This blog is about my experiences with flying radio controlled model airplanes and the associated trappings. I will be posting about pretty much anything I do related to radio controlled model airplanes. I will most likely post any time I feel that I have something to say, and hope to post at least once a week.
Please feel free to post comments on what you like or don't like or would like to hear more about.
So, what do you do when you have a flap servo go out in your Airfield/FMS T28? This is not a regular servo but the slow rate servo.
Well, if you're a normal person, you find a source for this special servo and order/buy another one. But, if you're a cheap Dutchman like me, you fix it!
This video shows the failed servo. When I first tried to move it, it was locked completely and did not move. By the time I made this video, it freed up and appeared to be working OK, but I think you can see (even with the bad focus) that was not working smooth and was catching.
One good thing this video shows, is that the servo circuitry should still be fine. It just needs new gears.
Here is the server just after popping it loose from the wing.
Here is the servo with most of the glue removed and sitting next to the tiny Phillips screw driver tip that was needed for the tiny screws (better get your glasses prescription up to date).
You may be asking by now "How are you going to fix this broken servo?" Well, it just so happens that I have the burned up servo from my front gear door repair, and this servo looks exactly the same (see the photo below). If you read my blog post on this, you know that the a jamb caused the burned up the motor and/or circuitry. Now this "donor" servo does not have the slow circuitry, but that's not what I need. I just need the gears, and they should still be fine. The broken flap servo should only need a gear or two replaced, as the circuitry is fine.
This below, photo shows the start of the tear down of both servos.
This photo shows the broken gears removed and set aside (on the right in the middle) and the gears from the donor servo (left) already removed and installed in their place.
There was one difference between the two and that was that the case screws from the original were slightly shorter that the donor screws. The donor screws also had longer threads for a more secure bite.
Since a test fit showed that the longer screws worked just fine, I decided to use them in the repaired servo.
Below is a video of the assembled servo showing that it is now working just fine. There's that focus problem again!
In this case, this repair saved me about $15 and shipping for a replacement servo. Some times it pays to be a cheap Dutchman keep all of your old broken crap that most people would just through away.
Ya, another one down. Still more to go.
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From my last post you know that I have several repairs to complete on my Airfield/FMS Trojan T-28. In this post I'll update you on how I repaired the nose gear strut.
The strut had a compound bend mostly back and to the side. I have no idea how it bent this much without any damage to the plastic parts or the servo.
Any way, this is how it looked:
A big concern of mine was "how am I going to bend this back without breaking the thing?" It really looks like any pressure on this thing is going to shatter any and all of that plastic.
My first thought was to use a bench vise and smash the thing straight again. The big problem with that is that this method does not always come out completely straight and, worst of all, it most likely would leave lots of marks that would prevent free movement.
What else to do? I thought about using a large pair of pliers or vice grips, but they tend to become unwieldy and would also most likely leave marks as well.
Needing some help, I browsed some forums for advice. I did find one post that reported the same repair to their T-28 gear and they did use a vise, but only as a support to pry against. They also mentioned that you could put a considerable amount of force on the plastic covered part without it breaking. This sounded pretty good, but my vice isn't mounted down well enough to pry against (just sits on my bench). So what next?
I was at work and thinking about where I might find something that I could insert the gear into that was sturdy and I could pry against. This wasn't exactly what I was thinking of, but it's what I found.
I used my Excelite driver handle. It worked great! What I did was to hold the gear in my left hand and the Excelite screw driver handle in my right hand. Then I used by thumbs to lever against the bent section. Sorry but I did not get any photos or video of the process. It did take some time as I took it slow, not wanting to over bend it or put too much force on the plastic. I started with correcting one direction and got that straight and then worked on the other direction until it looked straight from both sides.
Soon, I had something that looked like this:
This was enough and it slipped right back into the trunnion of the gear servo without any issues.
After this I realized that I could have used any sort of pipe or tubing that was sturdy and long enough. This sure seemed a lot better than using a couple of pliers.
So, with this resolved, I just had to take the landing gear servo apart and put it all back together with the strut back in place.
One down and how many to go?
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Well, the last time I took out my wonderful Airfield/FMS Trojan T-28, I was experimenting with the flaps and coming in for slow passes. I was having a log of fun with this. Until I came in low and hit that point where it tip stalled and did the left roll thing down into the ground. Everything after that was pretty much a blur. The air frame survived without much more than scratches, but a lot of little things suffered. Needless to say I now have a bunch of repairs to do.
So now here is my list of my needed repairs:
The nose gear strut has a nasty compound bend.
It's not real clear from this photo but the bend is mostly back and also to the side.
The nose gear door broke the horn.
I've tried gluing this part several times and with different glues and have yet to find a good solution. I've tried super glue, epoxy, and model glue. Nothing holds very well and eventually breaks loose.
The right wing gear came loose.
It was only loose, but I decided to take it out completely to make sure it gets secured in good.
The left wing flap servo is jammed.
This is a view of the servo after being removed.
This video shows how the servo is sort of functioning, but you can hear is clicking as the gears skip. Sorry for the blurry image. If it was clear you could see the current and voltage readings on the meters.
The motor mount/firewall is loose.
You can see from this video that something is loose and in multiple directions.
There are also several misc repairs such as a loose cowl exhaust flap.
The flap here isn't broken, but it is loose and a little floppy.
Well now you know what I'll be doing for the next few (or many) blog post.
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If any of you have been following my blog, you know that I had issues with my Airfield/FMS 1400mm Trojan T28 electrical system. In blog post T28 update and putting test equipment to good use the result was a smoked front landing gear door servo. In this post, I'll review what I did to fix this as it did not turn out to be as easy as it seemed.
On the outset, it looked like all I needed to do was to replace one servo and be done with it. Such was not the case. Not only did I need to source a replacement servo, but I still needed to make sure that what blew the first servo would not destroy the replacement.
Sourcing a replacement servo did not initially seem like a big deal as when I removed the original, it looked to be the same size as the cheep HK servos I already had. The only difference that I could see was the the mounting flanges were slightly off, with the original black plastic servo sitting a little lower (one, maybe two, mm).
This did not turn out to be that big of a deal and pretty soon I had the replacement in. I had already centered the servo and so I just screwed the servo arm in place at a 90 deg. angle, facing inboard, as the original was. Then I hooked up the linkage, in what seemed like a neutral setting. I then plugged it into the sequencer. Then I plugged the sequencer into into my servo tester. And finally, a battery pack into the servo tester to power everything.
Suddenly everything is going wonky! The doors are closing and the landing gear is cycling down! I reverse the servo tester and then the landing gear is retracting before the doors are opening. Dog gone it! I pulled the power.
What the heck is going on!?!
After some research on the Internet, I find out that the sequencer and my wiring are not messed up, but the front landing gear door servo needs to be reversed!
Out it comes again.
I don't want to wait and order just one reversed servo. Especially as I'm not even ready for another parts order. So, online I go again for more research and find a couple of good videos on how to reverse a servo. Since I have a background in electronics and am proficient at soldering, I decide to tackle it.
An hour or so later (I took it slow to make sure I had it right), I had a reverse servo ready to go (sorry, but I don't have any photos of this).
Back in it goes and I'm ready to test. Servo to sequencer, sequencer to servo tester, servo tester to battery pack.....and...phew! All is working fine and the doors and landing gear are sequencing as they should!
A little adjusting of the linkage and the doors are closing flush and appear to be opening fine. I can hear a little servo noise with everything sequenced open, but don't think too much as it seems like that is the norm with servos today.
Now, knowing that this is not the end, I add my servo and system power meter into the mix (check out this post on how I made this meter: Can't get enough test equipment). Low and behold, I'm pulling similar amp readings as when the original servo blew (over 1 amp!) I notice that this is when everything is sequenced open and when the servo is making noise. This is not just some stray noise. This is a jammed servo. No wonder the original blew out.
This is the original servo and arm position when closed.
I studied and studied the linkage and servo movement. The door linkage did not need to move as far as the servo was trying to make it go and could not move that far. I tried moving the pin in the servo arm in one hole, but then it did not have enough throw and the doors would not open far enough. What to do?
I thought about using my programmable radio to just reduce the throw, or end limits, of that servo, but with the sequencer in the mix, that would not work. No way was I going to try to set this up without using the sequencer.
The more I looked at it, the more frustrated I was getting. There had to be something to do. Then I looked again at the linkage and how the main push rod from the servo was slender and maid of spring steel, and how it had some flex to it. Then I remembered mechanical equipment that I had worked on in the past with levers connected to push rods, and how they would lock into place by essentially going past top dead center. Now any force on the lever (or servo arm in this case) is back toward the shaft and not back on the gears. That is what I would do. I set the arm position a few notches forward on the servo, adjusted the linkage so the doors would be closed in that position. With the doors unhooked, I watched as I sequenced the door servo. Sure enough, it went up to dead center on its rotation, compared to the link, flexing the push rod as it did. It came to rest with a little push rod flex but no strain noise from the servo! I tested it several more times and then connected the doors again. All was working well.
It felt good to resolve a problem and find a solution that I was happy with.
To help out with visualizing what I did, I added some pictures and a video below.
End position
Start position
The left photo shows the starting point and the right photo shows the end point of the arm travel. With the arm in this position, any pressure on the arm is straight back and not on the gears.
Please excuse the condition of the plane in these pictures and video as they were not taken after the repair, but after a subsequent crash that bent the front landing gear (that repair might be in a future blog entry).
While it was apart, I used this opportunity to take the pictures and video that I had not done before.
Some lessons learned:
If servos are making noise, check it out and make sure its not because they are jammed or stressed.
If you are replacing a blown servo, find out why.
If you run into a problem, relax and keep at it, and make use of the wisdom out there on the Internet.
And most of all, remember that this is supposed to be fun, enjoyable, and relaxing.
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Have you ever wondered what to do for a birthday party for an RC enthusiast? Have you ever wondered what to give an RC enthusiast? It can be tough to figure out. Especially when they are over 16. Everybody likes to have fun with their friends and family, so what better to do than have a birthday party fly-in with your family and RC enthusiast friends.
This is what Richie's wonderful wife did for him. She secretly notified all of his flying friends at Sacramento Area Parkflyers and organised a BBQ surprise at the Bilby flying area. This is a little bit of the RC Flying Fun that we had thanks to Richie and his wife.
Shaky Dave really puts Richie's birthday wing through its paces, and how!
Not just aircraft, but cars too! Squishy let's a couple of the guys try out his sic fast RC Ferrari before he smokes it's electronics.
A bunch (6?) of planes really put on a show with no collisions! These guys know their stuff when it comes to piloting these wings. I think that Dr. Bob as become one of the best and as far as I know he has only been at it with the wings since last summer.
Time to leave and everyone wants to get a last flight in. Stu gets the walk of shame twice! Ouch. I had to point this out since he called me on a failed take off and had to walk out to fix it. There's no film of my fail cause, well, too difficult to film myself. Richie is rightly proud of one of his new wings and touts its durability. Supposed to be one last quick flight, yeah right! Things wind down with Dr. Bob and Shaky Dave comparing motors.
As you can see, if you have the need to throw a birthday party or any sort of event for an RC enthusiast, then get a bunch of their RC flying buddies together at a good flying field with good food (preferably BBQ) and let the fun begin.
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I really wanted to put my test equipment to use and I needed to check out my Airfield T28 with possible BEC/receiver/servo issues. So I put it all together in this one big post.
This was a complicated subject with all the test equipment and airplane gear so I decided to try my hand at a video post. So, here goes.
Thank you for watching my video post, let me know how you like this format.
Update to the video:
Further inspection showed that the faulty servo was not the steering servo but the door servo. In the following photo you can see the bottom servo is the same servo that was over heating in the video. You can also see that the push rod from the servo is flexed a lot. This is obviously putting a lot of stress on the servo and is most likely the cause of the current draw. Something will have to be done about this during the repair.
Stressed servo that failed
I have noticed that the current generation of the Airfield/FMS 1400mm Trojan T28 do not use a servo for these doors but instead uses spring linkage. I may go this route for this repair and cut one servo from my count.
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I have this really cool Airfield T28 that I munched (on its maiden) and just recently put all back together. Its been sitting around just waiting for hanger rash. To resolve this, I decided to build something to hang it from the ceiling of my garage.
I didn't want to string it up with any sort of cord or wire and risk dents in the foam so I decided to come up with some sort of PVC rack. I have seen various renditions of this on the Internet and decided to assemble one of my own. Incidentally, I put this all together from spare parts I had in my garage (that cheep Dutchman coming out in me again).
To put this together, I started with a rough plan and measurements. I estimated how far apart the support sections needed to be to come within the landing gear and still outside the fuselage. Then I also made allowances for the wing width for the length of the supports. For the drop sections, I figured that I would need enough length so that neither the canopy or the rudder would hit the ceiling. I put this all down on paper (a bill envelope, I'm sure we all have those easily on hand) and mulled over what fittings I would need.
With the length of 3/4 inch pipe I had on hand and the fittings, this is what I came up with.
I didn't have enough elbows so I used T fittings instead for the top cantilever piece and to connect the support arms to the drop sections.
You can get a better idea of how the T fittings were used as elbows from this angle. Also, since I had two 22 1/2 degree elbows, I decided to use them for end caps. It's not like the plane would slide off without these, but I just thought it looked better.
Here's what it looks like setting near my plane. These two pictures were taken before I cut down the width of the top. You can see that the down sections are squeezed together at the bottom to fit in between the landing gear. I cut out a half inch from each of the short sections at the top to resolve this miscalculation.
From this side view you can see that it should support the wings just fine and give enough clearance for the rudder (once lifted up).
Here's what it looks like mounted to the ceiling in my garage. I used plumbers tape and molly screws to secure everything.
At this point everything is still dry fit together. I figured that if I can't pull it apart to glue it, it ain't comin' apart!
Now it's all safe and sound out of the way of everyone and there should be no problems with hanger rash. That is as long as I don't need my ladder out of the garage again.
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There is one final issue that I have not resolved yet in the reconstruction of my Airfield Trojan T28, and that is the canopy damage. When my plane crashed, the canopy was ejected into the propeller (just before it completely shattered). One of the propeller blades ripped through the front shattering it. Fortunately it was still in one piece.
OK, it's in one piece, but how do I fix it?
Some Google searching came up with a solution that I decided to try. This solution involved using tape to hold things together while thin CA glue is used to repair the cracks.
Another view of the tape
Taped up
So, here I go. These two photos show the clear tape that I used to cover and hold together the cracks. The tape also allows you to see better the extent of the damage.
CA applied
Finished product
It's maybe a little hard to see in the photo on the left, but all of the cracks have been run over with regular thin CA glue.
The photo on the right shows the finished product after the tape has been removed. Yes, it does look like it has been welded together, but it's together! There is also some clouding of the plastic near the glue (you can see a little of it covering the pilot), but I should be able to buff some of it out.
While this appears to have worked very well there is one thing that I would do different. If I have to do this again (and I'm sure that I will), I would tape it on the outside and glue it from the inside. Why? Well, the taped side left a nice smooth surface (surprisingly, the glue did not stick to the tape) while the glued side, well, feels like a raised weld seam.
Any way, I'm still very satisfied with the results. Especially since it saved me from buying a whole new cockpit (plastic, foam, and pilot).
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This is the account of my reconstruction of my crashed Airfield (FMS) Trojan T28. I hope you have time, because, although the damage was not that great, this was big task as there was a lot to do.
Surprisingly the motor and mount are just fine. With the impact and shattering of the prop hub, I thought sure that something here would have been severely damaged.
Humpty Dumpty of propellers
This is what I have to start with for the propeller and hub. I was just going to order another hub, but it was hard to find one that I could get for a reasonable price from a place that had one on hand. Nitro planes has them for only about $5, but they never seem to have any in stock. Other sources have them, but they are twice the price and then shipping doubles this cost again.
All fit back together
So, I decided to try to repair mine. I saw a post from another pilot who had the same issue and he mearly used Goop glue to put his back together and replace small pieces. I thought if he could do this and be successful, I could do it too. My prop blades are in great shape with no chips or gouges, so no issues there, just the hub. I started the repair process by dry fitting all the pieces together to see
Other side
how they would fit together. Once I was happy with how they fit together, I CA glued them to hold all of the pieces together. I did this for each half. I also test fit the two halves together to make sure that they would still mate up.
Epoxied together
Once I was happy with the two halves, I fill the void spaces with 5 minute epoxy. I used a narow wooden stick to made sure that the epoxy got down into these voids and filled them to the top.
When the epoxy was almost dry, I used the tip of a small flat blade screw driver to scrape off any overage and trim everything down.
Now I was ready to fit the blades back into the repaired hub. Although the hub was still a bit distorted, it fit back together better that it did originally.
This is what it looked like when I finally got it all back together. I was a little worried about tightening down the screws as I thought it might break everything apart again, bit this was not to be the case.
Now on to the cowling. There was only one broke off part but everything else had to be formed back together before this part would fit properly. So, I fit the parts together as best as I could and CA glued them in place. Then I secured everything with epoxy. The tape in the photos served two purposes. One was to hold things together and the other, to act as a glue dam. I glued this from the inside so that it would not show on the outside.
Once the cracks were glued up and everything was close to aligned, I was able to glue back on the air scoop piece that was broken off.
Now it's all ready to go back on.
Before the cowling can go back on the mounts need to be repaired. The cowling almost pulled out all three of its plastic mounting points. The picture shows the worst one. It will take some effort to repair to get these repaired. I started with the top center mount and used a pair of needle nose pliers to jockey it around until it looked good with the cowling. Then I used CA glue to hold it in place. Then I did the same with the other two taking care to stuff any loose foam bits back in. Once all three looked good and were secured with CA, I used hot glue to fill in the gaps and secure them even more.
Next, on to the tail sections. Both the rudder and elevator movable surfaces were broken off and so they needed to be put back on. Fortunately, there was no serious damage and the hinges were the only thing affected. The rudder was easy and only needed the plastic spike hinges glued back in as they pulled straight out. I used Goop as it gave me time to work and would not cause any serious issues if it got on the hinges.
For the elevator surfaces I used these really cool paper hinges that I thought I would never use. But, they were what I had and so decided to try them out. They worked great and now I love them. Check out my video and just see how easy they were to install. All that is needed is a hobby knife, the hinges, and CA glue.
In this video I show the basic installation steps for these hinges. I started with the movable surfaces. Since these used molded foam hinges, I had to start by trimming away all of the old hinge material. This actually helped me in locating the hinge line and made for a good guide to follow.
This video shows more detail in how the hinges go together and how they are glued up. The hinge material is made of a fiberus material that will wik the CA glue into the slot and make for a good bond.
You can see at the end of this video that even with the glue in the hinge material, they still move quite well. I will be using these when ever I need a hinge where tape will not suffice.
Here is a photo of the ailerons fixed back up with the same paper hinges. At first glance the wings looked fine but on closer inspection the aileron hinges on both sides were found to be badly cracked. I just cut them the rest of the way off, trimmed the excess material, and repaired them just like the elevator.
Clevis repair
One of several repaired clevis
I had several clevises that broke. At first I was going to just replace them but I had problems finding the right ones. My LHS did not have a decent selection of them and online it was hard to tell for sure what size they had and if they would replace what I needed. So, I decided to just repair what I had. I started by trimming off the remains of the pin. Then I used a small drill bit to make a hole where the pin was. Now all I had to do was to bend a trim a piece of paper clip to fit. A small piece of fuel line is all that is needed to keep everything secure. I have since found out that this is a common way of doing clevises.
Decal distorted by a fracture
Fracture can be seen here
On to more fuselage damage. This was not obvious for while, but there was a fracture across the fuselage above the back edge of the wing. I noticed this because of the decal distortion (stretching). Looking further revealed the fracture. Since it wasn't that deep I repaired this by opening it up enough to squirt CA glue in and then close it down. This seems to have done the job and it is holding well.
Front corner landing gear box damage
Another view of the damage
Doors and linkage broken free
What turned out to be the worst damage was the front landing gear. The gear was broken, just flopping around, both doors were broken off, linkage was broken, and finally the landing gear box was cracked in the front and pushed back.
I started by removing all the broken parts and landing gear.
Fixing the box required using a needle nose pliers to pry on the bent surfaces until they fit back together. I did this by inserting one jaw of the pliers down in between the plastic box and the foam. The other side jaw was then inside the box. I pushed them down until the tip was right at the bend. I then pried back on the plastic until the pieces were back in alignment. Then I used glue to hold everything in place.
Landing gear removed
Opened up showing
broken trungeon
Now I needed to repair the broken landing gear. This required the removal of the four small screws holding it all together. This revealed the motor, electronics, and moving parts. This gear works by moving a bar back and forth on a screw shaft rotating the gear itself. The pawls on this pivoting part (trungeon?) were broken off. Fortunately I had another one from the defective landing gear it originally came with. I pulled this one apart and removed what I needed.
Part replaced and
ready to go back in
There was one issue with this and that was that the replacement piece was not intended for steering gear but for the shaft to be held in tight. To resolve this I needed to drill out the strut hole so that it would pivot for steering. This was easily done with my drill press and I carefully drilled out the plastic and brass to enlarge the hole. Now I only needed to put all the pieces back together being careful to get all the pieces lined up and keep from pinching the wires.
Making sure the wires aren't pinched
You can see from these photos that it all went back together and now I have a functioning front steerable landing gear again.
Going back together
All back together
OK, the following video is a little lame, but what ever. I was holding the camera and doing the servo tester at the same time. Yeah, I could have used a tripod (I do have one), but I was in a hurry. Any way, it still shows that the landing
gear works!
Pin replacements
Closer view
Next, on to the doors. The obvious damage to both was that the servo horns were both broken off. Fortunately one was still hanging on and I found the other. These were glued back in place with a little CA glue.
Less obvious was the loss of the hinge pins on one end of each. At first I did not know what to do. I thought I was going to have to purchase new ones. Then I got the idea, why don't is just make new ones? I shaved the ends off flat and then drilled a hole where they used to be. Then I carved down a piece of bamboo skewer and press fit them in. These came out so nice I did not need to use any glue.
Covers installed
Now all was repaired and ready to go back together. It took a little doing, but I got everything back in place. Not easy to do with my fat fingers (not as dexterous as I used to be).
Ready for assembly
Everything is all fixed now and ready to be re-assembled. The picture at the right shows all the repaired parts.
Please ignore all of the other stuff on the table
OK, was that enough for everybody? I know it was for me!
Now I'm at that usual point of waiting for the right day and weather to go out and fly again.
Thanks for stopping by my blog. Please feel free to post comments, good or bad, and be sure to come back and check for future posts.
