Merlin negative G cutout too quick?

[TomcatViP]

Originally Posted by cheesehawk

Accelerometers we used in cars was to test suspension tweaks during cornering, they're computer electrical devices bolted to the floorpan (normally under the driver) that read acceleration in the horizontal plane (360 degrees). Pretty complex, broke one once, and cost us $10k to replace?

I know its not the same thing that a 1930 engineer would have used, but figured it works on the same principle, even if the scales/terminology would have been different due to use/time/language.

My guess is that they were some kind of piezoelectric (high frequency of the suspension system)). Take a look at Wiki to see how it works.

10k$ is a lot of money for a single one !

[Crumpp]

Combine it with typical onset rates and the tactical disadvantage becomes clearer.

It is actually fortunate that GOR is so rare in flight. Human threshold for GLOC is much lower for GOR than ROR.

[IvanK]

"Do you guys have copy of the actual Spitfire Mk I POH? "

Yes

[ZaltysZ]

Originally Posted by cheesehawk

Accelerometers we used in cars was to test suspension tweaks during cornering, they're computer electrical devices bolted to the floorpan (normally under the driver) that read acceleration in the horizontal plane (360 degrees). Pretty complex, broke one once, and cost us $10k to replace?

I know its not the same thing that a 1930 engineer would have used, but figured it works on the same principle, even if the scales/terminology would have been different due to use/time/language.

Depending on required precision and response time, accelerometer implementations can vary. In some case you can get away even with simple weight+spring.

[Crumpp]

Originally Posted by IvanK

"Do you guys have copy of the actual Spitfire Mk I POH? "

Yes

Ok, good.

[Viper2000]

Originally Posted by Crumpp

Yes the onset rate is extremely important. Very rarely do you experience gradual onset rates in an airplane depending on the definition. That is why I asked IvanK about the onset rate information in the report.

Onset rate doesn't make much if any practical difference to the carburettor's behaviour because the determining factors are the geometry of the float chamber, the position of the float and the fuel flow rates into and out of the chamber, none of which are going to be a strong function of dg/dt.

As soon as the g level falls below about +0.1 indicated, the float stops floating properly, and the carburettor therefore stops metering. Exactly what reduced positive g will cause misbehaviour will depend upon the friction in the system and any slosh in the float chamber, leading to slight variation on a case by case basis; but this sort of detail is way beyond the scope of a simulation of this nature.

Much earlier in this thread I calculated the approximate subsequent chain of events for both the reduced positive and negative g cases.

In both cases, I would expect a lag between departure from 1 g flight and cut behaviour due to the volume of the float chamber, engine demand, and fuel pump delivery rate.

(For this reason, normal turbulence would seem quite unlikely to produce cut behaviour.)

[Crumpp]

Onset rate doesn't make much if any practical difference

Only if you want to the answer to the question "WHEN does cut out occur?"

(For this reason, normal turbulence would seem quite unlikely to produce cut behaviour.)

Yes, it certainly will produce a cut out if the acceleration reaches the threshold.

As soon as the g level falls below about +0.1 indicated, the float stops floating properly, and the carburettor therefore stops metering. Exactly what reduced positive g will cause misbehaviour will depend upon the friction in the system and any slosh in the float chamber, leading to slight variation on a case by case basis; but this sort of detail is way beyond the scope of a simulation of this nature.

Once again, in an engine consuming 100 gallons per hour, the tiny bit in the float bowl will not last a cycle....

Even in a lycoming consuming 9 gallons per hour, a cut out and rpm change can be heard in turbulence or any negative acceleration.

Where do think kids get the airplane engine noises, "WAAAA waaaaaaaa WWWAAAAAAA" when playing from??

[TomcatViP]

Originally Posted by cheesehawk

LOL!! So do German kids make "vrrrrrrrp brattt bratttbratttttt" when they play planes?

"Meeeep Mep MeeepMeeep " here in the country of thundering Renault engines (excluding F1 obviously)

Regarding the cut out and turbulences : more consumption -> more flow -> higher capacity fuel pumps -> more fuel momentum -> less probability of a cutout from turbulences only

It seems as if some of us wld hve to compute the exact flow rates of the eng pump to end this debate

But definitively Crumpp is right for the Lynco.

[IvanK]

Originally Posted by TomcatViP

"Meeeep Mep MeeepMeeep " here in the country of thundering Renault engines (excluding F1 obviously)

Regarding the cut out and turbulences : more consumption -> more flow -> higher capacity fuel pumps -> more fuel momentum -> less probability of a cutout from turbulences only

It seems as if some of us wld hve to compute the exact flow rates of the eng pump to end this debate

But definitively Crumpp is right for the Lynco.

Ok some Maths for the Boffins. Knock yourselves out guys Here are the Maths used in the design of the first attempt at the Negative G solution. The Source is the First document I referred to in previous posts. Note Its Merlin XX data.

[TomcatViP]

Thx IvanK for providing such a valuable source.

I understand there that CoD devs has alrdy really worked the point.

Considering that if the 0.2g was the design limit to sustain for the CutOut on the converted engine, the CutOut began much earlier on standard Merlin's (although obviously bellow 1G).

Doing a quick calculation (to be refined) I have a 0.017G as the min value for the cutout to begin in a non-modified eng with an assumed similar geometry (you need then to add the time that the 2nd carb chamber emptied it self of its remaining fuel - Vip as done that before - negligeable).

So am fully converting myself to Crumpp idea now. As a culprit of false assumption I condemn myself to run around my neighborhood both arms raised like wings and making loudly sputtering "WAAAA waaaaaaaa WWWAAAAAAA" engine noise.