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Top-Flite Giant Scale P47 Razorback – Segment 4
The (failed) search for stupid
Text, photos and video by Tom Hintz
Posted – 2-23-2016
As the Top-Flite Giant Scale P47 Razorback nears maiden day we also venture into one of the most dangerous periods for any new RC aircraft. It is easy to think that the plane is completely done and ready for flight. However, history proves beyond a shadow of a doubt that it is likely that one or more things have been overlooked. The next segment of this build, Top-Flite Giant Scale P47 Razorback – Maiden Flight 1 will make that painfully clear.
Nuts and Bolts
I generally have the cowl off of a plane during the initial running of the engine so this is a good time to check all of the nuts and bolts holding the engine to the airframe and the engine itself together. Checking the muffler bolts is a good thing but there are many more that need to be checked. This is not a time to veer off into your macho mode to start snapping off fasteners but rather to make sure everything is good and tight. I include the bolts holding the engine cylinders to the crankcase along with the nuts and bolts holding the engine to the airframe.
Prop and spinner bolts need to be checked often, especially with a new engine and/or a new prop. All of these bolts need thread locking material but they also hold better after you apply that thread locker a couple times. A loose prop bolt can cause a vibration and even encourage the prop to blow up at speed. All of the prop bolts must be tight and better yet, they should all be applying roughly the same amount of clamping force to the prop center section.
Remember that wooden props will compress some and allow the prop washer to sink into the hub of the prop, loosening the clamping load on the bolts. I always leave the spinner off (if I even use one) during the initial flights to make it easier to check the prop bolts between flights. I usually can put another 1/8th turn or so on each of the prop bolts after each of the first 4 to 8 flights. After that applying roughly the same amount of force does not turn the prop bolts much if at all.
I use special wood screws (#3 X 5/8”) with a hex head that makes securing the servos into an airframe far easier than with the typical cross head (Phillips) screws. These screws also have a very sharp point that usually allows me to drive them without drilling a pilot hole. But if they are going to be driven near the edge of a piece of wood I still drill the pilot hole to help reduce splitting. After installing these screws initially, I will put a drop of thin CA on the screw itself or on the holes they screw into.
I also replace the cross head screws that hold the servo arm on with hex head bolts (2.5 X 8mm) for many of the same reasons. They are much easier to drive and remove without stripping the Phillips style screw head and let you apply more tightening force. I still use a small drop of thread locking material on these screws and usually apply that on the final check of the plane before the maiden flight.
Other nuts and bolts like those holding the landing gear on must be checked one final time. Screws holding ballast weight certainly need to be checked because we do not need chunks of lead flopping around inside an airframe.
Setting Throws – Checking Linkage
Now that the lane has been balanced and all of the equipment is in place we need to set the control throws. On my sport/3D planes I just set everything at “all I can get” and maybe program in a dual rate setting or two that let me be smoother or more aggressive yet remain able to tone the plane down for landing. A warbird is a different animal so following the kit manufacturers recommendations is a good idea, at least initially. Later, after the plane has been maidened and dialed in for normal flight we can adjust the throws to best suit your style of flying but still within the performance envelope of that particular plane.
While we are working on the control system the ends of the linkages at the control surfaces and at the servos need to be checked to be sure they are tight and move freely. I also move all of the controls through their full range of motion to be sure there are no conflicts where a control surface can get stuck or is limited.
Easily the most glaring problem with the Top-Flite Giant Scale P47 Razorback kit is the ¼-20 by 2”-long nylon wing bolts. They are simply too short by at least ¼-inch. I could only get one side to engage the threads of the factory installed blind nut (1/4 X 20) and then it only engaged what feels like a few threads. Nothing about this gives me the warm fuzzies and I certainly am not going to fly it this way. While searching for longer wing bolts I found that lots of outlets that sell wing bolts also think that 2” is all you need. I recognize that I am not an engineer and can’t spout the actual strength that few threads of engagement actually creates. I can tell you this Top-Flite Giant Scale P47 Razorback won’t fly until the 3”-long nylon wing bolts I eventually found at RTL Fasteners arrives. I am confident that too short is dangerous and too long is just fine in this case.
The other important thing about the too-short wing bolts is that it represents the only thing I do not like about the Top-Flite Giant Scale P47 Razorback kit. To improve this kit substantially Top Flite® would have to send a couple techs (with longer wing bolts) to come to my shop and assemble the kit for me.
Assembly Rack and Wing Bag
A very common issue with warbirds sporting a one-piece wing is that they have to be assembled in an inverted position. That means building a simple rack to hold the Top-Flite Giant Scale P47 Razorback while I attach the wing and plug in the flaps, retracts and aileron servos. All that is best done with someone or something holding the wing rocked up on the leading edge so I can make all those connections.
If you don’t already recognize the utility of PVC pipe there is a good chance you don’t have a warbird. Suffice it to say that in the scheme of building a Top-Flite Giant Scale P47 Razorback several feet of PVC pipe and the necessary connections is a negligible expense.
Hauling that one-piece wing to and from the field, even in a trailer is going to be tough, especially if you don’t want a bunch of trailer/hangar rash when you pull it out. I have a story on my site regarding making your own wing bags using a nifty insulating material called Reflectix. It’s not perfect but it does work and you can design the wing bag the way you want it.
Starting the EME 60
I like to do the initial running of a new motor at home because it can get frustrating very quick, but it is seldom the fault of the motor. The problem is likely the idle end of the throttle setting which never seems to be right before the motor is actually running. I should also note that running a gas engine is never totally safe so you need to be paying attention. I have a safety start fixture that I take everywhere I go because as long as I have grass to drive its stake into I can start my engines without getting run over by them.
No matter how much time I spend setting the throttle servo up, just getting the motor to start can mean increasing the idle end of the throw a bunch. The EME 60 used in the Top-Flite Giant Scale P47 Razorback is no different. The mixture settings appear to be dead on right out of the box but to get the motor to start I had to increase the sub trim for the throttle servo so that the idle was low enough. This bit of radio programming has nothing to do with the Top-Flite Giant Scale P47 Razorback but rather is a normal setting on a new motor/airframe.
For breaking the EME 60 in I am using gas mixed at 30:1 with petroleum based oil per the manufacturers suggestions. I carry a second gas can to the field with this “break in” fuel so I can comply with the manufacturer’s instructions with a new motor and run my normal 50:1 mix with Redline Synthetic 2-cycle oil. Aside from using the correct gas/oil mixture I frequently change the rpm during break in and never run it at wide open throttle for more than a few seconds and then only after I have half a gallon of the break in mix through the new motor.
The final work on the Top-Flite Giant Scale P47 Razorback before the maiden was to check nuts and bolts as I assembled it. The motor has nearly an hour of run time so I went over that and all of the bolt-in parts one more time to be sure all is secure. I finished all of these tasks on Friday so I loaded the Top-Flite Giant Scale P47 Razorback into the trailer and put my Spektrum DX9 Black Edition transmitter on charge to be sure everything was ready for maiden day.
However, my search for stupid mistakes failed to catch one and that would end the second day of test flying the Top-Flite Giant Scale P47 Razorback before it really got started.
See the previous Top-Flite Giant Scale P47 Razorback build and maiden stories
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