stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: Paul Walker on April 07, 2010, 01:11:27 PM
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I have finished my new "Impact"....
This one is as much smaller than a standard Impact then the previous electric versions were larger. This one is 650 in^2. AR=5.25, and the wing thickness was also reduced. This is a significant change from all previous Impacts. The span is now 58.5". The weight is SIGNIFICANTLY improved at 61.8 ounces, ready for flight. Not bad for containing a 14 ounce battery!
The first flights were interesting. I took the system directly out of my test Impact, motor, timer, prop, ESC, etc. I left the settings the same. It flew at 5.3 sec / lap in the "normal" size impact. In the new plane, it went about 4.6 sec / lap. A very significant decrease in drag! Once slowed down to 5.2 sec / lap, it was very nice. I especially notice the better corner than the other electrics. So far, only 5 flights. The weather has been abysmal since, and I haven't flown it since. I am eager to work with it to make it a real winner. I plan on using it at the '11 Nats, so I have a few months to get it working right!
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good style changes Paul!!! I like it!
I gather you are running A123 cells at 14oz - what capacity are they ?
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Hi Paul,
It sure looks nice. How about some photos of the business end?
Is it a top-loader? side? and all that curiosity stuff.
Thanks,
Dean P.
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good style changes Paul!!! I like it!
I gather you are running A123 cells at 14oz - what capacity are they ?
Thanks.
The batteries are LiPo's. 5S2P 4000 Thunder Power. Very light weight for the capacity!
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Hi Paul,
It sure looks nice. How about some photos of the business end?
Is it a top-loader? side? and all that curiosity stuff.
Thanks,
Dean P.
Well, the picture would be a little messy. I have lots of stuff in there that is relatively new to me.
1) The safety plug. Now that I use it, I don't know how I did without.
2) I have a Shultze battery monitor (LiPo Dimatic) that monitors the voltage level in each cell and doesn't let it discharge below 3.6 volts. If a single cell drops below that, it will immeadiatly slow down and stop, allowing enough time to recover, and saving the battery and potentially the plane from damage. It weighs ~14 grams.
3) It also has the Kim Doherty timer/processor in the compartment.
This all makes for a bunch of wires at this time. Maybe some day I can find a way to eliminate much of that wiring.
It is still a bottom loader. I am a conservative structures engineer and am leary of removing structure on both the top and bottom of the forward fuselage. It also has to do with cooling. I have PLENTY of air passing by all this equipment!
The ESC is a Shultze 18.46F2B and the motor is a Plettenberg Orbit 20 series. I don't remember the exact kv of the motor in it.
Paul
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Paul,
It looks great and I'm sure it will fly even better. Before you fly again buy a CD with owl and hawk calls and play it during your flights! :P
It looks like you are stirring the pot with the wording on the wing. ;D
Sent you a PM.
Mike
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I see we are going to learn a lesson how long the nose should be on a stunter VD~
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Looks great Paul!!!!!!!!!!! I like the style change to the Impact!
Does XS mean Xtra Small? H^^
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The first flights were interesting. I took the system directly out of my test Impact, motor, timer, prop, ESC, etc. I left the settings the same. It flew at 5.3 sec / lap in the "normal" size impact. In the new plane, it went about 4.6 sec / lap. A very significant decrease in drag!
Same prop and RPM? What was the battery drain when you were flying at 5.2?
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Does XS mean Xtra Small? H^^
Excess electrickery
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I see we are going to learn a lesson how long the nose should be on a stunter VD~
And this nose is longer than the last!
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Paul, I was looking close at the photo, and I saw that those leadouts, at least the rear leadout seems like it comes out all the way be the flap, and the front leadout around the middle of the wing. Am I seeing things, or is that how it actually is? H^^
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Paul, I was looking close at the photo, and I saw that those leadouts, at least the rear leadout seems like it comes out all the way be the flap, and the front leadout around the middle of the wing. Am I seeing things, or is that how it actually is? H^^
You're seeing the lines laying slack on the ground.
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Same prop and RPM? What was the battery drain when you were flying at 5.2?
It was around ~2800
At 4.7 it was ~3200
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Paul, I was looking close at the photo, and I saw that those leadouts, at least the rear leadout seems like it comes out all the way be the flap, and the front leadout around the middle of the wing. Am I seeing things, or is that how it actually is? H^^
Yes, you are seeing things. The flexible cables are hanging down, and what you are seeing are the flying lines going out to the handle.
XS = Extra Small
Paul
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I see we are going to learn a lesson how long the nose should be on a stunter VD~
I also looks short due to the angle of the photo. It really isn't terribly short.
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MOST excellent! Great sounding numbers, scary (lack of) weight. That was a HUGE change in drag too. Am really hoping to make the NATs this year so I can see it..
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Paul,
are you coming to Portland next weekend? would love to gander at this one up close.
You mentioned thinning the wing, were you refering to the percentage, or just the scale down effect?
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Very nice!!! I want one.
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Paul,
are you coming to Portland next weekend? would love to gander at this one up close.
You mentioned thinning the wing, were you refering to the percentage, or just the scale down effect?
Portland, ???? Maybe....Not sure, we'll see..
Thin...More than just a scale effect. It is 2.2 inches thick, as opposed to nearly the 2.5 of the Impact.
Paul
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That was a HUGE change in drag too. Am really hoping to make the NATs this year so I can see it..
[/quote]
I'll be there at the Nats this year, but not in a flying capacity!
Paul W
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IMPRESSIVE machine Mr. Walker. (and may be a bit "scary" too for those who will be contending in 2011...)
If it's not too personal, can you tell us more about the reason of the frase on the wing tip "Do You Believe it Now"?
Thanks and congrats!
Claudio
ARGENTINA
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IMPRESSIVE machine Mr. Walker. (and may be a bit "scary" too for those who will be contending in 2011...)
If it's not too personal, can you tell us more about the reason of the frase on the wing tip "Do You Believe it Now"?
Thanks and congrats!
Claudio
ARGENTINA
There are some who think that an electric stunt plane is NOT competitive at the top level. I intend to prove them wrong.
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psssst ... let them sleep further ;D ;D ;D
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Ignorance is bliss! ;D
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There are some who think that an electric stunt plane is NOT competitive at the top level. I intend to prove them wrong.
Paul
I really doubt that very much, anyone that is serious knows that there has been electric ships finish very high at the Worlds and at the U.S Team trials..I even heard rumors we had electric ships on the U.S team ;D
Randy
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I even heard rumors we had electric ships on the U.S team ;D
Randy
[/quote]
Yeah...Except it failed (pun intended) to make the trip!
Paul W
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Well Paul,
The Shrunken Impact has a really good new look to it! I like that Vertical fin.....Kinda reminds me of
the bigger All American Eagle.
O.K. You and Dave are all set to go get um at the WC's
1&2 Just don't know exactly which will be which yet, but with you tenacity. You could pull it off!
Jim Pollock
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I have now tried the prop that Dennis A generated. The APC 13 * 4.5, pusher.
I did a controlled experiment. First I made a 13 * 4.5 tractor from the very similar APC prop. Adjusted the speed to be about 5.5 sec/lap. Very nice performer and used less energy from the battery as well. It appears to be more efficient than the prop I had on it.
Then, I switched to the tractor. It flew at 5.4 sec/lap. I can see that I need to make a pusher prop pitch gage to compliment the tractor pitch gage. None the less, it was very noticable where it was "different" than the tractor. The takeoff, the outside turn on the horizontal eights, the outside portion of the vertical eight, the top of the hourglass, and the 3rd loop of the clover were all improved. I can see why some like it! I do see a decrease on the inside portion of the horizontal eights, but more testing in the wind is necessary to see if that is much of a problem.
All in all, I really like the APC props in this size on this airplane. I will have to try this pusher prop on the bigger planes to see if they work there as well.
Nice work Dennis in getting this prop to us!
Paul Walker
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Those look like really huge flaps! (or maybe a trick of the camera angle)....
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Glad to hear it, Paul!
How much less battery did you use?
Now we need to piece together a 3-blader using the same blades and do some limited testing before bugging our friends at APC for a new mold.
At least in Pattern, we foiund that their preferred mold base would at most accomodate a 13" 3-blader.
later,
Dean P.
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Thanks Bob,
I apparently forgot that Paul didn't fly at the Team Trials this year..... Oh well, there's always year after next!
Jim Pollock :-[
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Those look like really huge flaps! (or maybe a trick of the camera angle)....
It must be an illusion. They are only 20% flaps..Clearly not David Fitz size flaps, but not PatternMaster size flapseither.
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Glad to hear it, Paul!
How much less battery did you use?
Now we need to piece together a 3-blader using the same blades and do some limited testing before bugging our friends at APC for a new mold.
At least in Pattern, we foiund that their preferred mold base would at most accomodate a 13" 3-blader.
later,
Dean P.
Yes, sign me up for a test of the 13" 3 blader! I can't wait. A 3 blade pusher 13" prop! Yeah!!!
How much less....I was running about 2750 with the original prop. With the APC is is down to about 2250. Thats 82%...Quite a surprise it's that much to me.
Hope you enjoyed your party Sunday!
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Hi Paul
THANKS for the feedback. I was hoping to hear that you had a chance to fly the pusher, especially when I saw the numbers on the new Impact - seemed like it would be a great match. That is a huge difference in power draw - I thought there would be some but not THAT much. Heck you gotta chance to downsize your pack and score a couple fewer ounces if you choose.
When we first contacted APC they were dead cold to the idea of a 3-blader, but I'd really like to try one of those too... Maybe Dean & the RC pattern guys can get us an in???
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Pssttttt.,
don't LL~ tell anyone I showed this to you, its my total top secret setup lol,,
http://www.xoarintl.com/props/model-airplane/PJI-E.html
maybe they will flip the CNC machine language programing and mill a few pushers?
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Actually I emailed XOAR and asked about electric three blade pushers. here is the reply I got from them
*******
We have standard 13 x 4, 5,6,7,8 Price is $45/pcs tractor; $50 for pusher; Shipping & handling is not included;
However if you want to have 13 x 4.5, we can custom produce for you, there will be $100 tooling cost;
Those prop are considered as special prop, almost no dealer carries them, we will serve you on direct basis.
*****
so there is another option for you to consider.
Paul, if you want to see one of their props, I have several wood two blades, they are by far the prettiest wood props I have ever seen. every one I have opened has been balanced out of the package, and the finish is spectacular.
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Hi Guys!
Yes, Paul ... We had a blast. You should have been there.
Thanks for the info: 18% wasted (???!!!) energy. I gotta ask, was it really wasted or was there some benefit we should know about for educational purposes.
Maybe more testing is needed to be able to say if that is so.
Fred and Otto at APC used to be very accomodating, and I am sure they lost money on some of the goose-chases they were sent on.
Fortunately my main RC experimenting buddy Lockhart and I have sent them down way more good paths than some of the demanding big-name guys.
I will try, but only after we glue/screw a 3-blader together from the existing APC blades (That's how Bobba went to England in '88!) and fly it on a testbed. ~^
For $50 I'd order a pusher 3-bladed 13-5 from the XOAR folks. Expect maybe 7~10% more power consumption, but it'd be a great test.
If it works out well and APC never does make the 3-blader then you can thin the wooden blade airfoils and bag some carbon over them to restore stiffness.
later,
Dean P.
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Dean,
FYI, these props are pretty well thinned out already. They are very nice,, ( the electric ones especially so)
I should say, the two blades are, I havent stepped up to buy a three blade yet so I cant speak for them directly.
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At the cost of a prop and a half, one could make a 3-blade APC mold and crank out carbon copies.
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At the cost of a prop and a half, one could make a 3-blade APC mold and crank out carbon copies.
I'm glad to hear that you volunteered!
PW
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WoW!
Thanks Howard ...
(dog pile on the rabbit! dog pile on the rabbit!)
Dean
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Has anyone measured chords and airfoils of these lovely props? If somebody does that hard part, I can do a little advance comparison between the 2- and 3-bladers.
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Howard,
are you going to be in Portland? I will bring them with me. well the two blades, I havent invested in the three blade yet..
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I'll try to be there, but I kinda doubt it.
I was thinking of the APC prop. If the others hold together and are available to buy for less than $100, they wouldn't be worth making just for an experiment.
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I will try, but only after we glue/screw a 3-blader together from the existing APC blades (That's how Bobba went to England in '88!) and fly it on a testbed. ~^
You meant to say '78? ;)
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Howard, I have a couple of them (13-4.5 EP), I'd contribute. Would it take two or three? Guess it would depend on how you slice up the hub to get a mold. Might be faster and easier to get a subscription and get APC to do it, like the Adamisins did. I'd buy a half dozen or so.
John W
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Two oughta do it.
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If I understand the direction of this conversation correctly you are discussing taking an existing prop from a manufacturer, cutting it up, and molding a new prop from the commercially made prop. Before doing anything like that I would seek permission from APC or whoever's prop would be used. There is a lot of proprietary technology in these items and a lot of R&D expenditures, which I imagine APC (for example) would not like to see pirated. If for no other reason than avoiding bad feelings I would check with the manufacturer of the original before putting this idea into practice. These processes and the unique results (the prop) are intellectual property that is protected by federal and state law.
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I would mold these props for myself, for Science, and maybe for a friend or two. If they work, we can petition Fred to make some. If he doesn't want to make them, folks are out of luck: they aren't getting any from me.
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Hi Bruno!
Yes ... '78, exactly. HB~>
thanks and later,
Dean P.
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Paul,
I have been using the Orbit 25-12 with great results with the APC pusher prop. Just wondering what Orbit 20 you went to: the 20-12 or 20-14 and did you go to that due to the weight savings of 1.2 oz or just to reduce the power output??
Wayne
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Hello Wayne,
I'd be willing to bet that the Orbit 20-12 is not only lighter but makes more power on the same prop as the Orbit 25-12 due to its higher Kv.
Yes, motor losses might be a bit higher, but if the motor can stand the heat then why carry the extra weight?
Given that you don't want to keep putting bigger props on our planes for trimming reasons, this dictates a lower-bound Kv for a given size and battery voltage.
Sound right, Paul?
Dean
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Hello Dean,
Thanks for the info. Either one of these motors are very efficient and the 20-12 will indeed generate as much power as the 25-12 depending on the setting of the controller. I know the 25-12 is barely warm after a full flight so it is not being stressed much so I would expect the 20-12 to be close to the same but maybe a little warmer.
Wayne
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Exactly H^^
Even if the 20-12 wasn't very efficient, the motor with the higher Kv (just happens to be smaller) will put more power into the same prop at a given voltage, as well as into itself.
Dean
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Just for interest sake, the motor in Paul's plane is a Plettenberg Orbit 20 - 16 with 720 Kv
Battery is a 5S2P 4000 TP
Downsizing the battery to yield ultimate weight reduction kills the response of the ESC's governor mode. You MUST have sufficient overhead to feed the hungry beast. Too low a pitch and the effectiveness of the governor's boost comes in too late to be of optimum use. As the load increases in a corner you want the next revolution of the propeller to grab as much air as possible utilizing the largest amount of power possible to do the most work. Using a lower pitch prop, you will be further into the corner or past the corner because the esc needs to spin the rpm up much higher to achieve the same result. So IMHO higher pitch props work better.
Kim.
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Kim,
Thanks for your expert input. I realize that lowering the voltage will indeed affect the response of the esc and the response of the motor to those changes. Since you feel that a higher pitch prop would help minimize the problem, would a motor with a higher kv also help minimize the delay in the response assuming that the voltage is the same and the esc settings are the same?
Wayne
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Wayne,
If you hold the volts constant then rpm will be the Kv x Volts. So a higher Kv will yield just a higher potential rpm with an attendant increase in amp draw. It will not of itself make the motor spin up faster. The response rate is governed by the speed the ESC can recognize that the rpm has dropped, the power available to make the change (overhead), the torque available to turn the prop and the resistance to turning of the prop. IMHO if we had a power dependent system such that the model had less thrust than weight, then I might opt for the "lower" pitch solution. That is not the case however. My original power system could hover a 10lb model and climb out vertically. We never used all this power but it was there to be used and that is I think no different than the move to using .76 size IC engines with one important difference. There is a limit to how much more power you can "command" via a tuned pipe from an IC engine. There is no limit other than the potential energy available to the ESC from the battery pack to adjust the rpm of the motor. Since there is enough torque and power to turn the prop as fast as needed to restore the load induced rpm drop, I chose to run a "higher" pitch setup. This was part of our thinking in specifying the original system.
As Archie has said, there is more than one way to skin the cat. Your results may vary.
Blast away!
Kim.
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Kim,
Thanks for the explanation. There "is" always another way to skin a cat and I guess that is why there are so many flyers trying to find a system that will suit their particular flying style and get results that they are satisfied with if any of us can actually say we are "satisfied". Have a great flying season.
Wayne
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Kim,
Thanks for the explanation. There "is" always another way to skin a cat and I guess that is why there are so many flyers trying to find a system that will suit their particular flying style and get results that they are satisfied with if any of us can actually say we are "satisfied". Have a great flying season.
Wayne
Wayne,
I suppose if you are NOT using "my" system you might not be "satisfied". If however you ARE using "my" system I'm guessing
you are resonably content. :) y1
You have a great flying season too!
Kim LL~ LL~ LL~
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Hi Gang,
The old saying that, "There is more than one way to skin a cat" is true both in general and in this case, but choosing whether to start at neck, tail or a leg has to do with your priorities.
Kim is absolutely right when he says that voltage overhead is the key to excellent (not merely wonderful!) performance.
In my not-so bashful opinion, the combination of Kv and battery voltage should be much more than adequate for the chosen propellor and its pitch: so that there is at least 200 Wats per pound available under static conditions.
No, you'll never run that kind of power dissipation in flight, but "my" eventual goal is to end up with power management that will hit close to that figure for tenths of a second in critical places in the schedule.
Braking is improved with lower Pitch: Diameter ratios, especially in runway wind.
The downside is that prop efficiency and noise suffer.
It will make me quite sad if meaningful numbers of Electric Stunt flyers start running prop/pitch/RPM combinations that howl loudly.
(Historically speaking, the tuned pipe setup was largely created in order to deal with the criticisms heard in Hungary that the dominant 60 setups were too loud;
but eventually a fair number of pipe users adopted prop-noisy setups just because they liked the way they flew.)
My take on this is that prop tip velocities should be limited to prevent transonic tip noise (which also limits the prop efficiency loss some) so that RPM times diameter in inches is less than 130,000.
So 13" props should turn 10 grand or less ... Given a lap time and line length, we have a lower bound on pitch, and then it's a matter of picking a motor Kv and battery voltage that runs on 70 to 75% of the battery voltage.
Yes, motor efficiency and peak versus average battery currents will be higher than they could be with a system optimised for efficiency or battery weight but us lunatic fringe types like that!
On the other hand, if you are perfectly happy with a system biased in the "super quiet / super efficient / super light battery / low component stress" direction, then have at it! After all, it still runs great, time after time after time ...
Have I ranted long enough?
Actually, I will be happy to see the whole constellation of setups developed as time goes on, but please let's keep the prop tip howl at bay...
The rule makers bent over backward to make competitive E-Stunt possible, and the justification was and continues to be QUIET.
later Friends,
Dean Pappas
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Dean,
on the specific subject of prop noise, My UNDERSTANDING, not based on fact, more on circumstntial evidence, is that the shape of the prop tip seems almost as important as other factors in reducing prop generated noise. I have seen props on RC electrics that have a small "curl" ( Cant think of the name right of) Like the down turned tips on a lot of Cessna light planes. They seemed to be pretty quiet. Whats your take on the actual design of the prop, and specifically the tip, in reduction of noise?
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Hi Mark,
Well designed props can even be pushed to 140,000 rather than 130.
These are typically scimitar shaped and twist and resonance free because of their stiffness and blade width, which that makes them heavier than we want. HB~>
What is well designed? The scimitar shaped APCs are certainly among the most efficient and quiet out there.
Strangely the E-props APC sells are of somewhat different design, but they sure are light and efficient, and at our sizes and power levels I don't hear any flappy/gurgle-y sounds.
In the 20" diameter and 3 kilo-Watt sizes these problems have cropped up and APC are in the process of making subtle changes (small amounts of added weight to improve torsional rigidity)
The symptom there in F3A is that taking carbon cloth and CA to both sides of the prop actually reduced power consumption and raised W.O.T. ground RPM. Golly!
I've never seen the curled or Q-tips used to good effect in aeromodelling, but that's just 'cause I haven't seen a good setup yet. There aren't enough hours in a day, and yet some folks are bored ...
What sizes are offered?
later,
Dean
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I am on-board with Dean's 130k benchmark. Some empirical observation on noise - from a guy who wears hearing aids.
* Strega with 13x6.5 APC-E running 8200 RPM (106,600) = very quiet
* Strega with 13x4 APC-E running 11,000 RPM (143,000) = whiny loud
* Strega with 13x4.5 APC-E running 10,300 RPM (133,900) = noticable but not too bad
* Mythbuster with 11x5.5 APC-E running 9000 RPM (99,000) = uh, did you hear something???
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Dean,
The props I saw were on something like 40% IMAC planes if I recall, I dont know that I have seen them offered in our sizes, mine was a theoretical question mostly,,
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I just got this note from the folks at Xoar Props. I had inquired about the WWI line for my Jenny, but they also have a lot of different types including some for electrics.
Hello John - thank you for your email which was forwarded to us from Xoar Intl, we are their main US distributor.
Take a look at our website www.xoarprops.com where you'll see the range of props we carry. We have just extended our WWI range to include scimitar style WWI props from 10 x 6 upwards,
Please do not hesitate to call if you need any additional information,
kind regards
Julie
407 277 1248
Bob's Hobby Center "The home of Xoar Props"
> From: info@xoarintl.com
> To:jwitt
> Subject: RE: General Question
> Date: Tue, 20 Apr 2010 10:32:23 +0800
>
> Hey John,
> Thanks for your inquiry.
> Bob's Hobby Center have full Xoar line in stock.
>
> Please contact Steve or Julie: 407-277-1248
>
> Thanks for your support !
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I am on-board with Dean's 130k benchmark. Some empirical observation on noise - from a guy who wears hearing aids.
* Strega with 13x6.5 APC-E running 8200 RPM (106,600) = very quiet
* Strega with 13x4 APC-E running 11,000 RPM (143,000) = whiny loud
* Strega with 13x4.5 APC-E running 10,300 RPM (133,900) = noticable but not too bad
* Mythbuster with 11x5.5 APC-E running 9000 RPM (99,000) = uh, did you hear something???
So Dennis,
Do the hearing aids mean thatyou hear the highs better than many of us old codgers?
My teenager was demonstrating one of those "mosquito" cell-phone ring tones for me. I just barely heard it in a quiet environment.
later,
Dean
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Are we going to see a trend toward the 70's design now?
*cough* usa1 copy.. *cough.
;D S?P
I do like tho :)
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So Dennis,
Do the hearing aids mean thatyou hear the highs better than many of us old codgers?
My teenager was demonstrating one of those "mosquito" cell-phone ring tones for me. I just barely heard it in a quiet environment.
later,
Dean
For me it s mids to highs - like most of the tinkle tinkle musical ring tones. Also, the test Strega has a sound we have traced to the air ducting. I cannot hear it real time but can hear it on the video playback. WIth the t-coils active I can hear eletronic sounds - like when i'm driving and engaged the curise control, and I can hear the brake light switch. Have not tried listening for the PWM signal in the Phoenix tho...
PJ - I'd say your observation is pretty darned accurate!
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*cough* usa1 copy.. *cough.
;D S?P
I do like tho :)
I like it for the same reason too! This despite having been frightened by a man driving a '59 Caddy, as a small child.
Dean P.
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Looks good