engine temperatures

[JimCrawford]

Good Morning Nipper fans,

Can anybody give me an idea of the oil and cylinder head temperatures they see when flying their Nipper ?
{VW engine}

Ta

Jim

[Paul1954]

In order to make full sense of any replies you may get from others you will need to define your own aircraft equipment fit.

1. Which cylinder temp are you monitoring?
2. Do you have an oil cooler fitted, and what size?

[svenolivier]

My oil temps vary bwteen 70 to 81 (mostly around 78)
CHT around 110 (measured at the rear cylinders)
EGT around 580 to 640 (measured at the rear cylinders)

Hope this helps

Sven UDT

[JimCrawford]

Hi All,

My aircraft doesn't have any fit yet. My enquiry was prompted by disappearing down a rabbit hole whilst investigating a new exhaust system with silencers fitted. My current arrangement is four short exhaust stacks pointing down. This is the arrangement on the Nipper Mk3 drawings I have and is very noisy.
However there is an old photo of GAVTC with the exhaust stacks pointing aft out of the elephant ears of the cowling. It's also clear that the current arrangement is a fairly crude mod as the holes in the cowling are a bit rough, so probably not original manufacture.
So I took a trip down the rabbit hole into GINFO and looked at every Nipper entry with associated photos. There appear to be five variants of exhaust layout:
All four short stacks pointing down.
Two forward short stacks pointing down and the two rear pipes pointing aft through the elephant ears
All four pointing aft through the elephant ears, rather like the RF4.
Some sort of routing into the space under the engine and exhausting through either two or one pipes under the cowling. This variant also seems to close off the elephant ears into a streamlined tear drop shape.
And finally, cylinder heads out in the wind with no enclosed cowling.

These variants started me thinking about engine cooling and, in particular, the hot air exit from the cowling edge gap which is a fairly close fit to the firewall, certainly far smaller than the inlet area. Even coupled to unobstructed elephant ear exits the total exit area is far smaller than the 1.5 to 2 times the inlet that would be a rule of thumb for this sort of thing. That's not allowing for the obstruction caused by aft facing pipes. I think I'll run some tests on the existing layout to try to understand what is happening, in particular pressure drop through the cooling ducts and cylinder and oil temperatures - hence my original question. My proposed exhaust system exits via the elephant ears so will block a proportion of the area. The Nippers with closed off elephant ears must have some arrangement to assist cooling air exit.

Jim

[Neil Spooner]

Hi Jim,
First off I would throw away the original Nipper Cowlings. Too draggy and very ugly. The Barry Smith cowlings are worth about 7kts increase in speed. The "ears" are perfectly adequate for cooling airflow provided you do a good job of the baffling, the lower cowling is without a gap between the fuselage.
I build my own ex' manifolds from Stainless Steel "J" tubes as available from the likes of VW Heritage. They are of the rearward facing type with pinched and drilled ends. I doubt that they are any quieter than the downward tubes, and are heavier, but look much nicer.
EGT is a peculiar measurement, depending on the location of the sensor and other factors. It is only useful for looking for the peak of temperature when setting up the mixture.

IMG_4650.jpeg (2.07 MiB) Viewed 2174 times

[JimCrawford]

Thanks for that photo Neil, clearly worth a thousand words!

I've got a pair of the VW Heritage pipes as a starting point but they will need to be fettled as my VW doesn't have the prop extension so the pipes would touch the prop. My proposed pipes are similar to yours but with a longer perforated section ( everything aft of the firewall ) with a concentric cover packed with muffling material, probably glass felt. The pipe inside the cowling, not perforated of course, will have a similar cover to provide hot air for the carburettor. I hope to set this in motion with the manufacturers next week when I'm next out at Bicester. Somewhere I have a reference to where VW suggest the CHT sensor should go and I'd like to do a before and after comparison.

Cheers

Jim

[Paul1954]

Most peps put the CHT prob under the hottest cylinder spark plug; cylinder head #3, top plug.

[Neil Spooner]

That photo doesn’t show the heat deflector in between the ex pipe and the pushrod tubes.

[JimCrawford]

That photo doesn’t show the heat deflector in between the ex pipe and the pushrod tubes.

I guess my concentric heat exchanger tube for hot air for carb heat might perform that function.

Jim

[Neil Spooner]

Yes, it would, but you only need one hot air supply. A flat heat deflector on the other side will help stop unwanted heat being transferred to the oil flowing back down the push rod tubes into the engine.
The installation you are proposing is potentially quite heavy....The problem is that there is just no room for an effective silencer on a Nipper.

[JimCrawford]

Yes, weight is a concern. perhaps the outer tubes could be rolled light gauge aluminium, there's no necessity for them to be stainless the same thickness as the exhaust pipes. If it proves too heavy then the tubes can be stripped off and I'd end up with the RF4 style you have in the photograph.
Do you stabilise the aft end of the exhausts with a connection to the fuselage frame or is the joining of the lower to the upper with a strap sufficient to support the longer lower pipe?

Jim

[Neil Spooner]

The short rear pipe provides enough support.