Author Topic: P-51 Rehab (Read 2230 times)

john vlna · « **on:** January 18, 2012, 01:20:44 PM »

In Joe's what are you building thread, I stated that I was converting a RC ARF Bearcat to electric carrier. Well I am taking a short detour. I have a Great Planes P-51 that I converted to Class II glow, and have flown for the last 2-3 years. It is in need of some minor rehab. After looking it over I decided to put it on top of the list and convert it to electric at the same time. Since I plan to post more info on this project, I decided to start a new thread rather than highjack Joe’s.

Its dry weight is 24 oz so I think I can keep it under the 3.5 lb limit for Class I. Right now it looks like it will be about 52oz. That’s a bit heavy for the small wing, but about the same weight as with a glow motor. With glow, (I used a ST 45) I had to put a lot of tail weight on the plane. With electric I can position the battery to eliminate most or all of the tail weight. So even though the electric components are heavier it should come out about the same weight. .

I plan to use an Exceed Rocket 3520 900Kv on a 5 cell LIPO and a 70Amp ESC. Motor Control will be all electric using Clancy’s U/Tronics system and insulated lines. The Model is intended for RC glow powered combat, and is quite strong. More to come.

Fred Cronenwett · « **Reply #1 on:** January 18, 2012, 03:21:57 PM »

I have converted both the Corsair and the Spitfire for CL scale from the same line of ARF's from Great Planes. Right now they are powered with glow engines for now, but when I convert them to electric power I will put a top hatch that is removable so that I don't have the take the wing off to get to the battery.

Alot of the RC kits are now coming with a top hatch std so that the electric battery can be easily installed and removed. I plan on putting a hatch similar to this on my Corsair and Spitfire.

The attached picture is from the E-Flite AT-6.

Fred Cronenwett

john vlna · « **Reply #2 on:** January 18, 2012, 07:25:58 PM »

Fred,
I am considering a top hatch. I may have to build one. I have a Eflite PT-19 which is setup that way, and I usually do it for my glow scale class planes. For carrier I am way overpowering the P-51 model from what a scale or sport plane would need. And of course I’ll need bigger batteries. It is important that I get the batteries located so I don’t need any extra weight on the tail.

Although the motor hasn't been on the test stand yet, my simulation (Motocalc) shows that I should be around 1000 watts input, dropping off to about 800 in flight. Efficiency looks good, see the attached chart. In reality I have not seen as big a drop off as Motocalc predicts. Theory says the motor will unload, but actual data I have taken does not show much difference from static bench testing and in air.

The motor is rated for 1200 watts, but by weight it is only a 700 watt. Luckily we are only going full speed for a little over 20 sec’s. In any event the motor should take it.

John

john vlna · « **Reply #3 on:** January 20, 2012, 10:00:33 PM »

Well, I have ripped out all the glow stuff. I also did a motor workup and it looks like I can have options that will range from 44 to 53 oz all up weight. Since the P-51’s wing is so small I am going to go for the lighter weight options first. The lighter option will have lower high speed, but it should help low speed. I don’t turn so fast anyway.

The attached pictures show the internal cavity and battery platform I am installing. I decided to mount the batteries under the wing. If I decide to have a top hatch it can be added later. In picture 1 you can see a former to the left. I will cut a hole so the batteries can be shifted fore and aft for balance. You can see where the 3 line bellcrank was. There is room under the platform for the batteries to clear.

The glow version used a firewall mount. The electric motors need standoffs, as shown. The cowl is new. One nice feature of the Great planes kits is that spare parts are available. My glow cowl in full of cutouts not needed for the E version.

Fred Cronenwett · « **Reply #4 on:** January 21, 2012, 03:50:13 PM »

The P-51 Fuselage looks just the Spitfire I have from the same line of ARF's. I originally built the Sptifire with an OS-35FP, then installed an E-flite 25 size motor for test purposes and haven't intstalled the glow motor back on the model. These are a great ARF's for CL. The top hatch makes things much easier getting the battery in and out.

When I convert the model to electric power I'll have to get a new cowl to replace the one with the big cut out for the glow engine...

Good luck,
Fred

john vlna · « **Reply #5 on:** January 21, 2012, 07:29:49 PM »

Fred,
I also have the Spitfire, ST-34 with electric throttle. I plan to convert it to electric this year.
john

john vlna · « **Reply #6 on:** January 27, 2012, 09:40:01 PM »

I drifted off to some other projects but am getting back to the P-51. I found some interesting info on weight which has changed my plans a bit. Both motors (shown in the attached) use APC 10x8P props. The prop is heavier than I imagined. APC lists it at 1.02 oz, but my measurements are closer to 1.2 oz. This is a glow prop; there is no electric version to my knowledge. Although evidence from the stunt community seems to indicate that the motors hold up with only one point support, with a heavy glow prop it seems to me that mounting near that bearing that is providing support is best. I fly my profile with the red/black motor mounted in the front (it is shown rear mounted). So I have had to change things a bit too front mount the motor rather than rear mount as planned. The blue motor shown in the photo can be mounted either way. The red/black one has to have the shaft reversed.

john vlna · « **Reply #7 on:** February 06, 2012, 05:52:57 PM »

Well I am getting back to my P-51. I ran into some issues which needed thinking through. I found that I need to use two batteries in parallel due to their physical size. The length of Lipo batteries is dependent on their capacity. The battery compartment is to short for anything over 2200mah, and I need a larger capacity. I am also installing a safety plug as shown.

Attached are some pictures of the installation, and the arming switch

david smith · « **Reply #8 on:** February 07, 2012, 05:33:06 PM »

I meant to post a whole lot earlier but every time I remember I just don't have time to. Here are some pics of my mustang. John, this is the same one that I had at the nats that was unfinished. I decided that it was going to be too nose heavy as a class 2 so I put a nelson 40 on it for class 1. If I can find the pic that somebody took of me flying it I will post it. In that pic it looks to be doing a very good low speed but at almost 60 degrees it just scoots around the circle. I have decided against competing with it but it still looks cool.

David

john vlna · « **Reply #9 on:** February 07, 2012, 06:05:19 PM »

Dave
The nose heavy issue is why I went with a 45 for class II, even then I had a ton of wieght on the tail. I think I have worked out the electric so I'll be at 48 oz Class I, and about 52 Class II with no tail weight.
John

john vlna · « **Reply #10 on:** February 07, 2012, 09:13:08 PM »

Just found some photos of the P-51 in original condition. It is older than I remembered, built in 2007

john vlna · « **Reply #11 on:** February 09, 2012, 06:57:29 PM »

Some more progress. Photo 1 shows the BC, and on the, left buried deep is the ESC. The stub lead outs may, look odd, but they make it easier to attach the lines. Photo 2 &3 show the standoffs and motor installation. Photo 4 is the old glow cowl, I am using it just to test fit the installation, I have a new cowl.

john vlna · « **Reply #12 on:** February 27, 2012, 08:24:39 PM »

Well the P-51 is finished except to tighten some loose monocote. I haven’t flown it due to a hand problem which makes it difficult to hold a handle.

The weight ended up 3 lbs 3 oz, using 4 cell batteries. I prefer to operate the motor with 5 cells. But, 5 cell batteries put the weight over 3 ½ lbs making it a Class II on 5 cells and Class I on 4 cells.

I plan to use a 11x8 or 12x8 propeller on 4 cells and a 10x8-9 on 5 cells. When I get some numbers I’ll post them, although the sense I get from Joe’s musing thread is that an electric plane that can hang is not considered a real carrier plane by some.

Mark Scarborough · « **Reply #13 on:** February 27, 2012, 09:13:49 PM »

John,
for info,, there is an APC electric 10x8n prop.
well I think there is, I have a couple of them. I know they currently list 11 x 8 and 11.8.5
http://www.apcprop.com/SearchResults.asp?Cat=24

john vlna · « **Reply #14 on:** February 27, 2012, 09:58:49 PM »

I don't think there is a 10x8P electric APC, I use the 10X8 Glow Pusher on this motor (turnigy 3648-850Kv) There are 11x8 and 12x8 APC electric pushers. When possible I use pushers on carrier planes. They can be trimmed with either tractors or pushers but I find it easier to with pushers.
http://www.apcprop.com/SearchResults.asp?Search=10x8

Mark Scarborough · « **Reply #15 on:** February 27, 2012, 10:32:14 PM »

yeah in looking, I cant find it, but I have a couple here so I know the DID make them at least,,

well I should say I remember having them, but they are in the garage, and its like 15 degrees out there so I am relying upon my memory LOL

Wayne J. Buran · « **Reply #16 on:** February 28, 2012, 03:57:07 AM »

John, what happened to your hand?
Wayne

john vlna · « **Reply #17 on:** February 28, 2012, 06:14:54 PM »

I got out to the field for a few flights today. I was disappointed in the high speed, I was only getting in the 28 secs range with 4 cells. There may be some room for improvement, ( different props mostly). I also forgot to range set the esc so I may not have had full power on high speed. But I think it is just going to have to stay as a class II using 5 cell batteries. Due to a handle problem I didn't try low speed.

For Mark, don't freeze looking for an electric 10x8. The glow props work OK on electric motors. The only drawback is possibly that they are too strong and can cause the shaft to bend or even snap on a nose over.

eric david conley · « **Reply #18 on:** February 29, 2012, 07:04:02 PM »

John, what do you mean by "range set the ESC". I'm using a U/Tronics single channel unit, 3 wire control system,Cobra 150A ESC, 50 ohm linear-taper potentiometer, Scorpion HK 3226/1400KV motor, and a 4s 5000mah TP 30C battery. My first flight I had a HS in the mid 17s and then the next flight was a low 19 and then it would not go any faster than 19s. I changed out the ESC to a new one and it turned in the mid 17s again and then on the next flight it was back to the 19s. I called the supplier of the ESC and he said I needed to set the ESC before any flight. My understanding is that with my setup I don't need to set the ESC because I'm using the potentiometer? what do you think? Eric

john vlna · « **Reply #19 on:** February 29, 2012, 08:12:14 PM »

Eric,
I think you have to set the esc. If you look at the esc instructions they describe how to set the esc so it matches your transmitter, in this case the U/Tronics. It does not matter how you configure the U/Tronics. The procedure is generally to set the U/Tronics to high throttle, then connect the battery to the esc. You will hear some beeps (ESC Dependent), within 1-2 seconds shift to low throttle, the esc will beep some more. At this point I disconnect, I am not sure you have to but it makes sense to me. The esc is now matched to the range of pulse widths your transmitter puts out. I have measured the U/Tronics and several other timers and transmitters, they all vary some.

The nominal value is 1-2 ms but if for some reason your esc thinks 2.2 ms is full throttle and you can't get there, well you see the problem. I have also had esc's forget their setting, so I try to do it before ever flying session, just forgot the other day. It seems a bit unusal to have to set it every flight, what ESC are you using?

john vlna · « **Reply #20 on:** February 29, 2012, 08:29:30 PM »

Eric, I got focused on the esc and forgot to ask, what is you motor battery etc, Your times are very good.
John

eric david conley · « **Reply #21 on:** February 29, 2012, 09:11:54 PM »

I'm using a 4s Tunder Power 5000k 30C battery for those good times. I also have a 3s of the same kind and get high 21s to low 22s with it. I can get away with a 4s 4400k 65c battery in my profile but that battery is just not quite enough for the bigger motor in the MO. It seems that when you get so far in battery size things only get better in very small steps. I think I've reached my limit at 4s 5000k. After that things just get to heavy. Eric

skyshark58 · « **Reply #22 on:** February 29, 2012, 09:58:57 PM »

I believe Eric is using a hard wired system that has no transmiter. The speed control is controlled by a potentiometer that is moved by a Robert's/brodak 3 line bellcrank. Mike

john vlna · « **Reply #23 on:** March 01, 2012, 12:23:27 AM »

I used tranmitter as a general term. The signal the esc looks for is pulse width modulated between a nominal 1 and 2 milli-sec (ms). It makes no difference if the signal is generated on-board, up the lines or with a RC unit. The esc must be matched to your hardware. For example an esc setup for one of clancy's units will not work with most 'stunt' type timers until it is reprogrammed. Or as may be the problem in eric's case, you won't get a full correct range from the esc.