# WAM Engines

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### PMD

##### Well-Known Member
Ok, show me a modern diesel of the same hp which weighs less than a modern than a modern SI turbo engine. How could a diesel be lighter? They have larger/ thicker pistons, rods, wrist pins, cranks and blocks.
I will suggest the entire lineup of VW engines going way back to the earliest turbo indirect engines. They used the same dimensions of rotating elements and often the exact same parts. You KNOW why "they have larger/thicker pistons, etc." - simply because the RPM at which they are designed to make the HP and torque they are able to do - something most SI engines simply can NOT do because of detonation issues. That makes a car or truck so much nicer to drive when the fat part of the power curve is at cruising RPM (and, yes, I realize many SI engines are now learning to do this reasonably well - but diesels can do so until they run into some thermal or mechanical strength limit - and at same cylinder pressures so would an SI engine...IF it could run on an aspirated charge without detonating. Of course, in aviation this means direct drive is easy whereas to get those kinds of numbers out of an SI engine, it has to be wound up like a $2 watch. Let's compare modern aero diesels to modern liquid cooled SI engines like the 320T. Comparable cruise BSFC figures to diesels and much better power to weight ratios. again, I am totally unfamiliar with the "320 T" engine, but you put forward your very best at 40% BTE and the diesel people did theirs at 50% - so all of the theoretical advantages of the Otto cycle of the Diesel cycle just aren't materializing. The diesel won't start above 18,000 feet (or even 12,000 in some cases) because the ambient pressure is too low. True of a naturally aspirated engine - but the next thing you will see is e-turbos on aero diesels that can start at virtually any altitude and temperature with ease. The Austro AE300/330 is limited to -30C with Jet A and -5C with diesel. I have lived and worked in the arctic and sub arctic for decades. We use Jet B for that reason, but modern HPCR diesel have so much injection pressure the get fantastic atomisation at ridiculously low ambient temps. Starting is simply not an issue. Of course SI engines don't burn old fryer oil... I don't see your point here. We'll be filling up at airports in most cases with 100LL, mogas or maybe unleaded avgas like Swift 94 or 100. BUT: when the zombie appocolypse comes, there won't BE any Swift 94 or LL100 - but we dieselheads can stick up Rotten Ronnies and get into the air. Most turbine aircraft have fuel heaters just because you have pumping, gelling and vaporization issues below about -45C. Diesel aircraft will have the same issues. agreed, but the injection pressures in a turbine are miniscule compared with HPCR engines (that go up to 29,000 psi). This is one of the struggles in the aerodiesel design community: have a simple mechanical system and be stuck with low pressures and sensitivity to viscosity or go with full electronics so the programming boffins can make the engine dance on stars....at the expense of being 100% electric dependent. As I mentioned, we start diesels every day in cold places, and modern HPCR engines with ULSD do so very well indeed.[/quote] #### rv6ejguy ##### Well-Known Member I'm talking about existing aero diesels vs. existing aero SI engines here. I covered the original VW diesels in my video with their pathetic performance- less torque and hp with a turbo than the same size SI engine with no turbo They didn't need bigger components because they made so much less power and VW engines of that era were already very strong. Modern SI turbo auro engines with VG turbos often have torque peak down around 1400 to 1700 rpm- same as most light diesels. It's all about boost. Detonation isn't an issue with modern EFI/EI and knock sensors. Most turbo SI auto engines work realy well on 87 octane. I've pointed to real world examples of SI torque and hp being much higher than CI at the same boost pressure but you continue to believe it's not true. I'll put this out there like I have for the last decade on forums- show me just one example of a diesel of the same displacement and same boost pressure putting out more torque and hp and I'll believe it. Nobody has yet. Austro makes more aero diesels than anyone and have these temp limitations for a reason and that is running on Jet A in most cases. Aircraft can see much lower OATs at altitude than ground based vehicles. And no, you don't start diesels at -45C and 18,000 feet... Most of the aero diesels have lower MAP limitations of at least 40 inches at altitude because they may flame out at less than that. Experience with ground based diesels doesn't always translate to aero diesels. If the appocolypse comes, GA is the last thing you'll be worried about. You won't be flying very far on used cooking oil because there won't be any of that around either. #### speedracer ##### Well-Known Member I have plenty of customers cruising at 12,000 to 18,000 in their RVs, Glasairs, Lancairs etc. That's where you get best efficiency. I have over 700 hours cruising between 16 - 18,000' in my LongEZ. At those altitudes I've seen one airplane, one time. A king Air flew across my nose 1/4 mile out. It's almost always glassy smooth up there and EZ's are very well behaved that high, unlike some airplanes. Keep in mind the C1A world altitude record is held by a normally aspirated 150 HP LongEZ that went above 35,000'. FYI, I carry a hose in my plane that connects my ox. bottle to a big welding bottle for cheap refills. Have I ever gone VFR into the flight levels to get over weather? Maybe, maybe not, I can't remember. #### Geraldc ##### Well-Known Member edited quote missing #### Geraldc ##### Well-Known Member I'm talking about existing aero diesels vs. existing aero SI engines here. What is your opinion on the PSA DV6? 107kg (236lb) for 105 hp at prop verified with eiffel bar. #### rv6ejguy ##### Well-Known Member I don't know much about these engines since they are relatively uncommon in North America. Some flying in Europe. With turbo, the power to weight ratio of any engine improves considerably #### tspear ##### Well-Known Member Austro makes more aero diesels than anyone and have these temp limitations for a reason and that is running on Jet A in most cases. Aircraft can see much lower OATs at altitude than ground based vehicles. And no, you don't start diesels at -45C and 18,000 feet... Most of the aero diesels have lower MAP limitations of at least 40 inches at altitude because they may flame out at less than that. Experience with ground based diesels doesn't always translate to aero diesels. Recently on a Diamond forum I am on someone posted about a little know feature/bug/issue. They were trying to land in Leadville and found out the engine idle was almost 2000 vs 600 RPM. Diamond has an automatic minimum idle speed based on altitude; which made landing at high altitudes interesting. A few flight schools have also discovered this the "hard way". One had a plane land up high, they flew a second up there to pick up the student and instructor and had the same issue... eventually someone got ahold of Diamond and found out about the altitude compensating issue. Tim #### tspear ##### Well-Known Member @sotaro I am way out of my wheel house. But from what I have read, Bosch, GM, Ford and most of the Euro companies have solved the same issues as Skyactive from Mazda by utilizing multi injections of high pressure to produce an almost "continuous" thrust. This allows a much smoother and lower vibration, and the use of even higher compression; both of which also increases efficiency. A tertiary effect of the continuous injection is lower peak pressures which actually reduces the total package weight. From what I have read the EPS project was also using this technology. Tim #### Bigshu ##### Well-Known Member I will suggest the entire lineup of VW engines going way back to the earliest turbo indirect engines. They used the same dimensions of rotating elements and often the exact same parts. You KNOW why "they have larger/thicker pistons, etc." - simply because the RPM at which they are designed to make the HP and torque they are able to do - something most SI engines simply can NOT do because of detonation issues. That makes a car or truck so much nicer to drive when the fat part of the power curve is at cruising RPM (and, yes, I realize many SI engines are now learning to do this reasonably well - but diesels can do so until they run into some thermal or mechanical strength limit - and at same cylinder pressures so would an SI engine...IF it could run on an aspirated charge without detonating. Of course, in aviation this means direct drive is easy whereas to get those kinds of numbers out of an SI engine, it has to be wound up like a$2 watch.

again, I am totally unfamiliar with the "320 T" engine, but you put forward your very best at 40% BTE and the diesel people did theirs at 50% - so all of the theoretical advantages of the Otto cycle of the Diesel cycle just aren't materializing.

True of a naturally aspirated engine - but the next thing you will see is e-turbos on aero diesels that can start at virtually any altitude and temperature with ease.

I have lived and worked in the arctic and sub arctic for decades. We use Jet B for that reason, but modern HPCR diesel have so much injection pressure the get fantastic atomisation at ridiculously low ambient temps. Starting is simply not an issue.

BUT: when the zombie appocolypse comes, there won't BE any Swift 94 or LL100 - but we dieselheads can stick up Rotten Ronnies and get into the air.

agreed, but the injection pressures in a turbine are miniscule compared with HPCR engines (that go up to 29,000 psi). This is one of the struggles in the aerodiesel design community: have a simple mechanical system and be stuck with low pressures and sensitivity to viscosity or go with full electronics so the programming boffins can make the engine dance on stars....at the expense of being 100% electric dependent. As I mentioned, we start diesels every day in cold places, and modern HPCR engines with ULSD do so very well indeed.
[/QUOTE]
Just as a side bar to this discussion, in road fuel now that we're seeing more bio-diesel ( #2 , diesel, not jet), gelling and fuel system heaters are a big deal. People hate bio-diesel, and that's the direction that fuel stream is going. I can't imagine how that would work in the jet fuel side of diesel production.

#### rv6ejguy

##### Well-Known Member
Getting back to WAM, They had some durability issues with pre-chambers having to be replaced every 50 hours at a cost of about \$700US for the set of 3. That more than wiped out any supposed fuel savings which were in reality no different from an O-235 anyway, both having similar BSFC figures.

Also had some timing gear bolt failures, perhaps TV induced. This is a 2 stroke diesel with exhaust valves... https://assets.publishing.service.gov.uk/media/5422eea0e5274a1314000213/Vans_RV-9A__G-CDCD_04-14.pdf

#### dog

##### Well-Known Member
Was the WAM the motor that was pionering
a ball and socket arangement instead of a
wrist pin?

#### rv6ejguy

##### Well-Known Member
The 2nd generation design used a conventional wrist pin, 1st generation used ball and socket.

Straight from their own literature:
"Power / Torque / Engine RPM / Specific Fuel Consumption
T.O. – max 5 min: 93 kW (125bhp) / 323 Nm / 2750 / 255gm/kW hr (0.42lb/HP hr)
Max. continuous: 75 kW (100bhp) / 275Nm / 2560 / 250gm/kW hr (0.41lb/HP hr)
Economy Cruise: 62kW (83bhp) / 247Nm / 2400 / 240gm/kW hr (0.395lb/HP hr)

Cruise fuel flow is typically 25-30% less than gasoline engines at the same power setting."

This last sentence is nonsense. They are saying that a typical Lycoming has a cruise BSFC of .45-.51 where they are actually less than .40 running LOP. In fact comparing a couple RV-9s, one with an O-235 and one with the WAM, fuel flows were slightly lower at the same TAS with the Lycoming running LOP with carb heat.

At TO power, yup, the WAM is certainly better than the Lyc.

#### Yellowhammer

##### Well-Known Member
HBA Supporter
Diesels are infinitely more suited to aircraft than spark ignition. First of all, there is no reason for a modern turbo diesel to be anywhere near as heavy as a gasoline engine. Yes, one possible limit is piston crown temperature, but there is no practical difference between gasoline spark ignition and diesel compression ignition at the same cylinder pressures (=same power). What limits gasoline is cylinder pressure before ignition (i.e. MAP) that causes detonation - whereas diesels have no such limit as there is simply nothing in the chamber to detonate until the injection events begin. Turbocharged diesel engines simply add fuel and air until you reach some kind of limit - either mechanical or thermal - and that can be considerably higher than in an SI design at same RPM.

The fuel is much less critical (you can burn pretty much ANY hydrocarbon instead of the critically narrow range of fuels and mixtures required by gasoline SI engines. The fuel has better energy density, but most of all much safer as far lower flash point. There are none of high altitude issues with ignition as there is no ignition system. There is one extremely large advantage to turbocharged CI diesels in aircraft: You can pretty much tailor the power "curve" to be what you like at the RPM you want. That means you can go direct drive if you like (as in SMA/Continental 5.0 litre) but what nobody has bothered to do (yet) is to build a flat rated engine that simply makes its takeoff power at the start of the takeoff roll RPM and stays there as RPM increases - in other words, no need for a constant speed prop.

Then there are the more subtle advantages that can make an aviation diesel as light as or lighter than a gasoline SI engine: two cycle operation. Diesels simply do that far better at lower RPM than SI. On top of that, instead of just saving the wasted extra strokes of a 4 cycle, you can also gain a great deal of efficiency by going to uniflow scavenging instead of counterflow. Finally, there are diesel designs that don't have the complexity, weight, cost and thermal losses of cylinder heads - an option that IS available in SI, but just works better due to BTE considerations with CI.

I have to admit that designs now in production and certified are way too heavy for what they accomplish. Converting an automotive diesel is a dead end weight and complexity wise. The more aviation designs (SMA and soon EPS) come much closer to gasoline SI power densities, but both suffer the extreme penalties of being 4 cycles. There are designs in the hardware and test stages that go beyond these early attempts.

Worth remembering that the most efficient engine EVER installed in an airframe was a diesel in the '30s (Junkers Jumo).

BTW: I drive to the airport in diesel powered cars and trucks...in case you didn't guess.

Not to mention that in the auto world a diesel engine is just getting broken in at 300,00 miles!

#### rv6ejguy

##### Well-Known Member
Yet in the aero diesel world, most have TBOs or TBRs less than typical Lycoming engines.

#### Niels

##### Well-Known Member
Was the WAM the motor that was pionering
a ball and socket arangement instead of a
wrist pin?
Sulzer from Switzerland patented it 1937.
The bearing between piston and conrod lives a tough life in a two stroke engine .
Load is always one direction for normal piston speeds and Sulzer had a very good buisness doing two strokes for ships and generation plants.
Ball and socket

dog

#### PMD

##### Well-Known Member
Yet in the aero diesel world, most have TBOs or TBRs less than typical Lycoming engines.
Many Clunkinental and Lycosaurus engines started with low (1,200 hrs often) TBO. Thielert started at 1,000 and the 2.0 by Continental is up to 2,100 TBR and the new V6 is starting at 1,200 as well. Austro is at 1,800 TBO (IIRC) but worth noting that neither of these are actually aviation engines, but converted auto engines IMHO in way over their head. The SMA 305 is the ONLY genuine aviation engine, and even with few fleet hours is 1,800 TBO - but expected to be over 3,000 in time. What will be interesting is to see upper cylinder life with modern ULSD and Jet A1 - neither of which have the lubricity of good old D2. BTW: my last truck diesel went over the 1 million mile mark - that was about 20,000 hours without being opened up for anything.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
Of course SI engines don't burn old fryer oil...
WRONG! The peer-reviewed scientific consensus is that the dinos liked their French fries too much, which killed them off. Ergo, we’re all running on recycled fryer oil.

#### rv6ejguy

##### Well-Known Member
My friend who owns a flight school here usually gets 2500-3000 hours out of the O-360s in his 172s run on-condition.

#### PMD

##### Well-Known Member
My friend who owns a flight school here usually gets 2500-3000 hours out of the O-360s in his 172s run on-condition.
Similar stories from 0-320s that are used constantly. 3,000 hrs at car speeds = >150k miles = <300k at average flight training speeds. Not bad, but diesels should be able to go far beyond that - thus why the abject failure of putting Thielert engines/gearboxes into trainers (or anything else). IMHO, the whole Thielert experience was the aviation equivalent of the 5.7 GM damage to the automotive diesel world. VW fixed that in cars (then destroyed it all on their own) so we are just waiting for an aviation VW to show up with a decent diesel (expect 2 cycle).