All Us intermediate pilots, Lets Share

[Grossman56]

RE: All Us intermediate pilots, Lets Share

Okay, let me get this straight, the higher the cell count the smaller the pitch. Correct? A brief explanation maybe?
Right now, I've increased the pitch and went a 580kv motor over the stock 540kv. So, if I'm using the 4 cell I'm good, but if I go the 5 cell I should reduce the pitch, then what is there to gain by going the extra cell?

On another note, Pandora two got stripped down and she's  in the process of a repaint.  Right now she's bright yellow, pictures to come...
I found this great set of videos on repainting a foam airplane, check it out
https://www.youtube.com/watch?v=FXSSPvyPfVs
A lot of great information on them

Grossman56
[hr]
Here she is so far.  She was stripped of decals and rubbed down with Acetone, given a coat of Minwax and then hit with the paint.  A Spray paint/primer combination from Rustoleum.  So far So good...

Grossman56

[Lon]

RE: All Us intermediate pilots, Lets Share

Okay, let me get this straight, the higher the cell count the smaller the pitch. Correct? A brief explanation maybe?
Right now, I've increased the pitch and went a 580kv motor over the stock 540kv. So, if I'm using the 4 cell I'm good, but if I go the 5 cell I should reduce the pitch, then what is there to gain by going the extra cell?

On another note, Pandora two got stripped down and she's  in the process of a repaint.  Right now she's bright yellow, pictures to come...
I found this great set of videos on repainting a foam airplane, check it out
https://www.youtube.com/watch?v=FXSSPvyPfVs
A lot of great information on them

Grossman56

[hr]
Here she is so far.  She was stripped of decals and rubbed down with Acetone, given a coat of Minwax and then hit with the paint.  A Spray paint/primer combination from Rustoleum.  So far So good...

Grossman56

Gman,
Before i decided and switched to running 5s  on my FW Mustang. I did alot of research. With that, I felt comfortable that the motor was designed to run on 5s, but upgraded the ESC. With the way I fly, and the type of plane i'm flying. I'm very comfortable running with the same prop setup on 5s that i run with the 4s. Except for a few times when the temp was in the 90 range. My motor and ESC is just warm to the touch. And yesterday and today when i flew(47-52 degrees F) of course, everything was barely warm to the touch of my cold hands. I have over 300 flights on this setup now :).

[Konrad]

RE: All Us intermediate pilots, Lets Share

It has to do with how a prop absorbs power. Power = K x Dia.(4th) x Pitch x RPM(3rd). "K" is just a constant used to explain the shape of the prop blade. It often varies as a non dimensional value between 1.18 to 1.31 for our toy props.

Also lift for a wing is defined as a function of velocity squared through the air.

And drag on the airframe goes up by the cube of the velocity.

Now we know that the prop (pitch) speed is the motor RPM x Pitch. And the motor RPM is a voltage x (Motor Kv)
So the aircraft speed is; Speed = V x Kv x pitch

So for any motor to give the same airframe speed at a higher voltage the pitch needs to be lowered.

Now to stay within the power rating of the motor the diameter also should be lowered. Since the diameter effect power by the 4th function a small change in diameter has a large effect on power.

We can go into a lot more detail but I think you get the idea. To keep the power the same and the speed the same for the increased voltage the prop needs to be changed. Actually both the diameter and the pitch need to be lowered when going up with the cell count if one wants the model to fly much the same between both batteries.

All the best,
Konrad

[Konrad]

RE: All Us intermediate pilots, Lets Share

To answer Grossman56 question; "So, if I'm using the 4 cell I'm good, but if I go the 5 cell I should reduce the pitch, then what is there to gain by going the extra cell? You can gain efficiency from a lower amp draw (less heat losses) longer run time. And/or you can gain power as a result of the efficiency gains by bring back some of the amp draw with less heat loss than you had at the lower voltages.

But for the most part power is power, wether you get it by increasing the amp draw or increasing the voltage. Power =Amps x Voltage so you can play around with ether one or both to find the best balance with what you might have on hand.

Given a choice I go with the highest voltage I can as long as I don't have to change the ESC or my charger.

[Lon]

RE: All Us intermediate pilots, Lets Share

It has to do with how a prop absorbs power. Power = K x Dia.(4th) x Pitch x RPM(3rd).   "K" is just a constant used to explain the shape of the prop blade. It often varies as a non dimensional value between 1.18 to 1.31 for our toy props.

Also lift for a wing is defined as a function of velocity squared through the air.

And drag on the airframe goes up by the cube of the velocity.

Now we know that the prop (pitch) speed is the motor RPM x Pitch. And the motor RPM is a voltage x (Motor Kv)
So the  aircraft speed is; Speed = V x Kv x pitch

So for any motor to give the same airframe speed at a higher voltage the pitch needs to be lowered.

Now to stay within the power rating of the motor the diameter also should be lowered. Since the diameter effect power by the 4th function a small change in diameter has a large effect on power.

We can go into a lot more detail but I think you get the idea. To keep the power the same and the speed the same for the increased voltage the prop needs to be changed. Actually both the diameter and the pitch need to be lowered when going up with the cell count if one wants the model to fly much the same between both batteries.

All the best,
Konrad

Konrad,

Great information, but help me here.....I'm fairly new at flying here. But your statement of "To keep the power the same and the speed the same for the increased voltage the prop needs to be changed" Now i'm probably confused because of my life experience in boating all my life. But when it come to the pitch and diameter of my prop on the boat, whether that prop was being powered by a 4cyl 140hp engine, or a big block 500hp engine. At 3,000 rpms, the boat traveled at the same speed. So wouldn't that be the same with my plane? Same rpm=same speed? It's just that i have more voltage available, which means i can turn more rpm's, along with increasing rpm's at a quicker rate. Guess i try to keep things in simple terms, so as not to give myself a brain cramp.

[Konrad]

RE: All Us intermediate pilots, Lets Share

It has to do with how a prop absorbs power. Power = K x Dia.(4th) x Pitch x RPM(3rd).   "K" is just a constant used to explain the shape of the prop blade. It often varies as a non dimensional value between 1.18 to 1.31 for our toy props.

Also lift for a wing is defined as a function of velocity squared through the air.

And drag on the airframe goes up by the cube of the velocity.

Now we know that the prop (pitch) speed is the motor RPM x Pitch. And the motor RPM is a voltage x (Motor Kv)
So the  aircraft speed is; Speed = V x Kv x pitch

So for any motor to give the same airframe speed at a higher voltage the pitch needs to be lowered.

Now to stay within the power rating of the motor the diameter also should be lowered. Since the diameter effect power by the 4th function a small change in diameter has a large effect on power.

We can go into a lot more detail but I think you get the idea. To keep the power the same and the speed the same for the increased voltage the prop needs to be changed. Actually both the diameter and the pitch need to be lowered when going up with the cell count if one wants the model to fly much the same between both batteries.

All the best,
Konrad

Konrad,

Great information, but help me here.....I'm fairly new at flying here. But your statement of "To keep the power the same and the speed the same for the increased voltage the prop needs to be changed" Now i'm probably confused because of my life experience in boating all my life. But when it come to the pitch and diameter of my prop on the boat, whether that prop was being powered by a 4cyl 140hp engine, or a big block 500hp engine. At 3,000 rpms, the boat traveled at the same speed. So wouldn't that be the same with my plane? Same rpm=same speed? It's just that i have more voltage available, which means i can turn more rpm's, along with increasing rpm's at a quicker rate. Guess i try to keep things in simple terms, so as not to give myself a brain cramp.

Yes, on your boat the prop at 3K rpm will draw the same power regardless of the engine. But the 4 cylinder will be at full throttle and the Olds 455 will barely be above idle, yet both engines will be producing the same torque.

"Quickness" is how fast something accelerates, that's another issue.

But at full power the higher voltage set up with the same motor and prop will draw way more power (way more rpm). Now things get a bit more complicated as our ESC supply the motor with the full battery voltage no matter the throttle setting. The difference is that the amount of time the motor windings see this full voltage that gives us the apparent throttle control. This is why ESC manufactures say that running a partial throttle will not allow you to run an under rated ESC. On the oscilloscope peak volts x amps is still the same no matter the throttle setting. It is just that the "on" time is less for any clock cycle (frequency) at partial throttle, this is called pulse width modulation.

So for our models lower the pitch (and maybe the diameter a bit) to keep the peak amps within the design limit of the ESC and motor.  Lower the pitch to stay within the safe airspeed of the airframe (avoid flutter).

See Castle Creations FAQ last entry on the bottom of the page
http://www.castlecreations.com/support/faq/faq-general.html#gen6

[Lon]

RE: All Us intermediate pilots, Lets Share

It has to do with how a prop absorbs power. Power = K x Dia.(4th) x Pitch x RPM(3rd).   "K" is just a constant used to explain the shape of the prop blade. It often varies as a non dimensional value between 1.18 to 1.31 for our toy props.

Also lift for a wing is defined as a function of velocity squared through the air.

And drag on the airframe goes up by the cube of the velocity.

Now we know that the prop (pitch) speed is the motor RPM x Pitch. And the motor RPM is a voltage x (Motor Kv)
So the  aircraft speed is; Speed = V x Kv x pitch

So for any motor to give the same airframe speed at a higher voltage the pitch needs to be lowered.

Now to stay within the power rating of the motor the diameter also should be lowered. Since the diameter effect power by the 4th function a small change in diameter has a large effect on power.

We can go into a lot more detail but I think you get the idea. To keep the power the same and the speed the same for the increased voltage the prop needs to be changed. Actually both the diameter and the pitch need to be lowered when going up with the cell count if one wants the model to fly much the same between both batteries.

All the best,
Konrad

Konrad,

Great information, but help me here.....I'm fairly new at flying here. But your statement of "To keep the power the same and the speed the same for the increased voltage the prop needs to be changed" Now i'm probably confused because of my life experience in boating all my life. But when it come to the pitch and diameter of my prop on the boat, whether that prop was being powered by a 4cyl 140hp engine, or a big block 500hp engine. At 3,000 rpms, the boat traveled at the same speed. So wouldn't that be the same with my plane? Same rpm=same speed? It's just that i have more voltage available, which means i can turn more rpm's, along with increasing rpm's at a quicker rate. Guess i try to keep things in simple terms, so as not to give myself a brain cramp.

Yes, on your boat the prop at 3K rpm will draw the same power regardless of the engine. But the 4 cylinder will be at full throttle and the Olds 455 will barely be above idle, yet both engines will be producing the same torque.

"Quickness" is how fast something accelerates, that's another issue.

But at full power the higher voltage set up with the same motor and prop will draw way more power (way more rpm). Now things get a bit more complicated as our ESC supply the motor with the full battery voltage no matter the throttle setting. The difference is that the amount of time the motor windings see this full voltage that gives us the apparent throttle control. This is why ESC manufactures say that running a partial throttle will not allow you to run an under rated ESC. On the oscilloscope peak volts x amps is still the same no matter the throttle setting. It is just that the "on" time is less for any clock cycle (frequency) at partial throttle, this is called pulse width modulation.

So for our models lower the pitch (and maybe the diameter a bit) to keep the peak amps within the design limit of the ESC and motor.  Lower the pitch to stay within the safe airspeed of the airframe (avoid flutter).

See Castle Creations FAQ last entry on the bottom of the page
http://www.castlecreations.com/support/faq/faq-general.html#gen6

Konrad....yes....i am/was on the same page as you for sure. I just had to express(talk to myself) in more familiar terms from boating, and all the different things that are effected by just increasing horsepower in boats, and how just voltage increase effects so much on our planes.

[Konrad]

RE: All Us intermediate pilots, Lets Share

Now just a bit of a mind game here. That prop on that 140hp engine when driven at full throttle by that 500 hp engine might be turning 5300 rpm giving you an increase pitch speed of 1.76 time more speed. But to get that added 1.76 increase in speed took over 3.5 time more power.  This is assuming that the engine is not rpm or torque limited and the hull is still in displacement mode (not planing).

Now I often have to warn guys coming from the IC world (hot rods, boats and such) that an electric motor's power curve is sloped in the opposite direction from that of an IC engine. That is the power at full throttle for an electric motor goes up as the rpm go down. This is just the opposite for an IC engine. This has all sorts of ramifications when it come to unloading of props. An Ic engine often will jump into its power band when unloaded while the electric engine will see a drop in the amp draw when unloaded. This is a good demonstration as to why you should not run an electric motor driving a prop at full power on the bench for more than a few seconds.

All the best,
Konrad

[Lon]

RE: All Us intermediate pilots, Lets Share

Okay, let me get this straight, the higher the cell count the smaller the pitch. Correct? A brief explanation maybe?
Right now, I've increased the pitch and went a 580kv motor over the stock 540kv. So, if I'm using the 4 cell I'm good, but if I go the 5 cell I should reduce the pitch, then what is there to gain by going the extra cell?

On another note, Pandora two got stripped down and she's  in the process of a repaint.  Right now she's bright yellow, pictures to come...
I found this great set of videos on repainting a foam airplane, check it out
https://www.youtube.com/watch?v=FXSSPvyPfVs
A lot of great information on them

Grossman56

[hr]
Here she is so far.  She was stripped of decals and rubbed down with Acetone, given a coat of Minwax and then hit with the paint.  A Spray paint/primer combination from Rustoleum.  So far So good...

Grossman56

Hey Gman.....are you clear now on the higher cell and lower pitch brief explanation by Konrad?  :)

[Grossman56]

RE: All Us intermediate pilots, Lets Share

Well, I'll tell you.... I'm going to print it out and go over each step until I'm good with it.
Man, I do appreciate guys like Konrad and Lon, your knowledge is only surpassed by your willingness to pass it along.  Thanks guys, I really appreciate it!!

Grossman56

Busy hanging Christmas lights, the weather is beautiful here, that will change!!

[OV10]

RE: All Us intermediate pilots, Lets Share

Well, I'll tell you.... I'm going to print it out and go over each step until I'm good with it.
Man, I do appreciate guys like Konrad and Lon, your knowledge is only surpassed by your willingness to pass it along.  Thanks guys, I really appreciate it!!

Grossman56

Busy hanging Christmas lights, the weather is beautiful here, that will change!!

Hey Gman,
Those lights go on the house - not the Pandora !!!! :D

[Konrad]

RE: All Us intermediate pilots, Lets Share

My pleasure. I try to keep the math and esoteric discussions to a minimum. As an engineer I might go off the deep end. So let me apologize ahead of time. But if things still seem cloudy please keep asking for clarification, as my simplification of topics can at times actually make things less clear.

All the best,
Konrad

[Grossman56]

RE: All Us intermediate pilots, Lets Share

My pleasure. I try to keep the math and esoteric discussions to a minimum. As an engineer I might go off the deep end. So let me  apologize ahead of time. But if things still seem cloudy please keep asking for clarification, as my simplification of topics can at times actually make things less clear.

All the best,
Konrad

Hey Konrad, I sincerely appreciate the effort, thanks again!

Grossman56

[Pheonix]

RE: All Us intermediate pilots, Lets Share

Okay, let me get this straight, the higher the cell count the smaller the pitch. Correct? A brief explanation maybe?
Right now, I've increased the pitch and went a 580kv motor over the stock 540kv. So, if I'm using the 4 cell I'm good, but if I go the 5 cell I should reduce the pitch, then what is there to gain by going the extra cell?

On another note, Pandora two got stripped down and she's  in the process of a repaint.  Right now she's bright yellow, pictures to come...
I found this great set of videos on repainting a foam airplane, check it out
https://www.youtube.com/watch?v=FXSSPvyPfVs
A lot of great information on them

Grossman56


[hr]
Here she is so far.  She was stripped of decals and rubbed down with Acetone, given a coat of Minwax and then hit with the paint.  A Spray paint/primer combination from Rustoleum.  So far So good...

Grossman56

Hey Gman.....are you clear now on the higher cell and lower pitch brief explanation by Konrad?  :)

I am so glad I read this.  I think it is clear to me know.  Konrad, where is you book?   I want to read it.  Seriously, I think you should write a beginners guide to aerodynamics book.  However, you re probably like, rather fly than be tied down with writing a book.  Thanks for haring your knowledge with us.  I read all your posts hoping to pick up something that will improve my flying :)

[Konrad]

RE: All Us intermediate pilots, Lets Share

Thanks,
So I have to ask did you find anything to help improve your flying? ;-)

I have to say most of my electric motor and model prop discussions were/are stolen from Robert J. Boucher. You can find a lot of this and more in his pamphlet "The Electric Motor Handbook". It is bit dated as he barely covers brushless motors. Robert J. Boucher founded Astro fight and holds the patent for electric flight (U.S. Patent 3,957,230).

I'm happy to sit down and write (discuss) anything that will help you get the most out of this fine hobby. [Now if you have read any of my writing I owe you an apology as my writing is atrocious, even with english (American) spell checkers!] Now this gets me in trouble with a lot of the other forum sites as I don't post with concern for the vendors (sponsors) of the site. Again I post to help folks get the most out of this fine hobby, not help with sales of products. I have to give MotionRC a big hand in that have kept a hands off policy with regard to my posts even when I put the products they sell in a less than advantageous light. Now I do try to say how I think they or you can get better "performance" out of these products.

If you want to discuss model issues that are not inline with this forum, after all it is MotionRC's site, I can often be found at these forum sites. Again I'm happy to help if I can.
http://rctruth.com/index.php
http://www.hippocketaeronautics.com/hpa_forum/index.php

All the best,
Konrad

[Grossman56]

RE: All Us intermediate pilots, Lets Share

https://www.youtube.com/watch?v=IANwb_qT1gg
Talk about a squirrelly flight, watch this!

Grossman56

[Grossman56]

RE: All Us intermediate pilots, Lets Share

This is directed to all us Freewing P51 pilots. 
I noticed that the price for Iron Ass and Old Crow have dropped below $300.  Interesting that we were seeing Old Crow priced and $369 last time this year.
Anyway.  I need some advice as to what to adjust to get the main landing gear on the left side  to line up straight.  Right now she's canted to the outside, making it want to turn to the left, which is a pain as the prop torque wants to pull that way as well.  I've tried loosening the strut and turning it as well as the pin that goes into the retract mechanism itself, but no go , when you tighten it back up, it just settles into the flat spot.  It would have been ideal of you could loosen the bottom part of the strut  the part with the axle ) and turn it , but I can't, at least I can't seem to get it to.  Any advice would be great!

Grossman56

[Lon]

RE: All Us intermediate pilots, Lets Share

This is directed to all us Freewing P51 pilots. 
I noticed that the price for Iron Ass and Old Crow have dropped below $300.  Interesting that we were seeing Old Crow priced and $369 last time this year.
Anyway.  I need some advice as to what to adjust to get the main landing gear on the left side  to line up straight.  Right now she's canted to the outside, making it want to turn to the left, which is a pain as the prop torque wants to pull that way as well.  I've tried loosening the strut and turning it as well as the pin that goes into the retract mechanism itself, but no go , when you tighten it back up, it just settles into the flat spot.  It would have been ideal of you could loosen the bottom part of the strut  the part with the axle ) and turn it , but I can't, at least I can't seem to get it to.  Any advice would be great!

Grossman56

Here's what i do, to tweek the alighment. First of all, i check the landing gear connecting rod.  Make sure it's straight. With that verified, i go to adjusting the Landing gear supporting arm. At he end of the supporting arm where the wheel axle goes, is probably the culprit. I take a small set of vicegrips and clamp it down as close as i can to the curve of the supporting arm. I then take a pair of pliers and ever so lightly, turn the end of the arm(where the wheel axle goes). Until my alignment is to my liking. If you have a new unused spare supporting arm in your inventory.  Take a close look at it, and compare it to the one on your plane. The alignment your needing will jump out at you when comparing. But otherwise, the best test is to make and then check the adjustment by putting the wheel back on, setting the plane on the floor, give her a few pushing tests to see how she tracks...and of course, the ole eyeball look at her from the front will help.
I know from my experiences. I can have 8-10 flights or more. No issues..and then i start having problems with her tracking straight on take-offs or landings. Of course, i'm playing back in my mind the last few landings.  Hmmm, no hard landings....but sure enough, I check the alignment on the supporting arm. And one will need a little bit of a tweek. Make the adjustments, and she's tracking like new again.

[Grossman56]

RE: All Us intermediate pilots, Lets Share

Hey Lon!
Thanks for the advice.  Took a long hard look at her lastnight and played around with a spare landing strut to do just what you suggested, but I couldn't get it to budge.  Took the screw that's 12 o'clock to the tire right out of the unit to see if  could get the bottom piece off, or at least to twist.  All I accomplished was to dig up the metal.  I've had to re-glue the gear base back into the wings a couple of times, and I'm thinking that the last time was one too many.  So, in the name of spare parts, I'm thinking of buying a new set of wings and a complete set of left and right L/G, start fresh next season.
A set of wings is $47.90 and a set of L/G for both sides is $51.80 which is a total of $99.70. This would give me a brand new platform to work on.  Poor Old Crow had a couple of mishaps that knocked the L/G out a couple of times, so she's due.  I really love the plane and when she flies she flies well.
Think that's the route I'll go, it'll give me a chance to sort through all the nightmare of wiring as well and reposition a few things now that I know what I'm dealing with.
I promised the wife that after the P40, no more planes this year, which is fair as I have quite the variety to pick from.  But long term, I want another FW Mustang without the sound system.  I've got a line from one of the other guys for some chrome vinyl that looks great
http://www.brilliantvinyl.com/Siser-Metallic-Heat-Transfer-Vinyl/
, so .........
Grossman56

[Lon]

RE: All Us intermediate pilots, Lets Share

Gman,

the picture shows how I use a vicegrip and pliers to make adjustments.

Also, when you remove that screw at 12 from the wheel. It should pull right off....If not, you've had some serious stress put on the gear and it's binding now.

Even though you have glued the gear a few times, thinking you still should be able to get the wheels to alighn right with this technique.