modified merlin heads

[Blue Foam]

Re: modified merlin heads

The head work should be done,I was thinking about the trying of different superchargers/turbos,ect. How much more HP do you think the prop can convert to speed?

Excellent question. The current props are over super-critical already, so their np is pretty much flat lined at .65 to .70 Stuffing more power into them would convert to thrust at that efficiency up to about 550 or 600 mph. So speed would go with ~.65 x the cube root of the power gain. Shifting to supercritical blades would up the efficiency by 10 to 25% and extend the efficiency curve fall-off to over 600 mph at Reno conditions.

[Blue Foam]

Re: modified merlin heads

The intake tract is being continuously cooled by the intake charge and the evaporation of fuel. The stem and backside of the intake valve are cold, which is why we don't put TBC's (thermal barrier coatings) on the intake valve or port: we want those warm to keep fuel from condensing.

The exhaust side is hot, not because of combustion. The exhaust port has significant surface area (more than the head, don't take my word for it: measure it). This surface is continuously in contact with exhaust gasses, even when the valve is closed. This is the single most important area to coat for keeping heat in the exhaust and out of the head. The valve should be coated too, and this is where our Aussie head guy gets away with modern valves with thinner stems.

The piston should be coated, as this reduces oil temperature and coking as well as reducing detonation. Other than Unlimiteds, every other class of air racing and every other motorsport has been doing this for decades. I found out 6 to 10 years ago from all the other classes. Not everyone uses them, just the smart guys.

The head surface? When we look at how much area is taken up by the valves, it is third in surface area to the piston and exhaust port, and it would only make a small cooling difference if we left it un-coated. The TBC's serve a different purpose here: They reflect heat off the surfaces of the piston and head to prevent hot spots which are the source of pre-ignition, commonly called detonation which is a separate effect with the same symptoms and dangers.

Cylinder pressure does have an effect, especially with old designs. Mostly, excessive cylinder pressure strips out or shears the head and/or cylinder bolts. This is not that hard to visualize. Try molding a head out of clay. Put your fingers on the head bolt lands and your fist up the middle. It doesn't crack the thermal expansion makes them crack.

In a modern large-bore engine with higher compression ratios (4.5" cylinder bores, 10.5:1 compression, 140" MAP) only the heads are cooled, and then only on the exhaust side. Look at the heat flow and it makes sense.

Old heads are cooled all over, and what's funny is that the coolant is actually heating the intake side.

So the hottest parts are (in order) the exhaust valve, the exhaust seats, and the exhaust ports. The coldest areas are the intake port, intake valve, and intake valve seat. So take that clay head and stretch it on one side while not stretching it on the other. In the middle, between the exhaust and intake seats.

And Rich is right, just because it's experimental, that doesn't mean you can do whatever you want.

Actually, I have not see any reference to head mods in operating limitations. As far as approvals go, a well known shop has dropped 3700 lb thrust motors weighing 870 lb into an aircraft made for a 2100 lb thrust motor weighing 660 lb with nothing more than a log entry. No DERS or engineering of any kind. I personally would prefer a higher level of approval, but that's the facts.

[AirDOGGe]

Re: modified merlin heads

I think this has to be the most informative topic on Merlin heads I've seen. Lots of suggestions mixed with lots of actual hands-on facts.

Great stuff guys.

[Sparrow]

Re: modified merlin heads

I have been using coatings on the pistons for quite ahwile. In regards to Ltd or Exp categories, you can't simply modify one part of the engine without some basis of data. Once you modify a head, you have modified the whole engine, it comes as a pacakage. I suspect the engines your talking about are either nitro or alky engines. These, as everyone seems to think, old pile of $hit cylinder heads are pretty damned good. The bottom line of all this is it is still heat that causes the problem. If you keep it cool and under control, they don't tend to crack. As far as this shop doing what your talking about, probably shouldn't go adverstising that fact, they've got to have some type of info they are using. With the new regime and the rule changes at Reno, we put RRIII in Exp category for racing purposes, with the mods done to it if we had not done that it would've been a problem. There are certain changes that when made to an airframe that put it in Exp. category, instantly. If you were to show up with those changes in Ltd. category you certainly wouldn't be allowed to race, quite probably would'nt be allowed to fly it home.

[IcePaq]

Re: modified merlin heads

Managing heat and, better yet, temperature differentials between areas of a cylinder head would work better if all the cylinders had the same mixture ratio.

This is where modern engine management comes in.

[morerevsm3]

Re: modified merlin heads

this is still the old engine at a country fair near Joes home town, but with the motec engine management etc, it starts easily and will sit and idle for as long as you like, and rev cleanly, automatically adjusts the tune for air density changes etc

http://www.youtube.com/watch?v=0p7qv6vPFfY

[Blue Foam]

Re: modified merlin heads

this is still the old engine at a country fair near Joes home town, but with the motec engine management etc, it starts easily and will sit and idle for as long as you like, and rev cleanly, automatically adjusts the tune for air density changes etc

http://www.youtube.com/watch?v=0p7qv6vPFfY

Starts instantly, one revolution from hitting the button. No smoke, no misfires.

If anyone wants to put an ECU on an air racer with no, and I do mean NO risk, it's pretty simple:

Put a MAF on the existing engine and map the CFM, MP, MAF, and fuel flow. Insert this fuel map into the ECU installation. Port the cylinders, install runners, do whatever else anyone wants. Run the ECU off of the MAF. It automatically compensates for air density AND temperature, which no carburator can.

Now let's throttle up the engine (slowly) to the same MAF as before (MAP will be 30 to 40% less due to the porting and runners). Power will track with MAF and fuel flow. Since it's running the same gross mixture of air flow and fuel flow all this has done is reduce the cylinder-to-cylinder and revolution-to-revolution mixture variations.

The motor will make more power at less boost and have less chance of detonation. There is no risk.

Granted, we can boost back up to the same MAP as before and lean the whole thing out beyond this point in a quest for power. That's where the current engine builders rightfully have concerns. In aviation, the first use of porting, runners, ECU, etc. can easily be used to improve reliability at current power levels, without risk.

Considering the cost of the current level of reliability, it will eventually happen that someone will go in this direction with a Merlin, 3350, 4360, or 2800. It's already happened to several Lycomings and Continentals, and one inline and more than one radial program in work. The true race is on for someone willing to take that leap of faith. The money has already been spent many times over.

[wyhdah]

Re: modified merlin heads

Eric, what MAF would you use at the high boost levels, we have had very poor luck with Mass Air at boosted levels. That's why you see most high power drag cars, (over 2500hp) using Speed Density. I know on the street cars that sensor is pretty useless above about 15psi.

I've seen some of the aftermarket sensors and I was wondering which you think would be adequate for aviation.

Scott

[IcePaq]

Re: modified merlin heads

They do make 100mm maf but you can get away running MAP, IAT, TPS, CTS (head temp) to meter the fuel and use O2 sensors in a closed loop.

[Blue Foam]

Re: modified merlin heads

Eric, what MAF would you use at the high boost levels, we have had very poor luck with Mass Air at boosted levels. That's why you see most high power drag cars, (over 2500hp) using Speed Density. I know on the street cars that sensor is pretty useless above about 15psi.

I've seen some of the aftermarket sensors and I was wondering which you think would be adequate for aviation.

Scott

The Motec parts are as good as any in the industry and have proven pretty trouble free on the Thunder Mustangs. The trick to doing this is to put the MAF on the inlet of the supercharger, not in the boosted flow. We would need a velocity map of the inlet, so that the MAF sensor can be correlated to actual mass flow. Or we can do that on a flow bench. Yes, that requires building a flow bench that could flow that kind of mass; that's easier and cheaper than it sounds since we only need about 10% to do a decent calibration.

Everything Icepaq says about the rest of the sensors is correct, there are some challenges with all of the wet fuel and ADI randomly slinging around the areas where the sensors are mounted. O2 sensors would require a collector exhaust, or at least enough length of pipe that reversion of atmosphere up the pipe doesn't trash the reading. Easier to do on a radial than a Merlin.

[CH-Ignitions]

Re: modified merlin heads

Hello to everyone.
My name is Adrian Ciulei and I am a the new operator of CH ignitions that makes ignitions for the RC airplane world for over 30 years.
One of my things to do is building thing. For couple years now I have collected materials about Merlin/Packard V1650 and I will like to build a 1/5 scale of it. I was searching for technical drawings and I did not found those anywhere. I try in England at Derby and no luck there , they did not wanted to help.
If any one here has any type of drawings and will like to share those with me will be greatly appreciated.
I also look for parts that to you guys are no good/no use anymore.
Pistons, cam shaft (even a section of it) connecting rods , valves...etc.
I will take those and redraw them in cad soft to make the parts.

Thank you
Adrian

[AirDOGGe]

Re: modified merlin heads

The Aircraft Engine Historical Society have a 'model engines' section on their website and perhaps can diret you to a blueprint source, or at least a member who may know of one.

I've seen said OPERATIONAL mini-merlins on their website in the past. Here's an example featuring a scale Merlin V-12...Yes, it runs, and a video of it running is available there. The breakdown of all the component parts gives a good idea of the task ahead of you:

http://www.enginehistory.org/ModelEngines/merlin_xx.shtml

Here's how to reach them:

Aircraft Engine Historical Society contact address: webmstr@enginehistory.org

[morerevsm3]

Re: modified merlin heads

slowly some progress being made-









and the 3000hp dyno that will have no chance of holding it anymore (it used to make 2700hp@ dyno max of 3000rpm with 19psi boost

[morerevsm3]

Re: modified merlin heads

owner is now making up gear cases for the back of the motor, and helical cut gears to drive the double overhead cams, and eliminate the bevel gear drives that are a weak point

[morerevsm3]

Re: modified merlin heads

correction to above post, he has made straight cut gear train...