Hot starting a M20K Rocket

[Houman]

Hi,

doing a training flight today with about 7 or 8 stops, stuck at my 4th Start and The Rocket Is refusing to Start, engine is really really hot, so taking it easy and letting it cool down, but my instructor that has experience on this engine (Navaho twin) and others, says he never had this much trouble.

any good hot starting technique, do you guys use the low or high boost while starting hot ?

thanks...

[MooneyBob]

When I know I have to do hot start next day I can't even sleep at night. Sometimes it starts sometimes not. Tried all kind of techniques and followed all kind of suggestions. Hit or miss for me. Even with my Tempest Finewire.

[carusoam]

Don't stop?

Get it cooled as much as you can before shutting down? Deep ROP, low power setting

Park into the wind, with the oil door open.

Shut down with 1000 rpm on the tach (nice place to start).

Know where the fuel goes when the mixture is pulled out.

Some Continental engines return fuel back to a tank, when the mixture is pulled. Cycling cool fuel through the tubes is part of helpful process. There still may be a lot of fuel with vapor bubbles in the last end of the injection system. Getting through that will take some patience.

These are ideas that apply to all engines...

What does the procedure say?

Best regards,

-a-

[David Mazer]

Okay.  This is actually an easy problem to solve on the Rocket.  It works for me every time (including today in 95 degree weather).

 

1. Full lean - THIS IS THE SINGLE MOST IMPORTANT STEP FROM A SAFETY PERSPECTIVE

2. Throttle closed.

3. Low boost on for at least 60 sec.  At least.  More is okay.

4. Low boost off

5. Prime for 3 - 5 sec (until about 25 gph on the fuel totalizer)

6. Cold start with a little more throttle than usual and a couple extra turns.

 

Done.

[Houman]

Thanks David, I tried this and it worked, actually my instructor found the procedure on an old pas on Mooneyspace, the POH was worth nothing, I will be donating tomorrow to Mooneyspace.com, it saved my behind not being stuck middle of nowwhere..

Thanks to all !!!

[aviatoreb]

Okay.  This is actually an easy problem to solve on the Rocket.  It works for me every time (including today in 95 degree weather).

 

1. Full lean - THIS IS THE SINGLE MOST IMPORTANT STEP FROM A SAFETY PERSPECTIVE

2. Throttle closed.

3. Low boost on for at least 60 sec.  At least.  More is okay.

4. Low boost off

5. Prime for 3 - 5 sec (until about 25 gph on the fuel totalizer)

6. Cold start with a little more throttle than usual and a couple extra turns.

 

Done.

 

That works!  As David and I have discussed - it is written in http://www.avweb.com/news/pelican/182105-1.html?redirected=1  Pelican's Perch where I learned it.

 

But David - I have a new trick that I do before I bother with the above.  I find I can start a hot soaked engine 99% of the time as follows (and 1% of the time as above).  This takes a bit of technique - the above takes zero technique - just a good procedure.

 

Ok here is the trick - assuming you are hot soaked due to shutting down on a hot day just a couple of minutes ago: I give it 1-2 sec of boost pump.  Then I put the throttle in a position that will result in 1600-1800 rpm if the engine were running (that is a lot more than the 1000rpm setting for a normal start and a lot less than full throttle - somewhere in the middle but a bit less than middle).  Then start cranking the engine and as soon as it is really running but before it turns up to 1600rpm - about as it passing 1000rpm pul the throttle back to the 1000rpm position.  

 

This is my quick and easy hot start procedure.  Wy does it work?  I think because the engine driven fuel pump is giving a bit more juice in the higher rpm setting.  Why pull the throttle back as it is starting?  Because it is not kind to the engine to let it fire from a stop straight to 1600rpm - but obviously not seriously bad as if it were actually a cold engine.  Still better to pull it back before it gets there.  There is only half a sec between pulling it back too soon and waiting too long.

 

Seriously though except for quick and easy - the procedure David says works great too and I used that for years before I discovered the above quicker easier method and I still use it sometimes if quick and easy fails.

 

PS - your ignition system should be in top shape for easy starts (and for other reasons too).  Good strong mags, good leads, good spark plugs, strong starter motor and good batteries.

[David Mazer]

What Erik is describing is the traditional hot (vs flood start - open throttle, mixture off) start.  It will work most of the time but is harder on your starter and if your batteries are marginal and the attempt fails you may not get a second chance to use the method I described.  I haven't found the 60 sec delay to be of any significance as I'm always doing something else anyway so I make it my normal hot start procedure.

[aviatoreb]

What Erik is describing is the traditional hot (vs flood start - open throttle, mixture off) start.  It will work most of the time but is harder on your starter and if your batteries are marginal and the attempt fails you may not get a second chance to use the method I described.  I haven't found the 60 sec delay to be of any significance as I'm always doing something else anyway so I make it my normal hot start procedure.

 

Why is it harder on the starter?

 

(Its kinda funny this conversation between you and me since about a year ago I was very keen on the official hot start method you described and I believe I described it to you - and it works - but meanwhile I got good at this other thing to the point that I cannot remember it failing).

 

Yeah if I were not confident in my batteries I would go straight to the official hot start method.  Then I would replace my batteries at my next stop.

[David Mazer]

Credit where credit is due.  Erik did bring this to my attention some time ago.  It was not my intent to imply that I developed this technique just to spread the knowledge.

 

IMO, it is harder on the starter because it usually requires longer starter operation when I do it.

 

I'm always careful of battery use/drain.  I'm never confident that a battery won't fail unexpectedly.  Everything on a plane seems to fail at the most inopportune moment and in the most expensive way possible.  I suppose I'm just sensitive to it all now.  Whatever I can do to baby it and cause as little damage as possible, I do.

[aviatoreb]

:-)  No worry David - I wasn't meaning to be claiming credit either.  I was just trying to say I have successfully been doing it both ways and I have come to like the method I was suggesting above.

 

The thing I changed from a simple starts hot as if cold from years past is to place the throttle as if I am going to run the engine at 1600-1800rpms (to fast to start a cold engine) which as I said gets more fuel going through the engine driven fuel pump (turning by battery and starter) - then pull back smoothly but quickly just as it is really starting but before it runs past 1000rpms.

 

I hear you on babying battery - but we do have two 35mamp batteries - and with good mags and strong rest of the ignition system, my engine starts even hot soaked recent shut down within just a second or two.

[Jeff_S]

This technique is seemingly not different than the one Mike Busch describes for hot starting the IO-550, with one exception.  Busch's article specifically states that when doing the long prime for cooling, the throttle should be wide open.  And Deakin's article is a bit hard to interpret, in that he describes a process going from an attempted "cold" start technique right into his cooling technique. He does say to put the mixture at ICO, but he doesn't really mention the throttle setting.  Presumably he intends for the throttle to remain in the "cracked" position.

 

So what would be the difference to the engine between leaving the throttle just "cracked" during the cooling prime, or leaving it wide open as Busch suggests?  I'm not really clear on what would be different, or anything, since the mixture is at ICO in both cases.

 

Appreciate any insights from the more engine-knowledgeable folks. Thanks!

[kortopates]

I'd guess all these variations of the TCM Hot Start procedures originated from TCM literature. The TCM hot start is well documented in your specific TCM engine operations manual which you can order from the TCM Power store online. TCM engines are unique in that when you pull the Mixture to ICO, it prevents fuel from flowing past the fuel divider. TCM takes advantage of this of by recommending before you hot start the engine, to first put the mixture at ICO and operate the High Boost for approx. 1/2 minute, as it will replace all the hot fuel in the line up to the flow divider with fresh cool fuel, the hot fuel is sent back to the tank. It doesn't matter where you put the throttle while just running the boost pump in an injected engine, no fuel is running past the fuel divider and the throttle doesn't control the electric boost pump output - only the engine driven pump. Using the low boost pump to recirculate the fuel should work too but not as effectively and probably why its taking twice as long as needed with the high boost pump. Anyway, its a good idea to go back to the original source of these methods since Mooney didn't choose to include them in the POH's since some of the popular internet versions seem to misrepresent some of the details based on some the interpretations you see. But once you have a reliable starting method like Erick and David, you know what works for your engine and that's whats important. 

 

Perhaps one caveat to the last statement in regards to the cold start. I know some pilots prefer to use the high boost to prime their cold engine rather than use the low boost prime circuit when they have one. Using the high Boost is certainly an effective way to get the job done, but two points. Our TCM engines like a lot of prime fuel to get started and the high boost is pumping fuel directly into the cylinders. Some of the cylinders will have open intake valves allowing any excess to drain out into cylinder drain tubes and onto the tarmac (or even onto the engine if any of the lines are in need of maintenance). So just be aware using the high boost can put you at the risk of starting a fire at start up which I believe is a principal reason why our installations have a boost prime circuit that pumps fuel into the induction system instead eliminating the fire risk. So although it works effectively, it has additional fire hazard risks. It happens, but fortunately quite rarely. 

[Houman]

thanks to all, I had a stupid question, if the engine is hot, it is recommanded to open the cowl flaps and cowl oil door, would it also make sense to twist the oil stick cover a bit to open it and let the heat inside of the engine escape from there. Not necessarly remove the oil dip stick, but just open it a bit, would I be in danger of getting hot oil on my hand or face ( since the engine is off, there should'nt be any oil pressure, right ) ? 

 

Just wondering if it is worth it, I would'nt remove the whole stick in fear of getting dirt or dust in the engine, but wondering ?

[carusoam]

I always open the door to the dipstick...

There is moisture to be let out by opening the dip stick.

But...

There are things that can get in there as well.. Rain and dust come to mind...

It won't be forgotten, since you will be checking the oil level prior to start...

If you are storing in doors it will stay dry.

I don't recall discussing this topic before.

It is worthy of a new topic...?

Best regards,

-a-

[David Mazer]

I always open the oil door, remove the dipstick, and replace the cap with a different cap that I have drilled to hold a tube that flows to my dehumidifier.  The dehumidifier returns to the breather tube.

[Houman]

Hi David, I would love to see a picture of that. The mecanic that did my Rocket's pre-buy inspection was telling me that the hangar tempeature is not so good for the engine, since it keeps the humidity, so maybe your solution might be one that could help get rid of it...

[DonMuncy]

I built a one way valve adaptor that fits over the oil filler tube on my 231, that vents moist hot air when I plug my dehumidifier into the vent at the bottom.

[David Mazer]

Attached are the specs for the dehumidifier.  Total cost, maybe $50.

Engine_Dryer_Sport_Avi.pdf

[floridaflyer]

Hi All:

As a newcomer to this great forum, I searched hot start posts applicable to Rocket conversions. I think I've read them all, and I am now more confused than ever. If anyone can summarize their hot start procedure specifically for the Rocket with TSIO520NB with throttle and mixture settings for every step, I would be grateful and so would my starter.

My fuel system has an electric boost pump with HI/LO switches, but apparently no separate primer nozzle(s). Hitting the primer momentarily turns the boost pump to HI, same as the HI switch, with the obvious difference the HI switch stays on until switched OFF whereas primer stops when I release the switch. I understand the main purpose of the LO boost pump is recirculate fuel to cool down the engine-driven fuel pump and get rid of vapor prior to a hot start. LO boost doesn't recirculate fuel through the manifold valve or fuel lines forward of the engine wall. I know this because the fuel flow sensor installed between the fuel metering assembly and the manifold valve reads zero during LO boost and no fuel comes out of the injectors, this regardless of throttle and mixture settings. Maybe because the manifold valve doesn't open at LO boost pressure, or maybe it's the fuel pressure controller mounted on the firewall and referenced to upper deck pressure that cuts off fuel flow at low fuel pressure. All I know is LO boost = no fuel to cylinders. I still set mixture to idle cut off when running LO boost just to be on the safe side.  I don't have a fuel pressure gauge, so I can my observations are based on the totalizer fuel flow and watching fuel come out of the manifold valve fuel lines.

Both the primer and HI boost pump switch deliver fuel to the injectors, with fuel flow indicating 18 GPH after 3-5 seconds.

My current procedure for a hot start (OAT around 90F, high humidity, 15 mins after shutdown):

1. Throttle FULL OPEN, mixture ICO
2. LO Boost on 60 seconds
3. Throttle FULL OPEN, mixture FULL RICH
4. 3-5 seconds primer (watch FF go up to 18 GPH)
5. Throttle one-half inch open, mixture ICO
6. Crank while advancing mixture.
7. Burst of primer as needed to keep engine going.

I think the above is basically a flooded start procedure, it worked great on my Lancair IV with a TSIO550, but with the Rocket more often than not I have to repeat the procedure twice before the engine starts, with much cussing in between.

My engine refuses to start (or even stumble) if mixture is set to FULL RICH in step 5, which is my normal start procedure and works every time when the engine is cold. So much for what may posts are recommending, which is circulate fuel long enough to cool things off, then normal cold start.

Any thoughts are greatly appreciated!

[carusoam]

How hot are the cylinders ( CHTs ) after you land?  Do you follow typical cooling procedures to minimize vapor bubbles forming in the fuel system?  Park facing into the wind with the oil door open?  Do you hear fuel boiling?

Steps 1-2 pushes cool fuel through the system and dumps it back to a fuel tank (rocket specific).  Helpful for hot starts.  Vapor bubbles get sent back to the tank.  Bubbles after the mixture control are still a challenge....

Steps 3-4 primes the engine.  Not very helpful for a hot start.  Has some effect on the vapor bubbles mentioned in steps 1-2...  This one is a surprise to me.  Priming 3-5 seconds is a usual amount for cold and warm starts... But you didn't say if that was hi or lo boost....

Steps 5-6 Works during starting. Warm and Hot...

Step 7 works if not enough fuel gets evaporated in the intake system.  Usually typical of cold starting.

mixture off, all fuel goes back to the tank.  But, doesn't remove bubbles in the system forward of this point.

mixture full in, all fuel goes towards the engine.  Counting in seconds on low boost is a lot during a hot start.  

Throttle in delivers more fuel than throttle back. 

The objective of the hot start is to...

  - deliver a continuous stream of vapor bubble free fuel.

  - use a minimum amount of priming fuel because it evaporates completely and easily and can easily over power the mixture to be too rich.  Aka flood the engine.

Flooding the engine becomes extreme when a large amount of fuel is delivered to the engine and the liquid continuously evaporates making it hard to set the mixture properly.

 

sometimes it is a challenge to know if a hot start is going to be needed...  Flying and doing pattern work, landing to fuel up again. Start the engine.  Assume that is going to be a hot start.  If you have been sitting around having a nice lunch, that is probably not a hot start....

If you can grasp the details of when vapor bubbles form, where they are, and how to get rid of them...  That is key to understanding the hot start,

some people go with a flooded start in place of the un-sure if it should be a hot start.  Flood first, then start...  Requires strong batteries......

The procedures from Rocket engineering are pretty complete/modern. Adding a turbo to the procedure doesn't change much because the turbo isn't spooled up until after the engine is running.  The compression is a bit lower than a NA engine...

Not following procedures properly can lead to...

- mixture in during the fuel system cooling process, leads to flooding...

- mixture out during start could lead to doing it again and again until fuel is allowed in...

- Throttle out during priming allows less fuel in than usual, starting with an unknown adds to the challenge.  Don't forget to pull the throttle back prior to starting...

- throttle in during the start, leads to about a one second surprise as full power develops quickly.  Good to have the feet firmly on the brakes and hand on the throttle.  Expect cognitive distractions with such a complex procedure that has inverted logic.

PP ideas on Continental engine starting technique... Not a CFI.

Let me know if I have missed something.

Best regards,

-a-

[floridaflyer]

Thank you so much carusoam for your comments! Here is more on my plight:

• I'll check CHT's after next landing, my guess is in the 300's, likely vapor lock territory.
• I haven't parked into the wind with the oil door open, my typical stops are busy FBO's where I don't get to pick orientation, I thought I'd make sure I have the correct hot start procedure and see if it takes care of the problem before I change my FBO lifestyle!
• My typical hot start is within 20 mins from shutdown.
• I don't know what boiling fuel sounds like, but from what I've read about fuel evaporation vs. temp vs. pressure, I would bet I have vapor lock.
• My 3-5 second priming is using the primer switch, which in my plane is exactly the same as using HI boost. It's what the cold start procedure calls for and it brings FF to around 18 GPH. Your comments make me wonder if I'm flooding the engine with too much priming, which would be consistent with the engine never wanting to start with FULL mixture but more cooperative with mixture at ICO and advancing. I'll use less primer on my next attempt and report back.
• I will call Rocket Engineering about the hot start procedure.
• MIxture in during LO boost does not flood my engine because no fuel makes it to the injectors --regardless of throttle and mixture settings.

Thanks again for the useful feedback!

PB.

[carusoam]

Can you here the pump operating with the Lo switch? (Switch issue?)

On my engine the 3-6 seconds Hi is interchangeable with 15 seconds of lo.

I don't have a fuel pressure gauge, just FF.

Best regards,

-a-

[floridaflyer]

5 hours ago, carusoam said:

Can you here the pump operating with the Lo switch? (Switch issue?)

On my engine the 3-6 seconds Hi is interchangeable with 15 seconds of lo.

I don't have a fuel pressure gauge, just FF.

Best regards,

-a-

Yes my LO boost pump can be heard, same noise as HI boost but not as loud. You say your LO boost is interchangeable with your HI boost, how do you know that? Have you been able to use LO boost as primer with mixture set to rich? My LO boost doesn't prime (not pushing fuel to the injectors) no matter what my throttle/mixture is set at. I'm thinking if LO boost is supposed to push fuel to injectors with mixture rich and mine doesn't, it may not be producing enough pressure and I probably need to check it.

Other Rocket owners please jump in!

[carusoam]

My POH says they are interchangeable...(?)

Actually, my checklists from transition training says so.  They are based on an Ovation POH.  I have done it both ways.  I prefer using the lo boost for the improved precision.

Both settings show FF. It may take about a second for the flow to register.

A hot engine is more sensitive to excess evaporated fuel.

An interesting person to ask this question to is David at AAA...  David, as part of his job, demonstrates starting Moonies under all conditions.  He was my first contact with the various starting techniques for the Continental engines.

doing the mixture sweep from cut-off to full rich makes the most sense when not priming the engine.  The act of priming puts some fuel in the system when none may be required.  If none is required, it would be bad to add more...

Keep in mind I'm writing this from memory.  My checklists are on my iPad.  I will review momentarily and update...

Best regards,

-a-

I reviewed my hot start procedure.  The mixture sweep is not mentioned.  That comes from training.  It does include sending fuel back to the tank.  It has no priming step.  Mixture is full in.

i don't prime, and mixture will be swept...

check your procedure to see if priming has accidently been included in your procedure.  Compare to your STC/POH from Rocket Engineering. Since the engine is different from the original 231...

As far as the electric pump goes, it has two settings.  The only thing that can be different is the rpm that it is running(?).   One setting generates 5X the flow as the other setting.  How much, and Where it goes depends on the position of the throttle and mixture knob.  Throttle forward flows more than throttle back.  Mixture in, fuel goes to the engine.  Mixture back, fuel goes back to the fuel selector switch (on the O) circulating cool fuel through most of the fuel system.  Key word is 'most'.

know that I am only a PP, not a CFI. This is my best effort...

-a-

 

[floridaflyer]

Carusoam I believe the Ovation fuel system is different from the Mooney Rocket. The Rocket Engineering POH supplement does not provide cold or hot start procedures. Can you provide contact info for David at AAA? I appreciate your time!