Engine relight testing
Thread Starter
Join Date: Feb 2009
Location: Rayleigh
Age: 54
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Engine relight testing
I am trying to learn what happens during altitude relight trials. When is a trial considered successful or a failure ? What is normal behaviour for a commercial engine ? Is there an international specification which says that an engine has to relight by a particluar altitude for safe operation etc
Thanks
Thanks
Moderator
I don't have an answer, but I can broaden the question;
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'. So I asked the obvious, can you attempt a start on the ground at that altitude? If the engine is stopped, it does not know if it is stopped on the ground, or in flight!
The instructor did not have an answer, perhaps one will emerge here....
Pilot DAR
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'. So I asked the obvious, can you attempt a start on the ground at that altitude? If the engine is stopped, it does not know if it is stopped on the ground, or in flight!
The instructor did not have an answer, perhaps one will emerge here....
Pilot DAR
Thread Starter
Join Date: Feb 2009
Location: Rayleigh
Age: 54
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Thanks - that certainly has broadened the question as I hadn't thought of helicopters! I expect it depends on the temperature as well.
The reason for the question was that aviation fuel gets more viscosus the colder it gets, and so at low altitude it sprays nicely out of the injector, but as you go higher and it gets colder, the spray pattern slowly reduces until in the extreme condition it is just a jet rather than a fine mist. Then it is very hard to ignite.
I just wondered whether there is a measurement of how many times to try relighting, or how high or something ?
The reason for the question was that aviation fuel gets more viscosus the colder it gets, and so at low altitude it sprays nicely out of the injector, but as you go higher and it gets colder, the spray pattern slowly reduces until in the extreme condition it is just a jet rather than a fine mist. Then it is very hard to ignite.
I just wondered whether there is a measurement of how many times to try relighting, or how high or something ?
Thread Starter
Join Date: Feb 2009
Location: Rayleigh
Age: 54
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
thanks - that sounds like the sort of information which might help me. Are these manuals freely available on the internet ?
or maybe if not would you mind writing down some of the parameters for one of the plains you mention ?
or maybe if not would you mind writing down some of the parameters for one of the plains you mention ?
Join Date: Jun 2008
Location: USofA
Posts: 91
Likes: 0
Received 0 Likes
on
0 Posts
I don't have an answer, but I can broaden the question;
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'. So I asked the obvious, can you attempt a start on the ground at that altitude? If the engine is stopped, it does not know if it is stopped on the ground, or in flight!
The instructor did not have an answer, perhaps one will emerge here....
Pilot DAR
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'. So I asked the obvious, can you attempt a start on the ground at that altitude? If the engine is stopped, it does not know if it is stopped on the ground, or in flight!
The instructor did not have an answer, perhaps one will emerge here....
Pilot DAR
I suspect the key factors involved in re-light envelopes are:
-Igniter type and power rating (joules)
-Effective fuel air ratio at the point of ignition
DBW
Join Date: Jan 2008
Location: Wichita, USA
Age: 61
Posts: 127
Likes: 0
Received 0 Likes
on
0 Posts
Another couple of important considerations are:
Fuel delivery pressure and fuel vapor pressure - usually it's the latter that dictates when the engine is going to cough and give up on you and conversely when it's likely to start again.
We did some interesting work a couple of months back to try and get some MMEL relief for dispatch with a boost pump inoperative. The FVP got a bit too low and the engine surged and died on us several thousand feet below the predicted altitude.
Fuel delivery pressure and fuel vapor pressure - usually it's the latter that dictates when the engine is going to cough and give up on you and conversely when it's likely to start again.
We did some interesting work a couple of months back to try and get some MMEL relief for dispatch with a boost pump inoperative. The FVP got a bit too low and the engine surged and died on us several thousand feet below the predicted altitude.
Join Date: Feb 2006
Location: Canada
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Each engine/airframe manufacturer will specify a different procedure and limitations. In our operation, we demonstrate crossbleed and windmill airstarts at the outer limit of the envelope in the AFM for certification purposes.
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
Posts: 1,835
Likes: 0
Received 2 Likes
on
2 Posts
There is no requirement for a specific relight altitude for Part 27 helicopters anyway. There is only a requirement that a relight altitude be defined. Could be sea level and you'd meet the letter of the law.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'. So I asked the obvious, can you attempt a start on the ground at that altitude? If the engine is stopped, it does not know if it is stopped on the ground, or in flight!
The instructor did not have an answer, perhaps one will emerge here....
The instructor did not have an answer, perhaps one will emerge here....
I've always felt it important for any user finding such contradictions to squawk them to the OEM, and require a logical answer.
Join Date: Feb 2009
Location: Mostly at work these days
Posts: 22
Likes: 0
Received 0 Likes
on
0 Posts
The reason for the question was that aviation fuel gets more viscosus the colder it gets, and so at low altitude it sprays nicely out of the injector, but as you go higher and it gets colder, the spray pattern slowly reduces until in the extreme condition it is just a jet rather than a fine mist. Then it is very hard to ignite
Join Date: Dec 2005
Location: Wiltshire
Age: 60
Posts: 74
Likes: 0
Received 0 Likes
on
0 Posts
Thread so far seems to be focussing on altitude to actually achieve engine start. This is obviously important, however with helicopters (singles anyway) could I suggest you have a far greater concern in how long does it take to start. First thing you want to know is how much height am I going to lose during the start, so is it worth trying or just concentrating on walking away from the landing.
Join Date: Oct 2003
Location: Canberra Australia
Posts: 1,300
Likes: 0
Received 0 Likes
on
0 Posts
Hot Relights at High Altitude.
Just happened to try to determine the hot relight ceiling for a Vulcan newly fitted with Bristol Olympus 104 engines circa 1958. Here is an extract from memoirs.
"The performance of the new Mk104 Bristol Olympus engines was remarkable. Acceleration characteristics at altitudes up to and above 50,000 ft were better than any engine in the world at that time. I even found that I could close down an engine, perform a hot relight out to ten seconds after close down and achieve a rapid acceleration to high power from an RPM much lower than normal idle at those altitudes. My report stated that those engines were a credit to the manufacturer."
In those days there was no continuos ignition as installed in some engines now and the concept of relighting an engine whilst still hot was emerging. I do not recall the design of the ignition system and presume that there were a few high energy igniters carefully positioned in the combustion chambers.
My tests for reliabilty of hot relights were limited to within 10 seconds of flame out from closed power lever/throttle and did not extend to a determination of the threshholds where a relight became uncertain.
Were hot relights well known in Vulcan Squadrons?
Just happened to try to determine the hot relight ceiling for a Vulcan newly fitted with Bristol Olympus 104 engines circa 1958. Here is an extract from memoirs.
"The performance of the new Mk104 Bristol Olympus engines was remarkable. Acceleration characteristics at altitudes up to and above 50,000 ft were better than any engine in the world at that time. I even found that I could close down an engine, perform a hot relight out to ten seconds after close down and achieve a rapid acceleration to high power from an RPM much lower than normal idle at those altitudes. My report stated that those engines were a credit to the manufacturer."
In those days there was no continuos ignition as installed in some engines now and the concept of relighting an engine whilst still hot was emerging. I do not recall the design of the ignition system and presume that there were a few high energy igniters carefully positioned in the combustion chambers.
My tests for reliabilty of hot relights were limited to within 10 seconds of flame out from closed power lever/throttle and did not extend to a determination of the threshholds where a relight became uncertain.
Were hot relights well known in Vulcan Squadrons?
Join Date: Jul 2007
Location: Germany
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
During type training on the Bell 206 the other day, we were reviewing the Flight Manual instruction that an in flight relight/restart not be attempted above 12000'