My 13B engine configuration (tentative)

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dwalker

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dwalker, I've never had to exchange an Exhaust insert, is it difficult - I do like Ti. ? Pity about the cost.
George
Unfortunately, I have had to change out inserts, and it either goes super smoothly or is a complete pain! The common reason I have changed out an insert is that someone has an old FC (S4/S5) Normally Aspirated rotor housing and needs to use it on a turbo- FC S4/S5/ or FD S6/S7/S8 or race engine and thus needs to get rid of the exhaust diffuser Mazda cast into the insert. Since destroyed turbo housings used to be very common the inserts were easy to get, just pull the roll pin out, heat the aluminum housing a bit, and tap it right on out, installation the reverse of removal. Nowadays wrecked housings are a bit more rare, and many of them have been recycled, so if you did have to change an insert it might be difficult. I am not sure the rational behind the Ti insert as I would think it not particularly suited to the application, but then I have not really looked into which alloy they are using and for the most part, they are being used in drag race engines that get rebuilt a tick more than often.


It is a pity about the cost of the inconel tubing for the fabrication of a turbo manifold, and I may give in and build one, once I have the plane flying and manifold design tested and feel comfortable there will be no revisions needed. Once I have a jig built for the manifold- and that is my intent- creating a replacement becomes a matter of a few hours quality time in the shop with cutting tools and the TIG, and 321SSSCH40 pipe bends and tubing is common. I even have a buddy in the Denver area that could mass produce them in lots of 30 or 40 at a time if needed.

Cheers!
DW
 

youngwerth

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A bit off topic but I was out at the race track and got to talk to the guy that owns this bit of racing history:


and a little background:


13B naturally aspirated, 330HP with a Lycoming fuel injection system. They were having trouble hot starting it and I was sharing my FI airplane hot starting tips with them. They kept flooding it by running the fuel pump before a hot start. No mixture knob in the cockpit so can't run the fuel pump to cool the lines but I don't think they were having vapor problems. I think they were getting the hot-start routine figured out by the end of the day.

So maybe old analog FI isn't such a bad choice after all!
 

dwalker

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A bit off topic but I was out at the race track and got to talk to the guy that owns this bit of racing history:


and a little background:


13B naturally aspirated, 330HP with a Lycoming fuel injection system. They were having trouble hot starting it and I was sharing my FI airplane hot starting tips with them. They kept flooding it by running the fuel pump before a hot start. No mixture knob in the cockpit so can't run the fuel pump to cool the lines but I don't think they were having vapor problems. I think they were getting the hot-start routine figured out by the end of the day.

So maybe old analog FI isn't such a bad choice after all!
I sort of know Doc Bundy who drove those cars, neat guy.

MFI is a horrible choice compared to EFI.
 

dwalker

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I have located both a Ross and RWS "Tracy Crook" PSRU local to me for sale. I have chosen to pick up the the Ross PSRU as it is the version of the Ross that Tracy used to develop his redrive, and uses the same internal bits, but has a cast "bellhousing". It is a 2.18 ratio unit and was originally installed as the drive for the rear "pusher" engine on a Defiant, has 10 hours of "taxi" time on it and was removed because, as it seems too often happens, the builder passed and the plane was posthumously donated by the family to an air museum that pulled the rotary engines and installed Lycosaurs in thier place.
No kidding, the fellow I am purchasing the unit from is located less than 30 miles from me and among other cool stuff has rotary powered RV6 (flying) and Bearhawk (nearly flying) sitting in his hangar. Super nice guy and lots of cool planes.
 

rv7charlie

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Yellow flag: The ratio is going to significantly limit power (that's why Tracy moved on to the 2.85) unless you're willing to run major boost all the time. Might not be as big a penalty if you're planning another pusher installation (prop dia limitations let the prop turn higher rpm).

Red flag: It's almost certain that the Ross doesn't have an input shaft thrust bearing; the original motivator for Tracy to design his own drive. If it doesn't have a thrust bearing, the drive will destroy the engine's thrust bearing in short order.

Something to check: The early RWS 2.18 drives had 4 pinions; it's likely that the Ross does, too. Tracy's later 2.85s use 6 planet sets. Tracy's 6 pinion 2.85 has run more or less successfully on a P-ported 20B 3rotor on a Lancair ES (I now own the drive and the MTV18 prop from that a/c). Might be worth looking at peak torque issues if you're going to boost the engine and the drive has only 4 planets.

Who built the rotary -6? I passed on the chance to buy one of the very well done copies a couple of years ago, and I kinda regret it now.
 
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Vigilant1

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Sorry, working from memory: Over time, didn't folks also find that the Ross drive
developed an increasing/troublesome amount of gear lash when used with a 13B?
 

dwalker

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Yellow flag: The ratio is going to significantly limit power (that's why Tracy moved on to the 2.85) unless you're willing to run major boost all the time. Might not be as big a penalty if you're planning another pusher installation (prop dia limitations let the prop turn higher rpm).

Red flag: It's almost certain that the Ross doesn't have an input shaft thrust bearing; the original motivator for Tracy to design his own drive. If it doesn't have a thrust bearing, the drive will destroy the engine's thrust bearing in short order.

Something to check: The early RWS 2.18 drives had 4 pinions; it's likely that the Ross does, too. Tracy's later 2.85s use 6 pinion sets. Tracy's 6 pinion 2.85 has run more or less successfully on a P-ported 20B 3rotor on a Lancair ES (I now own the drive and the MTV18 prop from that a/c). Might be worth looking at peak torque issues if you're going to boost the engine and the drive has only 4 pinions.

Who built the rotary -6? I passed on the chance to buy one of the very well done copies a couple of years ago, and I kinda regret it now.

Most of what I have seen/read leads me to believe I will want the 2.18. 2.8 would work fine for a NA Renny but not for a turbo 13B, which is likely the reason for the ratio change. I REALLY would probably best be served with a 2.4, which as of now is only available with the Marcotte. 2.18 at 6000rpm, where I will want to run, gives me a prop speed of 2700rpm-ish, which is about as fast as i could get with a Lycoming. As far as boost needed,


The Ross uses the same Ford gearset as the RWS. I will check into the thrust bearing setup, and modify if needed.

Not sure who built the RV6, it is white with some black primer on it as of now and looks to be a very nice build. Not sure it came to him with the rotary, he may have installed it himself.

I will post more later, gotta run!
 

dwalker

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Sorry, working from memory: Over time, didn't folks also find that the Ross drive
developed an increasing/troublesome amount of gear lash when used with a 13B?
The "early" Ross drives used a 4-gear setup,the later went to 6 gears. The same as Tracy. This is a later unit. If it was an "early" unit I would have passed completely.
 

Lendo

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dwalker, The Later Ross Drives all seemed to have problems, some say lack of quality control.
All of the Ford gear sets had the thrust issues - not easily fixed!
All of the Planetery gear sets have LASH, it's part of the design itself and can't be completely eliminated.
I did hear of a later Ford Truck Planetery, with straight cut gears apparently very strong ( and no Thrust), I made a note of the part number, but finding it is another matter.
George
 

Lendo

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dwalker. My notes say . The new Process 273 4x4 FORD Transfer case behind the Power Stroke Diesel Engine has a Planetery heavier than the C6 with 31 spline input on the Sun Gear and will handle 3x Torque output of the 7.3L Engine. Don't know if it's straight cut gear, or that was in a Ford Ambulance.
Ratio 2.72:1
George
 

Richard Schubert

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Tracy's design philosophy included having some gear lash to help with the torsional vibration. This might have just been rationalization for using the planetary ;)
IIRC he had about 1/2" lash at the prop tip and measured it periodically. This is all from my poor memory so take it with a grain of salt.
 

dwalker

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dwalker. My notes say . The new Process 273 4x4 FORD Transfer case behind the Power Stroke Diesel Engine has a Planetery heavier than the C6 with 31 spline input on the Sun Gear and will handle 3x Torque output of the 7.3L Engine. Don't know if it's straight cut gear, or that was in a Ford Ambulance.
Ratio 2.72:1
George
My understanding, and I'm looking for the source of that understanding, is that the "early" Ross and Tracy drives used a 4 gear planetary and those have issues, some lasted forever, other failed in hours.
That prompted the change to the 6 gear planetary, I believe used in the HD version of the C6 transmission. The ratios were available in a couple of different options, including 2.18, 2.8, and 3.1 I believe.

The gear backlash as a method of dealing with TV is a subject of a lot of debate in not qualified or motivated to weigh in on, but as I understand it Tracy used an aluminum flywheel, rubber damper, and the gear lash to mitigate TV. Again, not qualified to render observations etc. on whether it works or not.
 

athomp58

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Guys, RV7Charlie is correct, to achieve full utilization of the rotary it should spin at around 7500 RPM at takeoff. So, a PSRU ratio of around 3.0 : 1 is optimum. Mistral, when designing from scratch, chose a ratio of 3.2 to 1. The Mistral drive had straight cut gearing. Copy success.

Aubrey
 

athomp58

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I think it would be useful to divide the discussion between a Low Power PSRU, using C6 hd size gearing, and a High Power PSRU, using diesel truck transmission gearing. The truck transmission gear sets are typically 5" to 6" in diameter compared to 3" to 4" for the C6 sets.
 

dwalker

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Guys, RV7Charlie is correct, to achieve full utilization of the rotary it should spin at around 7500 RPM at takeoff. So, a PSRU ratio of around 3.0 : 1 is optimum. Mistral, when designing from scratch, chose a ratio of 3.2 to 1. The Mistral drive had straight cut gearing. Copy success.

Aubrey
Mistral is not an example I want to follow.

Why is you you think with a 2.1 gear I cannot achieve 7000 rpm for takeoff? A lot of assumptions being made there with no focus on reality. Reality is the 180hp@7000rpm Renesis likely DID need the higher gear ratio. I am not using a Renesis. I am using a turbo 13B with semi-P port on the intake side, "high compression" rotors, and peripheral exhaust that will make over 200hp on little to no boost @5000rpm. At where I am going to consider my "max boost" setting of 18psi or about 32in/Hg the engine will make right around 400hp from above 4000RPM to its redline of 7000RPM. There is no scenario I can see where I will need 400hp to turn "enough prop" for a Long EZ. There is no scenario I can see that makes me want to spin the engine to 7000rpm. At 6500RPM I will have a prop speed with the 2.18 ratio unit of 2900rpm, which is going to be the upper limit for the prop diameter the Long will use, and I believe 200rpm HIGHER than the typical Lycosaur.
It is simple math. 7000rpm at 2,8 will give me a max prop speed of 2500rpm, which is less than a Lycoming, slow flight cruise with 1800 prop rpm will be about 4000rpm on the motor. The motor will live a long long time within that envelope. The advantage to a turbo rotary is not just the smoothness and lack of moving parts, it is the fact that I can turn more prop at the same RPM, and very likely not need a ton of boost to do it, of course that remains to be seen.

My friend flew his RV6 with a 2.18 RWS psru on a NA Rotary with low compression 4-port housings this weekend off his 800ft grass strip and said it flew fine. He did say he felt he would like a little more power to get off his grass strip a little earlier, so he may proceed ahead with adding a turbo to it.
 
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dwalker

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I think it would be useful to divide the discussion between a Low Power PSRU, using C6 hd size gearing, and a High Power PSRU, using diesel truck transmission gearing. The truck transmission gear sets are typically 5" to 6" in diameter compared to 3" to 4" for the C6 sets.
The problem you have in this is that Ross definitely used a 4-gear planetary and Tracy *may* have used a 4gear planetary in thier early units. Hi or low power has nothing to do with it, just when it was made or last serviced. When the 4-gear units started breaking the6-gear planetaries were installed in thier place. It absolutely is not helpful for me to discuss in "High" or "low" power terms, as it seems like the 4 and 6 gear planetaries were available in the same ratios. So you can have a 2.18 4-gear early redrive, or a 6-gear late redrive, or a retrofitted early redrive with 6-gear 2.8 redrive.
 

athomp58

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The C6 hd size gearing has been successfully operated at takeoff power levels of 250 to 300 HP by Tracy and others. So, it may be reasonable to set 300 HP as the maximum power for a Low Power design.

The Mistral gear box was designed for 1000 HP maximum. So, I think it would be reasonable to assume that the diesel truck transmission gear sets could operate at 700 HP for takeoff. The P3 gear set in the Allison 1000 transmission (helical) has a ratio of 3.1 to 1. Someone on the ACRE newsletter a few years ago presented a Dodge transmission gear set (straight cut) with a ratio of 3.2 to 1. I'll need to dig a bit to determine if the exact transmission was specified.
 

dwalker

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The C6 hd size gearing has been successfully operated at takeoff power levels of 250 to 300 HP by Tracy and others. So, it may be reasonable to set 300 HP as the maximum power for a Low Power design.

The Mistral gear box was designed for 1000 HP maximum. So, I think it would be reasonable to assume that the diesel truck transmission gear sets could operate at 700 HP for takeoff. The P3 gear set in the Allison 1000 transmission (helical) has a ratio of 3.1 to 1. Someone on the ACRE newsletter a few years ago presented a Dodge transmission gear set (straight cut) with a ratio of 3.2 to 1. I'll need to dig a bit to determine if the exact transmission was specified.
The problem is "designed for" is not the reality. I have to deal in reality, not mythology.

I have no interest in any gearset over 2.4. In my application 2.4 is about perfect, and I still may buy Guy Marcottes PSRU that is rated at 400hp and is available in 2.4 ratio.

I passed on a brand new Neil Unger 3.1 PSRU because I have no need to spin my engine that fast.
 

rv7charlie

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For most of its production life, the RWS drives (both the early 2.18 & later 2.85 ratios) used a flexplate from the car's automatic transmission, combined with a RWS-supplied aluminum plate containing 4 ea 'rubber' damper discs. I've never heard of any reliability issues with the early 4 planetary 2.18 gearsets. If memory serves, he switched to the 6 planet version because it became available. I don't recall if any 2.18s were built with 6 planets, but as far as I know, all the 2.85s use 6 planets, due to the higher engine output allowed by the wider ratio.

Near the end of RWS production, Tracy experimented with using an aluminum racing flywheel (~8 lbs) and eliminating the soft damper components altogether. He then made the new configuration (use limited to lightweight wood props) available for sale; I don't know how many were actually sold before he ended production. I do know that he's still flying the Renesis powered RV4 in that configuration.

Ratios: 3-1 sounds great, but in my opinion it's far too wide a ratio for a/c use. Consider normal Lyc use. Rated rpm is 2700 (both engine and prop). When cruising at 7k-8k feet and 75% power, that requires the engine and prop to be turning the same 2700 rpm. Running >3-1 ratio means that prop rpm would be <2500 at 7500 engine rpm; might be ok in a few airframes, but most have an issue swinging the larger prop needed for efficiency at the lower rpm. Now move to cruise altitude, and you'll be asking the engine to turn 7500 rpm continuously for hours on end. The rotary is a tough engine, but that's a lot of extra wear, and you're starting to get quite a ways away from the range where best BSFC is available (~5200 rpm), or lowest gear/bearing load (6k rpm). I obviously don't know everyone that's running a rotary, but no one I do know is running continuously much beyond ~6000 rpm in cruise. (A Renesis can make ~180 sea level HP @6k rpm; more than adequate for most 2 seat homebuilts). That puts prop rpm under 2000, almost demanding a controllable prop to get some kind of prop efficiency. Given the airframe-driven limits to prop diameter, and the relative difficulty in obtaining an optimized prop from prop carvers that are accustomed to working with Lyc-style rpm ranges, It seems more practical (to me, anyway) to design for Lyc-style prop rpm.

The math changes a bit with EZ style pushers & smaller dia props, but that drives a narrower ratio; not wider.

I could be wrong, but I'm pretty sure that Mistral's reduction ratio is narrower than 3-1.
 
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