Help for...

[Titus]

Hello everyone.

I'm a designer and this is my first post in this fine forum. I'm designing a custom airplane frame and I need of the knowledge of the v-twin expert members of the board .
In the plan of my project, installing an Evo type v-twin in an inverted position (upside-down, with the crankcase up and the cylinders down) would be more rational than a traditional configuration.
I know that the v-twins can be considered as a part of an aircraft radial engine, I know that the HD v-twin separated lubrication allows the inverted work. Of course, I also know that the history of aviation is rich of famous inverted v-engines or radial ones and that in the acrobatic aircraft the engines can work inverted for a while, but I don't know if a stock HD Evo v-twin, or a S&S bigger colleague (like the T124 for example) with fuel-injection system can work at the same and normally if mounted inverted without modifications.

If an inverted v-twin working is not possible without modifications, what modifications the v-twin would need of?

Or it's not possible at all?

Thank you very much in advance,

Greets,

Titus

[Dr.Hess]

I think you'll have oiling issues. Specifically, oil return from the rocker boxes. The oil to the rocker boxes on an Evo is fed through the push rods and returns down through the head and side of the cylinders by gravity. If you take the gravity away, you'll be pushing the oil into the rockers at systemic oil pressure and likely leak it out the rocker box gaskets which weren't designed to handle that. While it might be fine for a few minutes flying upside down, running it all the time like that will cause problems.

If you stick with EFI, I don't see a fueling problem.

The above, of course, is just my opinion. It could be wrong. The only way to find out would be to invert one and run it under load and see what happens.

[springer-]

You should checkout this link.....

http://www.v-twinforum.com/forums/v-...-airplane.html

[Titus]

Thanks for your replies.

Dr. Hess, you told:

"an Evo is fed through the push rods and returns down through the head and side of the cylinders by gravity. If you take the gravity away, you'll be pushing the oil into the rockers at systemic oil pressure and likely leak it out the rocker box gaskets which weren't designed to handle that."

So, in your opinion, could feeding it in the opposite direction be possible if the rocker box gaskets were designed to get a reliable tightness? If it was just a problem of gaskets it could be superable...

Springer, I sent few days ago to the Skyray/Hogair company an e-mail about the inverted v-twin, unfortunately they replied to me that they were no longer in business or selling the Harley engines for aircraft.

Greets,

Titus

[hardluk1]

Go to the dealer and ask to look at a manual. In it you will see how the oil flows and answer your own questions. Will work upright there is one at Wheel Through Time and say one on tv a couple years back.Had a belt drive gear reduction box. V=twins are not dry sump.

[RattFXR]

As Dr. Hess stated, you would have an oiling issue. However, you could tap the rocker boxes and drain the oil that way. You would have to have your oil bad below the motor, but the sump lines could still pull oil up to the motor with the pump. The only other problem I forsee is the residule oil in the crankcase. Yes a HD motor is a dry sump system, but oil still pools in the cases, which if inverted, would end up causing an excessive amount of oil burning. You really should read the HD manual and look at the oiling system. Fuel injection will definitely allow you to fly an which way you wanted to. What is the reasoning for inverting the motor anyways?

[Titus]

I'm beginning to understand better, and I'll try to understand more, studying the oiling system. Anyway, the main reasoning of an inverted V engine is that you can get a plane with a beautiful streamlined shape. This is a famous WWII inverted V engine: the Daimler-Benz 605:



and this is the most famous airplane on which it was mounted, the Bf 109:



These are the famous at the same italian Schneider Cup racers Macchi-Castoldi planes, with not inverted V engines:





Good guns room and greater visibility apart, the inverted V allows a better shape as you see. Moreover in a custom plane you could keep the v-twin cylinders out of the fuselage and mount the prop directly on the drive shaft.

[springer-]

The Harley v-twin style engines rely on gravity to bring the oil to certain places so the pump can return the oil to the oil tank. When inverted much of the oil return method would not work. Also consider the oil in the crank case. With the engine inverted all the oil in the crank case would fall into the pistons. There are no provisions to prevent that except the motion of the pistons themselves, throwing the oil back into the crank case.

The real question that comes to mind is why would you risk your life on a Harley engine in a plane? It's one thing when it breaks down and I coast to the side of the road. Good luck.

[nmaineron]

I think you would have problems,your talking about different crank setups.The auto motive journal type bearing VS a roller type bearing.You can contain the pressure to the journal and the crankshaft where you would lose your pressure in the Harley once the oil flowed into the bearing.From there it has no place to go except to the bottom of the pistons.It would almost seem like you would have to redesign the whole scavenging system.

As far as the oil flow to the lifter and rocker arms is concerned,I think you could get away with it but I think that you would have to modify the rocker boxes so that they could drain off .Maybe utilize the existing head breathing system somehow.

Interesting idea,they do it with 2 strokes all the time.You might want to take your maiden voyage landlocked....

[RattFXR]

I would definitely investigate the scavaging system. Other then that it would work. The valvetrain is oiled with pressure, as I stated before you would have to drill and tap the rocker boxes at the low point to drain oil back to the oil bag. The bearing set up in rotating assembly is optimal for higher revving due to the tapered needle bearing. I would assume you would run the motor between 3200 and 4000 rpms mostly. The down side is the length of the stroke, your piston speed would be high, a stock Evolution has a 4.25 in stroke, where as the Twin Cam has a 4. The twin cam would be a better choice, but remember rebuilding the top end is easy as pie, and not that expensive. Not to mention your probably not going to fly this everyday. Good luck, if you have any questions send me a message. I'm going to research inverting the motor myself. Oh I was going to put one on a twin sponson boat...... 10ft long by 4ft wide.....you can never go wrong with a v-twin.....