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P-38 Lightning Brotherhood

Old 08-26-2014, 10:20 AM
  #601  
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Well... just remembered: amps x volts = watts

50a x 22v = 1100w

Is this the watt reading that I should shoot for during a static/bench test run?
Old 08-26-2014, 10:56 AM
  #602  
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Yes there you go.
The larger prop and more pitch will increase the Amp load. The old saying up an inch down in pitch or whatever doesn't apply directly to electric planes. For fuel engines you have a peak torque and RPM range you want to keep the engine running in to get the best performance from it. You have more torque and adjustability in an electric system. So look at the problem from a load point of view and relate it to the models performance or intended use. Voltage is king and being able to add more voltage will decrease the Amp load. So any time you can run more volts that will be better performing and more efficient.

So for you if your limited by space or weight to run 6S thats fine. Now test props to get to 1100-1400 or so Watts.

How many pounds does your plane weigh? AUW (All Up Weight)

Another indicator of model performance is the power to weight or Watts/Lb. For a scale model your shooting for more than 100 W/Lb and opinions vary on what this ratio should be.
A simple reality check is to look at the HP claimed on the engines you would normally run on the plane. Then convert their number to Watts. So 742 Watts per HP. If you would run a pair of engines which have a combined 4HP then 742 X 4 = 2968W. So 1400W is close to 2HP per motor for this plane.
I dont know the planes specs but knowing how to convert in and out of fuel engine specs and relating them to electric power will give you a good perspective on what you need to get similar or better performance than fuel power.
Old 08-26-2014, 11:03 AM
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Also a good thing to remember about calculating systems is to use Peak Values not Nominal. So a 2S pack is 7.4V but its peak voltage is 8.4V.
A LiPo cells nominal voltage is 3.7V but the peak voltage is 4.2V. Use the peak value always.
Old 08-26-2014, 11:21 AM
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Good point. I hadn't considered IC vs electric. Electric power (I think) would be much more linear across the rpm range.

Due to space and weight concerns, I'd really like to stay with 6s batteries. AUW is likely to be 18lbs.

I calculated watts using 22.0 volts. Even at 22v and 1100w x 2 = 2200w, I get 122watts/lb.

Using your info above, is peak voltage for a 6s battery 25.2v? If so, that works out to 2520w and 140watts/lb.

Please remember... I'm still learning. Am I understanding you correctly?
Old 08-26-2014, 11:40 AM
  #605  
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Yes the power is linear for the most part you get a lot of torque all the way to peak RPM.

Yes 2520W for the combined power and 140W/Lb

So back track for a moment, what are the ideal glow or gas engines for your plane?
Old 08-26-2014, 11:56 AM
  #606  
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Ideal? Good question. Way back when VQ still sold these planes... they said it was a 46 size. They also claimed 14lb to 16lb. I'm betting that was with no retracts or flaps and the smallest two stroke that would lift it off of the ground.

In reality, I think alot of guys were using 90 size four strokes.
Old 08-26-2014, 12:02 PM
  #607  
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Just looked... the Saito .91 four stroke generates 1.7hp... which would give 3.4hp in my case.

25.2v x 50a = 2530w/742 would give 3.39hp

Again... am I on the right track?

Last edited by sudstad; 08-26-2014 at 12:13 PM.
Old 08-26-2014, 12:49 PM
  #608  
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substad

What diameter props do you want to run?
Old 08-26-2014, 01:13 PM
  #609  
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I don't have a specific size in mind, although I'd like to run a larger more scale like size. eFlite calls for a 16x8 two blade. Armed with the info that you and Chris have provided... along with others I think I'm going to start with MA 16x8 three blade. If too large, I'll back down to their 15x7.

Your thoughts?
Old 08-26-2014, 01:48 PM
  #610  
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Its a warbird, you need to have some speed to overcome the weight/wing loading. Lots of good info, and lots of different ways to do the same thing. I don't worry to much about static numbers, I certainly check them, and use that data, but it's the flight numbers that matter to me. Your CC Edge ESCs do have datalogging, so get yourself the data link and cable http://www3.towerhobbies.com/cgi-bin...&I=LXGVR8&P=ML. Pretty easy to use. I do a ground run and make sure numbers match the watt meter, as a sanity check. Once you are ready to fly, make sure you clear data history before each flight, and try to get someone to video the flight. Makes it very easy to see what the plane was doing, vs performance numbers. But back to your props


I guess the big question is, do you like the way the 16" props look on the plane, or do they need to be smaller? I'm don't think I've seen a VQ with 16" props.
Old 08-26-2014, 01:58 PM
  #611  
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I've got the older CC Ice 100's. Will check on data logging on them!

Props... As far as I can tell, not many guys have electrified their VQ Lightnings. I need to go back thru a couple of threads to see what props they used. I'm not sure how 16's will look. They'll physically fit with decent clearance, but I suspect they'll be a bit on the "too large" size.

Have you seen any epowered VQ's? If so, what were they running.. motors and props wise?


EDIT: per eflite, the Ice 100's log Battery Voltage, Currents, Motor RPM, ESC Temperature and more.
Old 08-26-2014, 02:54 PM
  #612  
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One of the most important things for electric warbirds that a lot of people don't realize, is that the motor will not unload and increase it's RPM like a IC engine. You will not get the top end speed as you do with gas or nitro, unless you prop for it. Biplanes, high wing, aerobatics, 3D guys don't really care about speed, its all about thrust.

For the sake of argument, lets say a DLE35 will spin a Zinger 20x8 at 7150 on the ground, in the air the prop will unload and let the engine rev up to 8700 RPM. With no losses, an 8 pitch at 8700 RPM is 66MPH
Lets overpower the same plane with a big electric motor, say a AXI5345HD/14 on 10S. It should be able to spin that same prop at around 7200-7400 on the ground, and give incredible takeoff thrust. Once in flight, the motor RPM will increase as the prop unloads, but only until it gets to around 91% of its no load speed, or just about 7600 RPM. That's 57 MPH

IMO, this is were so many make the mistake with electric. Take that same motor, and put the 19x16 props EDFNUT is running, and you are close to 115MPH...with no losses. Put that prop on the DLE 35, and it won't run. In this case, a 10 pitch on the electric would give comparable performance at roughly 70 MPH, 12 pitch 86MPH prop speed.

I hope that makes some sense, but back to your props.

Second question, in the video I posted yesterday, are you looking to fly like I was flying between 2-3 minute mark? Faster? Slower? For reference, I wouldn't slow it down too much more than that. That was a 65 MPH prop speed, plane was probably around 55ish. When I did the fly by coming back across the field, after the failed landing, it started getting pretty mushy and I had to give it a little more throttle, I would say that was down in the 40s.

The 8 pitch props on the eflite 90s on 6S is 50MPH prop speed, or mid to low 40s plane speed

Last edited by 70 ragtop; 08-26-2014 at 06:27 PM.
Old 08-26-2014, 07:01 PM
  #613  
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I really like the APC 15.75x13x3 props. Beside the 90" P-38, I used that prop on a ESM Skyraider, & FW-190 both 10S setups, and am still using one on a 8.5 pound 60 size Corsair on 6S, and they all flew great. The KV on the Corsair is slightly lower than yours with a 6000RPM no load speed. It is a very nice enjoyable scale speed. The Corsair is lighter, and has a lot of wing area than your P-38, so I think your 325KV motors on 6S with the APC props would also be a great combo. I think you want a little more speed avalible. What has me concerned with that setup is the 1110 watt rating. Pretty sure you are going to exceed that a lot of the time.

Master Airscrew has a lot of choices, G sonics are very nice props.

Maybe do your first couple flights with a pair of APC 15x10E or 14x12 thin electric two blade props. Would be no question they are going to give you enough thrust, speed, and no overtaxing your motors. Can use the flight data form those flights to help pick the right props. Just leave the spinners off until you pick the final props, helps keep the motors cool anyways....just a thought

http://www.ecalc.ch/motorcalc.php?ecalc&lang=en

Last edited by 70 ragtop; 08-26-2014 at 07:11 PM.
Old 08-26-2014, 08:18 PM
  #614  
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The best props for scale electric are Vario because you can have both the scale diameter and you can dial in the pitch to suit the target Amp load. There are speed sport and scale blade choices too.

Vario props aside I normally use APC's for everything electric. They are designed correctly for gas glow and electric flight. Dont waste your time on anything else to be honest if your looking for performance. Scale is another issue and I go back to Vario for that.

The way I calculate my set up is to start with 11000RPM and figure out what the motor needs voltage-wise to get there based on its KV. I know ahead of time the motor class and then I choose the KV. I tend to stay on the higher voltage side on set ups. The reason I chose 11K RPM is because I know these systems run at around 80% efficiency so the in flight RPM will be around 9K RPM which is a pretty sweet spot. The props are designed for about 10K RPM and anything more is for high performance set ups as they get more critical as the speeds and RPM go up. There are high speed carbon props for real speed.

Now I know the motor RPM, battery voltage and ESC. Looking at the props in the range of my motors capability I choose the highest pitch I can to get the load right on the bench. Now I compare that data back to the target RPM I was going for which gives me an idea of the efficiency of the actual system compared to the estimates. The final verification is in flight data. I have found my estimates to be very close to the actual performance in flight and the planes have been a lot of fun to fly.

Sudstad you seem to be leaning towards scale so I would direct your attention to the 3 blade Vario Props. Ive used them and own 3,4 and 5 blade hubs.
In terms of scale diameter the full scale prop on a P-38 was 11'6" if memory serves. So to get the right diameter lets figure out the basic scale of this plane, its a 90 inch wing right? The wingspan on the P-38 is 52'0" so 624 inches divided by 90 inches is a factor 6.933 so call it 1/7 scale. The full scale prop dia is 138 inches so divided by 7 is 19 inches.
Pretty sure the motors you are running and a three blade prop like Master are not going to work for a couple of reasons. Poor blade design being one.
It might be a stretch to try and get a 19 inch two blade fixed pitch prop to work let alone a three blade on the motors you have. So your going to have to test and see what the real numbers are to make a compromise on the size.
Once you settle on a two blade dia and pitch then take a good look at the Vario Props and choose a 3 blade hub to fit the motors. You can change out blades cheaply its the hub thats a little bit expensive but then you have it and you can change styles and diameters very easy.

Also keep in mind the highest stress you will put your power system thru is on the bench. The air is static and the cooling is not optimal because there is no boundary layer flow or air pressure from the speed. Things will run cooler and better in the air usually.

Last edited by Chris Nicastro; 08-26-2014 at 08:53 PM.
Old 08-26-2014, 08:48 PM
  #615  
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This is what 19.9" Vario props look like on a 100" P-38, very nice props, but I have no flight experience with them yet. I have learned it takes a lot of energy to spin props at IC RPMs. You can get better performance spinning higher pitched props at a lower RPM....for a given amount of power. Problem is finding the props you want. APC has a lot of higher pitch 2 blade props, but a very limited three blade selection. I think the 15.75x13x3 APC would be perfect on this plane (if they look OK) spinning in the mid to high 5K range (at your motors power level). I've been looking over my datalogs, and if the KV on the eflites was just a little lower, it would be okay on watts as well. At 6494 RPM, which is 90% of the no load RPM, I think it will be pulling more than 1110 watts most of the time.

I would maiden it with one of the APC thin electric two blade props and go from there. Will likely end up with MA 14x9 or 16x10 maybe trimmed and rounded to 15x10. Good thing is all these props are relatively cheap. Don't get hung up on static numbers with MA or G sonic props, they both unload a lot in flight

Links to check out G sonic props, vario props, and MA
http://www.ramoser.de/home_e/variopr...rioprop_e.html
http://www.allerc.com/props-graupner...-c-36_444.html
http://www3.towerhobbies.com/cgi-bin...2Fb%3E+3-blade

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Last edited by 70 ragtop; 08-26-2014 at 09:30 PM.
Old 08-26-2014, 10:34 PM
  #616  
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The DLE 35RA can only turn a 18x10 up to 7300 rpm, I just went thru this a couple hours ago here in front of the garage on the P-38 Im working on. The IC RPMs and the electrics are very similar in sport applications.

The reason IC props are thicker and heavier is because of the power stroke and the shock that imparts on the prop. The extra thickness is there to deal with the frequency they operate at. Since there isnt a power stroke in electric motors the props can be lighter and thin.

APC E props are designed to run optimally at high RPM. Take the diameter and divide their safety factor by the diameter you want to run. For E props the number is 145000. So 145000/16 = 9062RPM. Thats the max recommended RPM for the diameter. The RPM goes down as the diameter goes up. For a 19 in prop they suggest 7600 RPM.

Thats why, for me anyways, I set up for the more predictable 80-85% performance mark because there are too many factors and costs associated with trying to reach 90% or better. So starting with 11K RPM as a target and getting close on paper with the component specs the end result is good.

Setting up for high pitch and low RPM means your pulling more Amps and the flight times are generally shorter. Also the batteries run hot in flight which is ok if you can manage cooling them enough.
For me 5 min flight times are no fun so I shoot for 8-10 min.

You can turn a prop at higher RPM with less pitch and more voltage and reach the same speed but you will do it more efficiently. The components will run cooler while giving more flight time because the Amp load is less.

One could argue for a high KV but thats a losing battle because higher KV = less torque = higher Amps
Lower KV = more torque = lower Amps
For the same motor at a given KV you will do better with a higher voltage set up AND get better performance. There are limits of course. Volts are king, the single greatest improvement to performance for a low weight penalty or slight cost is adding another cell or two.

There is a whole other discussion on motor design (diameter, magnet length, KV, format) that should accompany this topic of KV and operating voltage. Understanding motors really helps when choosing a set up.
Old 08-27-2014, 05:15 AM
  #617  
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Chris
I used someone else's posting for DLE data. They got their in-flight numbers using telemetry, which is why I used it for a comparison.
"I am hoping this will improve somewhat with more time on the engine, I flew it last weekend with a 20" 10-6" (8" average?) woodie (not bad profile) and the telemetry showed me that it peaked out past 8700rpm in flight but on the ground I was only getting 7150rpm"

No idea what plane this was on, imagine is a light weight aerobatic or 3D type, but yes a 20" prop seems like a lot. We also know the AXI5345HD-14 will spin a much bigger prop than a 20x8. Wasn't going to get into the ZInger dual pitch, just called it 8. My intent was to try and show how the two will compare in flight during a warbird flight routine. You would be very disappointed if you propped a DLE and the AXI the same way

I land early by choice, but the setup has a lot of time left in it. Been down the road of spinning the props fast, and it works great on smaller stuff. My favorite plane is the Deuces Wild you see in some of my pictures in the shop. It is spinning a pair of APC 10x10E at 13K RPM, it is very easy on equipment, and is a blast to fly. In the larger sizes, I also went for the high RPMs initially, and they sound cool with lots of prop rip as they scream by, but those setups were harder on batteries, IMHO. I slowed down the RPMs, and upped the pitch, and they are just as fast, and easier on equipment and battery's. Yes, cooling is king. You can get away with a lot more if it is properly cooled. Another area too many don't address

We have different philosophies on setup, and that's fine. As long as it works, that's all the matters. I just hate it when people bad mouth electric as being under powered, when in fact its because they are not setup right from the start.
Old 08-27-2014, 06:41 AM
  #618  
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I agree once you get up to motors in the range of 50-60mm dia its ok to set up more pitch and slower RPM. Ive run a 5330/24 on a couple of planes and it works fine but you still mind the loads and test props. It could turn a 24in prop at 48A on 10S but that was years ago on earlier battery tech. Today with decent LiPos Im sure it would do even better.

I thought the DLE data you posted was ground tested I thought no way Im getting those figures! I just dont see the DLE 35RA really making good use from much more than the 18X10 at this point. Its like the 55RA I have I tried different props and like you I tried a 22x6/10 and the result was poor on a TF Corsair. It just screamed and went nowhere. I landed almost immediately and changed back to 22x10. The blended pitch lets the engine turn high revs but its not pulling as hard.

Point of fact about electrics is that there are no IC engines that can produce more HP than even a conservative out runner motor set up in each engine class. Brushless systems out perform gas and nitro engines in just about every application except turbines. Even then EDF set ups can out perform the smaller turbines until about 90-100mm and then turbines take over due to cost, performance and reliability. Plus a jet engine is a jet engine, you fire one up and everyone knows whats under the hood, the cool factor is 10! Thats why I prefer turbines but thats another story.
Old 08-27-2014, 08:12 AM
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I spent 7 intense years designing and developing brushless systems and batteries and going to Chinese factories. Im burned out on electrics to be honest. I really like the new smaller gas engines that have come out on the scene the last couple years. I dropped out of using the larger power systems because of maintaining battery packs and reliability issues in ESC's for the most part. So glad I never paid for them as we used a lot of packs up thru hard testing and destructive testing. The most reliable component out of the three used in a brushless system tends to be the motor. Then the battery packs if used within their range are very reliable, less than 1% defect rate in production. The ESC's... not so much. Remember Castles debacle a few years ago with exploding capacitors? Even they have problems keeping things together from time to time.
When it comes to ESC's you have to spend the money if you want performance and more reliability. Theres a threshold I believe that once you get past a certain amount of power like around 2.5KW you really have to watch what you do. Ive run up to 7KW systems in boats which are unforgiving applications and it gets real intense. Ive had several ESC's explode in testing and catch fire.
Ive seen more regular production ESC's of all kinds have more failures than any other component and from multiple companies. Its a very technically challenging component. The saying buy nice or buy twice to so true about ESC's. In this case nice is like Castle's upper end line and Jeti, Komtronics and a couple other European brands. Your going to drop a few hundred dollars on an ESC theres just no doubt about it and thats just to fly nice planes over 18lbs with great performance and especially EDF. All that being said a guy could screw up even the best ESC with a poor installation, wrong prop, or just improper usage. Theres no guarantee. So I didnt see the benefits only the costs and risks associated with high power EDF and I went ahead and got my turbine waiver.

I still remember a lot of the info on this stuff but I don't really practice it anymore. Im back to the really small stuff and some EDF and thats about it in brushless for now. I think its more practical and cheaper to run gas engines and turbines than to manage a bunch of different size LiPo packs all year round trying to protect and prolong your investment in batteries.

Sooo... How does all of this relate back to P-38's? Simple, take my advice and burn fuel! Lol, its so much better these days with small gas engines, cheaper, clean, sounds good, great power, light weight, reliable... What more do you want? Just remember buy nice or buy twice, it works the same in engines too!
Old 08-27-2014, 09:20 AM
  #620  
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Originally Posted by Chris Nicastro
Even then EDF set ups can out perform the smaller turbines until about 90-100mm and then turbines take over due to cost, performance and reliability. Plus a jet engine is a jet engine, you fire one up and everyone knows whats under the hood, the cool factor is 10! Thats why I prefer turbines but thats another story.
I'm a jet guy at heart, sold off all my ducted fan stuff late 90's early 2000s. Flying fields are a challenge around here. I have a BVM F-16 kicking around that I've been thinking of converting, and a bunch of foamie EDFs, but to be honest the Deuces Wild will spank all the foamies...at least all the ones that I have

I ran across a thread on RCG about the Jetfan 90 a while back....very cool. http://www.rcgroups.com/forums/showthread.php?t=1504718
Once I saw the old ICDFs getting converted to this fan, and the performance they were getting, the wheels started turning again. If you haven't seen these videos, you have got to go thru that thread and check out the videos, especially of Rainer's old Aggressor II

We were at Top Gun in 94 when Bob F flew both the Black Bunny F-14, and his twin Hornet, both Yellow models. Unfortunately the Hornet went in that year. That was also the first US demo of a Turbine, French engine I think...nothing like the performance we have today

Anyways, always loved the F-14, and seeing Bob put the Yellow model thru its paces left a long lasting impression. I ran across a NIB DCU/Jetmart F-14 a couple weeks ago, and we agreed on a fair price. It's a lot smaller than the SM, and the unspeakable FEJ F-14's, but I'm thinking its a good size for the 90mm Jetfans, just have to be mindful of weight. Maybe someday I'll jump back into jets with both feet, just need a farm, and a paved runway close by before I do! But for now, I am looking forward to this build, and learning another side of this hobby
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Old 08-27-2014, 09:34 AM
  #621  
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Originally Posted by Chris Nicastro

I still remember a lot of the info on this stuff but I don't really practice it anymore. Im back to the really small stuff and some EDF and thats about it in brushless for now. I think its more practical and cheaper to run gas engines and turbines than to manage a bunch of different size LiPo packs all year round trying to protect and prolong your investment in batteries.

Sooo... How does all of this relate back to P-38's? Simple, take my advice and burn fuel! Lol, its so much better these days with small gas engines, cheaper, clean, sounds good, great power, light weight, reliable... What more do you want? Just remember buy nice or buy twice, it works the same in engines too!

I'm still looking for my limit, and I think I'm there. Just finishing up a 50CC size ESM Dora. I have not flown it yet, but very close. I debated gas vs trons, and decided to try electric at this size. I'm really not sure I'm going to like it, but we will see. A G-62 would fly the plane around very nicely, they are super dependable, cheap, and last FOREVER. I might switch it back to gas, I might love the electric....we will see.

I do miss the twin gassers sound when they're sync'd up, and go screaming by. Have a ESM Tigercat kicking around that was slated for electric, but I'm thinking of going gas with smoke systems. Much bigger tail on the Tigercat. Much higher probability of saving it if you loose an engine. The P-38, not so much

Last edited by 70 ragtop; 08-27-2014 at 09:37 AM.
Old 08-27-2014, 10:11 AM
  #622  
sudstad
 
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Wow! Yet another tremendous amount of info for a noob to absorb! :-)

My VQ has an 82" wing and is 1/7.5'ish scale. I'm expecting 18lbs. Wing loading of 49oz/sq ft.

I don't know the net affect of going from a 16x8 to a 15.75x13 will be. Knocking-off 1/4" at the tip of a 16" arc is a fair amount of "swept area"(?). Can an eflite 90/Castle Ice 100/6s 5000mah combo swing it?

Unloaded rpm on 6s would be 8190. 90% of that would be 7371. What pitch would I need to get it into the 90-100mph range? I ask because my VQ FW-190 flew very nicely at 85mph... with 35oz/sq ft wing loading.
Old 08-27-2014, 10:27 AM
  #623  
70 ragtop
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My 90" p-38 was in the low 90's in that video. I don't think it broke a 100.

You loose a lot spinning three blade props vs two blade, my goal was to keep the motors happy spinning the 3 blade APC props, not top speed

Yes your setup will spin it, but I don't think you will stay within the rated limit. If the motors were in the airstream, would most likely be fine. Behind a spinner, with no cooling air... Most likely will not be OK for long

Since you have everything, I would try the APC 15x10, or 14x12 thin electric two blade props for your maiden. Get the plane sorted out, and use the flight data to help pick the right 3 blades

Edit. I don't think using full pack volts to figure RPM is right as the voltage drops under load, the higher the load, the higher the voltage drop. I am happy to email you the data files using a few different size three blade props. If you download the castle link software from their website, you can open the file using the Castle link graph viewer. You can scroll thru the data and see how much power it takes to spin a given RPM. It is not exact as different motors will require different power to spin the same prop, but its great reference data. Once a motor passes it highest efficiency range, it continues to try to spin the prop. The amp draw with increase, voltage drop increases, heat increases. That's why I switched motors, the APC were just a little to big for the Scorpions

Again, I think your are going to end up with MA14x9x3 (little too small), the MA16x10, or better yet, the 16x10 trimmed down with rounded tips to make them 15x10 to get a little more RPM. IMO, you need around a 14.5 -15x12x3 E prop, which I am not aware of anyone who makes one....except Vario prop adjustable props

Go on E calc, and use the spreadsheet I posted, great resources
http://www.ecalc.ch/motorcalc.php?ecalc&lang=en

Last edited by 70 ragtop; 08-27-2014 at 11:22 AM.
Old 08-27-2014, 11:24 AM
  #624  
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This is my yellow P-38 100 inch with zenoah 38s. This was done up in Richard Bongs plane with his girlfriends picture on the side named Marge. You can see the real one at the EAA museum in Oshkosh WI. These pictures are from the 2003 nationals at Muncie IN.
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Old 08-27-2014, 12:19 PM
  #625  
Chris Nicastro
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The reason I use full voltage values is because I deduct 20% off the total. My logged results came very close to my predictions very often. I know its not conventional but I needed someway to layout set ups quickly and then go test. That was before there was a lot of good community info on motors batteries and ESC's in common configurations. There should be good data on Eflite 90's and CC100 ESC's. However any data you find online or in an ECalc will still be an approximate value. You still have to test and use the Watt Meter and Data Logger to get your installed info with your components.
Ive seen several people do the "same" thing and get different results. Thats why Im making more general comments and encouraging everyone to go thru the motions.

Heres what we know so far on Sudstad's set up;

Eflite 90 outrunner motors - 50+ Amp rated 325KV
CC 100A ESC's
6S 5000mah packs
Rcommended prop 16x8

i just read the review on the motor on Horizons site and a guy posted good info, you should read that.

"I installed a power 90 in a Great Planes GeeBee R-2 13lbs6oz, then a Great Planes Ryan STA 13 lbs 14oz and again in a 86" PT-19. 13lbs6oz. In each case the Power 90 flew the airplanes better than a 1.20FS and a 108 (PT-19). On 8s5000, Castle 100, Zinger 16/8, full throttle is 62.3 amps, 29.52 volts 1839 watts, 8380rpm, all figures from a bench test, using a fully charged battery; verified in each airplane. 6 clicks throttle back produced 50 amps, 7740 rpm, which is great for cruise and smooth acro. Average flight times are about 7 minutes, cell voltage runs from 3.6 to 3.8 after each flight. So far 12 flights on the three airplanes! This is a great combination; the motor is underrated. My next conversion is the Great Planes Chipmunk. Great product, I'll put a Power 60 in a Great Planes Folker tripe after the Chipmunk."

Thats all you need to know and then you have some testing and choices to make. My personal opinion is to step up to 8S power and go ahead and fly on 16x8 APC E props. On 6S it looks like this motor will be weak. Seems pretty inefficient compared to an AXI 53XX series motor because those can handle more prop, 20+ inch dia, for the same basic power.

The RMP loaded on 6S will be pretty low from what Im seeing here. I would try testing the 18X8 prop because the rpm is going to be around 6600RPM and thats 2000rpm below optimal. Just have to see what the actual Amp load is and temps.

So for example I was saying deduct 20% and its pretty close right?
The guy that posted the review claims 8380RPM on 8S
Do the math and peak voltage on 8S is 33.6 X 325KV = 10920RPM
Thats 77% or 23% loss how ever you want to call it.
APC claims 9062RPM to be their safe limit so this guy is enjoying this set up because its spot on for what it is.

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