LiteFighters: P-40/P-36 and beyond

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TiPi

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So to elaborate a little on what we've been finding, most issues we have a pretty clear-cut solution for. We are adding full inter-cylinder baffles as to be expected for a fairly tight cowl setup. We also re-pitched the prop to bite harder, and re-jetted the carburetor to run a little richer. Both of those seem successful in full-power ground runs and the engine has never run as well.

Our main issue now is the oil system. The Verner has a somewhat unique form of dry-sump system in that it's more of a remote wet-sump; where gravity does the work of evacuating the engine and filling the primary oil tank. What we're experiencing is that once the engine gets to full RPM and temperature for about 30 seconds or so, the breather system just starts purging oil overboard, in pretty significant volume. So I'm looking at that as a must-fix. Probably need more headroom in our tank due to it being a fairly long but shallow setup. It technically meets the criteria but maybe not in an ideal way. Also I think our choice of having an air/oil sep return line is backfiring, literally, meaning I need to omit (use a catch can) or install a check-valve on the return.
Seems to me the oil is getting pumped or pulled into the air/oil sep through both lines and with nowhere to drain, it chooses the vent line out the side for overflow. Probably going to test using a catch can vs return and see if that gives us the same results. Then may use an expansion chamber directly above our oil tank to act as an intermediary and give more effective headroom. Worst case scenario may have to rip out the current tank and modify it, then spend big bucks on a more elaborate air/oil sep.
I'm hoping that by this coming weekend we've got baffles installed and a fair grasp on the oil issue. That should remove any reason not to get back to flying it. At the same time, we have no choice but to tow the beast to Oshkosh at this point, and we're pretty-well locked into going, so back in the trailer it goes.
Hi Scott, your symptoms do indicate that your headroom is insuficient. Full power will create the highest blowby volume and that will tend to drag oil droplets with it. I haven't seen the set-up in your P-40 but adding a riser tube with some SS mesh between the tank and vent outlet should help a lot. Ideally, the riser should have enough room for a coiled-up fine mesh to increase the surface area.
 

flitzerpilot

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Many congratulations, Scott. It looks wonderful in the air and totally authentic.

Regarding the oil blow-off with the Verner 7U, the oil tank designed for the Z-1 Schwalbe with the same engine may be demonstrating a similar problem, although it's only been ground run at present. Sufficient airspace in the tank seems an absolute must and the mesh suggestion above seems like an excellent idea as well. Z-2 test flight is due the month so I'll report on this situation then. I hope you get to fly it to Oshkosh.
 

Dana

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adding a riser tube with some SS mesh between the tank and vent outlet should help a lot. Ideally, the riser should have enough room for a coiled-up fine mesh to increase the surface area.
Kind of the same effect as the brass scouring pad in the oil separator I made for my Hatz (brass seems safer than SS should a fragment get into the engine).

Where does the return line dump back into the engine? If it's in an oily plane it'll push oil out, and even if not, absent a check valve it'll push any oil that has started to return back up to the separator.
 

Dominic Eller

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Well done! She looks fantastic in the air 👍
I imagine it’s great to be working with someone like Elliot for the test program, I’d love to observe the process.
All the best for the future testing 👍
 

proppastie

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Also I think our choice of having an air/oil sep return line is backfiring,
I once blew a crank seal when I combined my breather with the oil separator of my wet vacuum pump.....obviously something was not big enough and it produced enough pressure to pressurize the crank case and blow out the front crank seal and all but 3 quarts of the oil .....could have been much worse had I not seen the oil on top of the cowl and returned to the airport. .....so be very careful blocking up your vent line
 

ScaleBirdsScott

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I once blew a crank seal when I combined my breather with the oil separator of my wet vacuum pump.....obviously something was not big enough and it produced enough pressure to pressurize the crank case and blow out the front crank seal and all but 3 quarts of the oil .....could have been much worse had I not seen the oil on top of the cowl and returned to the airport. .....so be very careful blocking up your vent line

Yes that's not great! Glad it wasn't too catastrophic. And something to think about.

So the Verner engine doesn't have, as far as I've been able to find, any sort of main case breather. It relies on sufficient outflow from the case drains down into the tank, which is supposed to have the primary return at least above the 'waterline' of the tank in normal condition. One thing I'm concerned of is that our main case drain port is on the front face of the tank, and not the top. Presumably at times this means the main case return is submerged below the waterline when the engine is hot or maneuvering. I've not been overly concerned of this, but it could mean more air trapped in the sump oil than otherwise, exacerbating the job the air/oil separator is being given; and explain perhaps why our tank of 8.5L (for 5L oil) seems to be insufficient.
We're looking at an expansion chamber or maybe some kind of large diameter 'stand pipe' that we can plumb directly into the 1/2"-NPT breather port on the tank, to add another 2L or so of free air volume. Then from the exp chamber, a breather line to the existing air-oil sep. And for now at least, just run a catch can so we can monitor exactly how much is getting sent up the vent. Once we start doing more flights and find that the oil system isn't purging overboard any significant amount, we can look at returning the drain back to the tank, or maybe even the exp chamber.

One thing I remember seeing on a Corsair Part 103 from Germany with the Verner 3 that we did some work on down in NC, is they used a literal bicycle water bottle as a tank expansion chamber/vent. They simply ran some 18mm or so hose from the tank up to a port bodged into this water bottle, and then used the bottle's lid as a vent out the top, and the bicycle bottle mount bracket to affix it to the firewall. Certainly lightweight!
 

ScaleBirdsScott

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Another thing, I don't know how well this works for everyone else, but Elliot has been frequently updating his Instagram page over the weekend with his side of things for our tests, and using a lot of his GoPro footage to add some flavor. I am working on getting what little good ground footage we have into a short video but until we fly again not sure any will be better than what Seguin got.

 
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Another thing, I don't know how well this works for everyone else, but Elliot has been frequently updating his Instagram page over the weekend with his side of things for our tests, and using a lot of his GoPro footage to add some flavor. I am working on getting what little good ground footage we have into a short video but until we fly again not sure any will be better than what Seguin got.

What a great opportunity to have Elliot do the initial test work and "put it out there". His content is fun, relatable and will go a long way in your marketing of the kits. Bravo Zulu!
 

ZacYates

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Excellent news Scott and co! I've been watching from a far for a while and this is truly wonderful news.

Given the lack of retracts (in this version?) I can only add my chorus to those wanting to see a spatted Hawk - maybe someone will build one in that lovely Thai camo?

Big P-40E fan here so I'm excited to see what you come up with for the short-nose Allison variants.
 

ScaleBirdsScott

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A few more testing runs and one firewall coated with oil later, and still have some oil overflow issues, but we have ruled out some of the potential 'easy' issues/fixes. We're going to do some more testing on Saturday to try and sus out the source of things, cuz dealing with the issue at the root of things is the only way I think we can confidently move forward with things. I think this isn't something we can throw a little bandaid on that helps make the current system a little more effective. I think we need to change a few things in a critical way, I just don't know exactly what they are.

On one hand we can try throwing every potential solution into the mix at once; replace the oil tank with one that has more capacity and baffles around every corner, two expansion chambers above the tank, a fancy air/oil separator, moisture traps, a filtered catch can with a check-valve drain back to a holding tank, and vacuum systems on the exhaust, and drill/tap case vents to add into the line, and just overall brute force it with every trick on the Summit. And with all likelihood we will have solved it somewhere along that line. Certainly all of those things could help in certain situations and none would be bad, other than cost, weight, and just complexity of install.

On the other hand we can play around testing and iterating on small changes for 3 weeks, and coating the firewall with oil every few runs, and still not have much of a solution if we don't have the right ways to measure and inspect things.
So my hope is on Saturday's runs we can narrow down a few things, check some pressure and get a few visuals on things, and try to quickly narrow down where the problem starts and then quickly breadboard potential solutions with stuff strapped to the cowling, and try to get a working loop before we spend time and money making air-worthy version of that system.
 

ScaleBirdsScott

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I have looked at the 912 before since it does have a similar overall system, but, never all that close since they use a relatively small sump. But good call, I am reviewing their tank geometry and seeing some ideas about how they basically have their air/oil separator built into the oil tank/sump return; which is interesting. I think we can start there.
 
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