"Fat Boy" 12/118 thrust engine

[racket]

Hi Gavin

Yep , the starter gets hot , but not as hot as it once did ,3 X 15 second start attempts and it was too hot to handle, which could be an indicator that theres a problem inside it , I'll pull it apart and check the commutator for roundness , if one of the segments has come loose and is sitting a tad high the RPM suffer as the brushes "bounce" and lose contact , this happened with a previous starter I used on an earlier engine .

Maybe I might try a RPM test spin first before disassembly , the armature should run up to ~20,000 rpm unloaded which would mean my output shaft >60,000 , if theres a commutator problem the RPM will be down , might explain why I couldn't get past ~16,000 during the engine start last week ...........I'll track it down :-)

Good to hear your build is progressing along , looking forward to hearing about your next run .

Cheers
John

[racket]

Hi Guys

Took the starter apart and checked the commutator and noticed the witness marks weren't even around it where the brushes rubbed , half was OK the other half not so good .

Set the armature up between centres in the lathe and put the dial indicator on the commutator and found ~0.003" variation between sides , also found that the bearing lands weren't running true to the centres , seems like the recon starter isn't the best .

Skimmed the commutator and reassembled the starter, remounted it on engine and hooked up the starter battery pack that was charged up 48 hrs ago , so not "fresh" .

First "spoolup" produced 12,600 rpm ...........good.
Second "spoolup" produced 12,100 rpm .........still good .

Couldn't do a third 'spoolup" as the starter was too hot to handle ...................very good , lotsa power being produced from lotsa current flow .

Last Friday when I had all the start problems, I did 3 long spoolup attempts and the starter was still only "warm" in the hand

I might enquire about a new armature for the starter to be certain everything is running true.

As an aside , the comp was producing ~0.15Bar of pressure , ~2 psi , at >12,000 rpm

Cheers
John

[turboron]

John, I had a similar issue with an Austin Healy Sprite starter. When I took it apart the commutator was black with corrosion. I skim cut in a lathe and it was as good as new.

Thanks, Ron

[racket]

Hi Ron

A bit of rpm vs P2 video of a starter test youtu.be/ignxJCiVlw8 with 73 psi of cold oil pressure and 26.4 V on the batteries after charging

The P2 fluctuations are "interesting"

The test was conducted with an "open" jetpipe , I'll fit the freepower stage for the next test and compare .

Cheers
John

[azwood]

Oct 15, 2019 16:29:22 GMT -5 racket said:

Hi Ron

A bit of rpm vs P2 video of a starter test youtu.be/ignxJCiVlw8 with 73 psi of cold oil pressure and 26.4 V on the batteries after charging

The P2 fluctuations are "interesting"

The test was conducted with an "open" jetpipe , I'll fit the freepower stage for the next test and compare .

Cheers
John

Funny how areas can be the same but you get different results I suppose it's going round as well think I added about 4cm2 to my power stage seem to be happy temp wise.

[racket]

With freepower stage fitted

[azwood]

Oct 15, 2019 18:29:56 GMT -5 racket said:

With freepower stage fitted

Yeah

[racket]

OOPS ............. youtu.be/oHzX2UK8OGg with freepower assembly , 27.7 V on freshly charged batteries

The P2 g/g is bouncing around a fair bit , more than with the open pipe I feel , even though RPM similar

[miuge]

Oct 12, 2019 15:59:07 GMT -5 racket said:

I'm looking at fitting a "wastegate" into the interstage duct , I've got a short length of 75mm stainless tube that I'll "blend" into the ductwork to "unload" the gas producer when the freepower is stalled , it'll need some sort of blanking off arrangement for when the freepower is spinning at >25% N2

Hi John,

This type of exhaust cutout valve could do the job, they're available in various sizes up to 102mm:
www.aliexpress.com/item/1789883828.html

[azwood]

Oct 16, 2019 11:04:18 GMT -5 miuge said:

Oct 12, 2019 15:59:07 GMT -5 racket said:

I'm looking at fitting a "wastegate" into the interstage duct , I've got a short length of 75mm stainless tube that I'll "blend" into the ductwork to "unload" the gas producer when the freepower is stalled , it'll need some sort of blanking off arrangement for when the freepower is spinning at >25% N2

Hi John,

This type of exhaust cutout valve could do the job, they're available in various sizes up to 102mm:
www.aliexpress.com/item/1789883828.html

I've done something similar but I used a pneumatic valve but a wastgate one would be better it doesn't close Antill higher pressure like 15 psi but does seem to help starting.

[azwood]

Here's mine

[racket]

Hi Guys

Theres some rather nice electric ones I've been checking out since reading your suggestions, maybe wired into the fuel pump circuit with an axle RPM tach that cuts the power once past a certain speed and closes off the bypassing of gases ..............plenty of options .

I'll keep having a think on this, but they'd save a lot of work as they're not all that expensive to purchase .

Thanks for the input :-)

Cheers
John

[azwood]

Oct 16, 2019 15:49:07 GMT -5 racket said:

Hi Guys

Theres some rather nice electric ones I've been checking out since reading your suggestions, maybe wired into the fuel pump circuit with an axle RPM tach that cuts the power once past a certain speed and closes off the bypassing of gases ..............plenty of options .

I'll keep having a think on this, but they'd save a lot of work as they're not all that expensive to purchase .

Thanks for the input :-)

Cheers
John

Let me know how you go with a axle rpm circut that would be nice or a throttle acter attervated on so if it get off the gas it opens might help slow it down.

[racket]

Hi Guys

Fitted a 76mm/3" dump tube to the freepower scroll , for the time being I'll just leave it open rather than fit a butterfly valve as I'm not certain what type will be best .

Crappy job trying to weld the tube in place, just couldn't seem to get the welds right, shaky hands are getting worse :-(





I'll reassemble and think about doing another "hot" spoolup test soon :-)

Cheers
John

[azwood]

Should have success now can't see why not.