Random observations from a project site-visit
Posted: Thu Jun 25, 2020 6:09 pmI visited another builder recently who was working on the final push to finish his tri-gear AeroVee Sonex. He was at the point of finishing the canopy (fitting the plexiglass bubble), and was a bit stalled out. Most of the plane was nearly finished, including the first engine start on the airframe. I spent about an hour with him looking things over and offering a few observations and suggestions. I thought these same things might be helpful to others, so I've included many of my thoughts in this post.
In no particular order....
The AeroVee oil separator used a rubber hose as the return line, and it was piped back to the oil sump plate. This line passed within about 1.5" of the exhaust. Failure of this line (either due to the hose melting, the hose slipping off the barbed fittings, or the brass fittings in the sump plate failing) opens a direct leak in the bottom of the oil sump. The engine could drain of oil in just a few minutes, possibly even without the pilot realizing anything was wrong until it was too late. I suggested he consider modifying this, possibly using braided stainless line and AN fittings, a heat shield/heat deflector, fire sleeve over the line, re-routing the line, or other possible options.
We also discussed the oil separator and that if it runs too cool it will condense water, and if you return the collected oil to the engine it will send the water along with it. I suggested that he start with NOT returning the captured oil, but rather collect it in a catch-can, and after running a few hours inspecting the collected oil for excessive water. If all is good, then plumb the collected oil back to the engine.
The fuel line to the carb was routed about 1" away from an exhaust pipe. The fuel line did have fire sleeve, but it was still very close and risked heating the fuel inside the line to the point of vaporization. I suggested he re-route the line further away, and/or install a heat shield, as well as create a bracket to hold it in position so it wouldn't shift back towards the exhaust.
The engine baffles had a few spots that didn't fit well. We discussed the need to focus on the large gaps, such as the area around the starter. The cylinder nearest the starter is staggered further forward, and the rear baffle fits more than an inch away. You really need to tweak the baffles to close this gap. There's a take-away here about not getting mentally bogged down on the small gaps before addressing the big ones.
He mentioned that he was going to start fitting the cowling next, and was planning to cut in a cowl access door for the oil fill plug. I suggested that he think about how to physically pull that plug, as it fits really tightly, and it's hard to get your fingers under the lip to pull it out. You'll need a generously sized access door to get your hand inside, or some sort of grab handle to assist. An alternative is to skip the door altogether and simply check the oil thru the left air intake, fill small amounts of top-off oil using a large syringe, and pull the cowl if you need to add more than 4-6 oz oil.
The spark plug wires on the pilot-side secondary ignition were dangerously close to that exhaust pipe, and needed to be re-routed, or otherwise secured.
I noticed that he was likely going to have interference between the lower cowl and the aerocarb air filter. I suggested possible solutions: Adjust the rubber carb socket coupler a bit so that the carb was positioned as close as possible to the Y-pipe - it was hanging down at least an inch due to the rubber not being fully seated on the Y-pipe and the carb throat. You can also trim the overall length of the rubber to only what is needed (they are sometimes a bit long). Alternately, he could use a low-profile K&N filter.
The block-off plate on the front of the engine case for the oil temp probe was weeping oil, and needed to be resealed.
The fuel drip pan around the fuel filler neck was sealed with clear RTV sealant. This won't hold up well to the gas, and will eventually need replacement. I suggested using "The Right Stuff" RTV sealant. This product is very durable, sticks extremely well, and fuel/oil resistant.
I inspected his throttle cable routing to his AeroCarb (old style push-open unit), and pushed on the carb slide up thru the intake to simulate the engine suction at low RPM. His moved easily and smoothly, and is unlikely to "stick". The sticky throttle issue was one reason Sonex went to the AeroInjector pull-open design. The old style is sensitive to poor cable routing and you have to ensure you've done it right (he did).
We discussed the secondary ignition timing procedure using the in-flight method, and that getting this right will possibly lower his CHTs by 30 deg F. The initial timing method will get you close, but you really have to fine tune this in flight following the in-flight procedure contained in the AeroVee manual.
I noticed that he had used a separate starter solenoid in addition to the starter solenoid contained within the starter motor body. Although this isn't wrong, it also isn't needed. I've seen this more than once. There's some confusion when comparing the AeroVee to a Jabiru (Jabiru request a separate starter solenoid).
I noticed that he did have an extended pull handle for his fuel shutoff valve. I really think this is a best practice that everyone should follow. In an emergency you'll need to be able to shut off the fuel rapidly while fully strapped in. A pull handle to the lower dash make this simple and easy. Good job here.
We discussed the tools used for canopy fitting - permagrit cutoff disc for trimming, sand using a Harbor Freight belt file (what I like to call a "finger sander"), dress the edges using a sanding block with 80 grit to smooth the cut, and then polish the edge using 220 grit each and every time a trim is made (do this BEFORE moving the canopy bubble!). We also talked about installing additional canopy braces from the rear hoop to the cross bar to make it more rigid, and using multiple alignment marks to ensure the canopy goes back to the exact spot each time you remove it for trimming. Lastly, I suggested he listen to the SonexFlight podcast episode on canopy fitting.
I tested his flap handle and found that it fit very tightly in the full-flap notch. If this doesn't have enough clearance it will bind up in the notch, and you'll get to experience a full-flaps go around. Not fun. I suggested he file the opening a bit larger to prevent binding.
Lastly, I noticed that he hadn't yet installed his transponder antenna in the aft tailcone belly skin (the belly skin was still off). I suggested he install the transponder antenna on a new inspection panel in the belly skin. This provides an easy way to replace the transponder antenna if needed (those little rod and ball antennas are really easy to break off while washing the plane), as well as provides another point of access for things like greasing the elevator pushrod snap-bushing in the vertical support channel.
Overall, he was in great shape, and I was pleased to offer whatever assistance I could. I hope maybe this helps someone else as they evaluate their own projects.
Jeff
In no particular order....
The AeroVee oil separator used a rubber hose as the return line, and it was piped back to the oil sump plate. This line passed within about 1.5" of the exhaust. Failure of this line (either due to the hose melting, the hose slipping off the barbed fittings, or the brass fittings in the sump plate failing) opens a direct leak in the bottom of the oil sump. The engine could drain of oil in just a few minutes, possibly even without the pilot realizing anything was wrong until it was too late. I suggested he consider modifying this, possibly using braided stainless line and AN fittings, a heat shield/heat deflector, fire sleeve over the line, re-routing the line, or other possible options.
We also discussed the oil separator and that if it runs too cool it will condense water, and if you return the collected oil to the engine it will send the water along with it. I suggested that he start with NOT returning the captured oil, but rather collect it in a catch-can, and after running a few hours inspecting the collected oil for excessive water. If all is good, then plumb the collected oil back to the engine.
The fuel line to the carb was routed about 1" away from an exhaust pipe. The fuel line did have fire sleeve, but it was still very close and risked heating the fuel inside the line to the point of vaporization. I suggested he re-route the line further away, and/or install a heat shield, as well as create a bracket to hold it in position so it wouldn't shift back towards the exhaust.
The engine baffles had a few spots that didn't fit well. We discussed the need to focus on the large gaps, such as the area around the starter. The cylinder nearest the starter is staggered further forward, and the rear baffle fits more than an inch away. You really need to tweak the baffles to close this gap. There's a take-away here about not getting mentally bogged down on the small gaps before addressing the big ones.
He mentioned that he was going to start fitting the cowling next, and was planning to cut in a cowl access door for the oil fill plug. I suggested that he think about how to physically pull that plug, as it fits really tightly, and it's hard to get your fingers under the lip to pull it out. You'll need a generously sized access door to get your hand inside, or some sort of grab handle to assist. An alternative is to skip the door altogether and simply check the oil thru the left air intake, fill small amounts of top-off oil using a large syringe, and pull the cowl if you need to add more than 4-6 oz oil.
The spark plug wires on the pilot-side secondary ignition were dangerously close to that exhaust pipe, and needed to be re-routed, or otherwise secured.
I noticed that he was likely going to have interference between the lower cowl and the aerocarb air filter. I suggested possible solutions: Adjust the rubber carb socket coupler a bit so that the carb was positioned as close as possible to the Y-pipe - it was hanging down at least an inch due to the rubber not being fully seated on the Y-pipe and the carb throat. You can also trim the overall length of the rubber to only what is needed (they are sometimes a bit long). Alternately, he could use a low-profile K&N filter.
The block-off plate on the front of the engine case for the oil temp probe was weeping oil, and needed to be resealed.
The fuel drip pan around the fuel filler neck was sealed with clear RTV sealant. This won't hold up well to the gas, and will eventually need replacement. I suggested using "The Right Stuff" RTV sealant. This product is very durable, sticks extremely well, and fuel/oil resistant.
I inspected his throttle cable routing to his AeroCarb (old style push-open unit), and pushed on the carb slide up thru the intake to simulate the engine suction at low RPM. His moved easily and smoothly, and is unlikely to "stick". The sticky throttle issue was one reason Sonex went to the AeroInjector pull-open design. The old style is sensitive to poor cable routing and you have to ensure you've done it right (he did).
We discussed the secondary ignition timing procedure using the in-flight method, and that getting this right will possibly lower his CHTs by 30 deg F. The initial timing method will get you close, but you really have to fine tune this in flight following the in-flight procedure contained in the AeroVee manual.
I noticed that he had used a separate starter solenoid in addition to the starter solenoid contained within the starter motor body. Although this isn't wrong, it also isn't needed. I've seen this more than once. There's some confusion when comparing the AeroVee to a Jabiru (Jabiru request a separate starter solenoid).
I noticed that he did have an extended pull handle for his fuel shutoff valve. I really think this is a best practice that everyone should follow. In an emergency you'll need to be able to shut off the fuel rapidly while fully strapped in. A pull handle to the lower dash make this simple and easy. Good job here.
We discussed the tools used for canopy fitting - permagrit cutoff disc for trimming, sand using a Harbor Freight belt file (what I like to call a "finger sander"), dress the edges using a sanding block with 80 grit to smooth the cut, and then polish the edge using 220 grit each and every time a trim is made (do this BEFORE moving the canopy bubble!). We also talked about installing additional canopy braces from the rear hoop to the cross bar to make it more rigid, and using multiple alignment marks to ensure the canopy goes back to the exact spot each time you remove it for trimming. Lastly, I suggested he listen to the SonexFlight podcast episode on canopy fitting.
I tested his flap handle and found that it fit very tightly in the full-flap notch. If this doesn't have enough clearance it will bind up in the notch, and you'll get to experience a full-flaps go around. Not fun. I suggested he file the opening a bit larger to prevent binding.
Lastly, I noticed that he hadn't yet installed his transponder antenna in the aft tailcone belly skin (the belly skin was still off). I suggested he install the transponder antenna on a new inspection panel in the belly skin. This provides an easy way to replace the transponder antenna if needed (those little rod and ball antennas are really easy to break off while washing the plane), as well as provides another point of access for things like greasing the elevator pushrod snap-bushing in the vertical support channel.
Overall, he was in great shape, and I was pleased to offer whatever assistance I could. I hope maybe this helps someone else as they evaluate their own projects.
Jeff