Intermittent engine operation

[gethomas]

Thanks for all the input. Based on these comments it appears to me that the installation as shown in the AeroVee manual does not work. The manual (picture in my first post) clearly shows a gasolator installed low on the firewall at a level below the AeroInjector and length and routing of fuel line is depicted. The plans do show a straight route from tank to AeroInjector with in-line fuel filter (no gasolator). My understanding was that the plans were not for a specific engine (though it looked more like the recommended installation for a Jabaru) and the AeroVee manual augmented the plans for the specific engine. Is the Sonex/Aerovee design, plans and manual really this unreliable? Has Sonex ever built an airplane as shown on the plans?

[builderflyer]

As others have mentioned: It is important that the Aeroinjector is the *lowest* point in the fuel system. From the photos you showed, it appears that your gascolator is lower than the Aeroinjector. That is going to cause lots of problems. First, any bubbles or vapor will get trapped in the system with that layout. Second, by forcing the fuel to run “uphill” after the gascolator you may see dramatic losses in fuel flow as your tank empties out.

—Noel

Sorry, Noel.......I have to disagree with this entire paragraph. First, If one is using a gascolator, then it is always located at the lowest point in the system so that any water in the fuel lines will be collected in the gascolator bowl. If you're using a filter then yes, the carburetor should be located at the lowest point in the system. Second, the fuel pressure at the entrance to the Aeroinjector is determined by the difference in "head" between the fuel level in the tank and the carburetor. It matters not if the fuel line drops to a lower level somewhere in between other than a slight reduction in fuel pressure due to the additional friction associated with a longer fuel line

My Sonex was successfully run for many hours with the gascolator system shown in the photographs with these exceptions; 1. The fuel line was not run as close to the exhaust pipe as shown in the photo, 2. All fuel lines were insulated, and 3. There was a shroud installed around the gascolator with cool air directed at the bowl. This all was run with a Jabiru 3300 and it's higher fuel flow demands than the Aerovee.

See my other message under "Aeroinjector tuning"

Art,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,Jabiru 3300 #261

[Rynoth]

As others have mentioned: It is important that the Aeroinjector is the *lowest* point in the fuel system. From the photos you showed, it appears that your gascolator is lower than the Aeroinjector. That is going to cause lots of problems. First, any bubbles or vapor will get trapped in the system with that layout. Second, by forcing the fuel to run “uphill” after the gascolator you may see dramatic losses in fuel flow as your tank empties out.

I generally disagree with this. I don't see an issue with the gascolator being lower than the aeroinjector, and perhaps some potential benefits (catching water and sediment to be drained later.) The fact that the gascolator is lower than the injector shouldn't affect fuel flow at all for a fixed height of the injector (that "uphill" flow is balanced by the "downhill" flow on the opposite side.) The thing to avoid is "high" spots in the lines where bubbles can be trapped. In the OP configuration (as well as mine w/gascolator) bubbles shouldn't be trapped anywhere, they will either flow back up to the tank, or up to the injector. As for nose-high + low fuel quantity fuel flow rate that should have been tested before the aircraft ever flew.

[GraemeSmith]

Gotta say - I had the similar problems the OP reports when I bought my plane. Everything being fire sleeved and wrapped and the tuning being correct and the fuel flow test being 100% OK.

I carved a NACA scoop under my cowling and pointed a blast tube of outside air at the air filter. All the problems went away. I've even put the gascolator back that the builder had taken out.

YMMV

"Loss of fuel flow running uphill" - As I recall - liquid in a system self levels. So within reason - if fuel in the tank is higher than the carb - the fuel will get there - with the short runs involved there should be little in the way of friction losses. That said - I would not set myself up for failure by having a blatant high point that could hold a vapor bubble and break a siphon. That would need a good head of pressure to push the fuel through.

[sonex1374]

...[snip] it appears to me that the installation as shown in the AeroVee manual does not work. [snip]... Is the Sonex/Aerovee design, plans and manual really this unreliable? Has Sonex ever built an airplane as shown on the plans?

gethomas,

The plans and the AeroVee installation instructions both show acceptable ways to install the fuel system. These are starting points that might need to be massaged a bit to fit your particular situation. For example, the climate you operate within will dictate how much heat shielding you might need, but so does the details of how your fuel lines are routed, the proximity of the exhaust pipes, the airflow patterns thru the cowling, and so forth. The factory has flown their planes using either a gascolator or a filter, and with no special heat shielding at all, but that's not to say that will work in every case.

Over the years we've collected user data from hundreds of custom examples (all with their own sometimes-not-so-minor variations), and this has generated a body of best-practices that work in a broad range of situations. It follows the factory guidance pretty close, but expands on a few points such as eliminating flow restrictions and keeping the heat out of your fuel lines. Most of the suggestions you've gotten so far are along those lines.

It's very hard for all of us to take the information you provided and form a complete understanding of what's happening in your engine. With only a bit to go on, we're throwing out ideas that might possibly be contributing to your problems. Much of the suggestions are really are asking you to go back and verify what you think you've already done.

Here's my short list of what I think you should do.

1) Re-run your fuel flow test. There's something wrong in your numbers (you reported 1 gal in 60 seconds or 60 gph, which seems quite high). Disconnect the fuel line at the carb and hold the line at the same level as the carb (not handing down to the ground). If you get 10 gal per hr, then ok. If not, you need to fix the flow restrictions.

2) Install a 2.5 needle, ensuring the flat is towards the engine side of the carb.

3) Install a K&N E-3120 air filter. https://www.knfilters.com/e-3120-round-air-filter

4) Insulate all your fuel lines forward of the firewall. Use fire sleeve plus additional insulation wrapped in aluminum speed tape.

5) Double check the needle tuning at WOT to verify that the mixture is set rich enough. Start on the rich side and then as you get a bit of time flying the plane you can slowly lean the needle to "sneak up" on the perfect mixture.

6) Adjust the carb slide as per the manual. You'll want approx 1/8" to be still visible (e.g. not quite all the way open) when the throttle knob is at full throttle. You'll want the slide idle stop to ensure an idle of about 1100 rpm until the engine has 20 hrs or so - this will prevent too low of an idle and dying on landing. You'll lower it a touch after 20-30 hrs.

7) Inspect your cowling exhaust-air outlet and ensure you have sufficient exit area. Aim for 50-60 sq inches of flow area (not counting the area that might be obstructed by other objects).

8) Wrap your exhaust pipes with high-temp fiberglass & ceramic exhaust wrap. DEI Titanium is the best, and will last the longest. Don't waste your time with imitation knock-offs. https://www.amazon.com/Envoltura-t%C3%A9rmica-alta-temperatura-Exhaust/dp/B002R4U72I/ref=sr_1_1

Lastly, don't be afraid to lean as much as you possibly can using the cockpit mixture knob while at idle. Your engine will thank you for it, and there's no way you'll hurt it at low throttle.

It's quite a to-do list, but barring a problem with the engine itself it will work. Best of luck,

Jeff

[gethomas]

Jeff Shultz:
Thanks for your comments and recommendations. Regarding my comments on the plans and manuals coordination, I was on a bit of a rant from frustration of spending many hours reworking things because what the plans/manuals show and what works were different. My expectations going into the project were that Sonex had a good reputation and product and if I carefully followed the plans that I would have a flying airplane with minimal problems. I made not deviations from the plans; just the opposite, I tried to build exactly to the plans. I can't accept your comment that the plans are suggestions or a starting point and will require massaging. I expected Sonex to have verified that the design and construction as shown on the plans did not require additional builder modification , experimentation or guess work. Maybe I had unreasonable expectations?

[Panther16]

My Sonex has been flying for 430 hours with a gascolater installed per the plans with the tank to gascolater line on the aft side of the firewall. It has flown with an aerovee and now has a 3300 Jab.
The line from the gascolater to the aeroinjector is fire sleeved and wrapped with reflective insulation and contains a red cube for fuel flow. Exhaust pipes are wrapped but the headers are not. The fuel system works as advertised. I also drilled and taped the aeroinjector for a carb temp probe. Typically see 110-120 carb temp in cruise during warm weather. Also using no 2 needle.
Keith Rhode
Sonex sn 1009

[sonex1374]

... [snip] I was on a bit of a rant from frustration of spending many hours reworking things because what the plans/manuals show and what works were different. My expectations going into the project were that Sonex had a good reputation and product and if I carefully followed the plans that I would have a flying airplane with minimal problems.

gethomas,

Not all installations will need all or maybe *any* of the things I mentioned. However, each item adds an incremental degree of protection. Many of these things are discussed in the Sonex instructions (e.g. carb tuning, fuel system routing and parts selection, cowl opening dimensions) but sometimes we need a bit more explanation or elaboration to fully understand what the instructions are telling us in order to be successful.

In some cases we find ourselves in more severe conditions that require we take more steps to keep the engine running happily. For example, should Sonex specify that all installations use header wrap and fuel line insulation out of an abundance of caution? (We all have our own opinions... but I fly in really hot climates and always recommend users do this.)

I can't accept your comment that the plans are suggestions or a starting point and will require massaging. I expected Sonex to have verified that the design and construction as shown on the plans did not require additional builder modification , experimentation or guess work. Maybe I had unreasonable expectations?

Everyone has a different tolerance for the "experimental" in Experimental Aircraft. I think manufacturers should do everything they can to provide a roadmap to success. Sometimes that roadmap, however, gets touched up a bit along the way. People on this forum offer their suggestions and ideas to help with that. We all want other builders to be successful, that's why we share our experiences.

I'm really not trying to antagonize you, or poke blame at you, or throw Sonex under the bus. I truly believe that there are only a few things that might be standing in your way (namely carb tuning, engine cooling and fuel system insulation) and once you sort that out you'll be ready to rock.

Jeff

[gethomas]

I insulated my fuel lines and gasolator with pipe insulation and foil tape. Did a high speed run with temperature around 90deg. Engine ran better, did not quit, and EGT max and change with mixture control fell into place. I think heating of the fuel system is the problem and has been affecting my tuning and running issues all along. Subsequent runs did produce some rough running and a stop, but my local A&P says that is not unexpected considering the temperature and the the lenght of time I was ground testing. He thinks I've identified the heating problem and have the mixture set correctly and the engine is running well enough for flight test.

I will replace the insulation/foil tape with fire sleeve and fiber glass exhaust wrap (DEI Titanium) as several posters have described.

I may remove the gasolator and put in an in-line filter and shorter, more direct fuel line. This installation seems to be better (more heat tolerant) than the installation depicted in the AeroVee manual and that I installed. I hate to do this since the gasolator/plumbing is already installed and I think the gasolator adds a level of safety.

Please comment if anyone has additional thoughts on my plans.

Thanks to the web site and posters for educating a first time builder.

PS. My other problem of the fuel tank deforming (described in other posts) seems to be ok since I repositioned/remounted the tank.

[Bryan Cotton]

It sucks to redo work. I'm glad you have made progress though.