Merlin negative G cutout too quick?

Originally Posted by Deadstick

@Viper 2000, I am both amused and horrified. Thank you for the post.

+1

Viper, you need to get out more mate, think about all the hot birds you could have met at uni whilst the code was running

on a serious note, yes, your calculations are somewhat interesting (if I can suggest something, try and keep it simpler..), but not conclusive

two things though:

a) don't take Reno Racers into account, those folks really have more money than sense and 1) have custom built cylinder cases, pistons, piston rods, valves and modified superchargers (their special mixtures+the very low altitude means that the mixture gets VERY hot, and the intercooler of the two stages supercharger can struggle to keep things to the right temperature - the rule of thumb with Reno Racers is "don't believe in what they say, they play a lot on the "secrecy" thing..") 2) run on "special" fuels. It's fascinating but somehow appalling to see them do what they do with those machines..

b) not always warbirds owners fly their own planes. And when you're a pilot who's flying a £2mln warbird that doesn't actually belong to you, you might get a tad too jolly on it.. another important thing to take into account for modern warbirds is that most of the heavy stuff (old radios/batteries, central fuel tank, armour, ammunition and armament) is gone, a slimming process that makes the thing sensibly better in terms of perfomance.

[IvanK]

Repost of post 41 for your comment Sternjager:

Sternjaeger you said:

"Anyway, back to the topic, the videos I have seen seem show quite a jolly response, but then again if it's on full throttle they are quite spot on. "

So let me get this right in your opinion an Engine cut with entry into a descent as shown in my video where G never gets lower than say +0.8G is enough to induce
engine cut ?

In a previous post you said: "A sustained 0G or a minimum negative G load (-0.1) are enough to interrupt the flow."
In this video we don't get any where near those values .

An engine cut at 0G or negative G value I wouldn't have an issue with. Here we are positive G throughout.

Originally Posted by IvanK

Repost of post 41 for your comment Sternjager:

Sternjaeger you said:

"Anyway, back to the topic, the videos I have seen seem show quite a jolly response, but then again if it's on full throttle they are quite spot on. "

So let me get this right in your opinion an Engine cut with entry into a descent as shown in my video where G never gets lower than say +0.8G is enough to induce
engine cut ?

In a previous post you said: "A sustained 0G or a minimum negative G load (-0.1) are enough to interrupt the flow."
In this video we don't get any where near those values .

An engine cut at 0G or negative G value I wouldn't have an issue with. Here we are positive G throughout.

if you never get lower than +0.8G then no, it's not correct, but you need to be sure of the G-load value mate.

just had a word with one of the pilots, who confirmed me that as soon as you hit 0G with a float carburettor it's enough for the engine to falter or cut. He said the Harvard does it regularly (I never experienced stalls or 0G manouvres with it so I couldn't tell personally).

[IvanK]

Ok thanks for that, then based on that 0G is significant. If we accept 0G as the point at which the coughing starts then what we have now is GROSSLY over done.


I have a pretty good idea of 0G and the pitch rates required to achieve it in high performance aeroplanes and we are getting nowhere near it in COD before the engine starts coughing.

[Seeker]

It does seem very strange to me that the Merlin installation, lacking fuel injection as it was, though intended for an aerobatic use, is less robust to negative G than either a Prewar Matchless scrambler or the pilot's MG TA.

I can keep an MG TA for negative G for about2 to 3 seconds without it cutting out. The lube system is much more sensitive than the carbs, as merely throwing it hard into a roundabout can get the oil thrown to one side of the sump, but while I've heard bearing knock on round abouts and good hump back bridges, it's never had metering problems.

Of course it's a completely spurious comparison, but nonetheless odd that a machine designed for 2 D is more robust in this matter than a machine designed for 3D.

Originally Posted by Seeker

It does seem very strange to me that the Merlin installation, lacking fuel injection as it was, though intended for an aerobatic use, is less robust to negative G than either a Prewar Matchless scrambler or the pilot's MG TA.

I can keep an MG TA for negative G for about2 to 3 seconds without it cutting out. The lube system is much more sensitive than the carbs, as merely throwing it hard into a roundabout can get the oil thrown to one side of the sump, but while I've heard bearing knock on round abouts and good hump back bridges, it's never had metering problems.

Of course it's a completely spurious comparison, but nonetheless odd that a machine designed for 2 D is more robust in this matter than a machine designed for 3D.

..erm, you got me a bit confused mate, how can you exactly put a car into negative G load?

[II/JG54_Emil]

lol

the weirdest comparissons are made in this thread to find arguments to convince the developers to tune the favorite plane.

If this happens for blue side I instantly see 10 posts calling s.o. Luftwhiner.

[winny]

Originally Posted by Sternjaeger

..erm, you got me a bit confused mate, how can you exactly put a car into negative G load?

Crest of a hill...? Or, roll it.

[Viper2000]

Originally Posted by Seeker

Of course it's a completely spurious comparison, but nonetheless odd that a machine designed for 2 D is more robust in this matter than a machine designed for 3D.

In the official mind, interceptors go up, shoot a bomber or two, come back down, re-arm, refuel and repeat.

The RAF's aeroplanes are serious tools paid with using Public Money, not toys for pilots. Furthermore, pilots are reminded to fly directly to and from their targets, since prodigal use of fuel is burdensome to the Public Purse.

Or words to that effect.

If you just think of the interception task, and assume that the target is a cooperative bomber flying in a straight line, you really only need 1 g straight & level, plus axial acceleration/pitch changes to get the job done.

Is this silly? Of course. But if the people designing the aeroplanes have never flown them then it's unrealistic to expect them to imaginatively embellish the specifications given to them by the man from the Ministry, especially since they probably wouldn't be thanked for it anyway.