Who didn't build their own engine?

[SHIPCHIEF]

Just a poke at the traditional engine forum thread: Who built their own engine?
I built my own, after the (now retired) builder of my core engine made a cardinal error, and enlarged the upper spark plug holes on my rotary 13BT engine. These 'trailing' plugs need to have their holes completely covered by the apex seal during its passage over the plug to prevent igniting the intake charge.
Even tho I initially purchased the core engine, the mount, fuel injection system & reduction gear, I did build the intake & exhaust systems, the oil and water cooling systems, scoops, ducts, wire looms, cable ways etc.
a lot of it I built twice, some 3 times!
Non traditional engines are also available from commercial builders, but I think a lot of them are fabricated by the aircraft builder for the pleasure & challenge of doing it?

 

[rv7charlie]

Hi Scott,

Bummer about the 'pro' engine builder. But, you now know more about your FWF than almost all 'traditional' engine fliers. And be aware that things just as bad, or worse, have happened to guys flying Lycosaurs when they had 'pros' build their engines. Even L & C have had horrors like batches of brand new bad cranks (C actually had it happen to the 'fix' for their 1st bad batch), and those cranks cost more than your entire core engine.

We will have true experimentals. Most RV's are really EINO's. Where's the fun in that?

Charlie

 

[bret]

Just a poke at the traditional engine forum thread: Who built their own engine?
I built my own, after the (now retired) builder of my core engine made a cardinal error, and enlarged the upper spark plug holes on my rotary 13BT engine. These 'trailing' plugs need to have their holes completely covered by the apex seal during its passage over the plug to prevent igniting the intake charge.
Even tho I initially purchased the core engine, the mount, fuel injection system & reduction gear, I did build the intake & exhaust systems, the oil and water cooling systems, scoops, ducts, wire looms, cable ways etc.
a lot of it I built twice, some 3 times!
Non traditional engines are also available from commercial builders, but I think a lot of them are fabricated by the aircraft builder for the pleasure & challenge of doing it?

That is a very intersting project you have going there!

 

[SHIPCHIEF]

Thank you Charlie & Bret;
It's been fun for me, but I don't try to push it on people.
At our EAA326 chapter Burger Burn, I was asked about it in a polite way, because of the engine failing. I told them I don't mind talking about it, I just didn't expect anyone to be interested in it.
I rebuilt the core engine in a few days, and it's back on the plane now, while I make a few improvements I was putting off. I added a large manifold pressure gauge from a Cessna center line twin so I can read Turbo output boost (front) before the throttle, and true manifold pressure after the throttle (rear).
I'm adding a boost Blow Off Valve, home made to keep the weight down. And re-routing some of the engine wires for simplicity and to control RFI. I had some alternator, ignition or injection noise on the COM radio.

 

[rv6ejguy]

So Scott, how does it perform? Any numbers?

 

[SHIPCHIEF]

Ross;
Thanks for asking, as well as being a consistent advocate here.
I had about 5 hours of ground running, including tethered runs up to 44" Hg manifold pressure.
Cooling required several mods, some of them copied from 'those who have gone before'. Finally I got it to cool itself at idle thru 3800 engine RPM, which should be enough to fly about 100 MPH, 1700 Propeller RPM.
Tethered runs at full boost did show an alarming increase in oil temp, always arrested before exceeding 206 F. This may have been a missed message about the oversize trailing spark plug hole.
After the Airworthiness Certificate was issued, I installed the cowl & covers, and pushed 89SE out for a 'victory lap' taxi, then to put away for careful work-up to the first flight. I taxied down to the run up area, did a normal run-up, took the active runway for a 3 second burst of power, to be followed by a slow down to the turn off.
Well, the forward movement of the aircraft must have allowed the engine to build up more RPM, more exhaust flow, more power (I was impressed!) and as I started to pull back the throttle, came a POP! and the engine shuddered to a stop with grey smoke pouring out of the cowl.
All I can assume, is that the additional RPM allowed by the forward speed created the condition for flash over at the over size trailing spark plug holes, which stretched the rotor housing on the #1 rotor. The alignment dowel at the top, which is also the main oil galley forced the end iron out, cracked it and sent 100 PSI oil spraying, which was the source of grey smoke. The #2 rotor suffered detonation damage to an apex seal, which destroyed the rotor and worthless rotor housing.
I've discussed this with various rotorheads, and reassembled the engine with new rotor housings, a rotor, end iron, seals gaskets etc., so Phase 2 could happen in a week if life's other little adventures don't step in front.
For a second there, I was truly impressed.
Hat's off to Tracy Crook for the reduction gear and Fuel / ignition computer, Craig Catto for the prop, and Fred Breese for the motor mount.

 

[rv6ejguy]

Well, thanks for posting your candid tribulations here and the fact that you won't give up easily. Oil temps can be a bear on turbo engines and especially turbo Wankels.

Are you running an intercooler?

Looking forward to your first flight report!

I am finishing off my flight testing now with the new ventral rad which is amazing so far. Still learning and tinkering after 10 years...

I can confirm that my 6A was for "educational purposes". It's been a heck of an education so far.

 

[SHIPCHIEF]

Surprised myself;
Got the RV-8 Rotary 13BT running today. Runs like a champ.
I spent most of the day finishing the wiring and checking the tightness of all the fittings, and chasing down NGK BER9EQ and BER7EQ plugs. I only had time to warm it up with all the covers off, and inspect everything.
I only ran it up to 3200 RPM, which was 22"Hg. on the big Manifold Pressure gauge that I added. Electronic Engine Monitors are nice, but the one I have gives mostly text data, hard to see during take off.
Tomorrow I'll go at it some more, maybe I can get it to the power testing and Taxi stage before I have to go back to work. (vacation seems short somehow)

 

[rv6ejguy]

Any more updates?

 

[SHIPCHIEF]

Slow. Other projects always find their way I front of the RV-8, but I did continue to run and adjust. I set the ignition timing at 4000 RPM, according to the manual, and I tracked down a tiny oil leak at the swivel end of the first oil hose out of the engine. I installed a new hose with non-swivel ends.
I've fabricated a turbo Blow Off Valve to limit boost, It's a modified radiator fill neck welded to the turbo pipe ahead of the throttle body. I'm starting with a 4 pound cap. I also welded in a 1/8" pipe boss, where I tap turbo pressure. I have a twin engine manifold pressure gauge, with coaxial needles, so I can observe turbo pressure vs manifold pressure, and know the differential at the throttle body. This will help me know if the turbo is sized properly.
I'm taking it out to the airport this morning to play with it. Then tomorrow I start my work week, and won't be able to work on the plane for the next 7 days.

 

[rv6ejguy]

Slow. Other projects always find their way I front of the RV-8, but I did continue to run and adjust. I set the ignition timing at 4000 RPM, according to the manual, and I tracked down a tiny oil leak at the swivel end of the first oil hose out of the engine. I installed a new hose with non-swivel ends.
I've fabricated a turbo Blow Off Valve to limit boost, It's a modified radiator fill neck welded to the turbo pipe ahead of the throttle body. I'm starting with a 4 pound cap. I also welded in a 1/8" pipe boss, where I tap turbo pressure. I have a twin engine manifold pressure gauge, with coaxial needles, so I can observe turbo pressure vs manifold pressure, and know the differential at the throttle body. This will help me know if the turbo is sized properly.
I'm taking it out to the airport this morning to play with it. Then tomorrow I start my work week, and won't be able to work on the plane for the next 7 days.

Good to hear you are slowly working out the bugs.

Do you have a wastegate fitted or just rely on a blowoff valve to control manifold pressure?

The differential across the TB only shows you the pressure drop there, nothing useful as far as compressor matching goes. You can however look at ambient vs. compressor discharge pressure to get the pressure ratio, then look at compressor discharge temp vs. ambient to calculate the compressor efficiency. Then you can cross these values on the compressor map to see where you are operating.

 

[SHIPCHIEF]

I just got back from the airport. The blow off valve was a partial success, the turbo output pressure tap a complete success.
I drilled 3 ea 1/4' hole around the neck of the radiator fill neck - now - Blow Off Valve, to allow the excess boost air to escape.
Test running, this was essentially ineffective, with Turbo Boost reading 50" Hg, and manifold pressure 35" Hg. that's about 7.5 PSI differential across the throttle. The propeller was turning 2176 RPM. This is a CATTO prop 68X74 a direct match for a 180 HP Lycoming O-360. The rotary engine runs thru a 2.19:1 reduction gear, so it was turning 4767 engine RPM.
I hesitate to exceed 50" or 55" Turbo Discharge pressure, 50" being the highest reading on the indicator, and 55" being about where it pegs, which I saw on my last taxi test. I don't know what the intake air temp is yet, so I want to be cautious.
This matches the take off performance of a Lycoming O-360 with fixed pitch prop, which is my goal.
I do not have a waste gate, I'm trying to size the Turbo Exhaust Housing so none would be required. I'm running a .81 A/R housing now, there are two 'looser' sizes, .96, and 1.30 I'm hunting for the 1.30 A/R on center P trim housing P/N Garrett 442534-0001, or Turbonetics 20237-3.
I worked on the BOV some more, adding more peripheral holes and retesting. I can see the opening point, but the turbo output over powers the BOV and boost climbs rapidly, so it needs development.

 

[rv6ejguy]

Yes, a big TO4 compressor wouldn't even know a few 1/4 inch holes were there as you found out. The big problem with using a blowoff valve to control boost is it forces the the compressor to operate towards the choke region which pushes compressor discharge temps way up. Without an intercooler, this can be pretty dangerous from a pre-ignition point of view and you could possibly even exceed N1 limits at altitude.

Even wastegated 13Bs often run .96 to 1.3 housings. The .81 is very tight for this engine in an aero application.

Caution is good. Be very careful. There are really good reasons why most modern turbo systems have wastegates and intercoolers.

The 7.5 psi differential across the throttle plate indicates massive restriction and again forces the compressor to work harder. If this is at WOT, the TB is way too small. We usually see less than .5 psi drop.

A stock 13B with 50 inches and a good turbo system should make an easy 230-240HP at 4800 rpm.

Pressure ratio varies as the square of N1 so things can quickly get out of hand once the system reaches crossover.

 

[SHIPCHIEF]

Thanks for taking the time and interest to help me out on this.
The throttle is about 1/2 open with the data point I gave. that's why I take the pressure at two points, so I can know what the turbo is compressing to, and what the partially open throttle is holding back, by also knowing the manifold pressure.
The Throttle body is pretty large, it's from a 5 liter Ford Mustang. Maybe 52mm? nearly the same as the ID of the 2.5 OD turbo pipe, which is 'way bigger than the stock Mazda intercooler pipes (which I have, but have not yet installed)
I'm getting the impression that my power is less than ideal because the exhaust is choked by the .81 A/R exhaust housing.
Right now, I think I could safely fly the RV-8, but I would need to limit the take off power to about the equivalent of an O-320 Lycoming. That would give some reserve safety against overboost as the aircraft gains speed causing RPM increase, which increases the gas flow which increases the boost etc. etc.
It's controllable, but I can do better.
My 'new' 60-1 turbocharger is about 14 years old. The part numbers I'm seeking are not available new any more, as the To-4B or E that uses them has been re-designed or superseded. I really don't want to spend another $1000 on another turbo, this one runs great. I just want to get it 'adjusted' right.
On marine diesels, where I work, there are no waste gates or blow off valves. Everything is well balanced by design. That was my original goal.
I understand that ships stay at sea level, airplane with turbo go very high. I can accept that I expect too much, and can change as required.
The RV-8 is behaving very well. Although I have not flown it, I have repeatedly brought it up to 80% take off speed, brought the tail up, wiggled the ailerons, rocked the plane, slowed down tested the brakes, taxii'd all over etc. etc. It will fly fine once I have the engine where I want it. Heck it could fly right now. I just want a better experience. Cooling is totally under control.
By the way, I'm having a ball with this.

 

[rv6ejguy]

Thanks for taking the time and interest to help me out on this.
The throttle is about 1/2 open with the data point I gave. that's why I take the pressure at two points, so I can know what the turbo is compressing to, and what the partially open throttle is holding back, by also knowing the manifold pressure.
The Throttle body is pretty large, it's from a 5 liter Ford Mustang. Maybe 52mm? nearly the same as the ID of the 2.5 OD turbo pipe, which is 'way bigger than the stock Mazda intercooler pipes (which I have, but have not yet installed)
I'm getting the impression that my power is less than ideal because the exhaust is choked by the .81 A/R exhaust housing.
Right now, I think I could safely fly the RV-8, but I would need to limit the take off power to about the equivalent of an O-320 Lycoming. That would give some reserve safety against overboost as the aircraft gains speed causing RPM increase, which increases the gas flow which increases the boost etc. etc.
It's controllable, but I can do better.
My 'new' 60-1 turbocharger is about 14 years old. The part numbers I'm seeking are not available new any more, as the To-4B or E that uses them has been re-designed or superseded. I really don't want to spend another $1000 on another turbo, this one runs great. I just want to get it 'adjusted' right.
On marine diesels, where I work, there are no waste gates or blow off valves. Everything is well balanced by design. That was my original goal.
I understand that ships stay at sea level, airplane with turbo go very high. I can accept that I expect too much, and can change as required.
The RV-8 is behaving very well. Although I have not flown it, I have repeatedly brought it up to 80% take off speed, brought the tail up, wiggled the ailerons, rocked the plane, slowed down tested the brakes, taxii'd all over etc. etc. It will fly fine once I have the engine where I want it. Heck it could fly right now. I just want a better experience. Cooling is totally under control.
By the way, I'm having a ball with this.

Glad you are enjoying the experience, part of the fun of true experimentation!

The 60-1 is way too big for this hp level, you'd likely have surge problems at altitudeif you didn't have the BOV on there. Combined with the .81, it's just not a good match for what you are trying to do.

I think the stock 5L TB is 56mm and this is fine for this power level. The half open part explains the high pressure drop.

The exhaust won't be choked at this hp level with the .81 but you'll never get the throttle wide open with it on there so this is restricting the power and with the BOV and the throttle half closed, you are spinning the turbo needlessly fast which is eating up hp.

On an SI engine operating at different altitudes and with a throttle plate, it will be almost impossible to get an a/r ratio that works well everywhere. It will be a huge compromise and you'll have to use the throttle to protect the engine, especially at lower OATs.

With the FP prop, it will unload greatly in flight as speed builds and at higher altitude as the density drops off. Not too many aircraft work well with turbos and FP props up high without suffering poor TO performance.

Before you fly, be sure to get this sorted on the ground as you'll be task saturated on your first flight and can't be worrying about the engine part. Do lots of full power, WOT runs for several minutes each to be sure fuel flow, cooling, EGTs, AFRs, etc. are all good.

Will be interesting to see how it all pans out.

 

[BillL]

I think Ross has nailed the issues with using the turbo without the waste gate, you might consider one of the turbine housings with integral wastage so you can develop an adjustable one for altitude trimming. Blowing off exhaust is much more efficient than intake air. The power/speed demand curve for marine and aircraft is quite similar so a no waste gate goal may be achievable.

I read through here quickly, but see you are not using an intercooler. I don't know what the inlet manifold temp limit would be to prevent detonation but you definitely need some temperature sensing there to know what it is. Temp is the number one enemy of detonation. As you know apex seals don't like detonation. Not saying it won't work, because the hardware will speak the real truth, but certainly something to consider if there is any room in your packed cowling. Intercooler also reduces the heat load to the other components too. Efficiency wise, the intercooler typically pays big dividends unless the boost at your desired power allows the temps to stay in line. Modern diesels move past that point very quickly, and have not had non-intercooled for years.

I commend you for tackling this project, it is a very interesting one and full of technical challenges (mostly matching not limiting). The rotary engine is perfect for a turbo application due to the high exhaust energy. You also may hit that 1800 deg F turbine inlet temp, but that will come later in the development process.

Lastly, I have a NIB rotor # N3Y2-11-B00, does it match your engine?

Hey, Ross, based on your information what compressor P-ratio (sea level) do you think he should be running at T/O ( and INMAN T) for his desired HP?

I will eagerly follow your project!

 

[rv6ejguy]

There are big differences in the applications here, altitude and the prop unloading in flight plus larger variations in rpm in the aero app.

Pre-ignition is the real worry at high IATs, best to keep these below 60C with mogas. Of course cooler is way better for safety and hp.

With a well matched turbo and good induction system design, there would be no reason to have to exceed 40 inches to make 180hp at 4800 rpm so that is a PR of 1.33 at SL.

I agree, this is an interesting project and equally so to watch the progress.

 

[BillL]

There are big differences in the applications here, altitude and the prop unloading in flight plus larger variations in rpm in the aero app. <snip>

Granted: I just meant that the demand does not have lug, or need for rapid transient response like auto/truck/generators/industrial do from a turbo matching standpoint. Mostly steady state loads and limited high load rpm range "closer" to marine. Altitude is certainly another matter! So - he does not have to worry about compressor surge too much, assuming a reasonable initial match.

Dang, you are going to make me dust off my turbo equations! (not a real bad thing)

 

[SHIPCHIEF]

I think the problem is that I let a salesman talk me into a product, instead of figuring it out myself.
My testing seems to confirm your belief that a 60-1 compressor has too much pressure & flow, thereby puts a big load on the turbine end, which increases the exhaust back pressure on the engine.
I have been looking for an exhaust housing with a greater area ratio, but I understand that I might need to rethink the turbo assembly as a whole unit.
I recently bought a turbo locally off craigslist, just for fun. It turned out to be a TO-3 from a SAAB 9000. It has an internal wastegate with a control lever. It was cheap, and in need of rebuild, but had not rubbed the turbine or compressor.
I had a hoot taking it apart, cleaning, inspecting and installing a new cartridge kit. These things are not complicated.
I would be amenable to another turbocharger sized to match my application with an internal wastegate. I don't want to build a complex external wastegate with the associated weight, complexity and under cowl heat.
I usually can read performance charts & graphs with good comprehension, but I have not yet mastered the turbocharger map.

 

[rv6ejguy]

Granted: I just meant that the demand does not have lug, or need for rapid transient response like auto/truck/generators/industrial do from a turbo matching standpoint. Mostly steady state loads and limited high load rpm range "closer" to marine. Altitude is certainly another matter! So - he does not have to worry about compressor surge too much, assuming a reasonable initial match.

Dang, you are going to make me dust off my turbo equations! (not a real bad thing)

Surge is a real issue on aircraft at higher altitudes, especially with oversized compressors as we throttle back to cruise power.

 

[rv6ejguy]

I think the problem is that I let a salesman talk me into a product, instead of figuring it out myself.
My testing seems to confirm your belief that a 60-1 compressor has too much pressure & flow, thereby puts a big load on the turbine end, which increases the exhaust back pressure on the engine.
I have been looking for an exhaust housing with a greater area ratio, but I understand that I might need to rethink the turbo assembly as a whole unit.
I recently bought a turbo locally off craigslist, just for fun. It turned out to be a TO-3 from a SAAB 9000. It has an internal wastegate with a control lever. It was cheap, and in need of rebuild, but had not rubbed the turbine or compressor.
I had a hoot taking it apart, cleaning, inspecting and installing a new cartridge kit. These things are not complicated.
I would be amenable to another turbocharger sized to match my application with an internal wastegate. I don't want to build a complex external wastegate with the associated weight, complexity and under cowl heat.
I usually can read performance charts & graphs with good comprehension, but I have not yet mastered the turbocharger map.

I prefer the integral wastegates on Garretts if you can use a T3 hot side. Unfortunately the stock T3 stuff is too small for the 13B. You could use a Stage 4 or 5 T3 wheel from Turbonetics but on the Wankel, I'd worry about the thin margins in the housings plus the a/r selection is not good for this app. Looks like you might have to go for an external wastegate and it's associated issues.

Be sure to mark re-index the compressor and turbine wheels on a T3 on re-assembly as they are usually balanced as a unit.

 

[SHIPCHIEF]

I've combined your advise plus my recent practical experience to help understand compressor maps.
I can clearly see that the Turbonetics 60-1 compressor is not correct for my application. I'm looking for a little over 200 Hp, with 1.4:1 pressure ratio, maybe 1.6:1 at the high end. My last run yesterday indicated a pressure ratio of about 1.9 at part throttle and 72% rated RPM. Choke City.
The 60-1 compressor map shows 17 lbs/min (airflow of a 13b @ 6600 RPM) and 1.6 Pressure ratio to be very close to the surge line, and very low on the map's left corner, with low efficiency. That salesman....
A TO4B with S-3 compressor trim has a very nice map with the load line I would be using still in the lower left, but in the high efficency area and well clear of the surge line. The TO4B is the turbine I'm using, so an on-center P trim 1.30 exhaust housing and water cooled bearing would be a direct fit. This combination should operate under a low load and at a modest RPM.
The under cowl area I have set aside for an Intercooler would be crowded by a wastegate...I'll have to give this area some thought.

 

[rv6ejguy]

I've combined your advise plus my recent practical experience to help understand compressor maps.
I can clearly see that the Turbonetics 60-1 compressor is not correct for my application. I'm looking for a little over 200 Hp, with 1.4:1 pressure ratio, maybe 1.6:1 at the high end. My last run yesterday indicated a pressure ratio of about 1.9 at part throttle and 72% rated RPM. Choke City.
The 60-1 compressor map shows 17 lbs/min (airflow of a 13b @ 6600 RPM) and 1.6 Pressure ratio to be very close to the surge line, and very low on the map's left corner, with low efficiency. That salesman....
A TO4B with S-3 compressor trim has a very nice map with the load line I would be using still in the lower left, but in the high efficency area and well clear of the surge line. The TO4B is the turbine I'm using, so an on-center P trim 1.30 exhaust housing and water cooled bearing would be a direct fit. This combination should operate under a low load and at a modest RPM.
The under cowl area I have set aside for an Intercooler would be crowded by a wastegate...I'll have to give this area some thought.

Yep I've had salesmen try to sell me something that was totally wrong even after I told them exactly what I wanted. I guess they want to clear something off their shelf...

P turbine with a 1.3 a/r would be a good start on the hot side. The S3 compressor may be hard to find these days. Might look at a TO4E-50compressor. We have used this on several Subaru conversions in the 160-220hp range with great success. Your atmo mass flow would be around 22.5 lbs./min. for 180hp at SL.

 

[SHIPCHIEF]

I ordered the TO4E with 50 trim compressor, water cooled bearing cartridge, F1-68 turbine wheel and On Center 1.30 A/R housing with 4 bolt exhaust flange.
That's a direct bolt in replacement, except the compressor discharge looks like it's smaller in diameter than the 60-1 compressor it's replacing.
Hopefully it will be here in a few days so I can install it next time I get a few days off.
I reviewed some engine monitor video I took (iPhone) while running just less than take off power; I think the compressor was on the verge of surging, the manifold pressure was varying quite a bit. Looking at the boost pressure vs the atmospheric pressure (pressure ratio), and the flow rate of the engine, I compared it to the 60-1 compressor map, and it is very close to the surge line. This is very low on the map, and mild, but could get more severe as the power increases.
When I added the Blow Off Valve, the manifold pressure smoothed out. The BOV was too small to limit boost pressure from that big fan, but it did move the operating condition away from the surge line.
I won't be flying with the 60-1.

 

[rv6ejguy]

Will be interesting to see how this combination works out.

 

[SHIPCHIEF]

I've got a question about altitude performance and the compressor map:
How do you read the map for higher altitudes?
My fuel injection control is limited to 50" Hg manifold pressure, I used that for the problem:
Sea level atmospheric pressure is 29.92" Hg, and 10,000 ft is about 20" Hg, so roughly 50/30=1.66, the pressure ratio at sea level on a cold high pressure day. Climb to 10,000 ft, and 50/20=2.5 pressure ratio. Plot that on the (TO4E 50 trim) compressor map at 22 lb/min air flow, and the data point is deep in the surge area. It crosses the surge line about 8000 ft. Does this seem likely?
I thought turbo power just fades away above some defined altitude, in my case the altitude where I can fully open the throttle without exceeding the injection control limits, induction air temp limits or damage the engine. I didn't think there might be an altitude above which I can't fly because the turbo will begine surging ?
Is there a density constant that moves the data point on the compressor map?

 

[rv6ejguy]

I've got a question about altitude performance and the compressor map:
How do you read the map for higher altitudes?
My fuel injection control is limited to 50" Hg manifold pressure, I used that for the problem:
Sea level atmospheric pressure is 29.92" Hg, and 10,000 ft is about 20" Hg, so roughly 50/30=1.66, the pressure ratio at sea level on a cold high pressure day. Climb to 10,000 ft, and 50/20=2.5 pressure ratio. Plot that on the (TO4E 50 trim) compressor map at 22 lb/min air flow, and the data point is deep in the surge area. It crosses the surge line about 8000 ft. Does this seem likely?
I know that as the plane flies higher the air density drops off, the turbo must spin faster for the compressor to pull in thinner air and also the turbine exhausts against a lower pressure. So the data point must move to the right on the map? How much and how to calculate it?
I observed that the air density @ 10,000 ft is about .66 of the density at sea level, so I devided the 22 lbs/min sea level air flow rate by .66 which equals 33 lbs/min. plotting this against the pressure ratio 2.5 moves the data point back across the surge line into a nice efficient area on the map. The turbo RPM has risen from about 70,000 RPM at sea level, to about 106,000 RPM at 10,000 ft to maintain 50" manifold pressure.
Is this a legitimate calculation?

You are thinking right here. You need to convert pressure ratio to density ratio above SL to calculate compressor inlet flow. This is a function of pressure ratio and CDT (compressor discharge temperature). There are long calculations or you can use a quick chart to cross PR vs. DR at a specific compressor efficiency. The lower the CE, the higher the CDT and lower the density. Might find something on the web. I've got some dusty old books I use.

If we use a PR of 2.5 and 70% CE, DR is about 1.75. 1.75 x your SL mass flow gives you the approximate compressor inlet flow at altitude. In this case, we'll say 38.5 roughly. So, as you climb at the same MAP, flow moves right and upwards on the compressor map. This is a reason we don't like to use compressors with narrow islands on aircraft.

If you throttle back and reduce boost as well, you can head left on the map and encounter surge. This becomes quite critical in practice above 15-20,000 feet. The -50 trim TO4E wheel has pretty wide islands, good peak efficiency and high PR capability.

 

[SHIPCHIEF]

OK, Thanks.
I chickened out on my post and removed some of my thoughts...after you copied it. Good thing you got there first.

 

[skylor]

Efficiency wise, the intercooler typically pays big dividends unless the boost at your desired power allows the temps to stay in line.

My understanding is that most general aviation intercoolers (for air cooled engines, anyway), due to size, weight, and cooling airflow limitations typically do not result in much overall efficiency improvements because the IAT drop is not enough to offset the pressure loss across the inter cooler. HOWEVER, the IAT drop that they do achieve does yield significant improvement of detonation margin which is why they are used (again, especially on air cooled engines).

Perhaps intercooler efficiency can be better on a liquid cooled engine installation because there should theoretically be more cooling airflow budget to dedicate to the intercooler due to the use of more efficient radiators for the engine cooling side of things.

Skylor

 

[rv6ejguy]

My understanding is that most general aviation intercoolers (for air cooled engines, anyway), due to size, weight, and cooling airflow limitations typically do not result in much overall efficiency improvements because the IAT drop is not enough to offset the pressure loss across the inter cooler. HOWEVER, the IAT drop that they do achieve does yield significant improvement of detonation margin which is why they are used (again, especially on air cooled engines).

Perhaps intercooler efficiency can be better on a liquid cooled engine installation because there should theoretically be more cooling airflow budget to dedicate to the intercooler due to the use of more efficient radiators for the engine cooling side of things.

Skylor

Many factory certified turbo installations are pretty poor and this often extends to their intercooler setups as well. Some of the aftermarket companies offer much better STC'd intercooler/turbo setups which improve high altitude performance measurably, especially in climb where IATs are highest. Tornado Alley did some nice work on the Cirrus and others.

I see CDTs of over 110C on a hot day in the climb which would be very scary without an intercooler. With my new setup IATs are running 10-20C over ambient now. Total intercooler weight is about 6 lbs. A fair trade in my view since hp is upped by almost 15% at the same MAP. It is easier thermally on everything. At the low hp and mass flow levels most aircraft installations run at, pressure drop across the core is usually under 1 psi even though we run small cores by automotive standards. That 1 psi might increase CDTs a few degrees, the intercooler drops it 50-60C.

Intercoolers come with a drag penalty of course- nothing is free, but getting up high where air density and drag are much lower offsets this easily and more.

 

[SHIPCHIEF]

I'm wishing I had given this thread a different name.
I have installed the Turbonetics TO-4E with 50 trim compressor and 1.30 A/R exhaust housing. The compressor is much smaller than the 60-1 unit removed, so I had to use a 2"-2.5" adapter hose to connect the turbo compressor discharge to the air pipe. The new style exhaust housing is dimensionally 'similar'. The 4 stud holes for the exhaust flange is just slightly wider apart, requiring some hand fitting, and the housing flange location places the exhaust down pipe slightly forward, so I made a new pipe support bracket.
Last evening I ran the engine twice, briefly, before dark.
The O2 sensor, and engine behavior, indicate a lean condition. Although it ran very well with the mixture control @ full rich, at low RPM & load. This is easily re-programmed during the next session.
The new turbo, gaskets etc. all smoke, as usual, burning off finger prints and surface oils etc. the common effect of new parts.
SO I'm up and running again, but I'm back @ work, it will be a week before I can return to the RV-8.

 

[rv6ejguy]

I'm wishing I had given this thread a different name.
I have installed the Turbonetics TO-4E with 50 trim compressor and 1.30 A/R exhaust housing. The compressor is much smaller than the 60-1 unit removed, so I had to use a 2"-2.5" adapter hose to connect the turbo compressor discharge to the air pipe. The new style exhaust housing is dimensionally 'similar'. The 4 stud holes for the exhaust flange is just slightly wider apart, requiring some hand fitting, and the housing flange location places the exhaust down pipe slightly forward, so I made a new pipe support bracket.
Last evening I ran the engine twice, briefly, before dark.
The O2 sensor, and engine behavior, indicate a lean condition. Although it ran very well with the mixture control @ full rich, at low RPM & load. This is easily re-programmed during the next session.
The new turbo, gaskets etc. all smoke, as usual, burning off finger prints and surface oils etc. the common effect of new parts.
SO I'm up and running again, but I'm back @ work, it will be a week before I can return to the RV-8.

Cool. Thanks for the update.

 

[SHIPCHIEF]

I posted some of this on the flyrotary forum today, so if you read it there...
Today I got the engine cowl on and tethered the plane to my Pickup. I ran it about a half an hour. I reprogramed the mixture as it warmed up. Installing the new turbo caused the engine to run very lean compared to the old one.

When it got above 150F I started adding power and taking pictures of the Engine Monitor to get some data points.

The TO-4E 1.30 A/R turbine housing is not too loose. Today's highest recorded engine RPM was 4883, 35.0 "Hg manifold, and about 44"Hg turbo boost pressure before the throttle. So this is a huge improvement over the previous turbo, a 60-1 P-trim TO-4 with .81 A/R exhaust housing. Before, I was running about 55"Hg from the turbo, thru part open throttle to get about 38"Hg manifold pressure and 4600 RPM. About 17"Hg pressure drop across the partially open throttle. now with lower turbo boost I get only 9"Hg pressure drop across the partially open throttle, and the engine RPM is higher with a lower manifold pressure. The greater A/R exhaust housing must be reducing the exhaust back pressure, which also reduced the exhaust dilution to the intake charge.

I curtailed the experiment when I noticed the oil temp @ 204F. Water temp was about 185F. When I reduced power the oil temp started back down. I think it will be flyable, with excellent water temp control, and pretty good oil temp control at anything other than high static power.

This prop is a CATTO 2 blade, a left turning prop identical in diameter, pitch and area to that intended for a 180 HP Lycoming O-360. It should turn about 2200 RPM static to be equal to an O-360, which would be about 150 HP. I got 2229 Propeller RPM so that puts me in good company, and I still have more untapped boost pressure.

The 50 trim compressor discharge is smaller than that on the 60-1, so I use a 2" to 2.5" adapter hose to fit it to the existing charge air pipe. I know I should install an intercooler. I have a Stock Mazda intercooler, the only thing I've found in my on-line search which might fit my airframe, it has a 1.75" inlet pipe and a 2" outlet.

The turbo's 2" OD outlet is thick wall cast aluminum, so I'm betting the ID is pretty similar to the ID of the 1.75" OD inlet tube to the intercooler. I'm collecting the parts...

Meanwhile, I plan to give the auto-tune program on Tracy Crook's EM-3 Engine Monitor a try on the next tethered run.

PS: Ron F, thanks for the help with turbo selection and chart reading.

 

[rv6ejguy]

Much more encouraging!