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Jan 01, 2019, 09:42 PM
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Build Log

Top Flite 1/7 P-51B Kit Bash


Yes, another thread on the Top Flite 1/7 P-51 kit. However, after reading a lot of the other ones on this site and others, I'm hoping this build log will be different. This one is being modified for an electric power system and lot of scale details.

The basic plan:
  • B-model
  • Hidden control linkages everywhere
  • Hidden battery hatch
  • Retractable tail wheel
  • Functioning gear doors
  • Full cockpit with pilot
  • Fiberglassed and painted
  • Panel lines and surface details
  • Coverite the rudder and then paint it
  • Simulated navigation lights
The main components:
  • Rimfire 1.20
  • Castle Creations Phoenix Edge 100 Amp ESC
  • Prop - TBD (still looking for a good flyable 4-blade)
  • Robart 531RS 85 deg Reverse Pneumatic Main Retracts
  • Robart 121 Tail Wheel Retract
  • 4-inch tires
  • RDS for ailerons and flaps
Known compromises I will make:
  • Wing outline of the B-model will be inaccurate
  • Tail wheel will retract in the wrong direction
  • I may have to downsize the tires so they fit, but I'm really hoping not to
  • Rudder linkage may be exposed
I am not a building expert and I intend to use this kit to learn and apply some techniques such as building a full cockpit, fabricating gear doors, hiding control linkages, and kit-bashing in general to help prepare me for scale competitions. This will by no means be a competition winner and I'm expecting this airplane to come out around 11lbs when all done. I may not show or discuss the progress that was done by the instruction book, but only point out the deviations and any issues I may encounter. Let's begin.
Last edited by JonLB; Jan 02, 2019 at 07:45 PM.
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Jan 01, 2019, 10:01 PM
Sagitta Fanboy
Interesting,

Are you going to adjust the main gear location to be scale? The stance on the TF P-51 is wider and every gear door conversion I've seen looks odd because of that.
Jan 01, 2019, 10:06 PM
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I actually purchased the kit towards the end of 2017 and poked at it here an there while I was bashing an ARF. So, the empennage got mostly built only for me to come across the great idea of drilling some holes in the ribs to lighten the tail after it was already sheeted. Oh well. I can still take some weight off the rudder before it's covered.

In addition, I got the wing halves built up and worked on the aileron servo mounts. The book calls for a single standard sized servo mounted in the center of the wing to drive both ailerons via bellcranks. I decided to abandon that idea and use Futaba S3173SVi servos for the ailerons as they are thin, light, s.bus, and have plenty of torque. Combined, they are both lighter than a single standard servo.
Last edited by JonLB; Jan 02, 2019 at 07:32 PM.
Jan 01, 2019, 10:12 PM
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Quote:
Originally Posted by mawz
Interesting,

Are you going to adjust the main gear location to be scale? The stance on the TF P-51 is wider and every gear door conversion I've seen looks odd because of that.
That's the first I've heard of the stance being too wide. The majority of the builds I've seen are with unscale sized tires which brings the inner gear doors out and it may look odd because of that. I intend to use the scale sized tires and move the inner gear doors in to look more correct. It may not be exact scale, but afterall, this kit is sport scale. I have to make some compromises here and there.
Jan 01, 2019, 10:16 PM
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Speaking of compromises, I wanted to get a B-model wing sweep (less pronounced), but I just couldn't figure out how to do it have it still mate properly with the fuselage. So, I built the shape per the plans which is for a D-model. The scale enthusiasts will notice, but most people at the field would hardly know the difference.
Jan 01, 2019, 10:20 PM
Sagitta Fanboy
Quote:
Originally Posted by JonLB
That's the first I've heard of the stance being too wide. The majority of the builds I've seen are with unscale sized tires which brings the inner gear doors out and it may look odd because of that. I intend to use the scale sized tires and move the inner gear doors in to look more correct. It may not be exact scale, but afterall, this kit is sport scale. I have to make some compromises here and there.
The stance is only a bit wide, but since the design is intended for non-oleo legs, it looks odd compared to a scale P-51 unless the latter is loaded up to max weight, because the gear legs are short. That also creates the inner door issue, where the distinct location of the full-scale doors is off and it ends up just looking wide & short.

It's a big difficult to get everything right without a lot of effort, as the Mustang's gear has a fair bit of extension (fully extended, the leg door ends are above the hub, while on the ground, they usually sit right above the axle) and the stock retracts of course have no oleos.
Jan 01, 2019, 10:47 PM
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Yes, I agree with what you say, mawz. I do plan to use Robostruts and when the time comes in the build, I do hope to modify the springs in them so they can be fully extended with retracted and compressed some while extended with the weight of the airplane on the ground. In theory, that just requires two different types of springs in the strut. Stay tuned to see how that ends up!
May 05, 2019, 10:03 PM
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The wing is finally sheeted. Here are some pictures of some modifications from the plans. Aileron and flap server mount trays with tubing to each and the first ribs (middle) are close together to allow for scale wheel size and strut length to fit. I still have to make the inner gear doors before cutting the wheel wells open, but I need some fiberglass first.
May 05, 2019, 10:06 PM
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Since the wing was sheeted, I moved on to the fuselage where I had to relocate a former and servo tray aft in order to make room for a full-depth cockpit. I also installed the tail wheel retract and steering servo.
May 05, 2019, 10:14 PM
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One of the bigger challenges I was facing was building a battery tray without cutting a hatch in the top as that would produce non-scale panel lines. I finally got it designed and installed.

Since I'll have to use the included chin cowl, I built the battery access to be through the firewall and the chin cowl will come off to access it. I intend to attach the cowl with magnets so it'll be quick and painless to swap batteries.
May 05, 2019, 10:20 PM
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My next hurdle to overcome before I can really move on with the fuselage is hiding the rudder linkage. I cannot use an RDS setup like the ailerons and flaps as I'd need to put a servo past the tail wheel which I'm not keen on adding that tail weight. I'm looking at ways of putting a horn near the hinge-line, but that will require more torque from the servo to drive. I'd be interested to hear any ideas.
Last edited by JonLB; May 05, 2019 at 10:30 PM.
Jun 02, 2019, 10:20 AM
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The rudder linkage will remain stock as I could not figure out a good way to hide it and still make it functional.

Because I plan to add a full depth cockpit, the air tank had to be relocated. I opted to put it behind the air scoop in the radiator keel as it was really the only option and still have it serviceable.
Jun 02, 2019, 12:17 PM
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You can do the rudder like you posted. Just move the hinge line to the opposite side of the rudder.
Latest blog entry: In flight
Jul 05, 2019, 04:35 PM
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My kit provided two elevators with different grain and noticeably different in weight. So, I decided to make my own elevators using the basic technique found with the rudder and now they are a lot lighter and more scale than the kit and plans call for. Since I'm doing the B/C model, the elevators will be covered with fabric which mimics the full scale.
Jul 06, 2019, 03:41 PM
Sagitta Fanboy
Those look excellent. A few very late C’s had the metal elevators, but it’s nice to see the more common fabric ones. Even D-5’s had those


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