My flying buddy Kelly has one of the Top Flite P-40 Giant Scale ARFs. It’s a beautiful plane and if you are interested in this size and type of aircraft (50cc giant scale warbirds) I encourage you to check it out. It is a well built and good flying aircraft that shows that the designer has learned from the earlier models in the line and made some important upgrades that make this airplane fly nicely but also hold up well to a few “imperfect” landings and hang together.
Last year, he came to the field and while assembling the plane as usual noticed something disconcerting. After powering up the radio system with the plane fully assembled and ready for flight the flaps began jumping around in a random manor!! After dis-assembly, some testing and no flight whatsoever that day… (sometimes you have to wonder why we do it) we determined that the flap channel (6) was always affected, regardless of which servo we plugged into it. Off the receiver went to Spektrum for repair. They did whatever it is they do and pronounced it good to go with no problem found. They also “tossed” in at no charge a “software” upgrade while they had the receiver which was nice.
When we reinstalled, we did not see the issue again until… you guessed it, another day at the field and another day with no flying!! Now, I don’t blame Spektrum for missing the issue with this receiver as they did not have one key bit of information. What we discovered this time is that channel 6 only has an issue when channel 5 (landing gear) is at a particular extreme. In this case, down. I have further determined that it is the receiver and not the radio at fault as we removed the receiver and bound it to my DX-8 and saw the same issue. Here it is with just the receiver under test, a 2S A123 as a power source and my DX-8. I also show a meter to display the voltage to the receiver so there’s no question that the power supply is out of range.
Check out the video here: AR9000 Video
Apologies for the focus issues, but you’ll see that the servo attached to AUX1 remains perfectly still until I flip the gear channel and then the “twitching” begins. I show this not to pick on Spektrum but to simply display a very strange failure mode I have never seen before and spark some thought processes that might save an airplane or two. I
When you do your ground check, do you check with the various channels at full throw? With the gear up and down? etc… You may want to occasionally go through a “full throw” check if you can. This may require someone holding the airplane or a stand if your setup involves retracts. I think I am going to start doing an occasional control surface check with other surfaces at extremes.
I’m convinced that this would have meant a crashed P-40 if the problem had only shown up with gear up… i.e. Nothing at all would have been wrong until the plane was airborne and he hit that switch to raise the gear. Having the flaps randomly jumping back and forth in mid flight and with no clue as to why the plane started wildly pitching up and down would have likely been catastrophic. It may be a very rare occurrence but you can be sure I am going to do the most thorough surface movement checks I can devise on all my aircraft in the near future.
I’ll add commentary to this post or perhaps do a “part 2” when I get this back to Spektrum and get their feedback. For now the P-40 is ready to fly again with a different Spektrum receiver.