 3.5 ounces for the next three flights for a total of about 10 ounce gain. Here are the numbers:

BEFORE WEIGHTS:
39 oz
1750 mah used
115 watts/lb

AFTER WEIGHTS:
49 oz
2000 mah used
105 watts/lb

The numbers should have come out to needing 2200 mah at 49 oz to keep the same watts/lb (115). So it looks like that I won't need so much battery capacity (mah) than what I thought. Instead of needing a 3300mah (12 oz) I can get by with a 2500-2600 mah (8.5 oz) pack and save some substantial weight.

The only caveat is that I never flew entire flights so these are estimated numbers off the 1 min test flights. These numbers are close to what Alan Hahn seems to be getting with his 44 oz E-Nobler.

Why didn't the numbers come out close to both needing 115 watts/lb? Or even the heavier flights needing more?

Alan Hahn · « **Reply #1 on:** October 19, 2008, 10:06:54 AM »

One question I have is whether the plane was flying "well" at the higher weights--especially the overheads. (maybe hard to tell with a minute flight!)

Or in other words, did you optimize at each weight, or since I think I know the answer, how about optimizing at the max weight?

Usually these watts/lb numbers are just to get you in the ball park. Since stunt is a lot of boredom (the level flights) punctuated by brief moments of terror, your power draw is a complicated average of all the regimes.

But keep up the testing, it is important to get these numbers to try and make sense of what is important.

I made a post in the Old Time forum (the Y&O thread) about testing and rating of props. Given what we are finding here in electric- where at least one variable (the motor) is reasonably under control, I thought any rating of props using glow engines would tend to be hopeless. Maybe I'll be proven wrong.

Alan Hahn · « **Reply #2 on:** October 19, 2008, 10:25:26 AM »

One other note is that my 44 oz Primary Force Setup is pulling anywhere from <1600mAHr to just under 1700mAhr, depending on amount of breeze. Even then I think I need to increase rpm a little to make the overheads feel better (not bad now, but not as good as the Nobler). I wish I could figure out a way to subtract weight 3.5 oz at a time!

Crist Rigotti · « **Reply #3 on:** October 19, 2008, 12:46:15 PM »

Alan,
Each flight I did 3 inside loops, 2 inside squares, and 2 triangles. I wouldn't have hesistated going overhead either if I had a little more time. At the heaviest weight I could tell the plane wasn't flying like it should, but still good enough to do a whole pattern. I launched at the same rpms and all each flight. After 3 flights I even changed the battery to eliminate a change in available power from the battery. Interesting experiment.

Crist Rigotti · « **Reply #4 on:** October 22, 2008, 09:17:19 PM »

Hmm, not much feedback on my experiment. This brings me to another question. When we are figuring an ECL power system, weight of the model is one of the factors especially when figuring the watts needed. Could there be a better way to figure out what we need for watts? Has anybody else tried this experiment? Just add weight to their airplane and see if the total current draw goes up. Anybody? I'd like to see what others results are.

Mark Scarborough · « **Reply #5 on:** October 22, 2008, 10:08:46 PM »

Crist,
in your experiment, what is your goal, to maintain the airspeed, or to get the airplane to fly correctly at the higher weight. Your experiment has some interest but, until you establish exactly what prameters you are controlling and reaching for, it preobably is not conclusive, at least to me. Now another thought, in your test flights, I totally understand why you only did short flights, however, I think one factor that throws your results off, you didnt do any of the overheads, the vertical eight, the hourglass, the hori 8, and these are the real tellers as for power.
I agree that there is a lot more to be considered than simply weight. the ULTIMATE thing, is how the airplane responds, how it flies on the handle, and more important, how does it score. In my opinion, you really cant use partial flights as an indicator of what is really happening. It is a good starting point to explore but until you add the weight, then fly full patterns back to back with the light weight and the heavy weight, and the airplane trimmed for the weight, I dont think that really much can be said. If the airplane is not trimmed for the weight, then you are using more control deflection than you need to and thats drag and thats more power.
I was pretty surprised with my electric P-40 that weighs over 57 oz on 570 squares of wing. It flies extremely well despite the weight. I really dont want to add weight to this airplane for obviouse reasons, and leaving weight off isnt really an issue.
another thing I think to keep in mind is that if you are doing this experiment with purpose to use the info to set up a new airplane, keep in mind the Primary force doesn have flaps and the addition of flaps will potentially increase the power drain in manuevers from drag.
To make a long story short, I like your idea, to quantify the affect of weight on power drain, I think perhaps though a few more valid tests, full patterns, would really help to solidify what you are trying to show.
keep up the good work!

Larry Wong · « **Reply #6 on:** October 22, 2008, 11:24:41 PM »

Now that is vary intresting about weight. But Drag would be more effecting when a trick is being done it draws more power and for better over heads try a ( Pusher Prop.) it does wonder turning the other way as the air stream goes over the rudder it keeps the lings tight. That is what I have found out using a EP 12"x6"

Dennis Adamisin · « **Reply #7 on:** October 23, 2008, 05:48:15 AM »

Crist's fisinishing weight 49 oz he concluded that he could use a 2500 mah battery. My Swinger is 50 oz and uses 1850 mah out of a 2500 mah battery. Sounds like correlation to & confirmation of Crist's work?

I think the watts/lb is a good sanity check for sizing power, but just like with IC power, somewhat heavier or lighter will also work...

Crist Rigotti · « **Reply #8 on:** October 23, 2008, 08:41:44 AM »

Quote from: Mark Scarborough on October 22, 2008, 10:08:46 PM

Crist,
in your experiment, what is your goal, to maintain the airspeed, or to get the airplane to fly correctly at the higher weight. Your experiment has some interest but, until you establish exactly what prameters you are controlling and reaching for, it preobably is not conclusive, at least to me. Now another thought, in your test flights, I totally understand why you only did short flights, however, I think one factor that throws your results off, you didnt do any of the overheads, the vertical eight, the hourglass, the hori 8, and these are the real tellers as for power.
I agree that there is a lot more to be considered than simply weight. the ULTIMATE thing, is how the airplane responds, how it flies on the handle, and more important, how does it score. In my opinion, you really cant use partial flights as an indicator of what is really happening. It is a good starting point to explore but until you add the weight, then fly full patterns back to back with the light weight and the heavy weight, and the airplane trimmed for the weight, I dont think that really much can be said. If the airplane is not trimmed for the weight, then you are using more control deflection than you need to and thats drag and thats more power.
I was pretty surprised with my electric P-40 that weighs over 57 oz on 570 squares of wing. It flies extremely well despite the weight. I really dont want to add weight to this airplane for obviouse reasons, and leaving weight off isnt really an issue.
another thing I think to keep in mind is that if you are doing this experiment with purpose to use the info to set up a new airplane, keep in mind the Primary force doesn have flaps and the addition of flaps will potentially increase the power drain in manuevers from drag.
To make a long story short, I like your idea, to quantify the affect of weight on power drain, I think perhaps though a few more valid tests, full patterns, would really help to solidify what you are trying to show.
keep up the good work!

Mark,
My goal was to see what effect weight has on the total mah draw from the battery when everything else stays the same. The airplane was fitted with my Eagle Tree FDR and I ran the experiment like this:

1st flight was the baseline configuration of 1 minute. I know the total mah draw for a complete flight from previous flights.
2nd through 4th flights each 1 minute. I added 2.5 oz to each flight on the CG. I flew 3 inside loops, 2 square inside loops, and 2 triangles each flight.
I then compared the base line mah draw to each "weighted" flight and noted the difference. I came up with a percentage of change from baseline to fully weighted configuration. I then took my full flight mah draw, from previous flights, and came up with the new mah draw for the weighted configuration for a full flight.

I cannot fly a full flight in the weighted configuration because my batteries can't support the added mah draw, hence the shorter flights. I'll have to try a longer flight based on expected mah draw (weighted configuration) with my current batteries something like 4.5 minutes so I don't over stress the batteries. The weather is rapidly turning bad and I might not be able to get another flight test in this year.

Mark Scarborough · « **Reply #9 on:** October 23, 2008, 08:51:43 AM »

Crist,,Dennis
I find this all interesting and enlightening, as to using more or less watt/lb, I agree its a benchmark. I Have seen some local fliers here fly things that are visibly underpowered, and they finesse it throught he pattern and make it work, I have also seen others that hammer the corners and need the extra power to suit their style. I think as much as anything, my point was that in order for a test to be valid across the board you have to minimize the variables.
I was talking to a local RC electric pilot lately,, ( who incidently is in the process of being brought over th ethe enlightened side,, with us CL guys,, lol) He has flown many power configurations on many airframes. His general take is to look at the guidlines, then when you think your close, plug the silly thing in and make it work. so, as a basis for future exploration, tests are extremely valid, however, we must keep in mind the variables that can affect the test.
Yeah, now thinking about it,, lol, I really should sit back and listen, you guys both have more experience than I do, but, well thats how I learn, jump in the fire till somebody either rescues me, or adds more fuel, lol

FWIW, my all up flying weight of 59 with the data recorder, P-40 was using 3200 Mah for 6:20 flight time. Of course different prop, motor, and battery voltage,

Alan Hahn · « **Reply #10 on:** October 23, 2008, 12:50:22 PM »

Quote from: Crist Rigotti on October 22, 2008, 09:17:19 PM

Hmm, not much feedback on my experiment. This brings me to another question. When we are figuring an ECL power system, weight of the model is one of the factors especially when figuring the watts needed. Could there be a better way to figure out what we need for watts? Has anybody else tried this experiment? Just add weight to their airplane and see if the total current draw goes up. Anybody? I'd like to see what others results are.

Crist,
Don't interpret the lack of comment with lack of interest. I think we are all trying to understand how these pieces fit together!

Crist Rigotti · « **Reply #11 on:** October 23, 2008, 06:14:06 PM »

Thanks Alan. Good point!

Dean Pappas · « **Reply #12 on:** October 24, 2008, 08:45:52 AM »

Hi All,
Mark, corrected proportionally for both flight time and weight you get the same battery consumption as we do with Hunt's Genesis. (5:45 time, 2.6 A-H and 53 oz.) That is 0.71 Watt-Hours per ounce.
Sure enough, as Crist says, different styles produce noticeably different per-ounce energy consumption rates. Dennis, for example, has a gene that runs through his family that allows them to fly a schedule on about 10% less energy than the rest of us; wet or electric!

later friends.
Dean Pappas

Quote from: Mark Scarborough on October 23, 2008, 08:51:43 AM

Crist,,Dennis
I find this all interesting and enlightening, as to using more or less watt/lb, I agree its a benchmark. I Have seen some local fliers here fly things that are visibly underpowered, and they finesse it throught he pattern and make it work, I have also seen others that hammer the corners and need the extra power to suit their style. I think as much as anything, my point was that in order for a test to be valid across the board you have to minimize the variables.
I was talking to a local RC electric pilot lately,, ( who incidently is in the process of being brought over th ethe enlightened side,, with us CL guys,, lol) He has flown many power configurations on many airframes. His general take is to look at the guidlines, then when you think your close, plug the silly thing in and make it work. so, as a basis for future exploration, tests are extremely valid, however, we must keep in mind the variables that can affect the test.
Yeah, now thinking about it,, lol, I really should sit back and listen, you guys both have more experience than I do, but, well thats how I learn, jump in the fire till somebody either rescues me, or adds more fuel, lol
FWIW, my all up flying weight of 59 with the data recorder, P-40 was using 3200 Mah for 6:20 flight time. Of course different prop, motor, and battery voltage,

Mark Scarborough · « **Reply #13 on:** October 24, 2008, 08:57:17 AM »

Dean, thanks
I will humbly accept your observations, though my own experiments continue just cause I have to! lol,,
I know what you are saying, Pat Johnston, my flying buddy,, (well at contests) is my answer guy for most stuff, we run the same plane for profile contests Brodak(Johnston) P-40, same engine LA 46, same prop APC 12.25 x 3.75, Same venturi, same rpm, and he uses less than 3.5 oz of fuel, I use 4.25
Appreciate all the info,, next on my plate, the Hacker tests,, since my AXI ate a magnet,,

Dennis Adamisin · « **Reply #14 on:** October 24, 2008, 11:19:26 AM »

Quote from: Dean Pappas on October 24, 2008, 08:45:52 AM

Hi All,
Mark, corrected proportionally for both flight time and weight you get the same battery consumption as we do with Hunt's Genesis. (5:45 time, 2.6 A-H and 53 oz.) That is 0.71 Watt-Hours per ounce.
Sure enough, as Crist says, different styles produce noticeably different per-ounce energy consumption rates. Dennis, for example, has a gene that runs through his family that allows them to fly a schedule on about 10% less energy than the rest of us; wet or electric!

later friends.
Dean Pappas

HA! Actually the answer is 30% less power required than mere mortals - but to say that would be braggin!

All seriousness aside, I think the real story is that with E-power we can now with 2nd or 3rd decimal place accuracy determine how much power we are actually using. Ultimately even THAT really doesn't matter, when the flyer feels that he is POWERING through the pattern - that is the only mesasurement that really counts, all the measuring is just rationalization. I also really like that EVERY lap up to shutdown is equally flyable - meaning in a perfect universe we would cut off the flight timer exactly 2 laps after the clover and save a lot of electrons otherwise expended in level flight.

Put another way, I'll settle for the power-glass being 100% full, and let the gearheads (electron-heads?) push for EXCESS power.

Crist Rigotti · « **Reply #15 on:** October 29, 2008, 07:16:10 PM »

UPDATE........

I flew the EPF again tonight. I added the same amount of weight and flew it for 4.1 minutes vs 5.3 minutes for a full pattern. I flew the entire pattern only with 1 level lap between manouvers and just 2 inverted laps. After downloading the Eagle Tree I have some more date to look at. Here is what I came up with for the full pattern:

unweighted = 1750mah 115 watts/pound
weighted = 1988mah 105 watts/pound

Just as a reminder flying 1 minute flights I figured 1992mah! That's only a 4 mah difference! The weather conditions were almost the same too.

So my experiment flying 1 minute flights proved that you can use shorter flights and then use math to accurately figure full pattern flights.

BTW, the heavy airplane didn't fly very well because it had quite a sink rate at the square corners, but lap time were nearly idtentical. I had no problem doing all the stunts and line tension was very good.

Still doesn't explain why the watts/pound goes down the heavier the airplane got.....hmm?

Somebody else what to try the same experiment with their airplane and report back?

Mike Anderson · « **Reply #16 on:** October 29, 2008, 09:33:33 PM »

Quote from: Crist Rigotti on October 29, 2008, 07:16:10 PM

UPDATE........

unweighted = 1750mah 115 watts/pound
weighted = 1988mah 105 watts/pound

"...... but lap time were nearly idtentical. I had no problem doing all the stunts and line tension was very good."

Still doesn't explain why the watts/pound goes down the heavier the airplane got.....hmm?

Watts/lb (power loading) went down, so either Watts went down , or pounds went up or watts went up but pounds went up more - there ya' go. So MOST of the watts are spent just keeping the plane in the air at the desired airspeed (lap time). When weight goes up, if speed is the same, then the wing has to fly at a slightly higher angle of attack, giving a higher drag coefficient, requiring more power to maintain an equal airspeed, but only a slight increase in power required - (~14%, apparently). Weight however went up by over 25% (39 oz to 49 oz.) . So the ratio actually went down. My own conclusion would be that there isn't a whole lot of information in a singular computation of watts/lb - as someone else said, it can be used as a starting point but not much more.

Mike@

Dennis Adamisin · « **Reply #17 on:** October 29, 2008, 10:02:10 PM »

I am pleasantly surprised that the 1 minute flights extrapolated so well out to the 4 minute flights. Your experimental methods are obviously very sound. No surprise you found the weight limit for the PF too!

Let me ask an obvious question that I thik I know the answer to: when you add the weight, do you maintain the EXACT same CG location, or does it drift (even a little) fore or aft? I think a slight aft drift in CG would slightly reduce power used by the heavy config to maintain level flight.

Crist Rigotti · « **Reply #18 on:** October 29, 2008, 10:22:47 PM »

Dennis,
The weights were put near the CG. Might have been a little aft..maybe.

Mike,
Yeah, I know 1 experiment. I noticed the 25% increase in weight only required about 7% increase in power.

I know 1 thing, is that when I build an electric ship, I'll hold off on getting batteries till I test fly it with the ones I have to see what I really need, then get the batteries!

Alan Hahn · « **Reply #19 on:** October 30, 2008, 08:10:34 AM »

One thing I have done, for better or worse, is to "standardize" on the 2100mAHr cell. I first began to use the 3s version on my Super Clown. When I started flying the Nobler, I wasn't too sure what to expect, so I modified it in order to be able to carry two of the 3s2100mAHr packs (hooking them up in parallel to give an effective 3s4200mAHr pack), figuring that was surely going to be enough. And sure enough it was. I was only using about 2200mAHr of the combined pack. So I figured that in terms of battery energy, I needed just over 3 cells worth or energy, so going to 4 cells should give me the desired 20% surplus.

Now I could arrange those 4 cells in many ways, as a 2s2p4200mAHr pack (two 2s in parallel), or two 2s2100mAHr packs hooked up in series or a single 4s pack. In any case I needed to buy a different configuration. As it turns out, the 4s pack is cheaper than buying two 2s packs, actually by a considerable margin, so that's the way I went. And I think it works out ok. I should mention that there are other considerations as to battery configuration---one is that the lower voltage configurations supply more amps, so your ESC has to be able to handle the higher flow. Since I have 35A Phoenix ESC's, that tends to rule out the 2s configurations for me. The 45A ESC's are much more expensive-- I was able to buy the 35A ESC's for ~$70 on various sales, and I have never seen the 45A version less than $100 and change. Another detail is that these standard Phoenix ESC's are only rated for 4s to 5s voltages (current CC specs say 4s, but my original specs say 5s, so I'm not sure here), so you also are limited on the series setups too.

So now I am thinking about what to use with the Vector. I thought I'd go with the two 3s packs in parallel (= 3s2p4200mAHr), to establish the baseline. My "guess" is that I might be able to get away with five cells (in a 5s configuration). But as you can see, I would have to buy some 2s packs to put in series with my 3s packs (maybe three 2s packs to give me 3 "tanks" of fuel). I might just stick with the two 3s packs in parallel since they are still a great deal (I would still need to get two more to give me the 3 tanks setup). I can also just use my stock Scorpion 3020-12 which is perfect for the 3s configuration.

Of course the batteries have to fit inside the plane, and hopefully let it balance ok with no extra deadweight. In the NoblerArf, I couldn't fit in my Brodak 3s4000mAHr pack in the tank area. Just a detail! Also you can mix different capacity cells in parallel--so in other words I could use a 3s1000mAHr pack in parallel with my 3s2100mAHr pack to make the equivalent of a 3s3100 pack. This could be useful if you are hurting for space.