P-51D Mustang by ModelTech

  3 Jul 01 - Link to tail wheel door mechanism design added.

Electric 1 => P-51D - Electric P-51D - Electric - Tail P-51D - Electric - Centre P-51D - Electric - Nose

I.C. =>

P-51D - I.C. side view P-51D - I.C. through cowl opening    

Full Size

P-51D Mustang - full size

This is a ARC (Almost Ready to Cover) model with the major components built. The quality of the components is excellent saving a lot of time. It is designed to accept mechanical retracts (EZ) or have fixed gear and for between a 60 and 90 glow motor. I originally converted it for electric power, but I am reverting it to glow motor power for use in scale competitions.

N of launches / Time 1 2 mins

Flight times & numbers include all versions

  Electric power version 1 I.C. power version

Electric power version 2

Wingspan 64.8 in 1.65 m
Wing Area 777 in 50.1 dm
Flying Weight 11 lb. 14 oz 5.4 kg 11 lb. 0 oz. 4.99 kg To be determined To be determined
Wing Loading 35.3 oz / ft 107.7 g/dm 32.6 oz / ft 99.7 g/dm. To be determined To be determined
Wing Cube Loading 15.2 - Racer (Ouch - but flew well) 14.0 - Above Scale
(nearer where it should be)

To be determined

Motor Astro 40 Moki 135 To be determined
Gearbox Astro Superbox, ratio 3.1 : 1 None None
Propeller APC 14.5 x 11 - 4 bladed Initially 2 bladed 16 x 8 for running-in, then to be APC 14.5 x 11 - 4 bladed To be determined
Motor Batteries 24 RC-2000 N/A 2 x 5s1p E-Tec 3700mAh 20C LiPo
Speed Controller Gordon Tarling Micro-Star 40 - 40A - 30 cells N/A To be determined
Receiver

Hitec HFD-07RA - dual conversion PPM - 7 channel - 35 MHz

To be determined

Receiver Battery 4 cell 600 mAh 4 cell 1200 mAh

To be determined

Servos Ailerons 1 x Hitec HS-81 and 1 x Hitec HS-81MG (stripped a gear & replaced with metal upgrade) 2 x Hitec HS-81MG
Elevator Hitec HS-81MG Hitec HS-81MG
Rudder & Tail wheel Hitec HS-81 Hitec HS-81MG
Flaps Hitec HS-425BB Hitec HS-425BB
Retracts

Hitec HS-77 operates mechanical tail wheel & valve for pneumatic main legs.
Union Micro UM-9G driving tail wheel doors.
Additional servo to be added to operate the main leg inner doors (in due course).

To be determined
Static motor parameters  5,600 rpm at 25.6V, drawing 31.5A - awesome power. Thrust never measured, but estimated to be over 100 oz. Never measured Not yet tested
Flight performance First flight - Struggled to get off the ground due to the soft surface and long grass. Once into the air the model flew extremely well and near scale speed. Unfortunately on landing the main wheels were ripped from the model due to the same problem as take-off. Never flown Not yet flown

Electric Power Version 2

19 Jan 07 - With the much lighter power systems that are possible with brushless motors and Lithium Polymer cells I have decided to return the P51 to electric power.  As I no longer fly i.c. models it was never going to fly with a glow motor fitted.

Glow Motor Power Version

8 Sep 00 - I have now completed the repairs and installation of the Moki 135 motor. Unfortunately the muffler has to be outside of the cowl as there isn't any room left with the Moki in there. In the end I purchased a sport style muffler as it looks much better than the original inverted muffler I was going to fit. It also meant that the extension piece was not required which removed a little weight from the front end. With the relatively heavy Moki 135 in place, no lead had to be added to achieve the CofG position despite the heavier tail wheel installation. I weighed the model on it's wheel and the calculated CofG position is 3.9" (100mm) from the leading edge compared to a desired range of 4" to 4" (102 - 114mm). I could fit a slightly heavier tail wheel, but I don't think it is necessary. I have posted a couple of pictures showing the installation of the Moki 135 and muffler.

21 Jul 00 - I have now completed the installation of the motor. As I am using a bulkhead fitting quiet mount, I glued an additional plywood bulkhead to the existing plate. The mount was quite tricky to fit as there is very little space in which to work. I have had to remove some of the cowl to clear the cylinder head, but the head should not be visible from a side view. To get the muffler clear of the fuselage side, I machined up a " (20mm) extension piece from aluminium. I have made the cut-outs for the exhaust extension piece in the cowl and fuselage body. I needed to fit an extension arm to the mixture screw as it would otherwise have been completely within the cowl.

14 May 00 - I have decided to convert the model back to it's intended i.c. power form. I will be fitting a Moki 135 as the motor because I want superb performance (seriously over-kill motor). I have relegated the electric power version information to the bottom of the page. The Moki engine will be mounted almost inverted to minimise protrusion from the engine space - only the muffler should be visible.

Electric Power Version 1

4 Mar 00 - The first flight was completed today. It took 4 attempts to complete the take-off as the model kept nosing over due to the drag of the soft surface & long grass overcoming the elevator control. The Mustang was not the only model to have this problem - the grass really does need cutting. Once airborne the model flew extremely well and looked great. Despite a really smooth landing, due to the surface condition the main wheels were ripped from the model shortly after touchdown. The damage is not bad, but will require some additional stiffening to withstand further use.

1 Feb 00 - I have almost completed the model, with just a minor bits to finish. The final weighing is 11lb 14 oz (or 5.4kg), giving a figure of 15.2 for the WCL. This is higher than I'd hoped, but I'm sure it will be OK - time will tell. I will be finishing the last few bits & pieces over the next week or so and put final details in then. I have included 4 images at the top of the page taken using my video camera. All the lettering & markings, except the stars & bars, is home made using Solartrim or Fablon sticky back plastic.

30 Dec 99 - I have decided that the above solution will not work as the doors will close immediately (on to the leg) and therefore an alternative method will be used. I have designed a Simple Switched Servo Driver to get over the problem. This will operate the servo to close the doors only when the will has retracted. and will open the doors as soon as the wheel moves. This unit is built and functioning and the doors and mechanics are in process of construction. I will be using a closed loop system to operate to doors using thin rigging cord operated by the UM-9G servo via the servo driver. To simplify a few problems a Hitec HS-77 servo has been fitted to operate the tail wheel door mechanism and the main wheel pneumatic valve. The HS-77 servo takes approximately 1.5s to complete the 180 travel it has, and the servo slow is no longer required.

11 Dec 99 - I have decided to use a Union Micro UM-9G servo to drive the tail wheel doors and fit them now. This is primarily due to the moment arm, which could cause problems achieving the CofG position later (if I fix the batteries now).  This can feed from the same RX output as the servo slow, using a Y lead at the receiver. This will allow the door servo to operate at full speed, whilst the tail wheel leg operates slowly. I will not be fitting the main gear doors until later as they are almost on the CofG.

5 Dec 99 - I have completed installation and setting of the radio gear. I have also installed and set-up the retracts. This included setting the servo slow to give a 2 second retract time for the tail wheel and fitting including a restrictor to slow the main gear down to about 3 seconds retract time. I have also got far enough to static test the motor. I was amazed at the power the motor supplies and thrust seemingly produced. Once I complete the model I will find a way of testing the thrust, which should be about 8 lbs.

27 Nov 99 - I have now completed most of the finishing work and the markings and decals are applied. I have started the final fit of the radio gear.

23 Nov 99 - I have now completed the covering of the model and have sprayed the nose blue (as above picture). I have stuck on the "stars & bars" onto the wing and have started to prepare the decals for the remainder of the model. I am still wondering whether I should fit the air exit hatch in to the fuselage as per the full size. This would allow better air flow through the model and increase cooling.

14 Nov 99 - The wing is now covered with silver Solarfilm and just needs the markings applying.

13 Nov 99 - The expected weight of this project is 184 oz (5.2kg) which gives quite a high wing loading of 34 oz/ft (104 g/dm). To ensure that the loading is not too high, I calculated the Wing Cube Loading (WCL), which will be 14.3 - a little high for scale (normally 12 - 13), but under the region for racers (15+). This should mean a fast model with good performance, which will require the flaps to improve the stall speed. I have completed the construction as far as I can before covering.

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