New Onex guy- general Aerovee questions

[13brv3]

Greetings,

I'm set to build a Onex when the kit arrives, and of all the engines I've tinkered with in my life, I've never used a VW (or similar). I've read, and searched through the forum, but I do have a couple general questions if you don't mind.

1- What would be considered a "normal" time between corrective maintenance on one of these engines? I'm referring to overhaul type work (rings, valves, etc). I've seen some really low numbers (double digits) thrown around, though I do realize that people often go back into the engine for other reasons not related to wear (changing compression, oil leaks, etc). I have to believe the expectation will be at least a couple hundred hours between overhauls. Does that sound correct? I realize overhauls are cheap, and relatively easy, and I'd be satisfied to do it at every annual if needed.

2- Since I'm considering a turbo option, would you expect turbo use to make the overhaul time worse? I'm thinking it would, since generally more power means more wear.

3- Is there an explanation posted that states why they don't use outside ram air for the intake? Using warm air seems wrong, but with the amount of air that likely flows through the cowl, maybe the air temp really isn't that high in flight? Still, cooler ram air would have to add a bit of power. Using under-cowl air seems like giving away HP, so I'm wondering if there's a reason it isn't done, other than convenience?

Thanks,
Rusty

[Rynoth]

All great questions! Unfortunately I'm just getting to the point of my first Aerovee start so can't give any personal experience for the longevity of the engine between maintenance periods. That said, I'd think the answer to #2 is yes, to some degree.

As for #3, I think the stock setup is mostly from the point of simplicity. I know some builders have customized their own ram-air intakes for the aerovee and did indeed see some performance gains. It's something I may consider in the future. As much time as I've already spent on the cowling and baffles, I just don't have it in me to tackle adding a shroud and intake fit to the cowling for the carb just yet. It would need to be well fit and sealed to the cowling to avoid reducing the effectiveness of engine cooling, but it can certainly be done. Stock, the aeroinjector requires no carb heat, I'm not sure if adding fresh air intake would introduce the potential for carb ice (thus the added complexity of a carb heat system.)

[MichaelFarley56]

Hello Rusty,

Just like Ryan mentioned, I believe the truthful answer to most of these questions will ultimately be "it depends...", but that being said, I'd be happy to offer my two cents to your questions. Just remember that when talking about reliability of these engines, there is a lot of variation based on how much, and how gently the engine is ran. People who run their engines easily and often are normally rewarded with long and healthy engine lives. If you don't fly but once in a while, run the engine hard and hot, etc. it won't last nearly as long.

Okay...

#1: The inner core of the AeroVee is very robust. Most of the parts are aftermarket high performance VW racing parts and we're not running our engines NEARLY as hard as racers do. As such, you could easily expect hundreds of hours between tear downs if built properly and taken care of. The only thing that could possibly require more attention would be the heads; I know of several people who will remove their heads every 2 or 3 Condition inspections and get the valve guides looked over, but again I would call this optional. When I added my turbo I had 120+ hours on my heads over the span of a few years and they looked great. Again, how well you treat them will have a lasting effect on how long they last.

#2: This is a tough question to answer since no one really has that much time on their turbo AeroVee yet. Logic would say that the higher internal pressures could possibly lead to faster wear, but again remember these engines use racing parts that can turn 7000+ RPM, and with the relatively small boost we're putting through the engine my personal feeling is that any stress added is very minimal, if at all. I'd be more worried about additional heat but I think all of us turbo AeroVee guys will agree that, during flight, the engine runs just as cool (if not cooler) as the non-turbo AeroVee. I have yet to see any issues with mine.

#3: There are a few people that use ram air on their setups but like Ryan said, you may be adding additional issues by trying. Namely, you'll probably want to consider adding a carb heat setup when you wouldn't really need to. Also, the AeroInjector is really designed for non-ram air setups so tuning may possibly be an issue. This is ultimately up to you but for the very small performance gains you may get, is it really worth the complexity? Your call of course; I'm not trying to talk you out of it, just trying to offer points to ponder.

Great questions and let us know if you have any more! Thanks!

[13brv3]

Thanks for all the excellent comments!

I never knew the racers were running these things that hard. Come to think of it, I can't recall reading about any broken internal parts, which is definitely a good sign. The engine likely IS plenty robust mechanically for our use.

I definitely agree with the comments about taking care of the engine. A little care with regard to proper temps and pressures goes a long way, and while you can run up to the limit, you really can't expect the engine to last as long that way.

I do think they've kept the MAP limits at a reasonable level. 40" isn't much in the turbo world, and they only list that as being allowed for 2 min. The continuous limit seems to be 35", which probably isn't too much over the non-turbo power when you consider the extra heat, and some exhaust restriction.

I've also read comments about how much more even the temps run between cylinders for the turbo. I wonder if the turbo pressure is overcoming the differences in intake tubes, or more likely the fuel is being atomized better at the higher temps, and isn't forming droplets at turns. It's been so long since I've had an engine that wasn't fuel injected that I don't remember :lol:

This really is a tough decision. I don't need a turbo, because it's a single place, I'm only 180 lbs, and field elevation is about 800 ft. I do fly near mountains, but I can't see flying at really high altitudes often, or doing much cross country work. I also have to build this really quickly, like 6-8 months, so complications should be avoided. On the other hand, I don't see much more work to installing the turbo vs the non-turbo. I'll have to decide soon, since I need to get the engine and prop ordered.

Thanks,
Rusty

[13brv3]

Mike,

I'd like to publicly thank you for all the time you've spent making informative turbo videos. I've been working the graveyard shift with lots of time to kill, and I was on the second or third video before I put two and two together and realized that was you. Great videos, though they're not exactly helping me resist :)

Cheers,
Rusty

[Rynoth]

After building and installing the turbo for initial installation (along with the rest of the Aerovee) I'd say adding the turbo adds minimal overall work time to the installation. Most of the added work will just be coming up with a firewall layout that fits. The core engine build is exactly the same, with a couple more exhaust parts.

[13brv3]

Thanks Ryan. That's pretty much the way I was looking at it too. If I'm ever going to do a turbo, I think it makes more sense to do it initially, rather than as an upgrade. That way at least I'll know what space I have, and there won't be any rework later.

Cheers,
Rusty (dangerously close to ordering the turbo)

[Bryan Cotton]

When I upgrade someday I will have to spring for a new prop and exhaust. Of course you can sell your old prop and exhaust to defray the cost. That is how I bought my prop and exhaust! I tracked down a turbo guy. If you go straight to the turbo you won't have those extra costs.

[13brv3]

When I upgrade someday I will have to spring for a new prop and exhaust. Of course you can sell your old prop and exhaust to defray the cost. That is how I bought my prop and exhaust! I tracked down a turbo guy. If you go straight to the turbo you won't have those extra costs.

I'm way ahead of you on rationalization :lol: In comparing prices, the turbo has exhaust, and you have to buy it as an extra for the non-turbo, so that closes the gap in price some. The turbo also has the mini-sump with filter, which I'd probably want as well, so that helps as well.

Thanks,
Rusty (resistance is futile)

[Bryan Cotton]

A turbo 13B would be double super cool in a Onex.

My only experience with wankels was with the Cypher UAV when I was at Sikorsky. It had a 52 HP UAV engines single rotor motor. Weighed 50 lbs wet. UAV engines was a spinoff of Norton, and I believe related to the motor in the Johnny Players special race bike. Neat engine, and nothing could beat it for noise per horsepower.