View Full Version : Need help with a P-47

05-03-2006, 06:29 AM
I just finished assembling my E-Flight P-47 and have a question about the battery. I'm using a 3S 2100 mAh Lipo and it fits the compartment perfectly but I need some suggestions on how to hold it in place. I've put a piece of Velcro on the end of the battery (the end closest to the nose) and it seems ok. I'm a little concerned that it might not stay in place during flight, especially after they've been taken in and out several times. Any suggestions on how to make sure it stays put?

The second question is regarding the CG. It balances just very slightly nose down when held in the CG spots according to the manual. This is with no extra weight added. Is this how it should be or should it be perfectly level? I'm not installing the landing gear or bombs if that makes any difference.



05-03-2006, 08:12 AM
get some non sticky back velcro and glue opposite pieces into the compartment- forming a cradle, or loop...then simply close it with the battery in place.


Sky Sharkster
05-03-2006, 11:34 AM
Hi Tom, Tim's right, another piece of velcro at the rear or a wrap-around should do it. That's what I have on my GWS "Zero" and it's never shifted, even when trying to shake 4 "Corsairs"!
A slightly nose-down C.G. is good for the first flights. later you might want to shift it back a little (move battery) to increase menuverability and control response.
Good Luck!

05-03-2006, 12:38 PM
A slightly nose-down C.G. is good for the first flights. later you might want to shift it back a little (move battery) to increase menuverability and control response.
Actually, the E-Flite P-47D Grasshopper has requires substantial nose weight unless you use the can motor that comes with the kit. Usually it's a matter of removing the nose weight, rather than moving the battery...

Anyway, Grasshopper, all I use to restrain mine? I put a piece of sticky-back velcro on either side of the battery. Then I have another piece which I loop behind the battery once it's in place, attaching on either side.

It's not much -- just enough to hold the battery and wires down -- but it's enough. I square-loop my P-47, do vertical(ish) takeoffs, and generally loop, roll, and spin the crap out of the thing, and even with that fairly weak hold the battery doesn't budge.

The only time I get into trouble is when I forget to attach the loop :) Then I have an exciting tail-heavy landing!

That said, I tried putting some velcro on the battery, and matching velcro on the floor of the battery compartment. That works well, too, but I didn't like how quickly the sticky velcro separated from the foam due inserting and removing the battery, so I stopped doing that and went with my current solution.

05-03-2006, 03:42 PM
I like Tims idea better than mine. But it did work. I used a piece of carbon fiber. I ran it right through one side of the fuse, to the other. I just slide it to the left, or right to remove the battery. It is barely noticeable. And very quick, and convienient. Of course, I did install it at an angle. Just in case the battery moved up or down.


05-03-2006, 06:00 PM
Thanks Guys,

I'll try the velcro loop. As far as the CG, I am using the can motor so it seemed to balance out very well. I didn't need any of the clay that came with it. I also have a question on the control throws. The manual says 1/2" up and down on the ailerons and it's right on the money. However. on the rudder and elevator, it calls for 3/8" and mine is measuring about 1/2" on both. I've got the pushrod at the farthest holes on both the servo arms and the control horns. Should I put longer servo arms on or is 1/2" of throw OK? I sure don't want to have an over control situation on her maiden.

And another one.....I'm running it on a Spektrum DX6. I really haven't even got to go through the whole manual on this radio yet but is there a dual rate setting on it to where I can just change the rates on the rudder and elevator for a time till I get used to flying it instead of changing control arms?

Thanks again guys.


Sky Sharkster
05-04-2006, 01:29 AM
Hi Tom, I believe if you move the pushrod in (closer to the servo hub) on the rudder servo, it will cut down the throw. It's oposite the rudder hole placement. Put another way; To decrease throw (movement) move the pushrod closer to the servo pivot or farther from the rudder pivot.
The Spektrum doesn't have dual rates for the rudder, just elevator and ailerons. When trimming a brand-new plane, I usually set the recommended throws as the "Low" setting and add about 30% to each deflection for "High" rates. From there I generally (but not always!) end up adding more "High" rate deflection.
Don't know exactly where on your TX the rate-change switch is, but it's always near a "top" finger and it's usually a long, vertical 2-position toggle. Might have "H" and "L" marked on it. You may have to scroll to the "Servo" screen to activate it.
Good Luck!

05-04-2006, 03:45 AM
Hey thanks Ron,

You're right about moving the pushrod in on the servo arm. I don't know what I was thinking there. And to think I spent 17 years in mechanical design....Duh! That's an easy fix. As far as the transmitter, hopefully I'll get to sit down in a few minutes and go through the manual again. I've also got to read through the ESC instructions. Hopefully it will explain how to set the battery cut off for my 3S 2100 lipos. It's a Castle Creations Pixie 20-P. What should the cut off voltage be? Sorry for all the questions here but this is my first electric power that wasn't an RTF. Gotta say I do love this electric stuff versus always having to fuel proof everything. Never thought I would buy craft paint for touch ups.

I would also like to get any tips or advice on what to do or watch for on the maiden of these.


05-04-2006, 08:57 AM
As far as the transmitter, hopefully I'll get to sit down in a few minutes and go through the manual again.

If the actual throws are at 1/2", and the manual calls for 3/8", I'd suggest just using the EPA (End Point Adjustment) feature of your transmitter to remove the extra 1/8".

I'd disagree on the rudder throws. On this plane, I've found that I just can't get enough rudder. With it being so fat, and blocking so much of its own airflow to the rudder (a feature not shared by the full-scale bird), I'd err on the side of "too much throw" on the rudder.

Not so on the elevator! Admittedly, my CG is slightly back from the factory indicator, but the elevator on this bird can be REALLY twitchy. If you have expo or dual rates, you may want to use it to minimize your elevator control a bit. My end-point dual rate config is:
Rudder High: 100%
Rudder Low: 100% (yeah, I'm a rudder fiend, and I use low rates for landing. You don't have much rudder authority on the E-Flite P-47D. If you're less of a yaw-***** than I am, go with less.)

Elevator high: 90% (I had a little too much throw, too, just EPAd it out)
Elevator low: 75% (I've also done low-rate elevator at 60%, but got a little scared at the lack of authority.)

Aileron high: 100%
Aileron low: 75%

As evidenced by my other posts on this plane, if you make the aileron throws much more than stock, you pay the price in ripped foam at the aileron control horn! She's not going to be a fast roller. Neither was the original. But both have redeeming qualities which make up for the lack of roll speed.

What should the cut off voltage be?

On a 3S LiPo, 9 volts. I recommend NOT flying to cutoff if you can avoid it; tape a small kitchen timer to your transmitter, set it for 10 minutes, and enjoy yourself without worrying about a dead-stick.

I would also like to get any tips or advice on what to do or watch for on the maiden of these.

I'd say follow the usual advice for a maiden, with a few addendums to watch out for on this plane:

The elevator, as mentioned, can be twitchy. Few people crash on the maiden due to insufficient control surface movement.
Let the takeoff roll go longer than you think it needs to. Be sure the tail is off the ground before applying up elevator; once she's trimmed correctly at the factory CG, she will actually take herself off at full-throttle. (Not so if your CG is behind the markers at all, though...)
Be ready with some rudder when the tail lifts. Mine often veers a little left a that point, easily corrected.
The nose just mushes down in a stall, with very little indication a stall is approaching, and no clean "stall break" when it happens. Even though she lands nicely and "float-ish" for a warbird, she still needs to come in a little bit hotter than your average trainer to avoid a stall.
The landing gear glue to the foam is weak; avoid "dropping" her onto the wheels, as you'll almost certainly rip out a tail or wing mount. Three-point landings onto asphalt seem to be the least likely to rip out gear; "wheels" landings at a higher speed, using the wing as a brake, seems the most likely. This is unfortunate, though, because you can retain control of the plane through much of a "wheels" landing because the fixed tailwheel is off the ground; with a three-pointer, you're driving her whichever direction she was going at touchdown :)

Good luck on your maiden. Favorite plane in my hangar right now!

05-04-2006, 02:52 PM
Hey Redgiki,

Thanks for all the usefull info. I'll set the throws accordingly. I was up late reading the DX-6 transmitter manual trying to figure it all out. Yeah, I'm one of those who actually reads the manual word for word (Before I Use It). Regarding the cut off voltage, after reading the programming instructions on the Castle Creations Pixie 20-P ESC, the highest cut off voltage you can set it at is 8.4V. Is this enough? The instructions say to set it at 8.4V for the 3S 2100 Lipos.

As far as the maiden, it will be hand launched. I opted not to put the gear and bombs on it. For one to save weight but primarily because I fly off grass. I also just prefer the look of a warbird in flight without gear down.

05-05-2006, 10:54 AM
...the highest cut off voltage you can set it at is 8.4V. Is this enough?
If you are using any LiPos except the new Thunder Power Pro Lite 2 cells (which require a higher voltage cutoff, no lower than 3V, recommended 3.3V), yes, you should be fine (2.8v/cell). But still, a kitchen timer and an accurate measure using a wattmeter is better for your batteries than driving until cutoff.

As far as the maiden, it will be hand launched. I opted not to put the gear and bombs on it.
A perfectly valid choice. I fly mine that way a lot, too, whenever I'm going to be flying at the park rather than the flying field. Flies smoother, looks better, and the only time it matters is the landing! I don't know about you, but I spend a lot more time in the air than on the ground when my transmitter is in hand :)

One of my recommended mods is to ditch the wing panels entirely. This makes switching from gear to no gear an easy job with a screwdriver and no foam or paint damage.

05-05-2006, 03:00 PM
You've been a big help! But of course one answer creates more questions. In order to set your timer to know when to land before the cut off, I assume you have to fly it at least once to the cut-off to know when that is? Is this incorrect?

Regarding the watt meter, what exactly am I measuring? When, and where do I connect to measure?

Thanks again.

05-05-2006, 04:26 PM
In order to set your timer to know when to land before the cut off, I assume you have to fly it at least once to the cut-off to know when that is? Is this incorrect?
The safer, conservative method I use, is this:

1. Hook up your amp-meter in series to the motor. Virtually every digital volt meter (DVM) has an amp meter function. You may need to consult your manual on your DVM. I use the cheap $15.00 one from Wal-Mart. It says the limit is 10 amps, but I've found I can exceed that if I only use it for 5 seconds or so. You can hook this right between a motor lead and your ESC on a brushed motor. If it's a brushless motor, you have to construct a bypass or shunt between your battery and ESC.

(If you are using a Watt meter that doesn't require a series connection, I envy you! I don't yet have one of those. Just look at the amp draw, and ignore the watt reading for now. I believe you just latch a wattmeter's connections around the leads to your motor, but given that I'm a self-professed novice with them, don't believe me!)

2. Run the motor for about 5 seconds at wide-open throttle. Record the amperage used. Let's assume (because it's a convenient number) that it is drawing 10.5 amps at WOT after 5 seconds. There's always a dropoff in amperage in the first few seconds... you can go as long as 10-15 seconds if it's dropping off precipitously.
3. Your battery is 2100mAh. That's 2.1 Amp-Hours, which means a device could draw 2.1 amps for an hour solid before the battery is dead. Divide 2.1amp/hours by 10.5 amps, to get 0.2 hours.
4. 0.2 hours * 60 minutes in an hour = 12 minutes

Set your timer for 12 minutes, and you're off to the races!

The reason this works is two-fold:
1. You normally don't run WOT the whole flight, and
2. Your prop unloads in flight anyway, reducing your amp draw.

You will know, if you're drawing 10.5 amps on a 2100mAh battery, that there's no way your battery will last less than 12 minutes in that plane unless something has gone catastrophically wrong (damaged battery, stuck servo, burned-out motor bushing, etc.). You can almost certainly extend this number 10%-20%, but my perspective is, "why push it if I don't have to?".

Just FYI, this study in number analysis actually came from a ParkZone Stryker with the stock brushed motor, the same LiPo you have, and the "LiPo Prop" that comes with the B-Series Strykers. It was 10.4 amps, but who's counting? Anyway, the actual wide-open in-flight time was 15 minutes before cutoff, not 12, and I could go as much as a half hour on a battery if all I did was use the battery to boost for altitude and then hunt for thermal or slope lift. Heck, at the slope wth a strong enough wind, the Stryker could last hours, because I would rarely run the motor :) The lesson there is, if you fly conservatively, you can stretch that battery much longer. However, I always set my battery for the conservative WOT setting, because that way my little alarm beeps at me for 30 seconds to remind me I'm flying on borrowed time.

Some people also use in-flight data recorders and other exotic methods to track it. Or they do what you said, and fly to cutoff while timing it, using that as their baseline. My problem with that method and the P-47D is that, like other warbirds, she really likes to fly in under power. If you have to dead-stick the P-47, you're going to have to come in a lot hotter with a greater chance of breaking things.

05-05-2006, 04:37 PM
That helped clear things up. If using a watt meter, do you hook to the same place? I have a good industrial grade DVM but honestly don't use it much and am not sure if it has a watt meter in it or not. I assume WOT means wide open throttle? I can't wait to get this bird in the air. It just looks and feels like it's going to be a lot of fun (providing it survives the maiden).

05-08-2006, 08:03 AM
If using a watt meter, do you hook to the same place?
Between the battery and ESC, I believe (or between the ESC and motor, if it's a brushed motor, will also work fine). However, with a real "watt meter", from what I understand, it uses inductance to figure out how much power is cruising through a circuit.

I have a good industrial grade DVM but honestly don't use it much and am not sure if it has a watt meter in it or not.
Unless it uses some sort of clip-mechanism to hang onto the wires themselves, it's probably not a wattmeter. You probably need to put your DVM in series, and the easiest way (IMHO) to do that with a brushed motor is between the motor and ESC.

Usually, there are three jacks on a DVM. One of them is for measuring amps, and will list the maximum allowed amperage and time limit on it. You hook either lead to that jack, then put your DVM in series. It's not like a voltmeter, where you can just passively measure the flow by touching the positive and negative terminals with your leads; the current has to flow THROUGH your DVM to measure amps.

I'm gonna go get me a Watt's Up meter. I'm kind of sick of rigging shunts and stuff :)

I assume WOT means wide open throttle?

I can't wait to get this bird in the air. It just looks and feels like it's going to be a lot of fun (providing it survives the maiden).
I found myself wishing I'd brought that bird down to hang out at the Jet Rally I just got back from in St. George, UT (the Dixie Jet Rally). After the noisy birds were done for the day (sun in the eyes if you flew a big pattern), the foamies came out and flew for a couple of hours. It's a lot of fun hanging out with pilots who routinely handle $5,000+ machines at around 200MPH; for them, a $300 foam plane is the price of a replacement part on their "real" planes, and they fly pretty well...

05-11-2006, 03:21 AM
Grasshopper - I have the stock set-up with the TP 3S2100 Pro Lite. I also have the landing gear and bombs on board, as well as a steerable tail gear mod. With mixed flying between 2/3 and WOT. I get 15 minutes and have yet to reach ESC cutoff - also with the Pixie 20. I'm going to go up to 17 minutes for the next flights.


05-11-2006, 03:30 AM
Sounds good Larry. I'm hoping to maiden mine this weekend if the weather cooperates. I did add the rudder but didn't do the gear or bombs. I fly off grass 99% of the time. There is a large paved lot that runs right up to the field I fly in but the prevailing winds usually keep me from being able to use it.

It's good to hear you're getting that long of a flight time. I can't wait to get mine up. I'm going to have a guy help me hand launch it. I maidened my PZ-P51 a month or so ago and it was a little nerve racking. I'm usually by myself so I launched it and it did a little roll to the left. I got on the sticks and it straightened out fine but it seemed like everything was in slow motion getting my hand from the plane to the control.Of course the plane seemed to be going full speed. Everything turned out great but on this one I'd feel a little better having both hands on the controls the first time.

05-11-2006, 09:47 AM
I re-maidened my P-47 after some fairly significant repairs (bad hand-launch!), and came out a bit tail-heavy. After one nerve-wracking 5-minute flight of dragging the tail around like a kite, I brought her down (five landing passes, and on final on grass she still flipped over right before stopping).

I put her away. She's big enough, and flies fast enough, that I really need to fly her in a bigger park than this little one with a hill on it. The landing approach is just too long and too fast... and I forgot my screwdriver to remove the gear!

Anyway, "YOU'LL CRASH IT!" for your maiden, bud...

(Umm, that's the equivalent of "break a leg"...)

Air Trucker
04-10-2007, 02:30 AM
Hey I just flew my 47 sat. and I have about 2" of velcro strip on the wire end so all I have to do is get my fingers under the lip and out she comes. Max

Glacier Girl
04-10-2007, 12:26 PM
You'll love her in the air. She is a ***** cat. No bad habits. You have a rare one indeed if it didn't need the nose clay for weight. Lucky you.
I cheated on mine as it's running a lighter outrunner, to get away from adding weight, I carved out the battery tunnel all the way to the front, but slight ramped up the bottom of the tunnel. This allowed me to get the battery farther forward, hence no nose weight needed, and the ramped floor, squeezes the pack to help hold it. I too just use a velcro loop on the back of the opening, just in case.
You'll find you'll end up cranking the throws way up to get her to really react, after a few flights.
Big tips too. Tape the inside of the cowl with packing tape. It tends to crack easily.
Add a dab of epoxy to the wing nut inside the fuselage, if it breaks loose, you'll have a heck of a time getting the main wing off.
Umm glue a piece of a popsicle stick to the front side of the canopy, just big enough so that the one end just sticks out past the canopy, makes it easy to pop off the canopy, instead of digging into the joint between it and the fuselage.
Oh on the cowl, I built hood pins for mine so it's easy to remove. Real hard to do, Take 3 T pins and cut them down to roughly 3/8 to 1/2" long, poke them through the cowl into the foam. Remove the cowl, add a small dab of CA to each pin, and reinsert it into the foam. Pull the pins back out, and a little foam will stick to them. The interference fit you've now created keeps the pins tight when you reinstall the cowl. Pop the hood pins to remove the cowl.
Lastly, reglue the motor stick, it's barely in there, just a little hot glue from the looks of it, I epoxied mine in. Oh and check all the hinges, couple of them snuck through QC and didn't get glued.


04-10-2007, 03:45 PM
I think Tom's almost at his one-year anniversary for this bird and has it on a Park 450 outrunner now. Somebody revived a really old post. :D

04-11-2007, 01:48 AM

Been flying it for over a year now. Still like new.