Official FlightLine RC 1600mm P-38 Lightning Thread

[Mark 2]

I’d like to get a Pacific silver P38 to go with my Allied green one, but it’s out of stock at the EU warehouse, has the silver P38 been discontinued?

[GliderGuy]

Me too Evan! The other aspects are:
-How short of a charge time do you want and
-How long do you want your barrerie$ to last

Example: I have enough batteries and chargers so when the last full battery is used, the first “used” battery is re-charged and ready to go again. A bit tricky to manage, but experimentation is the guide. I can fly continuously with quick pit stops to load in another battery.

The other thing to consider is HOW LONG DO YOU WANT YOUR BATTERIES TO LAST! Drawing down to a lower voltage will shorten the life of the battery as Evan points out.

I fly a lot, so long battery life (not run time) is important. I also stop at 3.8V minimum.

Last point….the voltage fall off is not linear. Once a certain voltage is reached, the voltage goes over a cliff. Thus, getting close to 3.6V puts you close to the cliff’s edge. Go over the cliff, and you rapidly damage the battery.

-GG

[Evan D]

I don’t do telemetry and it may be a great thing… I simply have a timer that I adjust to have 3.8V/ cell when I land. 3.8 is what I use for storage and it’s also a great voltage to allow you a couple go arounds if needed.

[Warbird Nut]

More good stuff......OK. Back to my original question. I have seen posts on this forum where pilots say they got, for example, 7 minutes of flying time on their batteries and still were safe. This implies a voltage (not a percentage) that can be construed as safe. If the 3.65 is not a hard and fast number for safety of BOTH the battery AND aircraft control/power to allow a landing, then what is this limiting voltage? I confess I am confused. Maybe my question really doesn't have an answer? It seems that this is a fairly important parameter to have in our toolkits so we don't end up with busted planes while at the same time not landing after, say, 5 minutes are up just to be safe. As you may know, my background has been larger 120 size nitro airplanes for the last 40 years and I would have 12-14 ounces in the tank which would allow many minutes of flight, even wide open throttle. I do miss this aspect of this hobby.

Thank you for taking the time to try to help a newbie.

[Evan D]

Let me rephrase. Below 3.65V/ cell starts to damage the battery but you can live doing it, you'll see a shorter lifespan than a similar one not taken that low. 3.2 can be fatal to the battery.

None of that is talking about flying power. LVC can be set at different levels in the ESC both for the voltage level and if it's a hard cut off, soft cut off or no cut off.

Battery voltage sags with the amount of draw being pulled. If you have a prop plane with low draw the battery doesn't sag as much as a jet at high throttle. This effects how the LVC is sensed by the ESC. When you hit LVC it cuts the power to the motors, it does not give them any power. On the P-38 one battery could hit LVC before the other, you noted one battery lower voltage than the other. This is very bad on a twin where you'll have power to one motor and not the other.

If you do hit LVC, noted by a dead motor not responding to any throttle, you can reset it by going to idle/ low throttle for a second and then you can reapply some throttle. If you reset and give it a lot of throttle it will just hit LVC again and cut off again.

I don't use % of battery as different checkers have different ways to calculate it.

The difference between your batteries can be caused by many things. In order of likelihood... One side, the motor itself, simply pulls more power. The ESC could have different settings, specifically timing. On other planes one ESC may have an internal BEC to power the plane and the other be a OPTO ESC which does not have an internal BEC. On the P-38 both ESCs have internal BECs so this should not be your cause. Also some twins have two OPTO ESCs and a separate external BEC, again the P-38 is not like that. Last you could have something electrical going on, one battery connection not connecting well, bad solder joint or some other rare issue. Also you could have one battery that simply doesn't work as well as the other or a charger that charges one better than the other but since you have four pairs doing this I don't think it's likely.

Ok, so here are my takeaways: 3.65 volts is a minimum that I want to have in the tank when I land and take the plane back to the barn. Lower than that and I face the distinct possibility that I will have to be walking out to the field to pick up the pieces. This means that the motors don't have enough juice to get me home ( maybe if I'm lucky and I throttle down I can limp back home, not going to count on it). Don't discharge these batteries to 3.2 volts or below. Very bad for the batteries. I will ignore the % of battery left on the battery tester and only use volts remaining. No info on the consistent power draw on the right side of motor/electronics compared to left side. By the way, I have done several ESC calibrations to try to minimize this issue. LB, the NiCad comments struck home with me. I at least had a working knowledge of them.

Thanks for the expertise. Invaluable.

[Warbird Nut]

Ok, so here are my takeaways: 3.65 volts is a minimum that I want to have in the tank when I land and take the plane back to the barn. Lower than that and I face the distinct possibility that I will have to be walking out to the field to pick up the pieces. This means that the motors don't have enough juice to get me home ( maybe if I'm lucky and I throttle down I can limp back home, not going to count on it). Don't discharge these batteries to 3.2 volts or below. Very bad for the batteries. I will ignore the % of battery left on the battery tester and only use volts remaining. No info on the consistent power draw on the right side of motor/electronics compared to left side. By the way, I have done several ESC calibrations to try to minimize this issue. LB, the NiCad comments struck home with me. I at least had a working knowledge of them.

Thanks for the expertise. Invaluable.

[Elbee]

Warbird Nut,

What Evan D wrote/writes is "Gold". Nominal is also used as the rated voltage of a LiPo cell that is not considered a High Voltage cell.

You might have noticed a dry cell battery has a nominal voltage of 1.5 Volts, though if you measure the voltage of a new battery usually the battery will show at least 1.6 Volts.

Storage voltage of a LiPo cell is a good safety level and does not damage the battery.

I am no expert on the subject of LiPo batteries. There are many who have a greater grasp on the ins and outs.

I was very good with NiCad technology back when that was relevant, but today's tech is far superior.

Best, LB

[Evan D]

Yes, low voltage cut off that is when the ESC will cut power to the motors. You'll still have radio power. Typically when you hit LVC if you lower the throttle to idle it will reset and you can gently apply a little power to get you home. BEC is battery elimination circuit and it is normally part of the ESC and powers your receiver and servos. Some systems have a separate BEC, not internal to the ESC.

Nominal for a LiPo is the uncharged voltage and is 3.7V/ cell.

[Warbird Nut]

Great stuff guys, a question on nomenclature. LB when you use the term nominal, what does it mean for you? Nominal mean different things for different industries. Does nominal mean never fly below this voltage? Evan, what does LVC mean, low voltage cutoff? other? If so, what happens at LVC? Does the motor not develop power but you still have control for a short time? And what does BEC mean? Sorry for basic question.

[Elbee]

Warbird Nut,

Welcome to Hobby Squawk.
I guarantee there will be differing opinions with regard to your question, but some constants are similar for all LiPo's.

Voltage is the baseline parameter of a LiPo battery,

A fully charged LiPo voltage is 4.2 Volts per cell and a High Voltage LiPo can be charged to 4.35 Volts.

A single LiPo cell's nominal voltage is 3.7 Volts.

A proper LiPo storage voltage is 3.8 Volts per cell.

A LiPo cell battery should never be discharged below 3.2 Volts.

Hugh Wiedman is my resident LiPo Go-To Guru and an all around great guy.

Best, LB

[Evan D]

I aim for 3.8V/ cell but it's for battery longevity. I would say for aircraft safety 3.65V/ cell. This would be safe to stay off LVC. Receiver voltage isn't critical as the BEC will supply power to a much lower voltage than the plane can fly on.

[Warbird Nut]

Question: What is the consensus for how much in either percentage or voltage left on the battery for safety after a flight. I have always been landing after 6 min of flight time. I have searched but have not really found an answer I trust.

Also, I have about 10 flights on the P-38 now and I have about a 12% difference between batteries when I land after about 6 min flight. Consistently, the right battery is less than the left battery which implies I am getting more drain from the right motor I would assume? Using Admiral 4S 4000 batteries and use and charge them all as a pair. I have 8 batteries.

Thanks for your thoughts.

[Warbird Nut]

Just back from the hanger where the build is taking place. Hooked everything up and everything worked except the gear doors on right main will not close and nose gear doors won’t open. I think nose gear is trying to come out, at least a brief noise from that area. Blue box issues? I unplugged the bear door leads and changed ports in blue box, no change. Servos? Just not sure. Advice?

[GliderGuy]

Lights….See the manual page 11

https://cdn.shopify.com/s/files/1/1052/4162/files/p38.compressed.pdf

Do you solder? As Evan states/ solder a jumper from the ESC side red wire to the other connector’s ESC side red wire. Same for black.

-GG

[Evan D]

First you should decide what connectors you want to use on all your batteries and standardize. Then get some 12g red and black wire and some heat shrink and do a jumper between the existing connectors. Don’t make an adapter or add additional adapters, each added connection adds resistance and, especially on this, you don’t have the room for them.

[Warbird Nut]

More questions:

I went to the hobby store yesterday to get the "jumper" so that I could use two batteries but still have one of them be able to run both motors in case one of the batteries shot craps. The salesman looked at me like I was from Mars. Said it couldn't be done.......... What do I need to order?

I now totally get the problem of the lights..which lead gets plugged into which spot on the blue box. Anybody have a tip besides trial and error?

I have several 4S Spectrum 4000 batteries but bought some Admiral 4S 3300 as the Admiral are what the recommendations are. The Admiral are 35C The spectrum are 30C. What does the C mean? Charge rate it will accept? Other? Is the higher the number superior?

Also the Spectrum are EC5 connectors and the Admiral are XT60 connectors. I bought adapters so the the Spectrum batteries could plug into the motors XT60 ESCs. I also have a Spectrum charger with EC5 ends so bought adapters for it so the Admirals could charge from the Spectrum battery charger. Any idea why ends are not standard??? What a pain.

In the cockpit area where the nosewheel is etc, there is a lead attached to it looks like 3 lights in the bottom that has been wrapped up in a loose knot from the factory. Any idea what that should plug into as the blue boxes light plugins are full. Is that possibly an option if you have a spare channel on a receiver?


Going to program the Spectrum NX8 now.

[GliderGuy]

I agree 100% with the above. However, I can add to this wisdom with a TIP many are not aware of.

Foam-Tac is awesome…even for around the house stuff! BUT it takes time to set. So, to avoid having to figure out how to “hold” odd shapes still while the glue sets…I tack weld around the glue joint with a UV curing glue like BONDIC (Amazon has it).

The Bondic cures instantly hard when UV light hits it. So, it’s great to tack weld/spot weld the parts so they don’t move. Then the Foam-Tac sets over time, and you are good to go.

Note: Bondic isn’t to be trusted for stressed joints. But, it’s a great spot welder or for a quick small repair that won’t undergo stress.

-GG

[rlcamden]

Assuming the foam for the P-38...

Don't use epoxy to glue foam to foam. Foamtac or the white tube glue included in the kit is perfect for it. I softens the foam when it gles it together. Because of this be careful about using it with thin foam, example gluing a servo into a foam wing pocket. If you use a lot you will see where is melts the foam on the top of the wing. This glue is also great as a loctite type use on screws that go into plastic (loctite is corrosive to plastic) and a dab on E and C clips is great to keep them from popping off and getting lost.

I really don't use epoxy much. It does not stick well to foam. CA doesn't either. I use CA in the holes where the screws go in to strengthen the wood threads. Example is if a plywood battery tray screws to a ply rail in the fuselage or for the EDF jets where the EDF unit is screwed to a ply plate in the fuselage.

There are multiple types of gorilla glue and I sometimes use it, the expanding type, to glue plastic pieces into foam like a landing gear mount. But sometimes I'll use foamtac for this.

Glue gun... Well, I don't use it but I know a lot of people use it for everything.

I will add to Evan's statement about the glue guns. If you do use one, make sure to use a low temp one. The high temp guns will melt the foam before the glue cools enough to bond. Most may already know this, but I found out the hard way not thinking about the high temp setting.

[Evan D]

Assuming the foam for the P-38...

Don't use epoxy to glue foam to foam. Foamtac or the white tube glue included in the kit is perfect for it. I softens the foam when it gles it together. Because of this be careful about using it with thin foam, example gluing a servo into a foam wing pocket. If you use a lot you will see where is melts the foam on the top of the wing. This glue is also great as a loctite type use on screws that go into plastic (loctite is corrosive to plastic) and a dab on E and C clips is great to keep them from popping off and getting lost.

I really don't use epoxy much. It does not stick well to foam. CA doesn't either. I use CA in the holes where the screws go in to strengthen the wood threads. Example is if a plywood battery tray screws to a ply rail in the fuselage or for the EDF jets where the EDF unit is screwed to a ply plate in the fuselage.

There are multiple types of gorilla glue and I sometimes use it, the expanding type, to glue plastic pieces into foam like a landing gear mount. But sometimes I'll use foamtac for this.

Glue gun... Well, I don't use it but I know a lot of people use it for everything.

[Warbird Nut]

This is something so elementary, but I don't know it. My background is large nitro planes since 1974 when I was just entering high school and know all about glue for those beasts. With foam, when and when should I not use the following: BTW, I have nobody locally to help me with this type of stuff. On my own.

Epoxy
Foam Safe Epoxy (do they even make it?)
CA
Foam Safe CA
Gorilla Glue
Foam-Tac
Wifes glue gun

I don't know the rationale about when I should use one over the other.

Thank you for holding my hand with all these questions