Second Life for Asher Carmichael's Drag Queen

[Al Clark]

I was recently able to acquire the Drag Queen towplane designed and built by Asher in 2002. Asher had totally refurbished her with an overhauled engine, new fuel system, new servos, and new LG. He also removed the old Monokote from the wing and stab panels, applied glass cloth and resin, and put a nice white acrylic lacquer paint job on the entire model. I just had to install the RX, voltage regulators, switches, and batteries. On the recommendation of Don Apostolico (Don's Hobby Shop, Mr. Giant Scale), I moved the throttle servo aft away from the ignition module, replaced the metal throttle pushrod with a Nyrod, and replaced the steel rudder cables with Kevlar cables. I added some colors to help with visibility, and a few decals. So now I'm ready to test fly and do the fine tuning on the control throws. I'll be looking forward to towing folks at our monthly aerotow days next year.

[lenb]

HI Al
Congratulations on your acquisition. I had the opportunity to fly the Drag Queen in Georgia both before and after the overhaul. It's a fine flying plane and I'm sure you'll get many years of great towing with it.
I'd be interested into the reason Don recommended changing the items you did? Are you still flying on 72 Mhz ?
I know back when 72 Mhz was in use, radio interference was a real problem with ignition modules, metal push rods that had metal clevis on both ends and I guess cable pull- pull systems, but since 2.4GHZ came on the scene, those issues have pretty much disappeared. I'm curious as to Don's thoughts on this, I'm sure he's seen it all.

Thanks for sharing and good luck with the Drag Queen!!!

Len

[Al Clark]

Thanks, Len! My Pulldog towplane works well for 1/4 scale and up to 15 lbs, but it's nice to finally have a larger, well proven gasoline powered ship that will tow pretty much anything.

Don Apostolico is a very interesting and knowledgeable guy. As you might know, Don retired and sold Don's Hobby Shop a year or so ago. He moved here from Kansas to be close to his kids, and joined our model club. Don wrote the book "Gas Engines Giant Planes", as well as several others. I have had numerous discussions with Don at our field, and I also have his book. Don has worked directly with radio manufacturers, and many model manufacturers. He has told me about all kinds of problems with models, engines, and radios. Like you, I thought that the issues associated with ignition module RF were only 72 MHz issues, but Don says that is not the case. Don told me that gas engines use either resistor spark plugs, or more commonly, have resistors in the spark plug caps. If there is a failure of the resistor, enough RF will be generated to feed back through the servo and cause the 2.4 GHz RX to malfunction. He told me he has seen it happen personally, and related a case where a gasoline powered model went to un-commanded full throttle, took off by itself, and crashed, luckily not hitting anyone. Turned out one of the plug cap resistors had failed. He said you will not see a problem until there is a failure of the resistor spark plug, or resistor in the plug cap, and they do fail. He told me the throttle servo needs to be at least 8 inches away from the ignition module, and never use a metal throttle pushrod. So I moved the throttle servo way aft by the RX, and ran a heavy duty Nyrod to the carb.

According to Don, the 2.4 GHz radio manufacturers initially stated that 2.4 GHz is immune to electrical noise and random RF, but they later backed off of that. Which brings us to the steel rudder cables. Don told me that nearly all of the competition pattern flyers were having trouble with occasional lockouts on 2.4 Ghz. These models used long extension cables inside the fuselage to get to the servos mounted at the tail, a common setup. Eventually they found out the lockouts were caused by the movement of the steel rudder cables in close proximity to the tail servo extensions. When these pilots changed to Kevlar rudder cables the occasional lockouts totally went away - not one pilot had any more trouble.

Another thing I learned from Don was not to run a 5 cell NiMH battery pack without a regulator. Don told me he has worked personally with repair technicians and the technicians told him they can always tell when servos have been run off a 5 cell battery pack with no regulator - the pot wipers are damaged. The problem is that the 5 cell packs are above 6.0 volts when charged, and for most of the pack's duration. Don told me that JR will not honor the warranty on servos that have been run on 5 cell packs without a regulator. I did some research on the web and found out that is true - JR does not warranty their servos above 6 volts (unless they are the high voltage servos). I told Don that I called Hitec and they told me it is OK to run 5 cell packs without a regulator, but Don said don't believe it - the repair techs will tell you otherwise. He said he has run into numerous cases where company representatives provide erroneous, or wrong information. According to Don, servo life is shortened, sometimes considerably, by running them on more than 6.0 volts. So that is why I ended up putting regulators on both of my 5 cell, 4200 mah NiMH battery packs in the DQ. I did a bit of research on regulators and decided to go with the linear (as opposed to switching type) units that are made by Radio South. I like the linear type because they do not put out RF like switched regulators. I already had the JR 004 switches (another very interesting topic that Don has much experience with - some switches are to be avoided) in the DQ, so I just got simple voltage regulators. But Radio South also makes their regulators with an integral power switch, and the cool thing about their design is the regulator is activated when the switch is in the open position internally. This means that a switch failure cannot turn off your radio - a great safety feature. I am using these Radio South switch/regulators in my ASW 28 and my Pilatus B4 (both use redundant 5 cell NiMH battery packs).

When I first got the DQ from Asher, my initial thought was that a lot of guys have been doing OK on 2.4 GHz with the throttle servo up front, metal throttle pushrod, and steel rudder cables, so I should be OK. But after talking to Don, I found out he has over 20 years experience solving modeler's problems. He used to compete at the highest levels. He has flown giant scale for many years. He currently has 8 giant scale models, mostly 40% size, and has logged well over 1000 flights on each of them. After considering the potential for serious harm and/or property damage should any problem ever happen on the DQ, I decided to follow Don's advice. If I had not made any changes to the DQ I might have been OK for a while, or maybe even years. But thinking about having a problem, especially at an aerotow event with a lot of people around, really scared me. So I decided to go ahead and make the changes - I won't have to worry about it now when I'm at the field.

Al

[lenb]

I guess we better make sure the resister plugs don't fail.

Thanks for the very thoughtful and detailed reply!.

[Al Clark]

You're welcome, Len!
Al