Rocket Owners -- Operating Methods

[Openwheeler3]

For those Rocket owners on the forum, I'm curious as to what power settings and other operational methods you prefer to use during flights.  For example, what MP & RPM combination?  LOP or ROP?  Does your engine run well LOP?  What TIT do you run at?

Caveat:  I'm not looking to start a huge debate, just looking for input from fellow Rocket owners.  

Thanks!

-Derek

[carusoam]

Derek,

The coolest threads on Mooney engine operations come from the guys running rockets.  They have outlined techniques and issues for years.

You may even find discussion of hardware like inter-coolers and pressure controllers and a recent turbo failure.

let me know if you need help finding the threads.

Best regards,

-a-

[aviatoreb]

 

For those Rocket owners on the forum, I'm curious as to what power settings and other operational methods you prefer to use during flights.  For example, what MP & RPM combination?  LOP or ROP?  Does your engine run well LOP?  What TIT do you run at?

Caveat:  I'm not looking to start a huge debate, just looking for input from fellow Rocket owners.  

Thanks!

-Derek

Hi Derek.

I'll go first.

I have found the rocket can run pretty well lop, but not as well as some engines I have heard about from reading.

I found by swapping injectors around I was able to get an 0.3gph spread - without needing to buy gami's and they say at least 0.5 is needed.  So do the gami sweep, and see what is your spread and also note which injectors are leanest and which are richest and try swapping them.

Also, you need the rest of the system to be good - strong mags, and induction free from pin holes.  You want that anyway but it becomes more apparent if you are trying to run lop.

Anyway, tending to all that - yes my engine runs fine lop.  Do you know about the redbox concept?   I follow it.   Except I find it not prudent to run high power lop because I find the TIT gets pretty hot at otherwise suitable EGT/CHT/MAP/rpm settings that make for high power on the lop side.  I just don't want to be running around with tit near max 1650 for a standard cruise setting - even though I read it is not such a bad thing.  I am dubious.  So I self limit to 1590/1600 on the tit on the lop side.  That forces me to be ~60-65% max.  And often maybe 50-55% is what I will do LOP, and at those lower settings it is less sensitive running LOP since there is not much you can do bad to the engine - the redbox disappears.  

Also, I find I do get a bit rough if I try high rpm lop.  So I always do low rpm lop, 2200, and maybe 25'' through 30'' depending on how hard I want to go.   2200 just seems to work better - they say LOP is a slower burn so I figure it is because a slower rpm allows for more time for each burn event to sweep completely through a cylinder - I don't know if this is the real reason but it is what I tell myself.  I know 26-2200 is 18gph but LOP your power is proportional to fuel gph.  I am trying to remember what gph results from 26-2200 and I think it is around 13-13.5.   (Remember percent power LOP is measured by multiplying your gph by 13.7 hp/gph - for our 7.5:1 compression tsio520nb engines).  So 13.5gph * 13.7 hp/gph =184hp -> 60.6% power of the 305 max.  So you expect to be a little slower than the same 2200-26'' setting rop at 65%=198hp - but you would be burning 13.5 gph vs 18gph - a pretty big savings.  But you can recover the lost power now by pushing in the MP. The trick is to try and increase MP until you can push 14.4gph through the engine, while on the LOP side.  LOP the name of the game is to push as much fuel through the engine as you can within parameters.  BUT, if I do not touch the red nob while pushing in the black nob from that 2200-26'' 13.5gph setting, then the tit may increase.  This is where I wish I did not have my 1600 self imposed limit.  So now maybe I have 1610 or 1620 increasing mp to (I forgot what specifically because now I am just watching temps) to maybe 28'' and that 14.4gph.  But then to decrease the tit, and back out the red nob, great, but then so does the gph drop.  SO then I push in the black nob again, and maybe I am up to 29'' and the tit creeps up again.  SO I pull the red nob.  Fiddling like this, I would be at say (from memory - so it might be off a bit) that 14.4 gph, and 2200-30'' and <=1600tit.  Great.  But now in this process of backing out the red nob as I was progressively leaning and increasing MP, I was progressively going deeper lop.  So it is harder and harder to keep it smooth the deeper you go.  This is why this is about the max setting I will go as it is about as far as I can go and stay smooth.  I cannot  find a MP/RPM/lean setting all the way to 75%=16.7gph and LOP and TIT<1600 and smooth.  Can't meet all of those constraints at the same time.  I do believe there are some that do not worry about Tit<1600 and that is fine.

Of course once you have computed the gph for a given power setting, say 65% (vs what I see many people reporting the power of their lop setting by referring to the rpm/mp setting table in their poh designed for rop which is not correct - or even reference to your computed values in say your jpi computer, which usually is not correct either), then 65% power is 65% power and you should be making the same speed at 65% =198hp pushing the prop pulling the airplane through the air whether lop or rop.

Mostly I only bother with this in longer flights of at least an hour or so.   It does really significantly extend range.

[Openwheeler3]

Erik,

Thank you for your insight.  I have spent many hours reading on LOP and understand the theory and benefit (perhaps I should have alluded to that fact in my original post).  I recently began LOP operations in my Rocket after having GAMIs installed; it would not run LOP before.  The #2 cylinder is still too lean even after GAMI sent a richer injector, so I'm thinking I may have a small leak somewhere.  The lean #2 still causes some roughness LOP because it is at 50 LOP when the rest are at 20-30.  And my 26-2200 is right around 11.8-12.0 between 20-30 LOP and the TIT is between 1550 and 1600.  I can run 30-2200 around 14.0 at the same TIT.  Thanks for your discussion on TIT.  Running book fuel flows result in significantly lower TITs and I was wondering if anyone had noticed issues running LOP TITs.

I love the LOP range increase as well.  My wife and I flew home from the Florida Keys last weekend and, after a fuel stop in Ocala, ended up flying a 6 hour leg back to Texas due to high headwinds.  ROP and within weight limits would not have been possible.

Hopefully another owner or two will provide their insight.

[carusoam]

JPI calculations of %power should be straight forward for LOP.  It involves multiplying FF by a given factor.  Using the same technique for ROP would require Air flow to be multiplied by a different factor.  This uses the fuel that is limiting the power.  LOP power is limited by FF.  ROP power is limited by air flow.

airflow and MP are strongly related but not as easily used in the calculation by various engine intake geometries.

having balanced fuel injectors is key to having the same gasoline delivered to each cylinder.

having non-leaking tuned air intakes is the same for air flow delivery to each cylinder.

The Bravo doesn't benefit from such nice curvy intakes that the Rocket has. It can run LOP but at reduced power because of the less than curvy air intakes.

ROP and % power are a bit of a mismatch when the JPI has FF numbers but can't determine how much of the FF is used for cooling.

Best regards,

-a-

[Yooper Rocketman]

I bought the GAMI's and did the GAMI test back in 2001 when I bought my Rocket.  I swapped out injectors at least 4 times, ran more tests after every swap out, talking with either George or one of his staff, and was never able to get the engine to run anywhere near smooth enough to live with it.  I was starting to get concerned I was going to be reducing engine life with all the lean testing and decided the fuel savings were simply not worth it.  In the end, George admitted to me the TSIO520NB was not an engine they had a lot of luck with getting to run LOP.   If I recall, it had something to do with the updraft intake system on this engine.

I DO run our turbo normalized Bonanza (Northwood's Airlifeline) LOP, so have no issue with that procedure.  As Erik eludes to, everything must be working right with the rest of the engine components to allow reasonably smooth LOP operations (notice I said "reasonably" smooth).  We have several guys flying the Bonanza and some don't lean aggressively enough on the ground, and/or go full rich on final and I find after a few flights by those guys I need to have the plugs pulled and cleaned or it runs really rough LOP.

So.....how do I run mine?  I run 2300 RPM, 30 inches manifold, and 19 GPH.  I have flown one 5:45 minute flight (years ago with my "F" model) and decided I will never do that again.  Just too sore and tired after the flight.  I would much prefer to land after 3 and certainly under 4 hours for fuel, walk around, get fresh air and a potty break.  As far as those settings, 1 jug in 1840 hours (on a 1600 TBO engine), and still going, which my IA says is pretty unusual.  He works on a lot of twin engine Cessna's which use the same engine.

On both planes I fly, I never touch the mixture once it's set, including on descent and landing (LOP or ROP).  I have practiced go around's, both actual and in my head, and I verbalize "MIXTURE - THROTTLE" every time before touching anything.  I also do not pull back the manifold pressure or RPM's during climb.  I did that while climbing out of Atlanta after first purchasing the Rocket (was delivering the "F" model to new owner) and had cylinder temps climbing past 400 degrees at the approved 2500 RPM / 35" MP.  I went back to 2650 RPM and 38" MP and the temps all dropped below 400.  Both the climb and descent procedures I describe are pretty much the way Tornado Alley taught me to fly the Bonanza after the new engine and turbo install too.

Hope this helps.

[snowds]

Add me to the list that tried  GAMI LOP.  I ended up having to take it to GAMI to try to get the injector flows right; ultimately, they pulled the GAMI injectors, and used stock injectors for which they had measured the flows.  I ran it LOP for a while, and burned a hole in one of the exhaust elbows.  Maybe it was related to running maximum TIT so much, maybe not, but that combined with the not-quite-smooth running shied me away from LOP in the Rocket.

I cruise at 32 inches/2400 RPM, 75 degrees ROP.  Usually comes out to 21-22 GPH.  I generally do not add an inch of power per 10 degrees warmer than standard; the engine just gets too hot (I am usually in the high teens).  I go into the pattern at 22 inches, max RPM, which gets me to 130 kts abeam the numbers, drop the gear, down to 17 inches, slowing to 90 kts by final, 85 kts over the numbers.  For an ILS, 19 inches and 120 kts going into the FAF, gear down, 17 inches, half flaps, ride down the hill at 105 kts.

[Openwheeler3]

Thanks for the data point. Haven't had much time to fly on the weekends lately, but I'm still working on LOP. It runs ok but I want it to run smoother while LOP. 

[Openwheeler3]

This weekend I had my first opportunity in a while to fly a longer leg.  At 10,000 and 11,000 ft, I ran 33/2300 and 15.8 gph for a true airspeed around 190 knots.  Engine ran smoothly enough but TITs were about 1630, bumping right up against the limit.  At some point, I will try similar settings at higher altitudes and find out if the resulting TIT and if it is within limits.  My concern, as some have already voiced, it the stress on the exhaust system at those TITs.  I continue to wonder if running ROP will result in better longevity for all of the engine components.  I also found that increasing RPM from 2200 to 2300 resulted in an increase in TIT, but the engine ran smoother at 2300 than 2200.