|Wing Area:||210.8 sq. in.|
|Wing Loading:||15.5 oz/sq. ft.|
|Servos:||Hitec HS55 and HS81|
|Transmitter:||Polk Tracker III|
|Receiver:||Hitec Electron 6|
|Battery:||Maxamps 3S 2200mah LiPoly|
|Motor:||Ultrafly Frio E/10/10 (available with or without motor)|
|ESC:||Ultrafly Apollo 25|
|Available Online From:||Tower Hobbies|
On September 9, 1940, the first prototype of the P-51 Mustang, designated NA-73X, rolled off the assembly line of the North American Aviation plant. In all over 15,000 P-51 Mustangs of all types were built from 1940-1945. The P-51D became the version produced in the greatest quantities, 7,954 being completed. American Mustangs destroyed 4,950 enemy aircraft in combat and 4,131 on the ground in the course of 213,873 missions in Europe alone. Mustangs also saw duty during the Korean War, and they served in the air forces of some 20 other countries. The P-51D is probably the most recognized WW-II airplane (at least in the United States) and has been modeled more than any other design.
Ultrafly, through Hobbico, is now offering a foam parkflyer version of the P-51D Mustang that includes retractable landing gear and flaps, functions usually found only on much larger models. Your Mustang can be purchased either with or without the Frio E/10/10 brushless outrunner motor. The review model included the Frio motor.
Upon opening the box, I found all foam components of the model to be individually bagged. Unfortunately, the other components, particularly the Frio brushless motor and retracts, were not secured in the box and had caused numerous scratches, dings, and gouges to the foam components.
The included selection of hardware is very complete. All pushrods, control horns, hinges, wheels, Velcro, etc. are in the box. Also included are the vacuum formed cowl and canopy, retractable landing gear and 3 spinners in blue, red, and yellow.
All I needed to complete the model were:
Construction of the model went quickly following the 13 page assembly manual. The manual contains numerous detailed pictures with clear instructions. The locations for servos and pushrods were all molded into the foam, making the process as simple as possible.
I did, however find a couple spots that I wanted to highlight where I felt the instructions were not clear.
First, if you intend to set the model up with working flaps, then the radiator scoop should not be glued to the bottom of the wing until after the flap torque rods are installed. If I had followed the order of the instructions, I would have been required to cut the scoop back off in order to get to the flap torque rod slots. Once the torque rods are in place, then it is safe to glue on the radiator scoop.
Second, the flap push rod assembly required a little care and forethought. I chose to use Kevlar thread and CA to assemble my push rod, rather than the recommended solder procedure. It is important that when it is complete, both flaps have the same travel throughout their range. Otherwise, flap deployment will result in an unordered roll (don’t ask!)
Third, the spinner assembly was different from what I have encountered in the past. I am used to installing the prop adapter and spinner backing plate on the shaft, followed by the prop and finally the spinner cover. The included spinners (your choice of red, yellow, or blue) must be assembled in what seems to me to be backwards order. The prop adapter was pushed thru the backing plate and the prop secured to the prop adapter with the provided prop nut. The spinner cover was then screwed into the backing plate from the rear with two provided screws. The entire assembly was then pushed onto the shaft and held in place with two allen screws. The difficulty lay in that if I pushed the spinner and prop assembly far enough onto the shaft to minimize the gap between the cowl and the spinner, then there was not enough room to get the allen wrench in to secure the screws. I could either cut a small hole in my cowl for the allen wrench to fit through, or leave a slightly larger gap between the cowl and the spinner backing plate. I chose the easy route and left the larger gap. I recommend you apply a little Loctite to the allen screws just before final mounting to ensure that they don’t vibrate off, resulting in the prop and spinner departing the airframe.
My only other deviation from the instructions was to use tape hinges for the control surfaces rather than the included hinge material. This was done purely out of personal preference.
One item of concern that I had with the build is that the retracts were very hard to get adjusted properly. While they will lock, I had a very hard time getting the adjustments just right. Unless the retracts are properly set to lock, especially in the down position, the retracts will collapse on landing and it is possible to damage the retract servo.
The model was flown with the included Frio E/10/10 brushless outrunner motor. The Frio E/10/10 motor has a kV of 1050 and weighs only 2.1 ounces. It is rated up to 150 watts and 16,000 rpm. For a speed control, I used the Ultrafly Apollo 25 ESC. The Apollo 25 is a programmable ESC with a dual BEC which can accommodate up to 6 micro servos. It is rated for 25 amps continuous and 32 amps surge for up to 15 seconds. For servos, I chose Hitec HS55’s for the ailerons, elevator, rudder, and flaps, and a Hitec HS81MG for the retracts. My receiver was a Hitec Electron 6, a dual conversion 6 channel receiver which weighs in at only 17 grams.
To provide power for the model, I chose a Maxamps 3S 2200 mah LiPoly pack. The Maxamps 2200 is rated at 15C continuous discharge and is capable of a 20C burst for up to 10 seconds. The dimensions of the Maxamps pack are 35mm x 98mm x 26mm and it weighs in at 172 grams.
Once assembly was complete, it was time to head to the local park for the maiden flight. All control throws were set to the recommended values and the CG was set at 75mm from the leading edge of the wing.
The instructions recommend that first flights be made with the gear locked up and the plane hand launched. My feeling was, "What is the point of having landing gear, if you can't use them?" So, after a range check and with the gear in the down position, I set the aircraft on the runway surface and readied myself for the maiden flight. The lack of a steerable tailwheel was apparent in the first few feet as I accelerated, but the rudder soon became effective, allowing the model to track straight down the runway. The Frio E/10/10 provides plenty of power and the Mustang practically leaped off the runway after about 15 feet. A couple clicks of trim and the model was tracking straight and true.
Take-offs were easy. Landings were fine once I got the retracts setup settled; before that, I had them collapse a time or three.
Mt first task was to take the plane up to altitude to check the stall characteristics. My Mustang tended to drop the left wing as the plane stalled, but recovery was immediate with application of power.
My next step was to check the slow flight characteristics with the flaps deployed. It was at this point that I discovered that my flaps didn't deploy equally. I had managed to incorrectly set my flaps up so the left flap was slightly lower than the right flap at full deployment, resulting in a slow left roll. After two more attempts at setting up my flap control rod, I have corrected the problem. The model slows down to a crawl with the flaps at full deflection, practically eliminating the stall.
Aerobatic flight is just what you would expect from a warbird. Loops are as large as you would like to make them. An Immelman, Cuban 8, or a Split S is a pleasure to fly. My rolls were not perfectly axial, and inverted flight required about 50% down stick to maintain level flight. I did not have enough rudder authority to maintain level flight in a knife edge, but how many times do you see a Mustang make a strafing run on knife edge? This plane is at home in a high speed pass just off the deck. Landing was simple without the flaps and, once I had my flaps working properly, the Mustang would almost stop on a dime.
This plane is not for a beginner, but a pilot with a little low wing aileron experience will have no trouble.
Ultrafly has a real winner with this model. It's got great looks, but more importantly, the included retracts and flaps give the Mustang a big plane feel in a small package.
United States, CA, Bloomington
Joined Jul 2004
Wow an ARF P-51 with retracts and flaps in a .15 sized package...I'm all over it.
although in the video it looked to me it was pitching all over the place cause of
tail heaviness or wind... nonetheless the performance looked great!
I hated to see the antenna dragging behind this beauty - that's were I'm installing a DX6 ch. receiver with 3.5" antenna in mine.
Well done on the article review BTW.
Apollo 25A ESC
According to Tower Hobbies, the Utrafly Apollo 25A ESC "Supports up to 4 micro servos & Gyro on 3S LiPo". How were you able to get away with using 6 servos?! Is it because the retracts / flaps are not in constant use, therefore don't draw amps very often?
Jim, he says in the article the retract servo is a Hitec HS-85MG. That's a robust "regular" mini servo.
Yup - unless the gear servo gets stalled trying to lock the gear it and the flap servo aren't going to be very active and so don't figure much into servo-count limits.....
Niterói - RJ - Brazil
Joined Aug 2005
I had some problems with my flaps as well....I even sugested a change in the flap servo position in order to have the two arms moving the same length...Let the servo arm move vertically! Another aspect I sugested was the way the retracts should be calibrated... How many of you broke the plastic connection of the retracts?! The plane flies beatifully, the scale looks is amazing! My retract broke while sliding to the take-off site....Send inumerous mails to Ultrafly/Hobbico no answer at all! The mates from modelflight.com.au sent me a new set! They did not charge me! They told me the P51 was discontinued in Australia....I expected more....More support from Ultrafly/Hobbico....I have an Ultrafly´s Ultimate Bipe which is incredible! I do not know what went wrong....But at least the support should answer me don´t you think so??
USA, IN, Noblesville
Joined Dec 2004
A couple of questions please. Would there be any advantage or disadvantage to using a Frio 10-12 or 10-15. Also i noticed alot little holes or dimples in the foam. If I were to get the unpainted version could some type of lite weight filler be used for a totally smooth finish.
The motor choice will make a difference in you battery and prop selection. I had success with the 10-10 motor and a 3S battery.
The mold marks are very apparent in the foam. With the unpainted version, you could either sand and lightly glass or could use a light spackling to smooth out the surface.
Daytona Beach, Florida
Joined Oct 2005
Utrafly P-51 Batteries and Retracts
In the Utrafly P-51 . . .
Where is the best place to put the battery pack in the P-51 ? It looks like it will block the airflo thru the fus. if the battries are put in the opening in the fus. ahead of the cockpit.
Does anyone know ?
Also, since the retract servo keeps a load on the batteries I opted to use a separate battery and a separate receiver to run the retracts and the flaps.
For this I am using a 400 mah 7.4v Lipo at 1/2oz. This takes care of the constant load on the bats from the retracts and also reduces the servos to 3 on the main sys (Ailerons,Ruddr and Elevator) and two for the secondary sys for the retracts and flaps.
This only adds 0.7oz or 20grams.
I have a 2100Mah 11.1v Lypo for the main sys at 5.4oz and the 7.4v 400ah at 1/2oz for the retracts and flaps.
My total flying weight is 21.7oz.
I am useing a CF2822 EMAX Outrunner, 18A, KV ( RPM) 850 and recommended
Propellers 9x 4.5 to 10 x 5, and a 30Amp brushless controller.
For the retracts I tried a 47 oz Mini servo and stripped the gears. When I first activated the retracts they jerked and made some strange clicking noises.
I used a delay module from Hobby Lobby and this smoothed out the action a bit but they still jerked and made a scary noise.
(It sure LQQKS Cool though with retracts coming out slowly and retracting slowly like the real thing)
It's a bit pricy at $29 bucks but it's worth it !
So I just sent for a new servo from Aero-Nuts. DFM18100 Digital Servo (metal+nylon gears) $25.50
They just came out with three digital Mini servos that range from about 80oz torque to almost 100oz. I think this will make the retracts work like they should.
To check these out go to:
DFM18100 Digital Servo (metal+nylon gears) $25.50
Hi-Torque Digital Servo
Aluminum alloy body, durable and solid
Single Ball bearing
Amplifier type : Digital controller & MOSFET driver
Working Voltage : 4.8V~6V
Speed : 0.12s/60 @4.8V
Torque : 2.2kg/cm @4.8V = 77.6 ounce
Idle current : 4mA
Max running current : 1200mA
Pulse Width Range : 1~2ms
Dimensions: 23mm x 24.6mm x 12mm
DFM22130 (metal+nylon gears) $30.00
Stall Torque : 2.7kg = 95.2
I plan to fly the maiden in a few days. (This Week)
I will come back and ????
First off I relize this is an old disscusion but I see some errors in your math on the servo torque ratings, you converted the metric weight to imperial but you did not convert the arm length.
So the DFM18100 would really equate to 30-31oz/in and the 22130 ~38oz/in
Now for my question how do you like the DFM servos?
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