I'm interested in knowing what things related to installation have an effect weather positive or negative on spool up time. I have recently acquired a new 19 lb class turbine that is that is taking between 7 to 8 seconds to spool from idle to 100%. It seems to spend about half of its spool time between idle which is 50k rpm and 70k rpm. I can hear the flame in the combustion chamber snapping and popping in that 50 to 70k range. Once it is above 70k the snapping and popping quits and the acceleration is very quick. The turbine is on a test stand with about 4" of fuel line between the pump and the turbine and approximately 20" on the pump inlet into a 5 gal container. I'm running jet A with 5% of DTE lite and our field elevation is 3200 asl. Todays temp was 66 F and relitive humidity was around 35%. I don't know to what extent the weather conditions can effect the spool time but thought I would include them anyway. I don't want to disclose the mfg. of the turbine right now because I've just now made them aware of this. I'm just trying to get myself up to speed on the nuances of turbine spool up time.
Thanks
Luckyflyer

Lucky,

What engine is it. That will determine if something is wrong with your turbine or if it's OPS Normal. An old Jet Cat P-80 might take 7 to 8 seconds to spool up...a new SX or what ever they are called spool much faster. If it's a Falcon and it's messed up internally or the settings in the ECU are all mis set...that could be a reason.

So...what's the engine and how old is it?

Beave

Its a brand new german made turbine but I do not want to say what brand just yet.

Well...if it's brand new (as is new design ETC) and it's popping like you are saying, I would think something is wrong. Probably an ECU setting. Ring up the company reps tomorrow and ask them or maybe post a question in the turbine support forum. I would say the altitude is not the problem.

Beave

There is no pop or snap on thottle up just sound of stumble.

The engine he is referring to is an evoJet....there is no need for it to be a secret.

Anyway, after watching the video you sent, all ground operations are as they should be. The evoJet software measures airflow through the engine 20 times per second. On a ground run, there is no "ram-air" effect, therefore acceleration is slowed automatically by the ECU. In the air, there will be much more airflow through the turbine, thereby increasing the speed the turbine will accelerate.

There are other turbines that do not measure this airflow and have a set acceleration time. The problem with this approach is, if conditions are not optimal, it could result in a flame-out due to the lack of air-flow through the turbine.

Arno said there are two things you can do to lower the acceleration time, 1 is raise the idle rpm. This will also increase your residual thrust. 55k was the suggested mark. You can also lower the acceleration time time to 3.5 seconds in the ECU. They come set at the factory at 4. This time is measured in the AIR under RAM AIR conditions. If this number is lowered too much, it will result in a less desirable running on the ground, and possibly too fast in the air.

The weather, altitude, humidity, and temperature are also HUGE contributing factors. Ground testing is always worst case scenario for turbine performance.

Fly the engine Mark and enjoy it.

sent a PM

Something is wrong, here is a possibility:

Bad ECU settings(very high acceleration/ramping value), if this is the case, after you pass the 70K you'd have extremelly fast acceleration, you say you do, so this is a possibility, keep in mind that if this parameter is adjusted down you will also loose the fast acceleration on the high end of the RPM range. Popping is a symptom of un-vaporized(liquid) fuel being burned, this happens when fuel is being sent faster than the turbine can handle, just so you know, liquid fuel inside the running turbine is a bad thing.

Can you describe what happens to the temperature reading while on the 50k to 70k acceleration transition?

Just so you know, completely answering your question, other causes for slow/poor/uneven acceleration symptoms are:

- Bad bearings causing drag
- Bad combustion chamber with uneven burn
- Clogged or missaligned fuel needles not allowing proper fuel vaporization at the lower chamber pressure levels related to low RPM
This applies to ALL microturbines except the now dissappeared BMT's that had fuel injectors (they had no need to vaporize fuel as part of the turbine design)
- rubbing turbine wheel or compressor
- simply poor efficiency related to bad tolerances or improper assembly
- Rotating component mass itself limits acceleration velocity for a given turbine design, two turbines with same rotating components and their rotating components' mass being the same, but one with tighter tolerances than the other, the one with better tolerances will have faster acceleration (and will be more efficient than the other...).


The ECU verifies running parameters several times a second, fuel volume is increased, acceleration(RPM increase) is expected, if it does not happen, ECU waits before fuel flow continues to increase, this while watching temperature, this actually controls acceleration, the acceleration parameter controls how fast is the fuel flow is increased when the ECU decides it should. If the ECU parameters are set for faster acceleration than the turbine can physically obtain, the turbine actually bogs down, this is because fuel is flowing in faster than the combustion chamber can vaporize and burn fuel on the related chamber pressure, impeding RPM increase.

It does not make sense for a turbine to rely on ram air for acceleration, when you have the need for faster acceleration is when you actually have the less airspeed like when aborting a landing. Actually, many full scale turbine designs don't even have aerodynamic intakes that allow ram air pressure to build up.

All ambient factors (temperature, atmospheric pressure, humidity etc.) that impact air density do have an effect on turbine performance, but mostly on power output and acceleration speed, not on acceleration linearity, for example, on thin air you have less air for the compressor to bite, but you also have less air drag on the compressor, so it can rotate faster, those two cancel each other so everything else become equal, based on this, acceleration on less dense air could be faster, but it will also be more or less linear, same as in very dense air, based on your description, you do not have anything near linear acceleration on this turbine at this time.

SCJ can you explain how does the Evojet turbine measure airflow?

I used the words pop and snap which may not be the best choice of words to describe what I'm hearing. My friend little pistion simply describes it as a stumble which it is, he was here when I ran the turbine. With the total spool time beiing 7 to 8 seconds the turbine spends 1/2 of that time accelerating from 50 to 70 k rpm. As it is accelerating it is like the flame in the combustion chamber is encountering turbulance and is being whipped around, like the flame itself is struggling. To me it is a very subdued popping and snapping sound. I feel like 7 to 8 seconds for a test stand spool up in a current generation turbine is unacceptable. The exact words used when describing the spool time of this turbine before I purchased it was "fastest in its class". The 7 to 8 second spool time that I'm experiencing is niether fast nor fastest in its class. Arno the owner of evo when ask what the spool time should be for the booster 90 said 3.4 seconds. Quite honestly I cannot fly and enjoy this turbine with the spool time being so far out of spec. I will try the parameter changes as recommend and hope that takes care of it. If not I'll box it up and send it in. I want to say out right that I'm not flaming Chad or Evo. Chad has been great at returning my phone calls and helping me on both of the Evo turbines I own. It was my preference to not name names at this point but rather educate my self on spool up time as best as possible. The video I took which is not the greatest quality can be found here.

http://www.youtube.com/watch?v=VWd7De_KPjU
Luckyflyer

Based on the video,I must say that your turbine is accelerating a lot faster than most other brands, I would adjust the acceleration parameter down a bit to make it smoother, but on the video it seems OK.

Not to jump in here and bad mouth any manufacturer but I have a Jetcat p120 that i bought and it just fired right up with no problems. This is a turbine that the warranty expired many years after the initial purchase. I had it in it's original box and i am so happy I bought that brand. Will always be a Jetcat guy, I would send it back and get your issues resolved. This whole ramp up speed is just nonsense. I could get my Jetcat modified to the new std and i won't do it.

Lucky,

I just watched the video. It looks just fine to me.

Go fly and have fun!

Beave

It looks to me like the RPM indications are struggling to keep up with the acceleration as it is so quick I'm not an evojet user but if it was my engine I'd put it in a model and fly it!

Luckyflyer is this your first turbine?. Turbine Video looks ok.

It looks good........... Go fly and enjoy!!!

Rick

it's been asked already amigo so my curiousity is peaked also, is this your first engine?

if so, then welcome to jet portion of the hobby and good on ya for asking questions to some of your concerns. [sm=thumbup.gif]

if it's not your first engine then i'll only mention (in my experience despite being a rep) they are good lil motors but remember each manufacturer has their own quirks or unique sound. line 'em up, AMT, JetCat, Jet Central, Wren, JetJoe, Kingtech, PST, Evojet, Hawk, Frank, Merlin etc. etc. they all accelerate differently, some faster, some slower but by and large they are all very similar and produce their own distinctive sound. (I'll use Jet Central as my example because I could always tell when my buddy was firing his up during startup or during takeoff roll, very unique initial acceleration) same goes for Evojet during startup

IMO, the video doesn't show anything out of the ordinary amigo. stuff it in your jet and enjoy as others have already stated.

Sorry to disagree guys, but that accel. is not normal of the newer turbines in this class. 6-7 seconds is not normal (maybe for this brand, that I am not sure and I would error on the side of booster and say that this turbine has more potential to it.)

It could be a setting besides the accel. that can be adjusted. However I am not familar enough with the booster menu strut. to know.

However, when I get back in town I will post a picture of my rabbit accel time. I know this is a diff. turbine. However the booster 90 is advertised fastest in it's class (19lb. I assume) and as the video will show at the same alt. and similar temp my spool up time setup like his is will be right in the 3 second range.

I don't expect the booster 90 to accomplish this. However i would expect it to be less then 5 seconds and closer to 4. From what luckyflyer told me, the rep told him that the owner or president told him 3.4 seconds.

I am sure this turbine can be made to accel. faster. But when someone buys a turbine because it's advertised fastest in it's class, and gets one that has a 6-7 sec. accel. time then the customer is not happy.


Chad, please explain your statement "The evoJet software measures airflow through the engine 20 times per second". I assume you meant that it monitors temp and rpm's 20 times a second?

I hope to get the video up by Monday sometime if not sooner

Also, this is his third turbine...not his first. He is new to turbine flight, but not turbine operation. He has been around turbines for about 2 years.

I will say this, the Kero start on the Evo Boosters is really nice and smooth. The look to be very well made turbines. Being from Germany, what would you expect! lol.

A faster spool time?

The accel in the video takes as long as a green Wren MW44... and that thing is slow! I'd expect faster for a larger, newer turbine.

Hello Guys,

just click in to clear up a couple of things.

(+) The video shows a ground test-run in an unknown environmental condition, temperature, air-pressure, altitude etc.

(+) The actual spool-up time is controlled by ECU's software by a function of rpm, egt, pumpvoltage and their math derivations.
This compares to an 'indirect' air-massflow measurement and helps running the engine SAVE and STABLE at any time.

(+) The adjustable THROTTLE-UP time in the ECU is the minimum time value, that means if set to 4sec it cannot be faster, but slower if the environmental that required. Other brands may run it HARD always - compare yourself what is really useful ;-)

ONCE AIRBORNE THINGS WILL CHANGE - SO LET IT FLY !!

Best, Arno evoJet support

1. The temp, alt, enviromental conditions were listed in the first post.

2. Other ECU also monitor temp, rpms, pump voltage as well. However, if they can give you the spool time they do.

Guys, 6-7 seconds is not normal for a bench mounted turbine. Once induced into an airframe with longer fuel tubing, restrictions it will not get better. To depend on "Ram Air" to help spool up is not a good idea as there is a lot of airframes to don't "Ram Air" into the turbine but allow it to obtaing the necessary air for running.

This spool time is around were the older turbines run at. Hince the development of the newer models like the SX's and others.

So is it my understanding that this video represents what a typical EVO Booster 90 will do sitting still in an airframe on the runway before take off? What if you don't have the Ram Air effect?

Arno:

Thanks for clearing the "Airflow" measurement, I knew it had to be an "assumption" derived from other parameters (Indirect measurement)

As to the poster's original question. First off I want to state up fron that I do not operate RC turbines. However I am an A&P and have worked on Jet engines 22+ years.

1. The spool up time is controlled by either the ECI or FADEC unit. In essence what the computer does is to ensure the engine does not go into a "Lean" state and thus give you a Hot Start or hung start condition where the engine is running but is not at self sustaining speed and will not respond to throttle control,

2. This ensures the engine doesnot cook itself to death.

3. If allcomponents are working correctly the combuster depending on air flow will allow the engineto spool up while preventing flame out.. It is commonon corporate jets as well as the airliners to hear a popping orgurgle/surging as the engine spools up.

4. on a pure jet type design(non by-pass) engine suchas the military fighters of old, I will give as an example the J-79 (F4 phantom engine) when they first hit the frontlines they had spool up problems and the fix was touptrim the fuel control (Increase idle RPM) where the engine would transitionmore quickly.

5. As the previous postshave mentioned airflow once airborne will helpthe transition time due to ram air effect.

6. Thedown fall up an uptrim isthat the increased thrustcan have an effect on landing distance.

I have not watched the videoand I am just giving you some generalinfo. The others who have first hand knowledge I would listen to. I hope I have not confused you. However a turbineis a turbine is a turbine.

Regards
Glenn Williams
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Well I had a nice talk with Chad at SSJ today regarding my Booster 90. He called me and said well it looks like the people on the forum are agreeing that there is nothing wrong with your turbine. I said Chad that is not the way I see it (there have been more posts added to the thread since our conversation) it looks like the opinions are split. I pointed out to Chad that within the last 24 hours Arno the owner of evo said when ask by Chad at the Ca flyin what the spool time on a Booster 90 should be replied that it should be 3.4 seconds. Chad denied that Arno said that and said that his reply was 3.6 to 4.2 seconds. Ok 3.6 to 4.2 seconds not 7 to 8 seconds as shown in the video. The conversation quickly deteriorated,Chad is insisting that there is nothing wrong with the turbine. Chad's voice is elevated and strained mine probably is to. I said Chad lets ratchet this down a couple of notches we are getting nowhere, that suggestion had mixed results. I finally said Chad would you just give me my money back on the turbine? NO there is nothing wrong with the turbine! Chad said that I'm always having problems with my turbines talking down to me like I know nothing. I said that is not true I did have a problem with the booster 160 that I own but that was resolved with the help of some of the local jet guys. Guys I had heard all I wanted to hear at this point and just hung up. The phone rings, did you hang up on me? Yes I did I feel like you and I have nothing more to say to each other. I hung up again. Five minutes later the phone rings This is Chad, I tell you what I'll give you your money back on the turbine pack it up just the way you got it. If there is any thing that is damaged in any way you will be charged for it. I said Chad the only thing I can think of is the soft aluminum mounting ring the screws will have marred it a little. Well I'll need to charge you for that because we are going to need to resell this turbine. Also you will not be refunded the shipping amount which is $40. I agreed to these terms even though I don't totally agree with them. I don't mind paying for the shipping, I don't believe I should pay for the motor mount. Chad said to me I wil never ever sell you anything again. I said well Chad I think that you are a stand up guy for offering to give my money back. Chad said I am not a stand up guy I'm giving you a refund to make you go away, to make my life easier. Ok Chad whatever.

Guys the reason I post this is to make others aware of my personal customer service experience with Sincity jets. After spending $6500 in the last 60 days with Sincity jets I think better treatment is deserved. I have not added to or taken away from my conversation with Chad. I was talked to and made to feel like I don't know anything and I'm a trouble maker by Chad. There was at no point a suggestion made to send the turbine in to have it checked out. And the sad thing is I like the booster line of turbines, the kero start works well and I like the programmability of the hand held unit. Although I did have an issue with my Booster 160 that has been resolved and I'm totally happy with it. In closing I must say that yes I'm disappointed with the spool up time of the B. 90 turbine I received. But words don't really convey how much more disappointed I am with Chad at Sincity jets and his caveman approach to resolving my concerns. I will say however that Chads forum etiquette is exemplary, not so otherwise.
Luckyflyer.