Technical Talk

[Engine 711]

Excuse my ignorance but I take it the Orph' had to be shut down for refuelling for obvious safety reasons?

Its normal (aircraft) practice to do so, yes - to stop engines - then refuel. You could refuel with the engine on, the risk is probably small - but the consequences are rather severe, to put in mildly. Those chaps Elf and Safe-T would not approve, these days....

The Air Start system was supposed to give 6 starts. Believe the tests at Norris Bros, before going North, did prove 6 starts, but only with repeated recharging of the system. I suspect 6 starts was Norris Bros 'wish - seems fair. But the actual hardware that they had (from another aircraft, not a Gnat - the K7 on-board system supplied by Rotax) simply didn't actually do that. Oh well... Carry on, chaps....!

The numbers from Bill below, show that the 1st start could use up almost half the on-board air - ! Not great....

IanM

[Engine 711]

During the start of Run 1, DMC comments that Air Pressure Low is on

No, he didn't. There is no indication of starting air contents in the cockpit, only the small gauge visible at the side of the engine cover. Donald was commenting on a low pressure fuel indication, something Ted also reported on.

Ok.... Well, quoting directly from the Transcript, as reproduced in Neil Sheppard's book (page 246):

GMT 08.45

(DMC) Kilo, we are underway
OK, Leo, do you read me..?

(LV) Coming in loud & clear, Donald ... Coming in loud & clear

(DMC) Two bloody swans have just taken off going down the lake...

(DMC) I'm underway, all systems normal; brake swept up, er... air pressure warning light on... I'm coming on track now, and er...
I'll open up just as soon as i am heading down the lake, er doesn't look too smooth from here, doesn't matter, here we go.. Here we go...

(DMC) .... Passing through four... five coming up... a lot of water, nose beginning to lift, water all over the front again.... and the nose is up...
Low pressure fuel warning light on... going left... Ok, we're up and away....

(continues)


What did Donald mean.....?

IM

[sheppane]

During the start of Run 1, DMC comments that Air Pressure Low is on

No, he didn't. There is no indication of starting air contents in the cockpit, only the small gauge visible at the side of the engine cover. Donald was commenting on a low pressure fuel indication, something Ted also reported on.

Ok.... Well, quoting directly from the Transcript, as reproduced in Neil Sheppard's book (page 246):

GMT 08.45

(DMC) Kilo, we are underway
OK, Leo, do you read me..?

(LV) Coming in loud & clear, Donald ... Coming in loud & clear

(DMC) Two bloody swans have just taken off going down the lake...

(DMC) I'm underway, all systems normal; brake swept up, er... air pressure warning light on... I'm coming on track now, and er...
I'll open up just as soon as i am heading down the lake, er doesn't look too smooth from here, doesn't matter, here we go.. Here we go...

(DMC) .... Passing through four... five coming up... a lot of water, nose beginning to lift, water all over the front again.... and the nose is up...
Low pressure fuel warning light on... going left... Ok, we're up and away....

(continues)


What did Donald mean.....?

IM

Ian, Mike,

I've listened to it again ... actually about 10 more times and to my ears, the transcript is accurate to DC's commentary. I don't doubt what you say Mike, but I'm at a loss to ascribe any other interpretation to what DC said.

[sheppane]

I'm working from later on- page 157 of the second edition- when he definitely says 'low pressure fuel warning light'. That he may have said 'air pressure' earlier is obviously a mistake on his part as there was no 'air pressure warning light'.

Fair enough. It was said in a casual matter of fact way, that did not give it any import. What other warning lights could be referred to?

[rob565uk]

I'm working from later on- page 157 of the second edition- when he definitely says 'low pressure fuel warning light'. That he may have said 'air pressure' earlier is obviously a mistake on his part as there was no 'air pressure warning light'.

Fair enough. It was said in a casual matter of fact way, that did not give it any import. What other warning lights could be referred to?

The only other warning light on the main panel is for low oil pressure. This is normally only seen when the engine is not running. It normally extinguishes as soon as the engine starts.

[Engine 711]

I'm working from later on- page 157 of the second edition- when he definitely says 'low pressure fuel warning light'. That he may have said 'air pressure' earlier is obviously a mistake on his part as there was no 'air pressure warning light'.

Fair enough. It was said in a casual matter of fact way, that did not give it any import. What other warning lights could be referred to?

The only other warning light on the main panel is for low oil pressure. This is normally only seen when the engine is not running. It normally extinguishes as soon as the engine starts.

Could it have been 'Oil Pressure Warning Light on', perhaps....? Oil - Air - ?

I agree, that a Low Oil Pressure Warning should go out, once an engine spins. And Cold Oil (as on a cold morning in January) should give high pressure, not low. Perhaps it was just momentary, as the Oil system got itself sorted out, after engine start up....?

IanM

[Renegadenemo]

The LP fuel switch on the filter body is the original and was set to indicate 6psi. The single boost pump develops 9psi so the piston pump wouldn't have to pull too hard to get a low LP indication.

[rich1608]

Excuse my ignorance but I take it the Orph' had to be shut down for refuelling for obvious safety reasons?

Next job is to see if we can get a new pair of properly safe and tested start bottles to go on board so we can really see what it can/can't do.

I'm a little confused here Bill, does this mean you're having new spheres made to go in place of the originals so they can be repeatedly run at 3200psi with peace of mind, or are you going to fit a couple of conventional air bottles into the hull like the ones in the start boat on Bute?

[Renegadenemo]

I'm a little confused here Bill, does this mean you're having new spheres made to go in place of the originals so they can be repeatedly run at 3200psi with peace of mind, or are you going to fit a couple of conventional air bottles into the hull like the ones in the start boat on Bute?

There's not room in the hull to fit so much as a spare Thermos but a pair of new 300Bar spheres would let us get a good start out of the onboard system for only a small weight penalty. We'll see. We also looked at a pair of 12 litre kevlar bottles same as the fire brigade use so they can run up stairs in a burning building wearing them but there is simply not the space to store them and plumb them in, except for maybe in the sponson tops. That at least would allow us to augment the original system and keep its working pressure down but the packaging problems to get sufficiently large delivery hoses from the sponsons to the main hull unseen are immense. A couple of new spheres will do the job.

[Canopener Al]

Interesting discussion after my last post Gentlemen and i admit I have never seen the full transcipts of any of the trial runs bar on "Across the lake " and written in "the Record Breakers". I am an ex RAF Airframe guy by starting trade, tin bashing at first, did Mechanical ONC and HNC as education and did engines conversion at the end of my RAF career, then into the B1 world of civil aviation and all the taking of exams to refresh EASA that I knew what i was doing as a competent person. No engine in the world is not designed to be able to draw the fuel required to operate under its full range by its own plumbing system. That would have incudled the Orpheus. As Bill has mentioned however the HP fuel system on the prototype Gnat was not a standard engine. Also the FRAME fuel system was designed orignially for the lower requirements of a Beryl. The Intake design and loads of K7 for a Breyl was not strong enough for the Orpheus suction loading. Such is the way for low cost modifications that k7 got in 66. PV/T = C is thermodynamics Gas laws.. Fluid Dynamics is a little similar. Also, Blue Bird was on the plane under the four forces of Thrust, Lift, Weight and Drag. Remove one of them suddenly and the normal world is disrupted.