Gordon W

Returning briefly to the subject of BEC units, I've just stumbled on the operating instructions for my S-BECs by www.firmtronics.com (the prices on their website are in South African Rands (ZAR) ). The two 5-Volt units I have handle up to 12s Lipos, 2.5A continuous current, and up to 8 standard servos or 6 digitals (defined as JR DS368 with 53oz/in torque at 4.8V). They also produce 6V and 12V versions of the S-BEC - the 12V version could be useful for guys wishing to install a Benedini sound system for true-scale sound.

Up to now I've only ever used them on 6S lipos and 4 standard servos so can't vouch for them on monster models, but now I've refreshed my memory on their high voltage capability, they'll be going in a 12S-powered 1/4-scale Jungmeister I've been designing.

Gordon

Greg Covey

Hi Gordon,

Thanks for the reminder about the SBECS. They are also available from [link=http://www.aircraft-world.com/shopexd.asp?id=1940]Dave's Aircraft World[/link].

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I received some information about the bomb size from the scale guru of my group, Paul Weigand. He says that the plane is kind of an odd scale at 5.5:1 or 18%. Most models are ¼, 1/5, or 1/6 scale but the Hangar 9 P-51D has a 80’’ wing span and the full size plane has a wing span of 37 feet or 444�. This makes it an 18% scale or half way between 1/5 & 1/6scale. He believes that Hangar 9 probably designed the size to match some of the popular engines, rather than any particular scale.

The full size P-51D carried two 500lb bombs. Looking at the photos he has in his library of aviation books, the P-51’s bombs we have look just right. A WWII 500lb bomb was between 4-1/2 to 5 feet in length, depending on tail fin design, so at 18% scale, it should be between 9-3/4 to 10-3/4“ long. Anything close would be fine.

We should make these bombs manually releasable because we may want to fly without them at times. When the real bombs were on the plane, it restricted the maneuverability, because of the extra half ton of weight on the wings. The light ones we have won’t bother the model in flight but they will just look wrong when performing most maneuvers.
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Greg Covey

The Castle Creations Phoenix HV 110 ESC is an overkill for this application but it makes me feel safer that I will not be pushing the speed control to its limits. The HV 110 ESC can use up to 36 cells NiCd/NiMH or a 12s LiPo pack. The 110 amp current rating can deliver up to 5500 watts (or 7h.p.) of power. I plan to have about 3000 watts of full throttle power in my final setup.

Before mounting the ESC, it was prepared with a Dean's Ultra male connector and the mating connectors from the E-flite Power 160 motor. It mounted easily between the nylon spacers using a single tywrap. A few extra tywraps were used to hold the wires away from the rotating can and also make it possible to swap two of them if I need to reverse the motor rotation.

algutkin

My Feedback: (1)

Greg,

Please check that there is right thrust built into the firewall. My motor intallation is similar to yours, only I used an adjustable heavy duty motor mount made by Electrifly. The reason why I asked you about this is because I don't really know how to go about it, other than to just use the human eye.

I failed to check this on a previous Hangar model, and to make matters worse the motor mount was not adjusted properly and the motor had severe up thrust. Since the plane was overpowered to start, the shot upward on takeoff was not a pretty sight. To make matters worse, the resulting crash as I tried to get the plane around to land was very realistic, smoke and fire just like the real thing. I proved to myself that Lipos do catch fire when shorted, the only problem was that the other guys kept pushing me aside so they could take pictures. I couldn't save anything, The only thing left was one wire from the ESC and the motor, frozen, in place.

Take care
Al

drksyd

Greg,
In the secod pic of post 53, are the extensions screwed to that top plate of the motor box? If you have them going through and screwed to the actual firewall, that would be a great way to counter any torque problems.

Greg Covey

drksyd,

You can see the entire assembly on page two of this thread.

Al,

On this model, it is difficult to get the thrust line wrong as the top half of the cowl is built into the fuselage and any spinner backplate misalignment would be obvious. I made no changes to the angle of the firewall when adding my motor box extension and I would recommend that you do the same.

Many scale models simply need lots of rudder offset on take-off so you eventually learn to use the left stick during take-off. I am not suggesting that the P-51D needs this offset as I have not flown it yet.

After mounting the cowl bottom, the spinner backplate was perfectly oriented and extended 3/16" from the cowl. Note that the Graupner 16x8 3-blade prop is for testing the power system so I can decide on my final prop size and blade count. At this time, I suspect that an 18" 3-blade or 19" 2-blade prop is needed on a 12s LiPo pack. I am still researching 4-blade props. I have also not ruled out use of a 10s LiPo pack as I have both 6s and 4s packs to try.

Regards.

wollins

Greg,

Three questions:

1. How is the reliability of the CC HV speed controls? I've followed a few builds of yours and I seem to recall that a few of them have blown out prematurely? I THINK that I've read this in other threads as well. I'm considering getting one instead of my original plan of getting another Jeti 90A ... thinking about the CC 85A HV or maybe even the CC 110A HV.

2. How long is the battery side leads of the CC 110A HV that you show in your pic? The Jeti 90A's about 6 inches as I recall and anything is that range would probably be enough that I don't have to extend its leads in order to reach my packs in my next application.

3. I've heard (or read) somewhere that certain brands of ESCs like the Castle Creations HV models have a "no spark" feature? (which serves to eliminate the "arcing" that one gets when connecting high voltage packs) Is this true? Has this been the case in your application?

I've been a CC man for awhile, then I switched over to Jeti after I blew out a few CC esc's. However with this big application I'm thinking about switching back since it seems like you get more for the money at this level. (The biggest Jeti only goes up to 10 cells if I recall correctly) For roughly the same price I can get 20A more capacity and two more cells with a CC 110A HV!

Thanks!

Colin.

algutkin

My Feedback: (1)

Greg,

Perhaps my question and statement was misleading.

Most RC scale or sport airplanes, especially the better ones, have the firewall offset to counter part of the motor thrust. There have been many many posts about this on various forums. Left rudder is still needed inspite of the offset firewall, and in some cases with hi power motor/prop combinations, the plane can actually roll over if throttle is advaced quickly and adequate airspeed has not been reached for the control surfaces to work.

In my experience there are several ways to determine if the firewall is offset, birds eye view, measurement with a straight edge down the center of the fuse, the construction manual, or flight experience. My bad experience was based upon my failure to check the motor mount, which I hand built, and installed with incorrect offset. Your motor mounts have always been built by, or self constructed to be very professional

The question to you was an engineering question, as many layman just use the birds eye view method of determining if the manufacturer built in offset, or if the builder had to consider it. My motor install looks similar to yours, and in your picture there looks to be some right offset, just as mine does. I was simply wondering if you, being the engineer, actually measured it or found an easy way to measure it considering that the P-51 fuse is round, not square. Therefor, finding the centerline for the fuse would be more difficult.

In the meantime, I guess I answered my own question, there appears to be right offset built into the firwall. Everything should be fine so long as the motor mount spacer box is even on all sides. As I found, an uneven spacer box will cause the prop shaft to be offset in a way that could detract from the flying characteristics of the plane, or in my one case, fatal.

Al

Greg Covey

Colin,

The ESC battery wires are almost 7" long with the first 1" being shrink wrapped next to the capacitors on the end. It is true that I have had problems with the CC controllers but now have some newer models that have improved design. The one that I did have running on my Great Planes Little Toni pylon racer has been working very well. I was introduced to the Castle Link programming software at last year's NEAT Fair in September by Richard Landis (Dan's father). The Castle Link software lets you easily reprogram ESC parameters in a Windows environment. Typically, users like myself and Dan Landis prefer to disable all the safety shutdown features which enables us to be in control of the operational limits. I will be posting screen graphics of my setup using this program later on in my review.

I don't have sufficient experience to comment on the new CC ESC reliability level. We will see what happens on this project as it will be keeping about $2000 worth of plane and gear in the air. The Jeti ESC performance and reliability is unsurpassed. Jeti is also sold under the name of Hacker Master Controllers.

This newer HV 110 ESC is my first so-called "no spark" design but I have not yet powered it up. I'll report on that when the time comes. Lastly, the 12s capability of the Phoenix HV series is one reason why I selected it for this project. Another reason is the unsurpassed throttle response.

Al,

It's that West coast - East coast way of thinking that keeps us well confused.

My assumption on almost all new ARFs is that the needed thrust angle is already built into the firewall. I have not had any problems with most larger plane designs from Hangar 9, World Models, or Great Planes. The true way to tell if a plane needs a thrust line offset is in the air at full power, not on take-off. My normal assumption for scale planes like Cubs, Cessna's, and warbirds is that you'll need rudder correction for a nice looking take-off. When it comes to looking at the thrustline, I simply eyeball it. I usually only make measurements for incidence and stabilizer offsets. In the case of this P-51D model, you are forced into obtaining perfect thrust alignment with the firewall or end up with a backplate that looks uneven with the cowl. If you don't get it right the first time, simply pop out the T-nuts and slot the holes in the correct direction.

I could not find your thread on RC Groups so perhaps you can post a link here to it. I forgot to mention that I got a chuckle out of your initial comment wondering if I had heard of RCG. Way back when electrics flew on brushed motors and NiCd cells, I was moderator on the original E-Zone with over 5000 posts. Things were a bit crazy back then and I was asked to start up the Electric Aircraft Universe here on RCU in 2002. I no longer have the time to "hang out" on multiple boards.

Regards.

algutkin

My Feedback: (1)

I always took the offsetted firewalls for granted, some times it's easy to notice when it's time to install the cowls, as the prop shaft does not exit straight. However, a bad experience with one of the Graupner props scared me straight. The Hangar 9 Corsair never got to the end of the runway. That prop took soo much bite out of the air that the plane rolled over to the left, not enough rudder to offset the torque. I learned a big lesson on that one.

I am trying really hard not to post a bunch of stuff to deviate from this build, it's hard to keep qiet.

http://www.rcgroups.com/forums/showthread.php?t=596758

Keep building and I will post a picture of the neatest alternative electric motor mount. The Electrifly adjustable aluminum mount sold by Tower Hobbies will do away with those box spacers that we have been using. The largest size is the best and can be easily adapted to fit the largest motors.

algutkin aka "scalefan" on RCgroups.com

Greg Covey

Al,

I think you'll find that the spacers will cost less, weigh less, and not have side strength issues like the [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXMVU6&P=7]LXMVU6[/link] Great Planes Brushless Motor Mount. Further, these mounts typically position the outrunner behind the front plate requiring use of a shaft mounted prop adapter. Prop adapters that are mounted on the motor shaft (as opposed to being mounted on the rotating can) can subject the motor to a bent shaft on a crash and often have too much wobble to mount a heavy P-51 type aluminum spinner. This does not mean that it cannot be used as an alternative mount, it simply means that it will unlikely "do away with those box spacers". These mounts were originally designed for geared applications.

Another undocumented scale item in my P-51D box was the exhaust manifold. I now believe that these parts, along with the machine gun barrels, are part of the HAN4065 Scale Detail Set. Unfortunately, Horizon Hobby does not list this item on their site at this time.

I painted the pipes black and added some sticky-back rubber pads to change the shape a bit. The manifolds were attached to the fuselage with three black screws.

Greg Covey

The aileron and flap servos installed quickly. After first mounting the hatch blocks with Pacer 5-minute Z-poxy, the DS821 servos were screwed into place. I followed the manual's recommendation for servo extensions and routing the wires to the exit hole that will go inside the fuselage.

The aileron linkage uses a 2" threaded rod and the flap linkage uses a 1-1/2" threaded rod. A metal clevis and nut was included in the kit for each end of the rod but I added my own keepers from cut fuel line hose. I was pleased to see that control horn mounting for both the flap and the aileron is not visible from the top side of the wing. It is obvious that special attention has been designed into the Hangar 9 P-51D to keep it looking scale.

algutkin

My Feedback: (1)

My Hangar 9 P-51 D, 150 size is mostly finished. The only items left are CG and balancing, glue on the Canopy, glue on the exhaust ports and minor decorative items, cut out the spinner. The motor/battery performance was not as expected. I soldered Deans connectors on brand new batteries, but, forgot to charge them, perhaps that added to the dismal performance.

Here's the setup.

Axi 5330/18 motor
10S lipos, 4000 mah total. (more batteries on order)
Jeti 90 amp controller.
16X8 Master Airscrew 3 blade.

Preliminary performance at WOT

40 amps max draw.
1200 Watts max draw.
Approx 7500 RPM (I could not hold the plane and lean forward enough to get a precise measurement)

The plane will probably fly, but, not nearly as expected. It will fly like a trainer. I need to work on the power system, charge up the batteries and try again, perhaps with larger props.

Edit:

I just checked and Model Airplane news has two reviews for the 150 size P-47, and P-51. The prop size was un-readable for the P-51, however the P-47 flew great with a 1.80 Saito and a 14 inch prop. I must be doing something wrong with my setup, I recharged the batteries and will try again today.

Al

Greg Covey

Al,

Here are my measurements from Part 2 of my 33% Edge 540 review using a 20C 10s LiPo supply.
[ul][*] AXI 5330/18 motor [*] 2700 watts at 86amps[*] 6500 RPMs[*] APC 20x11 2-blade e-prop
[/ul]This suggests that you will want a 18"-19" 3-blade prop.

I also used an APC 21x14 e-prop for 3500w at 113amps. With proper air cooling and a 10%-15% unloading in flight, the AXI motor and Jeti ESC had no problem with occasional full throttle bursts.

I'm working with Desert Aircraft on a 4-blade prop for the P-51D so I'll report on that soon.

Regards.

algutkin

My Feedback: (1)

Greg,

I sure hope that my results were based on lipos in badly need of a charge. My goal on these conversions is to emulate the gas performance with electric. My point is, if I can get the electric to put out the same RPM with the same size prop as a 4 cycle, we are home free. Using the same theory, a larger prop could turn less RPM, so the 16X8 should have worked. I originally thought the 16x8 or the 16X10 would be overkill, boy, was I wrong. How the heck could a gas 4 cycle motor turning a 14 inch prop put out enough RPM to enable the P-47 to do areobatics?

Befor I buy anymore props, I'd better mount the wing, extend the gear, and check clearance.

Edit,

The first thing that my wife said when she saw the plane together, was "the prop looks awful small, doesn't it?" I'm going to fix that really fast, plenty of clearance for an 18 or larger prop.

Al

Greg Covey

Al,

There is merit in what you originally thought about matching the prop size and RPMs of the gas engine. Where you "missed the boat" is in the Kv or RPMs/v factor that you are stuck with in the AXI 5330/18 motor. To obtain a similar performance to your glow engine example, you must increase the prop size due to the 10s LiPo supply limitation. What you really need for your 16" prop is an AXI 5330/12 or a 12s-14s LiPo supply. This compensation difference is why I preach the benefits of watts per pound. When using watts per pound, you can't go wrong unless you want to change speed.

See if my article called, [link=http://www.gregcovey.com/Glow_Conversions_Made_Easy.htm]Glow Conversions Made Easy[/link], helps at all.

Regards.

algutkin

My Feedback: (1)

Greg,

I did read your paper and I alway was able to match desired RPM and watts without much of a problem, this is the first failure. Had I used one of those China motors that has more kv per volt, I might have been able to spin that 16 inch prop the 9,000 to 10,000 RPMs that I shoot for.

Motocalc showed the 16X8 three blade as being adequate, but, not so in the real world. Not only is the prop too small, but, the cowl blocks 1/3 of the thrust from doing any good. I have now modified my goals to coexist with your advice and ordered some 18 and 20 inch two blades and a aluminum True Turn spinner. I was going to get a 18 inch 3 blade from Desert but, at 67 bucks per prop I didn't want to guess wrong.

More testing at the end of the week when the props arrive, till then, it's just more TV and BS.

Thanks for the link, I passed it on many times on the other site.

Al

Greg Covey

Al,

Keep in mind that the outer third of the prop does most of the work so blocking the inner half has little ill effect.

Also, be certain that your LiPo packs can deliver the needed current. My 20C 5000mAh packs can deliver 100amps continuous but I will only go to that level for burst power. Most of the time, the current will be 30-60amps.

I heard back from Brian at Dessert Aircraft. Unfortunately, none of their manufacturers are making an 18" 4-blade prop. I will likely test fly my P-51D with a 10s LiPo pack and some APC 2-blade e-props since I have them up to 22". This will also let me experiment with smaller 18" props on a 12s LiPo supply.

algutkin

My Feedback: (1)

Revised performance with two bladed prop.

18X8 two blade Master Airscrew
10S batteries, only 4200 mah total.

Wide Open:

47 Amps
1600 Watts
7100 RPM

I have an 18X10 and two 20 inch props to try, however, 4200 mah of batteries is not enough, waiting for more 5S 20C batteries to arrive from China.

At least the plane will fly like a scale Mustang with this configuration, just not this weekend.

Edit,

I have a feeling the 18X10 Mejzlik three blade prop will be perfect for this bird. Right now the the 18 inch two blade is not even warming up the ESC with 47 amps.
Al

igoren

My Feedback: (23)

hi to all of you ,
i was reading tonight all of you thread about converting the p - 51 to electric and i am imprest from the info that will help me to convert mine.
i have a 60 size p - 51 that is probably 20 - 30 years old took 300 h to built as i told came with new never started inverted k & b 60 2 stroke motore ,
with custum exost to the scale p - 51 exost stack.
spec : wing span 65 " , length 53" weight : plan - 9.8 lb , electronics - 1.5 lb = 11.5 - 12.00 lb , befor motor , fule etc,

other spec : full retrac main and tail wheels ( air , oil cobination )
full mecanical doors main and tail ( main inbord out board doors )
sliding canopy on air.
detail cokpit , pilot all hand maid and paited .
the 2 botom radiator scoopes open and close with tail wheel retract.
full navigation lights,
all controls are hiden, flaps, all panel lines , rivets etc.
the plane never flown.
the fuse is fiberglas , the wing is fome , balsa, glass combo.
i dont know the make of the kit , but very true scale with doc.

i will post pics later on .

originally i planed to put saito 100 in it but it will not fit unless i will do major fix .

at the last show in ontario ca , i was chacking diferent set ups.

neumotors 1912/2.5y , 2 x - 4s - 4900 , and phx 85 hv speed control.

after reading your articles i am puting my mind on :
e - flight 160.
110 c.c speed control
not sure yet on " fule "
but definatly 4 - blade prop.

i think 4 blade zinger 15-8 will do the job with scale alumimum 3.75 spinner .
www.zingerpropeller.com


so tell what you think of my set up
let me know

isaac goren
[email protected]

GerKonig

Al, where do you buy the batteries in China? I need to buy LiPos and I am looking for a good price:-)

Thank you

Gerry

algutkin

My Feedback: (1)

Aero-nuts.com
Unitedhobbies.com

Aero-nuts is out of the 5S 4100 mah batteries
United has them.

Al

algutkin

My Feedback: (1)

Greg,

Converting to electric with the batteries installed in the same area as the fuel tank results in a severe nose heavy situation.

The CG is located slightly forward of the fuse servo tray, 6 1/2 inches back from the leading edge of the main wing. In my opinion the servo tray has to be moved aft, and the batteries mounted in the general CG area, in order to avoid weights being placed in the tail.

Al

Greg Covey

Al,

I am not to the point of balancing the P-51D but moving the servo tray sounds like an extreme solution worthy of further consideration.

Isaac,

Please re-post in a separate thread so readers don't become confused about the different size models. The E-flite Power 160 would be an over-kill for your 65" 10lb model.

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The wiring harness for my P-51D is greatly simplified by the new 6970 Arming Switch from [link=http://www.maxxprod.com/mpi/mpi-21.html#arming]MPI[/link]. It can be mounted right in the fuselage and will either arm or disable my entire power system with a single plug. I can recharge both packs right in the plane and I don't even need an additional On/Off switch to the receiver.

Although I made my own series pack adapter, they are now available from [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNKY9&P=7]Great Planes[/link].

Greg Covey

The MPI Arming Switch mounted easily in the soft thick balsa area of the fuselage side. I used the supplied screws, washers, and nuts to keep it secure.