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Need Help with Fox 15 Davis Conversion

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Old 10-11-2012, 08:29 PM
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Default RE: Need Help with Fox 15 Davis Conversion

If compression seems low a phone call to Fox may be in order, really think the head is out of the loop martin
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Old 10-11-2012, 08:53 PM
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Default RE: Need Help with Fox 15 Davis Conversion

How easily does it start? If it's starting all right then I can't see either ether content or compression being the problem. The figures quoted seem way low, even for a worn-out engine.

If it can do 15500 in standard glow form, I can't see that Fox would be particularly sympathetic.

Out of interest, have you tried something like an 8x4, 8x6 or 9x4 with it running as a diesel? 9x6 and 10x6 are both more than I would normally use for a .15 (I fly CL), so I'm wondering how it would go on a smaller prop.
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Old 10-11-2012, 09:25 PM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: steve111

How easily does it start? If it's starting all right then I can't see either ether content or compression being the problem. The figures quoted seem way low, even for a worn-out engine.

If it can do 15500 in standard glow form, I can't see that Fox would be particularly sympathetic.

Out of interest, have you tried something like an 8x4, 8x6 or 9x4 with it running as a diesel? 9x6 and 10x6 are both more than I would normally use for a .15 (I fly CL), so I'm wondering how it would go on a smaller prop.
Pretty much my thoughts on the starting Steve, something is being missed here.

What I want to know is, does it misfire when running as a diesel?

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Old 10-12-2012, 10:09 AM
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Default RE: Need Help with Fox 15 Davis Conversion

I think the problem may be the Cylinder to piston fit, if you look at the wear pattern on the piston it is wearing at the top on one side of the piston, and at the bottom on the other. I talked to Chris at Fox and he is going to send me a piston and Cylinder Assembly that is on the tight side, and I will spend an evening hand lapping it.
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Old 10-12-2012, 10:48 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Nice- hope that fixes it nice to deal with folks that care, did not mention it before but thought that might have been issue, glows can scream on lower compression
diesel a lost cause martin
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Old 10-12-2012, 05:24 PM
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Default RE: Need Help with Fox 15 Davis Conversion

Martin, I'm going to run my Fox .15 conversion tomorrow with a variety of props. One problem though, I need to either make or scrounge up some kind of bushing for the props. Not a single one fits the Fox shaft.
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Old 10-12-2012, 05:40 PM
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Default RE: Need Help with Fox 15 Davis Conversion

Hobbsy I have a variety of K and S thin wall aluminum tubing some even telescopes like a rc transmitter antenna so can fit almost any engine a must in the small ones, you can wrap some tape around the shaft to bring up the diameter so a good fit in I guess 1/4 inch is the standard prop bore I have done it you may have to
do a re-wrap when you change props martin

scotch tape to the rescue

K and S bush for prop
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Old 10-13-2012, 08:41 AM
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Default RE: Need Help with Fox 15 Davis Conversion

OK, here are the props I ran,

A MasterAirscrew Scimitar 9x5S rpm====12,100
A Taipan 10x4 rpm================9,200
A Graupner 10x5.5 rpm=============9,000
Idle==========================3,100

I only got a single outside photo to take, its really difficult to take them in the fall, as you can see. This one about two clicks from the peak. I don't seem to have a 10x6 of any brand. I think you can take a look at the Taipan and see why it made only 9,200 rpm but that dude makes some serious wind.

The fuel was Davis ABC blend.
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Old 10-13-2012, 09:46 AM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: Hobbsy

OK, here are the props I ran,

A MasterAirscrew Scimitar 9x5S rpm====12,100
A Taipan 10x4 rpm================9,200
A Graupner 10x5.5 rpm=============9,000
Idle==========================3,100

I only got a single outside photo to take, its really difficult to take them in the fall, as you can see. This one about two clicks from the peak. I don't seem to have a 10x6 of any brand. I think you can take a look at the Taipan and see why it made only 9,200 rpm but that dude makes some serious wind.

The fuel was Davis ABC blend.
I'f I'm able to sort things out and get those kind of numbers I will be a happy camper

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Old 10-13-2012, 10:37 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Tweedy most likely you will get those numbers everything i fly diesel or 4 strk glow we get 9 to 10K on the revs and sure they unload a bit in the air, an other 300 at least martin

I should have my digital fish scale early next week so I can see the real numbers on thrust on the planes should be interesting and not "well feels like a lot"
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Old 10-13-2012, 01:33 PM
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Default RE: Need Help with Fox 15 Davis Conversion

I finally found a 10x6 that I thought was a 10x8 because it was buried in a stack of props on a peg board hanger. It is a Graupner 10x6 Scimitar.

Graupner 10x6 Scimitar rpm ====9.250, the idle with this prop is a very steady 2,400. It is about 40 degrees right now and there was no idle cool down at all.
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Old 10-13-2012, 03:50 PM
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Default RE: Need Help with Fox 15 Davis Conversion


not bad at alll, but Brrrrrrrrr on the temp high 80s here today MARTIN

FOOD FOR THOUGHT A 10X6 IS A COMMON FOR A 40 GLOW
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Old 10-13-2012, 06:10 PM
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Default RE: Need Help with Fox 15 Davis Conversion

Quote:
ORIGINAL: AMB
FOOD FOR THOUGHT A 10X6 IS A COMMON FOR A 40 GLOW
Too windy to fly yesterday so we ran engines. A bloke ran a c/l unmuffled Norvel 40 BB on an APC 9x7 and I tachoed it at 15200 RPM.

I ran my Oliver Tiger MOD 2.5cc on a Master 10 x 6 and got 7600 RPM consistently with a maximum of 8200 RPM. However it would

only hold the latter speed for about a minute before overheating.

It turned the full RAM 8 x 6 comfortably at 12100 RPM.

It also turns an APC 7 x 6 at 16500 and an APC 8x4 at 15400 which makes it a goodin!

Regarding the claimed Davis RPM figures my gut feeling is that they're fantasy and as far as I'm concerned the myth is busted!

A fair amount of salesmanship in the claims?

Ray




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Old 10-14-2012, 02:36 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Should do the quoted rpm on a single blade 10x6 methinks.
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Old 10-14-2012, 02:44 AM
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Default RE: Need Help with Fox 15 Davis Conversion


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ORIGINAL: Diesel Fan

Should do the quoted rpm on a single blade 10x6 methinks.
... or the 10 x 6" with an inch and a half off each blade.

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Old 10-14-2012, 04:24 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Coming within 750 rpm with a fairly new engine isn't exactly myth busting and comparing a .40 to a .15 isn't what I'd call fair either.
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Old 10-14-2012, 06:08 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Hi Hobbsy I just thought it was interesting that a 10x6 prop was listed as a common size for40 size glow engines, a 15 diesel has no issue turning one
Just checked my factory sheet on PAW and indeed a 10x6 one of the suggested props so I guess in the 9 to 10K rev range on a 10x6
is the norm for a 15 diesel, the Davis sheet list 9x7 so a 10x6 I think pretty equal to a 10x6 best regards martin

Post note just became a grandfather yesterday was told about time since just hit the 80 mark in Sept
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Old 10-14-2012, 06:19 AM
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Default RE: Need Help with Fox 15 Davis Conversion

I thought it made 9250rpm on a 10x6?

That would make it 1250rpm less than the claims, and on pair with other .15 diesels. Perhaps not a myth busted but certainly a marketing bluff being caught. I would prefer to think of it as a missprint though.
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Old 10-14-2012, 06:26 AM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: AMB
Post note just became a grandfather yesterday was told about time since just hit the 80 mark in Sept
Congratulations on both milestones!

BTW, I turn 71 next month and I have two grandsons...both in college.

George
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Old 10-14-2012, 06:36 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Sorry Mr. Cox, my memory is more flawed than my math, Like George I'm currently 70 and so far that has not been a bad thing. I am still searching for an APC 10x6 although I doubt I'll see that kind of rpm with it either. But as the guy said at the end of that Dirty Harry movie, "I gots to know."

Congrats on the grandchild Martin, I have 17 of em, I wonder how that happened.
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Old 10-14-2012, 06:51 AM
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Default RE: Need Help with Fox 15 Davis Conversion

Mr Cox think it is a miss-print Mr Davis has very high ethics do does not resort to false claims has no need too martin see my post and replys dated'10/3 and replys of others martin
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Old 10-14-2012, 01:13 PM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: AMB



Post note just became a grandfather yesterday was told about time since just hit the 80 mark in Sept
Congrats on both Martin. Are you a grandfather or grandmother....errr is it a boy or girl?

I've got two granddaughters - they're so great, I sometimes think I should have just gone there first. hahahhaha!



Greg
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Old 10-14-2012, 01:27 PM
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Default RE: Need Help with Fox 15 Davis Conversion

HOBBSY`.. 17?? must be the baby virus, no cure LOL had to say that, family get togethers must really be an event martin
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Old 10-14-2012, 01:50 PM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: Hobbsy

Coming within 750 rpm with a fairly new engine isn't exactly myth busting and comparing a .40 to a .15 isn't what I'd call fair either.

A new engine which is now getting what seems to be a much needed new p/l.

I'd say it was fair comment.
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Old 10-14-2012, 04:15 PM
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Default RE: Need Help with Fox 15 Davis Conversion


Quote:
ORIGINAL: Hobbsy

.........and comparing a .40 to a .15 isn't what I'd call fair either.
Hi Dave,
that comparison was already done when a .15ci engine was quoted using a 10x6 - the extropolation was linking that prop to what sized engine normaly would use one.

The unfairness lies in fair placing a 10x6 with any .15ci engine and then saying it does 10500 rpm in any usable form.

By democratic vote here, it just ain't possible.
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