WAM-120 Diesel RV-9A first flight

[kgood]

I haven't got that scientific yet. The numbers I gave are at my normal cruise, which is 85/85. You're right, I can get more speed at 100/100, but not that much. I really don't intend to cruise at 100/100, so I haven't checked it out at altitude. I have heard from another RV9A/WAM owner that 100/80 gives a lot more speed, so I tried it for a few minutes and he was right. I contacted the factory to see what they thought, but they did not recommend it, as they had not tested that way.

This morning I was fueling my plane and emptied my supply tank. So I did a little math: 155 gallons of fuel used in 35 hours = 4.42 gph average with 42 T/O and landings. I might be off a gallon or two, but not much.

BTW, there are a few VW Parts, but not on the engine. The coolant expansion tank, low coolant sensor relay are sourced from VW.

So far, so good. This may not be for everyone, but as a diesel guy, I love it.
Kurt

[osxuser]

Originally Posted by kgood

BTW, there are a few VW Parts, but not on the engine. The coolant expansion tank, low coolant sensor relay are sourced from VW.

So far, so good. This may not be for everyone, but as a diesel guy, I love it.
Kurt

Yep, the coolant tank was what caught my eye. I like the installation so far.

[ergie63]

What do 85/85, 100/100 and 100/80 mean?

[Dave_Boxall]

Originally Posted by ergie63

What do 85/85, 100/100 and 100/80 mean?

They are manifold pressure (MAP) / RPM. Manifold pressure is absolute pressure, 50 is 1 atmosphere, 100 is 2 atmosphere. RPM is % max propeller RPM (2750 RPM).

The engine is cruised with MAP=RPM 85/85 90/90 or 95/95 are nice relaxed cruise powers.

85/85 is 62hp
90/90 is 67hp
95/95 is 70hp
100/100 is 75hp
120/100 is max continuous power 100hp
140/100 is full power - 120 hp (5 mins limit)

Dave

[ergie63]

Thank you. This is interesting and revealing. Prior I had assumed that the WAM turbo just 'normalized' or maintained sea level manifold pressure like most aircraft applications. It appears that in order to produce any power at all the manifold must be boosted beyond sea level. Duh. I should have realized this before (I'm not an engineer). This is a 2-stroke diesel and the rules are a little different. The intake mainfold must have higher pressure than ambient in order for the flow to be in the right direction. On the power stroke the exaust port must open slightly before the intake port to ensure the cylinder pressure is closer to ambient so that a fresh charge can enter the cylinder from the intake manifold for the next power stroke.

I can see why 85/85 is a preferred cruise. A propeller at 2,750 RPM would be a bit noisy for a long ride. I can also see why an overbored WAM has been discussed. Set to 62 hp for a comfy crusie seems to leave a fair amount of the RV-9's performance potential unused.

Is it correct to assume that a constant speed prop is necessary to finely control MAP/RPM numbers?

I like it. When can I start?

[Dave_Boxall]

Wilksch are using a fixed pitch prop on their 100hp version, but the 120hp version needs a VP prop. At the high specific power the engine is producing then you need all the revs to keep away from the smoke point at high power.

With the new big-bore engine you'd probably be able to use a fixed-pitch prop with it rated at 120hp, but need a VP if you went much higher.

Dave

[6ato14a]

Are there any updates on this thread
Thanks

[charosenz]

Outstanding. Good job. I truly can appreciate the extra effort it took you get to where you are.