2 rotary vs lycoming comparisons

[Sprint100]

I am reading up on the actual conversion from an automotive engine to a aviation engine. Here are two comparisons I always get asked about.

What is the cost and what is the exact weight.

Q. What is the cost to install the rotary in an aircraft and how long does it take?
A. It is impossible to say what any given builder will spend on their engine installation. The exact cost will depend a lot on how resourceful you are. For example, if you order custom heat exchangers from Griffon for radiators & oil coolers, you could easily spend over $2000. I used automotive air conditioner evaporator cores from the junkyard and spent $10. Intelligent use of available materials like this does not mean you are looking for trouble. I have no argument with those who insist on using the very best on their airplane. Here at Real World Solutions, we have one Guiding Principle on the subject: It is better to fly a good airplane than to dream about a perfect one. My total installation costs in 1995, was around $5000 including initial cost of the engine, redrive, engine instruments, cooling system, engine overhaul, exhaust system, etc (i.e. everything). Time-wise, I spent 4 months (almost 40 hours a week) designing, procuring parts, fabricating & debugging the installation.
For another point of reference, to replicate the Renesis installation on my RV-4 would cost about $12,000. Not cheap, but a lot less then an IO-360 Lycoming at around $30,000 (July, 2004).

Q. How much does the rotary weigh?
A. Weight was one of the primary reasons I chose this engine. The only thing that really counts is what the total system with re-drive, cooling systems, engine mount, etc weighs. This is called firewall forward (FWF) weight. In my case, this is about 345 pounds. From my research, it appeared to be the only auto engine available which would equal the weight, power and reliability of the O-320 or O-360 Lycoming. ANY automotive V6 piston engine will be much heavier.
Update 7/31/04: By careful attention to details, I have reduced the FWF weight by about 30 lbs in the Renesis installation.
Here is the breakdown of system weights in my airplane. This list is a bit out of date because it does not reflect many changes I have made (like the EFI system) but will give you a good idea of what you can expect.
<!--mstheme--><TABLE borderColorDark=#003333 cellPadding=3 align=center borderColorLight=#66cccc border=1><COLGROUP span=2 vAlign=top align=left></COLGROUP><TBODY><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Mazda 13B Engine Core<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]180 lbs. (incl. water pump)<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]RD-1B<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]42 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Starter (RX-7)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]7.5 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Alternator (Mazda 70Amp)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]9 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Evaporator Cores (Qty. 2)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]7 lbs. (total)<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Oil Cooler (stock Mazda)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]8 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Intake Manifold + fuel rails<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]8 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Coolant (7 qts.)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]14 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Ignition Coil Assys.<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]2.5 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Total Engine Weight<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]278 lbs.<!--mstheme-->[/FONT]</TD></TR></TBODY></TABLE><!--mstheme-->[FONT=Arial, Helvetica]<!--mstheme-->[/FONT]<TABLE borderColorDark=#003333 cellPadding=3 align=center borderColorLight=#66cccc border=1><COLGROUP span=2 vAlign=top align=left></COLGROUP><TBODY><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Exhaust System<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]8 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Engine Submount<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]7 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Main Engine Mount (Modified RV-4)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]15 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Brackets, Hoses, et. al.<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]5 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Oil (6 qts.)<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]12 lbs.<!--mstheme-->[/FONT]</TD></TR><TR><TD width="50%"><!--mstheme-->[FONT=Arial, Helvetica]Total Installed Weight<!--mstheme-->[/FONT]</TD><TD><!--mstheme-->[FONT=Arial, Helvetica]325 lbs. (Firewall Forward)<!--mstheme-->[/FONT]</TD></TR></TBODY></TABLE>

 

[Cessnaflyer]

But doesn't the rotary need to be at crazy high speeds to get rated horsepower? It just seems like not a good idea.

I'd rather put a PT6 on it

 

[Killtron2000]

Car engines aren't designed for what airplanes need. Rotaries work differently but still I personally wouldn't fly something like that with an ejection seat over a field of marshmallows.

 

[Kestrel452]

Rotary engines are significantly less efficient and less powerful when compared to a V or straight engine. They sounds like ricers anyways.

 

[Sprint100]

Rotary engines are significantly less efficient and less powerful when compared to a V or straight engine. They sounds like ricers anyways.

Pump yo brakes. One of the reasons I am choosing rotary is because of the efficiency in a Mazda 13b engine. All the builders I know with a rotary won't put in a less efficient engine, period.

 

[Sprint100]

Car engines aren't designed for what airplanes need. Rotaries work differently but still I personally wouldn't fly something like that with an ejection seat over a field of marshmallows.

You need to stop listening to old tales. During my research I found those not knowing much about the subject saying the exact same thing. Another builder with a turbo rotary in his had his turno go out and it spit metal shards from the compressor into the combustion chamber and he still flew it , with power, safely back to the airport.

 

[Sprint100]

But doesn't the rotary need to be at crazy high speeds to get rated horsepower? It just seems like not a good idea.

I'd rather put a PT6 on it

A prop speed reduction unit is bolted on to keep the power curve on the engine high while spinning the prop at a reduced RPM.

 

[Killtron2000]

You need to stop listening to old tales. During my research I found those not knowing much about the subject saying the exact same thing. Another builder with a turbo rotary in his had his turno go out and it spit metal shards from the compressor into the combustion chamber and he still flew it , with power, safely back to the airport.

I've heard stories first hand of lycomings having cylinders fly off and still running. It's your decision but I'm just saying if I break my arm I don't go to the vet to save money. Those engines are pretty amazing when you think about everything they have to do I just don't think you could replace that with something that was designed and built for an entirley different application. Just my $0.02.

 

[Sprint100]

I've heard stories first hand of lycomings having cylinders fly off and still running. It's your decision but I'm just saying if I break my arm I don't go to the vet to save money. Those engines are pretty amazing when you think about everything they have to do I just don't think you could replace that with something that was designed and built for an entirley different application. Just my $0.02.

You are using the wrong analogy which shows me how much you know about both sides of things. Whatever you choose to build and how you choose to build is entirely up to the individual but on a board like this I'm going to make sure I only say accurate information and dispute the inaccuracies. Although a rotary isn't "plug and play" like a lycoming when an automotive rotary install is done right it is just as good, and in my mind better. The horror stories come from guys that either heard a horror story from some guy that did an improper setup in their planes or someone that tries to use logic by saying that auto engines and airplane engines are entirely different with nothing solid to go on to back up what they are saying. Many kits use an conventional 4 and 6 cylinder auto engines, using an auto engine is nothing new. There are many steps needed to be done to make a mazda rotary or other auto engine truly aircraft worthy. That fact alone deters many individuals that like auto engines but won't even think about using one because of their mechanical learning curve.
Simply stated, when done right it is just as good if not better. Keep in mind, I am not against the lycomings or continentals at all so if someone chooses one then that is their perogative for whatever personal reason.

 

[Clearblue]

Car engines aren't designed for what airplanes need. Rotaries work differently but still I personally wouldn't fly something like that with an ejection seat over a field of marshmallows.

I've heard stories first hand of lycomings having cylinders fly off and still running. It's your decision but I'm just saying if I break my arm I don't go to the vet to save money. Those engines are pretty amazing when you think about everything they have to do I just don't think you could replace that with something that was designed and built for an entirley different application. Just my $0.02.

Killtron could you expand on why you think a wankle is a poor choice for an aircraft? Please exclude any anecdotal evidence from you response, thanks.

 

[Cessnaflyer]

I don't like the whole electronic ignition and only a single ignition system at that.

 

[Killtron2000]

Killtron could you expand on why you think a wankle is a poor choice for an aircraft? Please exclude any anecdotal evidence from you response, thanks.

Nobody designs a car engine expecting it to be run at full throttle for extended periods or have a heavy propellar with all it gyroscopic forces exerted on it. There are probably plenty of other less obvious demands placed on an aircraft engine that non engineers wouldn't know about. Because a wankel is a simpler machine doesn't mean things can't go wrong with it when you make it do things it wasn't ever intended to do. But if you feel comfortable with it be my guest I don't really care if you want to use rubber bands and hampsters as long as I'm not onboard. There are levels of understanding on this subject most of us aren't even aware of and it's way to technical to risk your life to some amateurs estimate.

 

[Clearblue]

Nobody designs a car engine expecting it to be run at full throttle for extended periods or have a heavy propellar with all it gyroscopic forces exerted on it.

Wow, good point killtron. Sprint have you read anything concerning mounting to prop to the end of a wankle engine? If so, how have builders dealt with it? Bolting the PRU directly to the frame?

I agree about the full throttle thing. Though I imagine if any engine was adept to do so, the wankel would have the best shot. Using automotive engines for aircraft use is going to have it's issues,but it would be nice to see some serious development in the area.

I don't like the whole electronic ignition and only a single ignition system at that.

The Renesis has two spark plugs per rotor and one coil per plug.

 

[OhioStatePilot]

Automotive engines may not be expected to run at constant throttle settings for extended periods, but that actually creates a lower amount of stress on the engine than continually changing throttle settings and varying loads. Regarding a propeller mounted on a Wankel, you seem to be neglecting the fact that any engine sees gyroscopic forces. Flywheels aren't light.

There is a key design feature of the Wankel that you're overlooking Killtron. You feel more comfortable with a reciprocating Lycoming than a Wankel rotary. The forces exerted inside any reciprocating internal combustion engine far exceed those inside a rotary engine. The rotor in a Wankel never reverses direction, which results in a drastic reduction in forces seen on the rotor when compared to a comparable piston engine. You can see this for yourself by calculating the piston velocity at any given power setting for a reciprocating engine, and then calculating the forces exerted by acceleration when the piston changes direction at the end of each stroke. This happens thousands of times per minute and the stresses are seen on the piston, wrist pin, rod, cap, rod bolts, crankshaft, etc.

I'm not attempting to knock the standard piston engines we use today, but merely trying to show you a mechanical comparison. In addition, I'd suggest looking at NTSB reports involving Wankel engines. You'll notice that there are a relatively small number of failures associated with the converted automotive engines. I feel safe behind a Lycoming, but even I believe it's more likely to suffer a mechanical failure than a Wankel engine.

Interesting notes:

Curtiss-Wright was one of the first to have license for the Wankel. You might know the name as being associated with aircraft. Their RC2-60 Wankel engine powered an experimental Lockheed aircraft for the military. The soviets also used the Wankel engine to power aircraft, including helicopters.

 

[OhioStatePilot]

Here's some math I've dug up just for reference:

Mean Piston Speed (ft/min) = 2*RPM*Stroke Length (in)/12 (in)
MPS = RPM*Stroke/6

Lycoming IO-360 
Stroke = 4.375 in
Max. Cont. HP/RPM = 177/2700

Source - Type Certificate Data Sheet

Now with the above formula and data,

MPS = (2700*4.375)/6
MPS = 11812.5/6
MPS = 1968.75 ft/min

(1968.75*60)/5280 = 22.37 mph

Now remember the piston has a speed of 0 on both ends of the stroke. This acceleration doesn't occur in a Wankel engine.

 

[CoffeeIcePapers]

Killtron could you expand on why you think a wankle is a poor choice for an aircraft? Please exclude any anecdotal evidence from you response, thanks.

That is a pretty tall order, IMO. I doubt there is much scientific data, since these are experimental engines in aircraft. Just about every argument will be theory based or anecdotal.

I don't like the whole electronic ignition and only a single ignition system at that.

This is my biggest concern, as well. I am sure it has been addressed, however.

EDIT: I found this:


http://www.dmack.net/mazda/information.html

ELECTRICAL/IGNITION SUBSYSTEM: Additional features relative to safety is that each rotor chamber has two spark plugs with two independent ignition coils for each plug set. There is one plug per rotor chamber referred to as the "Lead" and one referred to as the "Trailing" plug. The trailing plug in the automobile application is set to fire approximately 15 degrees after the lead plug fires. The engine will run on just the trailing plug setting for auto application, however, there is considerable power loss. While the trailing plug was designed principally to meet auto emission and fuel economy standards, it can be recalibrated to fire essentially in sync with the lead plug providing true redundant ignition for the engine in aircraft application. An aftermarket ignition computer is used which provides two independent ignition CPUs and a feature for checking each ignition coil subsystem independently similar to a checking of the aircraft magnetos.
The adaptation includes two 25AH Concord RG batteries, each of which is capable of carrying the essential minimum electrical load for up to 2 1/2 hours should the alternator charging subsystem fail. Additionally, there is an automatic battery charging/management subsystem that automatically keeps each battery fully charged and give visual indication of abnormal voltage conditions. Furthermore, each battery can be manually isolated from the bus circuit should it malfunction (such as an internal electrical short in the battery).
The electric charging is accomplished with a Bosch alternator (know for its reliability in automotive usage).
Electrical Subsystem Instrumentation: The electrical subsystem is instrumented with a High/Low voltage visual indicator as well as a voltmeter which can be switched between each of the two batteries and the alternator.

 

[Sprint100]

Wow, good point killtron. Sprint have you read anything concerning mounting to prop to the end of a wankle engine? If so, how have builders dealt with it? Bolting the PRU directly to the frame?

That is a logical fear but unfounded. The reduction unit is mounted directly onto the engine. If there was any substance behind that then there would have been props falling out of they sky or so many damaged engines from the conversion that noone would even consider an automotive engine.

The Renesis has two spark plugs per rotor and one coil per plug.

The fuel injector and ignition systems that are made for conversions all have redundancy.

 

[Sprint100]

In regards to Mojo's post, I think most think the engine is taken straight from car to airplane with little modification. The engine is stripped down to just that, the engine itself, or the block, then parts suitable for aviation are put on.

 

[Kestrel452]

Pump yo brakes. One of the reasons I am choosing rotary is because of the efficiency in a Mazda 13b engine. All the builders I know with a rotary won't put in a less efficient engine, period.

Rotary engines just are not as efficient at utilizing the most power per drop of fuel like a piston engine is. I will bet you dollars to donuts that the FAA is not going to like your proposed engine swap. You are sacrificing tons of safety for just the ability to say you swapped an engine. You said it yourself, you have to put a speed reducer in between the engine and prop, which says in itself that it will be even more inefficient since you are literally dumping a chunk of that power.

Seriously, what is your obsession with the Renesis, an engine that is clearly NOT built to aircraft specs?

 

[CoffeeIcePapers]

Rotary engines just are not as efficient at utilizing the most power per drop of fuel like a piston engine is. I will bet you dollars to donuts that the FAA is not going to like your proposed engine swap. You are sacrificing tons of safety for just the ability to say you swapped an engine. You said it yourself, you have to put a speed reducer in between the engine and prop, which says in itself that it will be even more inefficient since you are literally dumping a chunk of that power.

Seriously, what is your obsession with the Renesis, an engine that is clearly NOT built to aircraft specs?

Rotax Engines use a reducer, as do many others. Remember, this is for homebuilt aircraft, so the FAA doesn't care, at all. Again, you have no real proof, just your opinion.