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.
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.
Now, before you get a little upset that I may be being rude about my friends, let me make it clear that I mean my Sacrament Area Parkflyer buds. You can check us out and get some more information about where we commune and fly at this site parkflysac.com.
I went out to my favorite flying area to have some RC flying fun (I like the Bilby site because it's the closest to me) and hit a snag. I was in such a hurry to get out there that I forgot the wing spar for the one airplane I brought! Since I could not fly, I decided to video those that were out there and record the fun and commerrodery. The video isn't great because all I had with me was my cell phone, but I think you will enjoy them anyway.
In this video a nice 4 stroke 3D plane has problems with stalling before take off as a nice foam jet comes in for a landing. While waiting for the 3D plane to take off, Dr Bob gets ready and tosses up an insanely speedy little wing of his and puts it through its paces.
In this video the 3D 4 stroke comes in for a nice landing while Richie is getting ready to take off his big wing with landing gear. It's a big heavy wing so he gives himself a lot of run way. Those of us parked at then end are grateful for the courtesy. Surprisingly it takes off quickly. It wobbles around quite a bit but Richie soon takes control and flies it quite nicely. Then someone gets ready to maiden their Apprentice but is troubled with steering issues.
In this video, a really cool foam jet takes of. This is the same foam jet that landed in a previous video. No, this video is not out of order, this is another flight. It took some distance to take off and from my angle, it almost looked like it was going to end up in the back of my Jeep.
This next video starts with a really nice flyby from the foam jet that took off in the last video. Just after if flew by, Richie landed his big wing with landing gear. Unfortunately he came down a little heavy and collapsed the nose wheel. We take a closer look while the foam jet makes some sweet flybys. After a few more low and casual passes he comes in for a nice landing.
Dr Bob takes out another screamer. Too bad about 3/4 of the way through while going vertical, the motor screws come loose and the prop catches the right side of the prop slot. You can hear this in the video. The result is that the torque causes the motor to spin and rip all of the motor wires out! Despite this, Dr Bob deftly brings in this wing with a nice glide and drops it right at his feet.
Quite often we have someone maiddening their new plane. That is the case with this beautiful new WW2 biplane. Unlike the Apprentice earlier, this one actually gets a chance and flight. Let's see what happens.
Yeah, OK, I don't know what happened, but needles to say, it didn't last too long. He'll get a lot of help and make another attempt soon.
We have a lot of fun out here and also at the other sites around the Sacramento area. Come out and join us, the more the merrier. There are no fees or dues, we just ask that everyone fly and behave respectfully and also take care of the areas we fly at.
Hope to see you out there!
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.
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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Time to assess the damages to my Airfield Trojan T28 after my recent crash. First, I have a bag of parts and damaged fuselage and wings. Starting with the bag, I have a propeller that is now in about 10 pieces (the hub shattered), two elevators (the foam hinges completely failed), rudder (the pin hinge pulled straight out), front landing gear doors (rear hinge pins sheered off), cowling pieces, and left landing gear cover.
These are easily repaired
Now to review the wings and fuselage. The wings look really good, but closer inspection show that the aileron foam hinges are half torn and will need to be repaired. The fuselage shows a lot of damage. I'll start from the rear. Well we already know about the tail surfaces, so I wont review these, but hears a picture.
The crack can just be seen here
running down the middle
Side buckling provides a hint of
more damage
Just past the cockpit and under the wing mounts, the fuselage is cracked all the way across, but only about half an inch deep. Moving forward the battery almost completely blew out the foam blocks (sorry no picture).
Underneath, the leading edge of the front landing gear housing is buckled and pushed back some and the nose wheel flops, up and down, lose.
Front landing gear just flops around
The impact caused both doors to break loose sheering off the rear hinge pins and breaking both horns attached to the middle of each door sections.
The propeller hub, while scratched,
was undamaged
The cracks can really be seen here
The cowling had the air scoop section broken off and was cracked along the air scoop recess and around the motor shaft opening. Also, all three cowling mounts were ripped loose and the foam around them torn.
The crack is worse
than it appears
This was the most damaged mount
Finally, several clevises have had their pins broken, but all control horns, push rods, and servos are in tact.
Oh, almost forgot, the cockpit canape has been cracked in the front, but the pilot did not come loose and there appears to be not other damage here.
You can see from the scuff in the prop hub that this thing hit pretty hard, but surprisingly enough, the motor and shaft sustained no damage and so far seems perfectly fine!
Now comes the repair process and that will be the subject for my next post.
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I have this beautiful new new Airfield T28 Trojan and I finally have a chance for it's maiden flight!
I feel that I should note here, before I go on, that I have discovered that the Airfield name is actually a re-brand by Nitro Planes of FMS products. Not that that's a bad thing, just that FMS T28 enthusiasts are included too!
Its Easter weekend and I will be visiting my folks near that cool park and the weather is expected to be great for flying.
Look at all those wires
We start packing for our trip and I realize that this plane is huge and would not fit in the trunk of my car (Mazda 3). It wouldn't be so bad, but this plane is not made to be taken apart like most planes. There are four screws that bolt the wings on from underneath. This isn't so bad except that there are a million wires that come from the wings into the fuselage! OK, OK, there are 5 sets of wires from one wing and 6 from the other (landing gear door, landing gear, flaps, ailerons, and wing lights) and not a million. These are routed through small openings that make dis-assembly/assembly difficult and something to be avoided at all costs! OK, I'm being dramatic again, but this is not trivial. As it would happen, I did end up unbolting the wings, separating them, and disconnecting all of the connections for the servos and lights to get this big plane to fit.
Wow, this really made me think that I need to take transportation into account with planes in the future, and explains why serious RC pilots have trailers.
Once we arrived (we were early for once) I unloaded the plane into my Dad's workshop and started assembly. Of course this was not until after we greeted them, brought in our dinner contribution, gifts for recent birthdays, and visited a little. I'm not that crazy focused on RC planes. Now I only had to wait for the meal to be over and for all of the other guests to leave! I have to say that I did not really want that meal to be over because my Mom made this lamb that was to die for (hm... not sure that was worded appropriately). Any way, it was really good.
Hooking up the battery
Snapping on the cockpit
Testing the throttle
Finally everyone is gone and I still have 45 minutes before we also need to leave. Off to the park. We arrive at the park. I have to thank my daughter who rode in the back seat with the airplane tail in her face (I also have to thank her for being my photographer). There is about a 5mph breeze, but this shouldn't be an issue. We get the plane out and I get it setup. Wow, it sure looks good sitting out there on the dirt runway! I tested all of the control surfaces, I tested the motor, and then I taxied the big Trojan T28 out and around the runway. I let her sit there for a bit off to my left facing into the breeze, giving me time to collect my courage.
Ready for take off
Leaping into the sky
I gave her full throttle and hoped to keep her straight. Half way down I could see her wanting to take flight. I gave her a little elevator and she shot straight up into the air. Wow, beautiful! I struggled to level her out and bring her around as the controls are a lot touchier that I'm used to. Watch out, this thing can really snap around! I eased up on the throttle and pulled in the landing gear as I made a big loop around the airfield in front of me. I'm just now thinking that I should start working with the trim. I go for another loop but this time decide to try turning away from myself as I'm coming across the back field. At this point she is downwind and about 100 yards off to my right at about a 45 degrees.
It hit about 10ft back
Dad and I assessing the damage
This is where things go terribly wrong as suddenly I feel that I have no control! I had given more power, but she is not going any faster! I gave her up elevator, and she is not climbing! I gave her left and right aileron and she is not banking! The next thing I know is that my beautiful $280 Trojan T28 is headed straight for the ground! At the last moment she started to respond the my elevator command and pulled up just enough to avoid drilling in! Pieces flew just before that terrible WHUMP sound reached us. Nothing left to do but start that dreaded walk over to see what was left.
Still assessing the damage
Point of impact
Small pieces everywhere but the fuselage was intact! So, this was bad, but not as bad as I anticipated. We collected all the parts putting them in a bag. Took the wing apart again and loaded it up, in the trunk this time. No need for careful placement and handling.
Next post I hope to feel well enough to review the extent of the damages and reconstruction.
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