Real world rocket numbers?

[FloridaMan]

I’ve been feeling out the performance of my Rocket and it seems to be a bit off from what I’d expect and I need to determine what portion of the airplane and what portion of my expectations need to change. I’m in Florida and it’s hot as hell right now. My empty weight is 2203. Today I did some mid afternoon trials and with full fuel (105 gallons) I was making around 1000fpm in the full power climb and I calculated my TAS at 15,500 at 198kts (31”, 2400RPM, 21gph, IAS 150kts). Book shows 203kts at 12,000 and 218kts at 18,000 at those power settings. Outside air temp at 15,500 was 7C and altimeter was 30.05. 

I felt like it was misfiring intermittently in the climb and performed an inflight mag check, which didn’t cause any alarm, but I then relaxed my climb speed to 120kias and 2500/35”. Per the Rocket manual, I also performed the peak TIT check at 10,000ft and was only able to reach 1575 on the gauge, so I ran a conservative 1450-1475 on TIT.  I do not yet have a modern engine monitor (ordering an EDM900). The single CHT and oil temp looked fine. 

On the return leg of my flight I did 14,500 and the same power settings. I calculated tas at 201kts. I would’ve been 18 gallons lighter on fuel. I was seeing closer to book numbers in the climb. At around 13,000, I heard a ticking sound. I wasn’t sure if it was something in the plane rattling or if it could’ve been detonation so I backed power off and lowered the nose again. The one CHT looked fine, but I wasn’t going to take any chances without better engine info. 

I don’t have detailed performance charts for the rocket, so I eyeballed those from the POH for the m20k. Unless I’m reading the charts incorrectly, the POH shows increase cruise speed at higher temps for the same power settings. This sortof surprised me coming from the NA side of things and knowing what pigs turbocharged cars can be in the heat. 

[gsxrpilot]

I'm glad you're getting a proper engine monitor. It's hard to tell what's happening, and better to stay safe in the middle of the envelop until that EDM900 is installed.

[carusoam]

All that raw power in one hand, bounded by two data points on the other hand....

Gotta get more data points!

Antares, your purchase of JPI900 has been approved.... you still get to keep your CB member card...  

Best regards,

-a-

[kortopates]

On 6/17/2018 at 1:51 AM, Antares said:

I don’t have detailed performance charts for the rocket, so I eyeballed those from the POH for the m20k. Unless I’m reading the charts incorrectly, the POH shows increase cruise speed at higher temps for the same power settings. This sortof surprised me coming from the NA side of things and knowing what pigs turbocharged cars can be in the heat. 

Yes, we get another 2 kts TAS for every 1000' of density altitude. (I assume you were looking at Speed vs Alt/temp vs Power) IAS is staying the same but TAS is going up with altitude and that's why its silly for us to fly low.

[M016576]

53 minutes ago, kortopates said:

Yes, we get another 2 kts TAS for every 1000' of density altitude. (I assume you were looking at Speed vs Alt/temp vs Power) IAS is staying the same but TAS is going up with altitude and that's why its silly for us to fly low.

And that’s the key of a turbocharged airplane.... the increase in density altitude means thinner air.  The turbocharger “re-compresses” it... so you get the effect of less parasitic drag, without paying the price of loss of manifold pressure (when you think of it like a NA airplane).

And that is where a turbo charged aircraft really shines... a high density altitude day.

with a turbo-charged car- you still deal with the road (drag), and you don’t really set the TIT and MP in exactly the same way.... depending on how the turbocharger is built/integrated you can see degradation in performance in higher temps.... partly because you’re kind of NA until the turbo “kicks in” in some builds (ie turbo lag).

 

Edited June 19, 2018 by M016576

[jlunseth]

You might have the mag pressure system checked.  I don’t know the Rocket mag system, actually I don’t even know for sure if you have pressurized mags, but it must be if the aircraft is to fly in the flight levels.  Leaks develop in the tubing, sometimes the tubing wears through or something else fails like the seals.  The purpose of the pressurized mags is that air acts as an insulator to prevent tracking on the mag cap.  Lose the pressure lose the insulator, and the mag begins to skip or crossfire because the spark is going, or at least trying to go, to another plug by running across the cap.  High altitude miss can be severe, you may be experiencing the beginnings of it at 13 k.

[N201MKTurbo]

I’m no Rocket expert. I only have about 30 hours in Rockets with one long cross country and six short cross country flights.

Your numbers look very close to what I was seeing. You didn’t mention what your TIT and FF was in climb. We had to adjust the max FF a bit higher than book to keep the TIT in check at full power. All the roughness we had was mixture related.

[Parker_Woodruff]

Get Tempest Fine Wires if you don't have them installed yet.

They're exceptional at high altitude.  Both in getting good spark and controlling temps (my EGT/TIT were lower after installing them on my 252/Encore).

[13scrappy]

Your numbers are similar to what I see in my rocket but I dont remember ever having less speed (TAS) up higher.  I can't get the speed up to the book numbers.  I have the engine monitor and climb at 35/25 and 120indicated or better to keep temps down most of the time, but I am usually starting out at over 100 degrees on the runway in AZ.  I usually run at 31/22 and find I am 10 short of book speed and about a gallon higher on my ff from book.  A friend has an STC for lead in the tail near the battery and he gets most of the speed back but loses a passenger or quite a bit of gas.  The plane is super nose heavy so anytime I have less weight up front or more in the baggage area I see higher speeds.

[carusoam]

Welcome aboard, scrappy!

Really, Congrats on your first post!

Can I count you as another happy Rocket owner?

We have a few around here...

That and flock of 252s and 262s...

Best regards,

-a-

[aviatoreb]

10 hours ago, 13scrappy said:

Your numbers are similar to what I see in my rocket but I dont remember ever having less speed (TAS) up higher.  I can't get the speed up to the book numbers.  I have the engine monitor and climb at 35/25 and 120indicated or better to keep temps down most of the time, but I am usually starting out at over 100 degrees on the runway in AZ.  I usually run at 31/22 and find I am 10 short of book speed and about a gallon higher on my ff from book.  A friend has an STC for lead in the tail near the battery and he gets most of the speed back but loses a passenger or quite a bit of gas.  The plane is super nose heavy so anytime I have less weight up front or more in the baggage area I see higher speeds.

Did you type that right?

31/22 is not a book number.  31/23 (72%) is or 30/22 (65%) is.  I worry that you may be running too low rpm for that mp pressure setting - or maybe it was a typo.

Most rockets are nose heavy - except mine - when I changed props to a MT it took 35lbs off the nose which completely reworked the W&B to a much more balanced airplane.

[13scrappy]

It was late and a typo.  30/22 at 65% which at 12000 should be 195kn and 19gallons.    I need to get to 16-17000 before I start to see those numbers.  If I don't move into a twin I will have to look at the lighter prop.  I don't like the idea of putting lead in back and having a permanent reduction in useful weight. 

[13scrappy]

and thanks Curosoam.  

 

When I bought it 6 years ago I read everything on here and other sites that I could.  The site really helped out on a nose wheel issue I had a year ago.  The maintenance shop overturned the nose wheel and broke something with the tug at my local shop.  After the repair the plane acted like a drift car on landing.  I brought a post from the site to the mechanic and he took the advice and properly fixed the setup on the nose so it acted normal again.  There is a wealth of knowledge here.  

It has been a wonderful plane to own.  After the purchase, I upgraded it to all glass, the non-garmin less expensive route, and never have regretted the choice.  I love turning 7 hour drives into 55 minute fights here in the mountainous southwest.  It has been a time machine and the family loves it.  I have a smile on my face all day when I hear Center call out to the bonanzas and 310s that they need to watch for the Mooney overtaking them.

[exM20K]

To the OP:  Congrats on your new ride.  You won't regret having a turbo.

Book speeds are, in my experience with an M20K and now an M20TN, optimistic.  Both my planes had/have TKS, the book speeds in the TN are calculated with the step removed, etc, etc.  I flight plan 5% under book speed and slightly less fuel flow.

Some things to consider:

1. I'll second the recommendation to get a modern engine monitor - and especially one that logs data.
2. Check all your gauges: Is the fuel flow reading correctly?  Mine on the G1000 wasn't (dirty connection read a few GPH low).  The TIT sounds low.
3. While there are no live APS classes now, perhaps the online course is still offered.  It is very worthwhile in understanding what's happening within your six co-joined power plants.
4. I don't know if the TSIO520 in the Rocket will run LOP.  If it will, that is a great SOP.  You can much more easily diagnose ignition and fuel distribution issues LOP, the engine will run cooler, life will be better.
5. LOP, you set power by fuel flow, not by MP/RPM/Fuel flow.  The charts that come with the Acclaim are silly in this respect.   Get your engine operation manual from TCM (I have a soft copy I can share), and fly fuel flow.
6. Ignition issues:
   1. 15,000 is pretty low to see arcing/crossfire in the mags
   2. +1 on the fine-wire plugs.  They are standard in TSIO550 Platinum engines now
   3. LOP mag check will tell you very quickly if you've got a harness problem, bad plug, etc.
7. I would defer spending a lot of time diagnosing this stuff (except maybe checking fuel totalizer K-factor and TIT reading) until you have a good monitor and logged data.

Enjoy your new plane!

-dan

[FloridaMan]

I’ve put about 50 hours on the plane in the past six weeks. I’m still running conservatively rich and cool on the TIT until I get the engine monitor installed. I noticed that I cannot get book fuel flow in the climb. At takeoff with full power I’m showing 37gph, but when climbing in the flight levels at 2500/35” and the mixture full rich I’m only seeing 24gph at 1550 TIT with book showing 26-27gph and max 1500 TIT. At that point I stopped my climb and went to 55% running on the richer side at 14.5-15gph and 2200/26” and maybe 185-190KTAS at FL220. I noted that I had to be very gradual in tuning that setting as the RPM would fall off quickly; I’m guessing it was boost related. In the teens I attempted full mp to see if it affected fuel flow and noted around 27-28gph and a max of 37”. I paid for an expensive PPI at a reputable service center, but I am skeptical that they flew the plane because the 696 did not show flights between delivery and when I picked it up. 

My IA has recommended performing SID97-3 for fuel flow calibration and I know the cowl flaps are badly out of adjustment (hang about 4” when closed) and are likely creating some drag along with a lot of extra antennas. 

[aviatoreb]

54 minutes ago, Antares said:

I’ve put about 50 hours on the plane in the past six weeks. I’m still running conservatively rich and cool on the TIT until I get the engine monitor installed. I noticed that I cannot get book fuel flow in the climb. At takeoff with full power I’m showing 37gph, but when climbing in the flight levels at 2500/35” and the mixture full rich I’m only seeing 24gph at 1550 TIT with book showing 26-27gph and max 1500 TIT. At that point I stopped my climb and went to 55% running on the richer side at 14.5-15gph and 2200/26” and maybe 185-190KTAS at FL220. I noted that I had to be very gradual in tuning that setting as the RPM would fall off quickly; I’m guessing it was boost related. In the teens I attempted full mp to see if it affected fuel flow and noted around 27-28gph and a max of 37”. I paid for an expensive PPI at a reputable service center, but I am skeptical that they flew the plane because the 696 did not show flights between delivery and when I picked it up. 

My IA has recommended performing SID97-3 for fuel flow calibration and I know the cowl flaps are badly out of adjustment (hang about 4” when closed) and are likely creating some drag along with a lot of extra antennas. 

There is something funny with your fuel flow numbers.  My max is 31.7gph at max take off and its right at 27gph at 35-25 cruise climb.  So its odd your max fuel flow is so high - 37 but too low at 35-23.  But the thing that makes me most scratch my head is that you say you got 27-28gph in your mid altitude test at 37'' - was that at full rpm?  2650?   I wonder if something is either mistuned or even out of spec with your fuel servos or something?

[exM20K]

58 minutes ago, Antares said:

I’ve put about 50 hours on the plane in the past six weeks. I’m still running conservatively rich and cool on the TIT until I get the engine monitor installed. I noticed that I cannot get book fuel flow in the climb. At takeoff with full power I’m showing 37gph, but when climbing in the flight levels at 2500/35” and the mixture full rich I’m only seeing 24gph at 1550 TIT with book showing 26-27gph and max 1500 TIT. At that point I stopped my climb and went to 55% running on the richer side at 14.5-15gph and 2200/26” and maybe 185-190KTAS at FL220. I noted that I had to be very gradual in tuning that setting as the RPM would fall off quickly; I’m guessing it was boost related. In the teens I attempted full mp to see if it affected fuel flow and noted around 27-28gph and a max of 37”. I paid for an expensive PPI at a reputable service center, but I am skeptical that they flew the plane because the 696 did not show flights between delivery and when I picked it up. 

My IA has recommended performing SID97-3 for fuel flow calibration and I know the cowl flaps are badly out of adjustment (hang about 4” when closed) and are likely creating some drag along with a lot of extra antennas. 

That fuel flow (24GPH) doesn't sound right - way too low.  Odd that you're lapsing fuel flow with altitude.

 

Many 231's are run with the cowl flaps set to trail open a finger's width when set for close.  Big help in cooling and not a meaningful speed penalty.

[FloridaMan]

I’m thinking from the automotive side here, but could there be a leak in an air line to the fuel pressure regulator? That would have a more pronounced effect as altitude increased as more air would be relieved through such a leak when the outside pressure is lower. 

[FloridaMan]

Spoke with my IA. He mentioned there’s an altitude compensator that is likely out of adjustment. 

[Guest]

Clean the fuel nozzles, leak check both the exhaust and induction systems then set the engine up per SID97-3G the engine manual and the STC if it has different values.

Clarence

[kortopates]

On 7/4/2018 at 2:20 PM, Antares said:

At takeoff with full power I’m showing 37gph,

The TCM calls for max of 31.7 GPH, but the Rocket Engineering STC raises it to 33 GPH despite de-rating the engine to 305HP with a max 2650 RPM.

So 37 GPH is about 4 GPH high, which should translate to plenty of fuel in cruise.

On 7/5/2018 at 5:27 AM, Antares said:

Spoke with my IA. He mentioned there’s an altitude compensator that is likely out of adjustment. 

That would be a normal aspirated engine that has altitude compensating fuel pumps, which include some the IO-360's and most of the IO-550. But the turbos do have aneroid in them but its referenced to upper deck pressure, not ambient, and its adjustment is what regulates max fuel flow. So getting the desired FF at max MAP would suggest its working fine. But ....

 

On 7/4/2018 at 2:20 PM, Antares said:

In the teens I attempted full mp to see if it affected fuel flow and noted around 27-28gph and a max of 37”

FF should match the same takeoff FF you reported at takeoff with 38" and you should be able to maintain that 37 GPH and 38" all the way to the engines critical altitude. Since you report FF has dropped off by nearly 10 GPH in the upper teens perhaps you have a UDP pressure leak somewhere between the upper deck and the fuel pump which could include the aneroid on the fuel pump and the line to pump. I am betting the pump aneroid metered fuel flow adjustment on the ground is set to compensate for any leakage now but the leak would grow with altitude causing resulting in FF dropping if the pump senses less than actual upper deck pressure - assuming a leak is responsible rather than the servo. Let us know what you and your IA find. 

Edited July 6, 2018 by kortopates

[FloridaMan]

I thought it odd for him to have mentioned an altitude compensator in a turbocharged engine. Although turbocharged automotive engines have external barometric pressure sensors. I assumed those were for measuring air density with airflow. 

[Stephen]

@FloridaMan, just curious how this resolved?

[FloridaMan]

On 3/14/2019 at 1:23 PM, Stephen said:

@FloridaMan, just curious how this resolved?

I'm still flushing data out. I think I've picked up a few knots since I bought the airplane. The old sparkplug electrodes looked like footballs. The ailerons were about 1 inch up in trail during flight, timing was 2-3 degrees behind where it should've been. We removed some weight from the radio stack and added 19 lbs to the back of the empennage and removed some high drag (ADF/LORAN) antennas. 

I'm still flushing out data with the engine monitor. Since replacing the spark plugs, I get 1-2gph better economy with the exact same TIT temperature. I believe the reason for this is that the new plugs give the same effect as more timing advance and helps to ensure the fuel has a more complete burn before the exhaust valve opens (If you ever have a magneto fail or a plug foul, you'll notice the EGTs go sky high on the cylinders that are only running on one spark plug). If I had to do it again, I would've spent the extra money on fine wires (the massive electrode plugs were fine on my M20F). The reasons is that the new plugs seem to be more prone to fouling than the old worn out ones and occasionally the engine just purrs like it's a turboprop, but sometimes a plug will foul in flight and I have to clear it out, but even afterwards it just doesn't feel quite as smooth. This might be in my head, just as you hear your engine misfire and run rough when crossing over hostile terrain or open water. 

I can say without reservation that she cruises at over 220kts TAS at FL240 when it's warm outside and 2400RPM/32" and 20-21gph. I think that I still have a few knots that I can pick up through changing antennas and rigging. I've only put a few hours on the plane since installing the EDM-900. I need to take some long trips and really flush out what I can achieve with economy cruise settings, max cruise and what my normal cruise should be. If I can drop 20% in fuel burn for a 20% reduction in speed, I don't gain anything, but if I can do it for a 5% loss in speed, then it would be worthwhile for saving fuel stops.