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Cessna 152, Balsa 30% Scale Rescue from Hostetler Plans
- Thread starter Joker 53150
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An email has been sent, thanks!
Weather this weekend is nice, so I brought the Cessna up and out of the shop again to see what happens. Some fuel was added, the carb primed, and a couple flips later she was running. The throttle pushrod adjustments I made appear to have done the trick as I've got much smoother throttle response, but the big news is that the flutter at the tail is GONE! 
My guess is that the former servo for the steering servo was the culprit.
I ran about 1/3 tank of fuel through it all at fairly low settings with a couple bursts of power to about 2/3 throttle to keep it cleaned out. After a little adjusting of the low speed from the servo it was idling very nicely. Tomorrow I'm taking it out to the sod farm to test with wings on. If things go well I *might* see if it'll fly. More fuel will be run through it first just to help it get broken in.
My guess is that the former servo for the steering servo was the culprit.I ran about 1/3 tank of fuel through it all at fairly low settings with a couple bursts of power to about 2/3 throttle to keep it cleaned out. After a little adjusting of the low speed from the servo it was idling very nicely. Tomorrow I'm taking it out to the sod farm to test with wings on. If things go well I *might* see if it'll fly. More fuel will be run through it first just to help it get broken in.
Weather this weekend is nice, so I brought the Cessna up and out of the shop again to see what happens. Some fuel was added, the carb primed, and a couple flips later she was running. The throttle pushrod adjustments I made appear to have done the trick as I've got much smoother throttle response, but the big news is that the flutter at the tail is GONE!
I ran about 1/3 tank of fuel through it all at fairly low settings with a couple bursts of power to about 2/3 throttle to keep it cleaned out. After a little adjusting of the low speed from the servo it was idling very nicely. Tomorrow I'm taking it out to the sod farm to test with wings on. If things go well I *might* see if it'll fly. More fuel will be run through it first just to help it get broken in.
Please send photos of your plane and flight. For all of us other guys whose flying field was shut down due to the Coronovirus
Please send photos of your plane and flight. For all of us other guys whose flying field was shut down due to the Coronovirus
Will do. Since it's a sod farm and not an actual flying field (at least it's not got any signs stating it's a flying field...
) I'm hoping we stay under the radar. It'll be extremely easy to practice social distancing when there are hundreds of acres for us to work with. The field my dad flies from was shut down, but it's on county land.
The short answer is "no". The long answer is "nooooooooooo".
I got it all set up to ground test and filled the tank 1/2 way so I wouldn't be tempted to try flying. It fired up easily with the Chicken Stick and I spent a few minutes just taxing it around on the ground. The engine has a ton of power, plenty for this plane. After a few runs back & forth I went in for a closer inspection.Aaaaand, the servos started twitching again....
Since all of the electronics except the ignition module have been replaced I guess that's the next step. It's rated for 4.8 - 8.x volts and I'm putting around 6V into it, and it's completely exposed to the propwash so it shouldn't be overheating. The throttle pushrod is metal, but is connected to the carb with plastic to avoid interference. I'll have to look at the plug to make sure it's a resistor-type, but if memory serves me it is. This is really irritating me, the plane runs very well and the weather was darn near perfect for a maiden!
OliverW
Legendary member
That sucks!!The short answer is "no". The long answer is "nooooooooooo".
Aaaaand, the servos started twitching again....
I'll have to look at the plug to make sure it's a resistor-type, but if memory serves me it is. This is really irritating me, the plane runs very well and the weather was darn near perfect for a maiden!
Yeah, but it could have been far worse as the twitching didn’t start after quite a bit of ground testing. If I had filled the tank I’d have been extremely tempted to try flying it before seeing the problem.
Besides the ignition module, the only other piece of the puzzle which hasn’t changed is the receiver. Not sure if it could be the culprit..??
Sooooo, I pulled the trigger on a new plug to replace the original "Torch" brand. It's marked as a resistor plug, but I've never heard of the brand so it'll be swapped with a new piece as an inexpensive first step.
If that doesn't work I'll swap in a new Rcexel ignition module.
If that doesn't work I'll swap receivers.
At that point, everything electrical should have been replaced.
If that doesn't work I'll swap in a new Rcexel ignition module.
If that doesn't work I'll swap receivers.
At that point, everything electrical should have been replaced.
This may be the rare occasion where the interwebs are being useful. I posted on Face Book asking for input on the interference problem, and along with ideas including grounding the ignition case, etc., was a comment about the FrSky X8R receiver having problems with the high frequency from an electronic ignition. A minimal amount of digging resulted in a maximum amount of chatter on this subject.
So here's the new plan for the Cessna. First, the plug will get swapped when the new one arrives. Going to a name-brand plug is cheap insurance either way. Second, the X8R receiver will be swapped with an X8R-Pro that is supposed to fix the problem when used with an electronic ignition. The plane will be ground-tested for a while to see if the noise comes back. If so, then the new ignition module will be tried. This can all be done at the field so I don't annoy my neighbors by running the engine for a long time in front of the house.
This got me thinking about the X8R I've got in the Rascal 110. While it doesn't have any issue with chatter of the control surfaces, it does give me "low RSSI signal" alarms a few times per flight. I've been playing with the antenna placement thinking that was the issue, but it may be related to the Cessna's problem.
So here's the new plan for the Cessna. First, the plug will get swapped when the new one arrives. Going to a name-brand plug is cheap insurance either way. Second, the X8R receiver will be swapped with an X8R-Pro that is supposed to fix the problem when used with an electronic ignition. The plane will be ground-tested for a while to see if the noise comes back. If so, then the new ignition module will be tried. This can all be done at the field so I don't annoy my neighbors by running the engine for a long time in front of the house.
This got me thinking about the X8R I've got in the Rascal 110. While it doesn't have any issue with chatter of the control surfaces, it does give me "low RSSI signal" alarms a few times per flight. I've been playing with the antenna placement thinking that was the issue, but it may be related to the Cessna's problem.
I must have missed that you are using an X8R receiver. Yes, this is a very well-known issue and part of the issue with adoption rate of gas pilots. Given your symptoms, I would give a nod to this issue as well.
I probably never mentioned which receiver I was using, not realizing there was any issue. It never crossed my mind that I'd have to research compatibility on an item like that, and I don't read all the message boards, facebook, etc. that regularly to have run across it, I guess. Oh well, the new receivers should be here in a couple days and I'll try that out. The X8Rs I've got can be moved over to electric planes in the future.
Here she is moving under her own power for the first time since I got the plane. This is prior to the surfaces twitching. I kept the taxiing along the drive as that was the highest and driest ground at the sod farm.
Cessna update - I installed a new Champion plug to replace the OEM "Torch" plug, and also replaced the FrSky X8R receiver with the FrSky X8R-Pro receiver. The Cessna was then strapped down to the new test stand and fueled up (I'm still using Tru-Fuel, and still really liking it). The engine was choked and after about 3 turns of the prop the carb was nice and wet. Two flips later it popped, the choke turned off, and within 6 flips it was running. We let it run for a few minutes to warm up before giving it more throttle, waiting and watching the tail surfaces for any signs of twitching. After about 5 minutes of nothing but goodness we shut it down to put the wings on. Maybe having the additional 4 wing servos would make a difference...?
With the wings on I moved the plane to the front lawn. The exhaust blasting down onto grass was far quieter than running it on the test stand. I taxied around the lawn a bit, and had a lot of neighbors walking by stopping to watch. Total run time today was around 20 minutes with absolutely no signs of problems.
Well, ONE problem... The muffler gasket was leaking around the front bolt and creating a mess across the whole left side of the plane. The bolts were plenty tight, so I took it apart to fix the problem. At first I thought it was the exhaust gasket. It's thin gasket material with this engine, but another Turnigy 58cc I have uses a heavier/thicker material. Looking a little further I think the original gasket wasn't sealing because the hole for the front muffler bolt is just a hair too shallow, as I could see marks where it was bottoming out on the cylinder wall. This would keep the front bolt from tightening properly, resulting in an exhaust leak. The fix is pretty easy. First, I'm swapping to the heavier gasket to see if that makes a difference, but I'm also grinding the bolts shorter by about 1mm.
Next time I run the engine I'll know if it fixes the issue, and I'll also know if it wants to fly!
With the wings on I moved the plane to the front lawn. The exhaust blasting down onto grass was far quieter than running it on the test stand. I taxied around the lawn a bit, and had a lot of neighbors walking by stopping to watch. Total run time today was around 20 minutes with absolutely no signs of problems.
Well, ONE problem... The muffler gasket was leaking around the front bolt and creating a mess across the whole left side of the plane. The bolts were plenty tight, so I took it apart to fix the problem. At first I thought it was the exhaust gasket. It's thin gasket material with this engine, but another Turnigy 58cc I have uses a heavier/thicker material. Looking a little further I think the original gasket wasn't sealing because the hole for the front muffler bolt is just a hair too shallow, as I could see marks where it was bottoming out on the cylinder wall. This would keep the front bolt from tightening properly, resulting in an exhaust leak. The fix is pretty easy. First, I'm swapping to the heavier gasket to see if that makes a difference, but I'm also grinding the bolts shorter by about 1mm.
Next time I run the engine I'll know if it fixes the issue, and I'll also know if it wants to fly!
MAIDEN REPORT:
First, a report on the last issue I had with the Cessna, the leaking muffler gasket. Trimming the mounting bolts a bit and the new gasket worked great, there was no visible residue after running the engine today.
Now, on to the flight report. It was a bit windier than I'd like, but the winds were steady and not turbulent thanks to a lack of trees at the sod farm. The engine pulls gas extremely well when priming the carb, and maybe three rotations is all it takes to get gas to the carb and fully prime it. A handful of flips of the prop and it was running nicely. I let it warm up for a few minutes and watched for issues with the servos twitching again, but all was good. The grass was getting a little longer, so I ramped it up to full power for the take-off, and it gently lifted off the ground! The engine was burbling a little bit, but nothing that a little tuning won't fix. It cruised nicely at about 2/3 throttle, a little more than expected, but it is a BIG bird!
I did a couple circuits of the field and found it only needed a small amount of down trim and a couple clicks of right aileron. Even with the wind it was incredibly stable and predictable. After trimming and getting the feel of it, I did a couple lower passes for my buddy Mike to take some pictures for me. After the second low pass I throttled up to get some altitude and continue the flight, and then the engine quit. No real warning, it was like I turned off the ignition. I still had full control of the plane about 40' up, but I was heading towards a low area of the sod farm with some standing water. My only other option was to circle back and land with a stiff tail-wind, so that's what I did. The plane made the turn towards dry ground very well and touched down about 100 yards away from me. It was a pretty darn good landing, in my opinion, until the wind kicked up and flipped it straight up and over. I was expecting damage to the vertical stabilizer, but that just had some dirt on it. The wings were fine, as was the landing gear and the prop! Then I saw the damage.... First it just looked like the base of the rear window had come unglued, but a little further investigation told me the fuselage has a pretty good crack in it from side to side. My guess is that I'll have to strip a little bit of covering to get in and strengthen it, unfortunately.
So my big question is WHY it quit. The engine didn't seize and wasn't showing any signs of problems other than running a little rich.
- Our first guess was that the fuel tank was vibrating and a big air bubble got in the line, but the rest of the line was completely free of bubbles.
- The next guess points to the throttle servo. When I opened the door to check for damage I found the entire throttle servo tray had come loose, letting the throttle close completely at the carb. The carb has a spring to close the throttle if the pushrod comes loose (or if the entire servo lets go...). Some people say to remove that spring completely, but in this case that could have resulted in an engine that is stuck at full speed and won't slow down. The screw that keeps the throttle from going too low wasn't installed (another thing some people say to remove) so *IF* the throttle servo came loose there was nothing to stop the carb from shutting the butterfly completely, killing the engine. The servo could have come loose when the plane flipped, but it wasn't an aggressive flip and damage was limited to what I can now see as a weak spot in the design, so we're leaning towards the servo tray as the cause of the engine quitting.
So will it fly again? Heck yes!!! This year? Maybe, it depends on how deep I have to dig to fix the damage.
First, a report on the last issue I had with the Cessna, the leaking muffler gasket. Trimming the mounting bolts a bit and the new gasket worked great, there was no visible residue after running the engine today.
Now, on to the flight report. It was a bit windier than I'd like, but the winds were steady and not turbulent thanks to a lack of trees at the sod farm. The engine pulls gas extremely well when priming the carb, and maybe three rotations is all it takes to get gas to the carb and fully prime it. A handful of flips of the prop and it was running nicely. I let it warm up for a few minutes and watched for issues with the servos twitching again, but all was good. The grass was getting a little longer, so I ramped it up to full power for the take-off, and it gently lifted off the ground!
The engine was burbling a little bit, but nothing that a little tuning won't fix. It cruised nicely at about 2/3 throttle, a little more than expected, but it is a BIG bird!I did a couple circuits of the field and found it only needed a small amount of down trim and a couple clicks of right aileron. Even with the wind it was incredibly stable and predictable. After trimming and getting the feel of it, I did a couple lower passes for my buddy Mike to take some pictures for me. After the second low pass I throttled up to get some altitude and continue the flight, and then the engine quit. No real warning, it was like I turned off the ignition. I still had full control of the plane about 40' up, but I was heading towards a low area of the sod farm with some standing water. My only other option was to circle back and land with a stiff tail-wind, so that's what I did. The plane made the turn towards dry ground very well and touched down about 100 yards away from me. It was a pretty darn good landing, in my opinion, until the wind kicked up and flipped it straight up and over. I was expecting damage to the vertical stabilizer, but that just had some dirt on it. The wings were fine, as was the landing gear and the prop! Then I saw the damage.... First it just looked like the base of the rear window had come unglued, but a little further investigation told me the fuselage has a pretty good crack in it from side to side. My guess is that I'll have to strip a little bit of covering to get in and strengthen it, unfortunately.
So my big question is WHY it quit. The engine didn't seize and wasn't showing any signs of problems other than running a little rich.
- Our first guess was that the fuel tank was vibrating and a big air bubble got in the line, but the rest of the line was completely free of bubbles.
- The next guess points to the throttle servo. When I opened the door to check for damage I found the entire throttle servo tray had come loose, letting the throttle close completely at the carb. The carb has a spring to close the throttle if the pushrod comes loose (or if the entire servo lets go...). Some people say to remove that spring completely, but in this case that could have resulted in an engine that is stuck at full speed and won't slow down. The screw that keeps the throttle from going too low wasn't installed (another thing some people say to remove) so *IF* the throttle servo came loose there was nothing to stop the carb from shutting the butterfly completely, killing the engine. The servo could have come loose when the plane flipped, but it wasn't an aggressive flip and damage was limited to what I can now see as a weak spot in the design, so we're leaning towards the servo tray as the cause of the engine quitting.
So will it fly again? Heck yes!!! This year? Maybe, it depends on how deep I have to dig to fix the damage.
Crash damage is an interesting thing. Sometimes it's super obvious, and other times is completely hidden. The Cessna damage is leaning towards the hidden end of the spectrum, and at first I didn't even notice it. Then I thought it was just just a tear in the covering.
Both sides have the same damage, from so much weight at the tail getting lifted and dropped when the plane went over 180*. The more I look at it, the more I see this as a weak point that really needs some additional strength, especially if I want it to last on bumpy landings, during aerobatics, etc.
I'm going to sleep on this for a few days, but here's what I'm thinking for repairs. First, the doors will be removed (easy) and the covering along the pillars behind both doors needs to be removed or opened up to gain access to the structure. The tail will then be lifted which will close any gaps in the broken wood and put the tail back where it should be. The areas where it broke would be hit with thin CA to wick in and hold the pieces together again. The red lines added to the picture below show where I would then add carbon fiber tubes, epoxied in place. This would bridge the gap where it was broken, where I think the design is weakest. There would also be a CF tube added inside the rear window along the ply stringer. It would extend up into the wing's center section and down into the tail. Again, this is an area I think is under a fair amount of pulling stress just due to the way the plane is designed.
The last step of the repair (other than fixing the covering) is one I'm still kicking around. The design of this plane uses a "double wall" - the outer wall is the outside of the plane and the inner wall is the interior, and they're separated by about an inch of dead space. In this case it's fully sheeted inside and out, so my thought is to drill a couple holes on the inside, and squirt in some Great Stuff Expanding Foam. That stuff sticks to EVERYTHING, is reasonably strong, and weighs next to nothing. It would essentially tie the entire structure together where it is used. Thoughts...?
So overall the damage isn't too bad, and I *THINK* it'll be a fairly easy-ish fix. It also gives me some information that'll be useful for when I eventually get back to building my giant L-19 Bird Dog (also a Hostetler design). Since that plane is currently uncovered balsa it'd be easy to make some of these modifications before it gets covered.
Both sides have the same damage, from so much weight at the tail getting lifted and dropped when the plane went over 180*. The more I look at it, the more I see this as a weak point that really needs some additional strength, especially if I want it to last on bumpy landings, during aerobatics, etc.
I'm going to sleep on this for a few days, but here's what I'm thinking for repairs. First, the doors will be removed (easy) and the covering along the pillars behind both doors needs to be removed or opened up to gain access to the structure. The tail will then be lifted which will close any gaps in the broken wood and put the tail back where it should be. The areas where it broke would be hit with thin CA to wick in and hold the pieces together again. The red lines added to the picture below show where I would then add carbon fiber tubes, epoxied in place. This would bridge the gap where it was broken, where I think the design is weakest. There would also be a CF tube added inside the rear window along the ply stringer. It would extend up into the wing's center section and down into the tail. Again, this is an area I think is under a fair amount of pulling stress just due to the way the plane is designed.
The last step of the repair (other than fixing the covering) is one I'm still kicking around. The design of this plane uses a "double wall" - the outer wall is the outside of the plane and the inner wall is the interior, and they're separated by about an inch of dead space. In this case it's fully sheeted inside and out, so my thought is to drill a couple holes on the inside, and squirt in some Great Stuff Expanding Foam. That stuff sticks to EVERYTHING, is reasonably strong, and weighs next to nothing. It would essentially tie the entire structure together where it is used. Thoughts...?
So overall the damage isn't too bad, and I *THINK* it'll be a fairly easy-ish fix. It also gives me some information that'll be useful for when I eventually get back to building my giant L-19 Bird Dog (also a Hostetler design). Since that plane is currently uncovered balsa it'd be easy to make some of these modifications before it gets covered.
OliverW
Legendary member
If you haven't gone too far on the L-19, it would be wise to use a wing tube instead of hostetler's joiner. You know of the issue with ours lol. My dad just ordered another hostetler skymaster from national balsa
I haven't had great luck with "Great Stuff" expanding foam in modeling because it still remained partially flexible after it cured - which might not be ideal for your situation either. On the other hand, some flexing would still mean energy used to flex the foam is being bled off from impacting the rest of the structure, so it certainly wouldn't be useless. I know that I've run into some of this expanding foam that does get hard before - I just don't know which brand it might be, or if that's just a function of time curing it differently.
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