Fly RC

July 27, 2015July 27, 2015

Very odd failure of a Spektrum RC AR9000

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.

May 9, 2015

Taft Hobby DO-27… Last Flight!

Unfortunately, Steve’s DO-27 didn’t make very many flights between it’s first and last flight. Steve was never thrilled with the flight characteristics, though it seemed to be quite capable. I think he was expecting it to fly a bit slower/lighter and it required just a bit of speed to maintain control authority. In addition the wing mounting method seemed to always need at least 3 hands to accomplish and the servo wire connection into each wing was painful to accomplish. If you get one of these, you should plan on modifying those servo wires to move those connections to a more easily accessed area. I also wonder how long the plastic/spring wing connecting clips would last? I’m not a big fan of those either. Bolts have always worked well so not sure why they decided to use something different here.

Having said all that, the DO-27 is an oddly attractive aircraft and did seem to be fairly capable of some nice rolls and similar basic aerobatic maneuvers. Unfortunately we never got a chance to fully explore its capabilities. On the first flight of our most recent day at the field the plane suddenly lost all power and dove into the ground nose first… rolling slowly while gathering more speed as it fell.

Here is what the crash scene looked like….

Ugly, I know. The impressive thing is that the wing not only didn’t break in half on impact but wouldn’t even break over Steve’s knee when he tried to do so in order to shove it in the trash bag!! When I picked through the wreckage and sorted out the good stuff, I did a little exploratory surgery and found there were a pair of CF square tubes embedded in each wing half. No wonder this thing is tough!

It also took no time to find the cause of the crash and it was NOT (unusually in my experience) pilot error. Or at least not a case of dumb thumbs. The apparent cause of the crash was a poor solder joint on the positive lead of the battery load wire which had broken off in mid flight! So Steve’s mistake was trusting his mechanic/electrician (that would be me) to make this solder connection. I hate that this happened… sorry Steve… but it does make the case that maybe a separate battery to run the receiver and servos would be a good option… especially for the larger/more expensive electrics. Will have to look into that soon for my 90 size Extra and maybe for the Carbon Cub.

The problem was a combination of several things. One, the battery has 10 gauge stranded wire which is a bit unusual for a battery this small (4c, 3700mah). Second, the supplied speed controller connectors were some smallish bullets which is a bit unusual in my experience and we had nothing to match them and even if we had it would have been tough to get these big wires into the matching bullet connectors. Third, we decided to swap these for Deans Ultra connectors. While I love the Deans for current carrying capability and the snug connection that results, this is another case of having problems connecting the wires to these blades. Easy to do for 14 gauge and smaller but for these 10 gauge I was having a lot of trouble getting things attached without melting the housing. I thought I had pulled it off but in the case of the positive lead the wire had pushed away a bit and the gap between the back of the blade and wire was filled only with solder. Unfortunately solder bends easily but also quickly fractures under a repeated bending as will often occur when installing batteries in our airplanes. Mind, I am not making excuses… I should have done a better job on this solder joint. I just want to point out that getting this right would have been a lot easier if we had picked a more appropriately sized connector considering the wire size involved. I must be slipping.

RIP DO-27… it appears all the electronics, including the servos, receiver, speed controller and motor have survived. What can we do with all of this?

April 29, 2015

Taft Hobby DO-27… First Flight!

If you read the first look post on this plane you will recall that we ran into problems trying to install the first wing set due to (apparently) a misaligned tube in one wing. Once again the folks at Falcon took good care of their customer and shipped out a new wing set and tubes. The new set slid right into place but at this point we noted another issue.

As you can see one of the servo leads in the wing is so short that it is very difficult to plug in at all when you are assembling the aircraft. You don’t have a lot of wire coming out of the wing root either, though it is adequate. The problem is you can’t hold onto this servo lead and apply any pressure to assemble it… Forceps are NOT optional! This is an annoyance, but not a showstopper.

Finally, the last complaint I have about the Taft DO-27 is the hinging of the control surfaces. The folks at Taft obviously know these things are a bit fragile as they include a bag of hinge points to install in case the molded in hinging fails. We added some wound tape in the aileron hinge line on Steve’s plane and we will see how it goes but both the returned wing set and the new set are already showing signs of hinge failure so I think I would consider adding tape to all hinge lines or cutting them loose and installing the hinge pins from day 1 if it were my airplane.

The good news is, once we got the plane assembled and at the field… It looks good and flies really well. The scale details really add to the look and the lights are a nice touch as well. Taxiing on our grass field was easy and with almost no wind and a short takeoff run the DO-27 picked itself up and climbed quickly. Steve shortly had it doing loops, rolls, snaps and more. Power was good and flight times look to be 8-10 minutes of general sport flying… maybe longer with some throttle management.

I’d like to rant about how nice the plane is and in the air it really is. Flying characteristics (based on the two flights so far) seem to be excellent. Plenty of wing, good roll rates, just a generally good flying airplane. Looks too are a plus with nice lights and a distinctive shape and color scheme with a few details thrown in makes for a nice combination. Assuming the wing tube problem is unique, you have to deal with a few issues… First rearrange things to get the tail linkage setup correct. Second, you should probably get some short extensions to permanently attach to the 2 shorter servo wires and make them easier to connect and disconnect. Third, get out your hinge tape or go ahead and install the hinge points day 1. With those 3 things out of the way, the airplane should be a winner. Time will tell for sure.

April 19, 2015

Taft Hobby DO-27… First look

During his recent trip to the Weak Signals show in Toledo, my flying buddy Steve made an “impulse buy” from the good folks at Falcon Hobby Supply and came home with the Taft Hobby DO-27 in Red and White.

The purchase started out with a bit of misstep when the folks working the booth there assured Steve that the plane would accept the 6S LiPos that he had on hand. This is not the case! The DO-27 is setup for 4S use and I very much doubt the speed controller or motor would last long if a 6S was installed! With no 4S batteries in his inventory, Steve was considering returning the aircraft but the folks at Falcon stepped up and offered to send a free battery at no charge. Shortly thereafter Steve has a 45C Pulse Ultra battery in hand and is looking forward to flying his new airplane.

Today, Steve brought the DO-27 over and we started unpacking and assembling. Visually the airplane is striking with a nice paint scheme, quite a bit of scale detail and a very distinctive look. Packaging seemed to be excellent with no damage noted and everything held tightly in place. The model is also very complete with everything needed including a nice wood prop, spinner, nice looking wheels, etc… Assembly is very simple with only a few steps to complete but during the process we did note a couple of issues. Two were especially troublesome.

First, the front wing tube in the port side was impossible to install. It went in an inch or so and then became very stubborn. After forcing it a bit further it just continued to get more difficult to slide in. Visual inspection seemed to indicate the tube was misaligned with the plastic wing root as a lip can be seen on one side. With no way to move the tube (it seems to be quite securely installed) we tried using a drill bit to open up the entry to the tube and eventually managed to get the tube in place but it is very difficult to install and I think another call to Falcon is imminent!

Secondly, when Steve attempted to connect the linkage to the tail surfaces we quickly realized one was far to short and the other far to long! It was quickly decided that the linkages were simply swapped at the factory so we traded them out and things looked a bit more promising until we realized that both were now to long… a bit more head scratching and we realized that if we physically reversed the servos, essentially moving the output shaft forward a bit, we might have something that would work. With that done, we got to a workable linkage layout and all seems well.

Another minor issue was clearance between the landing gear blocks and the foam hatch that screws on over it. Once the straps were added to hold the landing gear in place, the belly hatch was held slightly away from the body of the plane. Some simple trimming in the area took care of the problem.

We still have high hopes that solutions to all the issues will be found and Steve will get to actually fly the bird soon. With any luck it will fly as good as it looks and we can leave the issues behind. More to come….

November 30, 2014March 13, 2015

First flight on a Parkzone UMX B-17G

Saturday night at our local indoor fly I had the opportunity to fly the new Parkzone UMX B-17G. Here are the specs from the Horizon website:

Wingspan: 26.0 in (660mm)
Overall Length: 18.3 in (465mm)
Wing Area: 87.5 sq in (5.65 sq dm)
Flying Weight: 2.75 oz (78 g)
Motor Size: 6mm in runner (Left and RIght Rotation)
Radio: 4+ channel DSM2/DSMX transmitter required
CG (center of gravity): 38mm back from leading edge at wing root
Prop Size: 72×65 3 Blade
Speed Control : Brushed ESC (included)
Recommended Battery: 3.7V 1S 250mAh 20C LiPo Battery
Scale: 1/48th Scale
Experience Level: Intermediate
Is Assembly Required: No

e-flite U5380 Umx B-17g Flying FoRTRess

Parkzone UMX B-17 <– Click here to view purchasing options on Amazon

The first thing you need to be aware of is that there is no steering on the tail-wheel so you need to get some forward speed quickly so that the rudder becomes effective and you can turn! Not a big issue as doing a ROG takeoff was accomplished fairly rapidly and without any real need for rudder input. The counter-rotating motors and three blade props seem to provide good power without causing any yaw that I noticed. I was flying in a gym that consists of 3 side by side basketball courts and was off the ground in about 10 feet. The B17 flies fairly slowly though I would rate it moderately fast for an indoor venue of this size. I had to apply a fair amount of down trim to keep it from nosing up but I suspect the battery could be moved a bit more forward to offset some of that. Probably 15 clicks of trim before I got level but this was not my radio so I don’t really know what the trim steps were set for (it was a DX9 I believe).

I’m fairly sure no expo or rates had been set, just a very vanilla setup. In spite of this the B-17 flew smoothly with a fairly wide speed envelope. Roll and Yaw seemed to be adequate though I did not try to do a full aileron roll, stall turns or any thing of the sort considering it was not my airplane nor did I have much room to work with. All I can really say is that it flew smoothly and turns were easily accomplished though a bit of rudder coordination seemed to make for much better turns. In a gymnasium you quickly learn to turn while maintaining altitude or you will be bouncing off the floor or dodging rafters on a frequent basis. With the help of the AS3X system, this was not very difficult. The only concern is on landing as the B-17 does what all my AS3X ships do… it wants to keep level and will attempt to do so by applying more and more elevator as you back off on throttle until the plane stalls abruptly!! This can be a bit disconcerting the first time you experience it so my advice is bring the B-17 in a bit hot to stop this from happening until you learn the stall speed of the plane at altitude. A few clicks of throttle will keep this at bay until you learn the characteristics of the plane. This seems to be an AS3X thing, not exclusive to the B-17.

All in all, the plane flies much better than such a small multi-engine like this really should! And it is really impressive how much scale detail they pack into such a small package. Flying it isn’t difficult, the intermediate rating they apply seems appropriate. I’d love to fly one outdoors to see what it can really do… I’m going to guess that basic aerobatics (more than a B-17 should be doing) are within its grasp and flying smooth and looking impressive it can certainly pull off. Wind handling will be interesting but based on other AS3X craft I’ve tried I expect a 5-10 at most would be within reason with a little practice.

It’s hard to believe that all 4 engines running at around half throttle didn’t kill the battery after 8 minutes of flight. I thought I could detect it slowing a bit at that point but it was still flying when I landed it with only a minor bump into the wall as the roll out lasted a bit longer than expected! No damage, so NO, I don’t own one yet! I do encourage you to get one though… and then let me know when you’d like me to come over and fly it for you a bit!

November 2, 2014November 2, 2014

Sharing some pics and video from 2 recent float flys

Over the past couple weeks, I have attended a couple of events that were in whole or at least primarily float flying oriented. I enjoy being out near a lake or pond as they generally add to the natural beauty of the setting and flying off of water adds a different challenge to RC flight both from an aircraft handling approach and for the technical challenge of setting up a float plane to fly well. I highly recommend you take a shot at “float flying” if you have the opportunity. But be warned, like many things in RC, it can be addictive!

Lake Lemon – Monroe Counry RC

The first event was put on by the good folks at the local RC club in Bloomington, IN and was held at Lake Lemon just to the NW (I believe) of that city. The second was a couple weeks after and was an event put on by my “home” club, the Indianapolis RC Modelers. Below are a few picturess of the “goings on” from each. The Bloomington club had a good turnout with about 15 pilots I would guess, including 3 from my club… myself, Corey Lucas and Steve Woods. The venue is almost ideal with a nice big, low to the water dock as well as a huge body of water with almost no obstacles to contend with. They also had 2 retrieval “party barge” boats and served up a nice lunch as part of the registration fee of only $10 per person.

Here are some pictures from the event

Corey and the Nexstar are ready to try some float flying!

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Also while we were there, Steve tried his hand with his .120 size cub… Here’s a video clip of the takeoff… and landing.

No real damage was done… Steve had the engine running again after a brief dry down period. Did you see what went wrong? The consensus around here is the wake allowed the plane to leave the water a bit to soon and this added to Steve doing a bit to aggressive a pull up caused a stall… Better luck next time Steve!

Wilson’s Pond – Indy RC Modelers

The second event is one we have done every year for the last 5 or so, sometimes twice a year, and is held at a pond owned by the family of one of our members, Roy Wilson. It’s obviously not as open around the pond and the size of what you can fly there is a bit more limited as a result, but we consider ourselves lucky to have such a beautiful spot to enjoy ourselves and it is not difficult to fly off of for planes up to about 60 size or so. In the last couple years, we have not had much attendance… perhaps somewhat due to weather being “unkind” for several of the events and undoubtedly because we have few opportunities to do this sort of flying around here so getting a proper float plane setup isn’t the top priority of many folks. We all have to decide where best to spend our model budgets and something you won’t use often doesn’t rank highly with everyone. Another factor is that we have not really tried to promote the event as much as we did in past years so many folks just don’t know it’s going on.

A nice added attraction for this event is that there is a fairly nice field adjacent to the pond that you can fly most anything from so it is not limited to water based aircraft! I flew several planes and played with my air boat this year and had fun as always. I flew the PZ T28 on floats, the Carbon Cub (the micro version) as well as the Flyzone Beaver. The Beaver excels at this (once you re-engineer the water rudder) and I fly it primarily as a float plane so it doesn’t get a lot of flight time away from the water. My flying buddy, Corey, flew his Electric Nexstar from the water and his DLE 20 powered Cap Maniac from the runway. Here are some photos of the action.

One of our members does a little boating...

Image 1 of 5

Here’s a video clip of my Dumas Windy air boat eventually doing it’s signature spot spin manuever.

And one of Corey’s first landing at the pond with the Nexstar… ignore the first 5 seconds or so while I attempted to find the plane in the sky!

The basic idea here is: Water plus RC airplanes = lots of fun!! Try it, you’ll like it!

August 28, 2014December 20, 2014

Hangar 9 Alpha 40 Trainer… Experiences good and bad.

At my local RC Club we have had several of the Alpha 40 RTF trainers (the orange model) used by students while learning to fly. In general, these have been excellent flying airplanes. Stable and well behaved with the included Evolution engine providing more than adequate power. We usually ended up swapping the three blade prop for a 2 blade, especially if the 3 blade got broken. Two blades are more efficient and much more widely available. We would often eventually remove some of the limiters on the motor (needle valve collars) to get more power out of the engine as well. After all, to much power is almost enough! Generally these planes have been pretty trouble free and fly well.

Given all of this, when one of our younger members lost his Alpha to a battery problem another was purchased and the job of assembly was mine. We presumed the new ARF would fly similar to the old RTF… especially using the same motor, servos etc… Pretty much everything except the battery, switch and one of the servos survived and was moved to the new plane. As I was building the new airplane I noticed they had redesigned the firewall and added a bottom hatch (surely a side effect of adding an electric power option, which I applaud).

Unfortunately I also noticed a few issues I was not particularly happy about. First, the throttle rod routing is not ideal. This is not the first plane I’ve seen with this problem so I did a bit of creative warping and rigged up something that was workable. I’d recommend skipping installing the rod and substituting a cable type linkage to make the throttle linkage work with much less binding. Likewise, the nose steering rod binds. For this one it appears to be a problem with the routing of the rod combined with the flat ground on the steering strut and the straight steering arm. As the arm rotates back toward the firewall, the wire binds against the edge of the guide and puts a lot of stress on the rudder servo. If you position everything perfectly and limit the end points during your radio setup you can get a workable setup. Luckily, there really isn’t much travel needed on either the rudder or the nose wheel so I managed but this seems like a poor design to expect a beginner to be able to successfully handle.

Another of our members suggested the use of an offset steering arm might accomplish the relief of this stress and allow for more travel. I think it is certainly worth trying. In the meantime we had a workable arrangement if not ideal. Onward to the test flights.

A bit of tweaking, a balance check and the usual post build checks and we made a few test flights. At that point, we started to notice a pattern of difficult takeoffs followed by lots of trim inputs, etc… This was not good. We couldn’t hand this ill behaving plane to our young member and expect good results. He was still just getting comfortable flying without an instructor and not ready to handle this ill behaved ship.

It took a lot of left rudder to keep the plane flying straight down the runway and if it was trimmed for straight takeoff rolls the plane would constantly turn in the air and had to be re-trimmed for straight and level flight. We tried many different adjustments, re-aligning the front wheel and rudder several times, trying various landing gear bends, insuring the wing was centered etc… but we could not keep the plane from at least often, if not always, veering sharply right when it was near rotation speed. We also tried to add some lead to the left wingtip after noticing the right main wheel often stayed on the ground longer than anything else which seemed to help.

At that point we tried another Alpha wing which did NOT resolve the issue entirely even though after it was removed it was proven the first wing was very off balance… being heavy on the right wingtip. This is an ongoing investigation at this point but after spending 3 hours working with 2 other RC pilots with probably 50 years RC experience between us… it makes me wonder what would cause this plane to act so oddly during takeoff. I don’t believe the new Alpha ARF has this problem generically… it’s just this particular model that is vexing us I’m sure. Once we figure it out… or get tired of this and just move on to another trainer… I’ll post an update.

For now, I can honestly say the Alpha 40 ARF doesn’t seem to be quite as good as the predecessor RTF model but is still a pretty good deal for the price and the only downsides should be readily avoidable if you know what to watch out for and spend just a few extra dollars on a throttle cable and a different steering arm! Hopefully with these tweaks you can assemble a good flying airplane suitable for a beginner and still enjoyed by those of who have been flying for 15 years or more.

June 10, 2014

“Bargain” battery? Maybe now it is..!

While working with a new pilot at our club field the other day he mentioned that in order to get his charger to properly work with the battery he was using for his on board glow (a pretty standard 4.8V NiMH pack) he had to bend the wires just right and/or stick pins in the connecter, etc…

I immediately told him this was NOT the norm and he should not continue this practice. This is a warning that something isn’t right and we need to figure out what and why. He took the battery out and we tried to check the voltage and sure enough the connector was almost impossible to get a good connection on… I volunteered to take it home for further investigation and likely swap out the connector. It was clearly labeled as a 2300mah NiMH from one of the more recently arrived web based resellers and a quick browse showed claims that it is a low discharge NiMH variant. Some call these Hybrid NiMH and there are other terms. The nice thing about this type of NiMH is that have a low discharge rate when stored so they don’t tend to drop their capacity between flight sessions like many NiMH batteries do. I wouldn’t use a standard NiMH if I could avoid it because I just can’t count on them to be ready when I am and I don’t always know I’m going flying, sometimes until a couple hours before leaving for the airfield. Standard NiMH with their high on the shelf discharge rates just don’t work for me. This is especially true when you combine that with the low charge rates most will tolerate. I can’t store them fully charged and expect them to hold for long and I can’t fast charge them…. just doesn’t fit my flying habits at all.

This battery looked like a nice combination of low price and a reasonable battery technology for our needs in RC aircraft. Combine that with a low price and maybe there was something to be happy about here. But what about that connector? When I got the battery home I decided the connector was just not very good quality. The pins (sockets really) were moving to much in the plug and didn’t appear to have been crimped evenly. Next I noticed that the wires were significantly smaller than the average servo wires I’m used to. Maybe 26 gauge instead of 24? I’d rather replace the lead than splice it anyway so I took off the outer shrink wrap and this is what I found….

First of all, I wonder if using what appears to be masking tape as the insulator to keep the wires from laying directly on the battery ends is the best choice or just an economical one? I guess it’s not terrible since I presume it’s there to prevent chafing more than electrical insulation or perhaps just to aid in assembling the battery. I’m used to seeing strapping tape/fiberglass tape here. Seems like the masking tape might attract some unwanted moisture though. Anyway, that isn’t so bad but the wires being so thin I did not like. Seems like some slightly larger gauge silicon wire would be ideal but I guess you can only expect so much for single digit (dollars) pricing.

I then started to strip the tape and de-solder the wires when I noticed the following.

Do you see the insulation cut on the black wire? This was caused by the outer shrink wrap around the battery cutting into the insulation on the wires. Either the shrink wrap should have been applied differently/softer heat shrink used or perhaps a wire shield/wrap/guard of some sort used around wires. I’ve seen others use a nice rubberized sleeve (maybe just some appropriately sized heat shrink) to keep this from happening and add some stress relief in this area. Hmmm… bad connectors and questionable construction/poor quality control… Makes me think the savings on this battery might not have been such a bargain after all.

My point here is really just a long winded way of saying that very often in this hobby, “you get what you pay for” applies. Even when you are buying something as mundane as a basic 4.8V NiMH pack. I have no idea how good the cells that make up this pack really are. Time will tell. But even if they are top end like Sanyo Eneloop, the short cuts they took to make this pack more of a “bargain” could easily have resulted in a high cost to the user. If the cut had been in the red wire and it had shorted to the negative can of the battery it was sitting on top of, the best cells in the world wouldn’t have helped. Same for the connector that wouldn’t reliably do its job. Every little bit of quality I can get in my airplane products is welcome.

Hopefully, with the new lead attached and a few wraps of some decent quality electrical tape, this “bargain” battery pack really will be.

June 2, 2014

Building the Top Flite Giant Scale P-40 – P5 Wiring

I’ve finally gotten back to some work on my friend Kelly’s P-40. Lately I’ve gotten the plumbing done on the fuel tank and sorted out the electronic kill switch, battery and switch wiring. Here’s a shot before I buttoned up the throttle servo tray. 2014-06-01 10.51.59

The A123 2300mah battery is bundled up in the blue foam and tucked up against the bulkhead just above the back of the tank. With a couple of custom fit foam spacers to hold it in place it has no where to go. The circuit board for the ignition kill is also sandwiched in between the battery foam and the spacers. The ignition kill indicator light projects up through the fuselage just forward of the instrument panel but is protected inside the canopy.

Here’s another with things a bit more “buttoned up”.

Not quite finished up… throttle linkage is hiding in the sidewall, one of the remote receivers is not plugged in yet but most of the wires are wrapped up and the radio/servo tray is in place and hopefully will not need to be removed again before the end of this build. One more short session buttoning up the wiring, fuel tank and ignition and I should be able to finish up the fuselage and move on to the final steps to complete the wing. From there we will be nearing flight ready!

June 2, 2014June 2, 2014

Building the Top Flite Giant Scale P-40 – P4 Cowl Mounting

After we built the first P-40 (this one being round two) and got a few flights on it we began to immediately see problems with the cowl mountings. It seemed impossible to keep the screws from backing out and even around the ones that didn’t the vibration immediately started chewing up the mounting holes. No amount of reinforcing of the fiberglass helped and while bonded washers have proven to be effective in this role they would have completely trashed the scale lines of this bird. So when cowl number two arrived I got creative and decided we needed a better mounting system that didn’t result in having to put a bunch of (I don’t remember the exact number but it seems like 20) holes in the cowl. I came up with a system of mounting using blocks epoxied inside the cowl with 2 guide pins and two bolts. It seemed to be working quite well… right up until an unfortunate lack of airspeed, altitude and ideas destroyed more than just the cowl. So fast forward to today and I had to recreate the mounting method.

This time I thought I’d document a bit in case someone else wants to try it. It worked well but it’s a bit devilish to get the alignment right. It’s amazing how tightly it holds though with only two pins and two bolts holding it and zero holes in the cowl to mar the great looks. The basic idea is to use the two bottom mounting blocks on the firewall for alignment pins, then using the the blocks on the bottom front of the motor box to accept bolts that are reachable via the (already needed) exhaust cutout.

Here is one of the firewall mounting blocks after drilling and the addition of an “alignment pin”.

Then I marked and drilled a block with a matching hole. Where I was careful not to drill all the way through the firewall, this block can be drilled all the way through. I matched it up to be flush with the outside edge of the block attached to the firewall and also beveled the hole so that the locator pin could be inserted easier. Here it is after the initial fit.

The tricky part is to then put the cowl on and get it aligned as perfectly as possible. Using the spinner back plate helps. Once it’s right, mark the inside of the cowl and get prepared to apply some epoxy.

2014-04-06 14.13.50

Importantly at this point, where the block is going to be glued to the inside of the cowl, you need to clean the cowl inside surface with something that will cut through the mold release agent (think wax) that was applied when the cowl was made. You can use some acetone (caustic stuff so be careful and make sure you have good ventilation) and/or sand the surface before applying epoxy. Standard clamps can hold these blocks in place until they are set. If you do this in the general area before you mark the block locations it will make you life easier in the long run. Ask me how I figured that one out!

Similarly, the forward mounting blocks must be carefully aligned, marked and glued in place. These I pre-drilled to snugly pass an 8-32 bolt and drilled and tapped the existing bottom motor box blocks to match. Thin CA (very thin preferably) will harden those threads nicely, though you may have to re-run the tap 15 minutes later to make sure the CA didn’t block the threads. Here is one method of holding the forward blocks in place while the glue dries… This method used masking tape and a “cut to length” dowel. If you look closely you can see the holes to pass the bolts through have already been pre-drilled.

In order to be reachable from outside the cowl the bolts are inserted from the bottom. Happily this results in a very firm mount. I used allen bolts which require a fairly long ball driver to access in this position. Once you have these all in place you may (if your like me) find the blocks don’t perfectly match the surfaces to which they are attaching and one or more may need to be redone. Sometimes a little sawing or sanding to make the surfaces match will suffice. Otherwise a hammer will remove the block and a layer of the fiberglass with it (if you epoxied it well).

I’ll edit this post in the next few days to add a picture showing the mounting bolts in place. I’ve done this twice now and it probably took me 3-4 hours to get it right, even the second time. It’s time consuming and painstaking work but it leaves no marks and the cowl seems rock solid when it’s done.