Need Help with Fox 15 Davis Conversion
 

Just finished a Sig LT-25 with Fox 15 Davis Diesel Conversion and am having a hard time getting even close to the 10500 rpm with a 10-6 prop quoted on the davis performance chart I would be happy with 9000rpm but am not able to get anything over 6000rpm. What should I really expect?

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy Is your fuel ok?? Also make sure not over rich and overcompressed... martin
also steel liner I think, know piston is iron may need a little run time to seat in
is the liner in correct orintation in case

A call to Bob Davis would not hurt either go to the source

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy

Here is an earlier thread on the Fox .15 BB with DDD conversion head:

http://www.rcuniverse.com/forum/m_11..._3/key_/tm.htm

RE: Need Help with Fox 15 Davis Conversion
 

Hard to say for sure, but you might need to break the engine in good though.
One thought is what is the fuel you are using? That could affect performance a lot in some cases.
You could also check to make sure the cylinder sleeve is aligned properly in the crankcase. Maybe it moved a little when they were putting the head on the engine.

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy EarlWB stated same thoughts give them a try martun

RE: Need Help with Fox 15 Davis Conversion
 

I would be surprised and amazed if a .15 with a 10-6 would do over 10,000 rpm.  I have glow GP and LA .40's that pretty much only do that.  I think a 9" prop would be more suited, or even an 8".  I am not a diesel buff, but realize their potential is good on large props too.

RE: Need Help with Fox 15 Davis Conversion
 

“You could also check to make sure the cylinder sleeve is aligned properly in the crankcase”
I think this might be the likely culprit will try running it again in the morning.
“I would be surprised and amazed if a .15 with a 10-6 would do over 10,000 rpm.”
I’m just going by what the Davis Diesel performance chart is quoting, I would be happy to see 9000 rpm. Before the conversion it was turning a Kavan 8-4 nylon at 15500rpm.
We are at 6000 ft. elevation I am using a J-Tec baffle less manifold with a carbon fiber arrow shaft extension on the exhaust with a I.D. larger than stock exhaust.

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy after you check the cylinder alignment** try a 9x6 prop and go from there martin

you are at 6000 ft I am about 60-100 that has effect

** Have a gut feeling the cylinder is off alignment

RE: Need Help with Fox 15 Davis Conversion
 

I don't get this at all, on the DDD site it gives an MVVS 21 doing 9800 on a 10X 6 prop and the smaller Fox 15 is supposed to do 10500 with the same prop?

And -
http://www.rcuniverse.com/forum/m_37...tm.htm#3748241
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RE: Need Help with Fox 15 Davis Conversion
 

I don't have any converted fox engines, but try a 9x5-9x6 prop instead. A 10x6 is a good match for .20-.25 diesels.

RE: Need Help with Fox 15 Davis Conversion
 

You would need to use the same fuel DDD did. You also do not know which brand or type of prop DDD used to match it up. Then you have to have the same ambient temperature, altitude, barometric pressure, and humidity levels used when DDD did the engine runs too. The OP is in Cedar City Utah which sits at about 5,840 feet altitude but DDD is in <font face="Arial,Helvetica,Geneva,Swiss,SunSans-Regular">Smyrna, TN which is at about 940 feet altitude. Thus engine performance would suffer a lot at the higher altitudes. There is a significant performance loss being higher up like that.
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RE: Need Help with Fox 15 Davis Conversion
 

It sounds more like a missprint to me (should possibly have been a 9x6 prop), I can't really see any .15 engine spin a 10x6 at 10500rpm. That would take a strong .20-.25 engine.

RE: Need Help with Fox 15 Davis Conversion
 

TWEEDY if cylinder thing ok chuck a 9x6 on and see what you get best regards martin

JUst looked at the data sheet on the Taipan 15 props
10x4 apc 9800
graupner 9x5 10300
apc 9x4 12500
graupner 8x-5 13000

granted classic design but still a 15

MVVS 15D 8x4, 8x5,9x5

10x6 equals low revs on a 15

RE: Need Help with Fox 15 Davis Conversion
 

I would agree with you all too. I think it might be a typo as well. A 10x6 seems a little too large to turn 10K rpms.
I need to fire up and run my Fox .15 sometime and see what it does.

RE: Need Help with Fox 15 Davis Conversion
 

Thanks Guys:
Had the plane out this morning, and it was the cylinder sleeve alignment that was causing the problem. Put in a flight of 45 minutes and still had half a tank of fuel left when I landed, power was adequate and seemed to improve as the flight went on, so I suspect it is still breaking in. It was also idling much better when I landed than when I took off, just ticking over, I had to pinch off the fuel line to get it to quit. Prop was a 10-6 Kavan I’ll have it out again tomorrow and post numbers with several different props.
Thanks again for the help

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy glad its solved, the cylinder alignment was the most logical based on the symptoms martin

about 45 minutes air time and land with a half tank left, Ha try that on glow sure it made an impression on you club buds

RE: Need Help with Fox 15 Davis Conversion
 

Love that inverted installation Tweedy. Where's the exhaust outlet?

Scenic background too.

RE: Need Help with Fox 15 Davis Conversion
 

See the black line below the blue stripe exiting the Fuselage in front of the Stab it ends about 1" aft of the elevator T.E. it's a carbon fiber arrow shaft.

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy nice Mr Clean special all out the "stack" not over the plane martin

RE: Need Help with Fox 15 Davis Conversion
 

Nice ...

What is the covering? Airspan?

RE: Need Help with Fox 15 Davis Conversion
 

Here is its "big brother" a 50 fitted with r/c fox carb the black one is a Perry carb bigga muffler

RE: Need Help with Fox 15 Davis Conversion
 

Graphics done wwith a CAD program (DeltaCad), Printed on Dollar Store tissue, applied with Nitrate Dope, then silk, then topped off with a sprayed coat of Klass Kote. If I did it again I think I would put the tissue over the silk also well over $100.00 of ink.

RE: Need Help with Fox 15 Davis Conversion
 

In the background in the gap between the wing and stab is the runway of the Cedar City Airport, our flying field is at the base of the hills in the distance.

RE: Need Help with Fox 15 Davis Conversion
 

I'm a diesel NUBE I've known of them all my life but the first one I have ever seen run was the Enya !! That I put in a Royal Coachman earlier in the year most of the guys in the club had had no idea a model diesel engine even existed.

RE: Need Help with Fox 15 Davis Conversion
 

these were also printed on tissue

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy How big is your tank?? fly 45 minutes, land and about half left?? martin

RE: Need Help with Fox 15 Davis Conversion
 

Love the mass launch of simple rubber powered aircraft.

I am glad to see entry level, low cost, 'real' aeromodelling involving youngsters is not dead in your part of the world.

RE: Need Help with Fox 15 Davis Conversion
 

It's a Hayes 12 oz. I only have the one flight on it so far, so still lots of set up to do still managing the CG trim from full to empty is going to be a challange. I need to find out how far aft I can shift the CG with empty tank and not have the plane become a handfull.

RE: Need Help with Fox 15 Davis Conversion
 

It will be if we don't get them involved I was amazed at how many of their parents had never seen or heard of a rubber powered model airplane. they were in every five and dime when I was a kid.

RE: Need Help with Fox 15 Davis Conversion
 

It is great it was a simple cylinder sleeve twisting on you. That happens a lot more than people realize too with all sorts of engines no less. The worse are the screw on cylinder head types of engines where the sleeve can turn as the head is tightened up.

Are you going for a long distance or endurance type of flight? Usually one doesn't need a fuel tank larger than a 4 ounce with a .15 engine. A two ounce might do quite well too. A four ounce fuel tank with your .15 diesel would help let you balance the plane a lot better than having all that fuel weight of a 12 ounce to deal with causing the big CG change on you.

Once upon a time many stores used to sell hand launch and rubber band powered model planes. Now it seems to be a few hobby shops are the only ones that do now. I remember buying and flying them a lot when I was a kid.

RE: Need Help with Fox 15 Davis Conversion
 

EarlWB is on the money on the tank thing, if you flew 45 minutes on half a 12oz tank tank thats 7 1/2 minutes an oz engine run
Also that plane is designed for a 25 to 32 glow that Fox 15 diesel is really doing its job in a plane that weighs maybe 4 1/2 Lbs and 63 inch span
You aced it on engine choice
martin

RE: Need Help with Fox 15 Davis Conversion
 

Any progress on numbers mate?

Iwould love to see what the Fox does on a 10x6 when its run in.

Cheers.

RE: Need Help with Fox 15 Davis Conversion
 

Had It out today and could not get a consistent engine run, felt like a fuel system problem, got home and took apart the carb and the spray bar was completely clogged, will try again tomorrow.
The idea of the large fuel tank was so that at a public event, I could keep the plane in the air for an Hour and a half, and let many people take their turns on the buddy box without having to land every 10 min.
Plus I just thought it would be Neat-o,Kool,Boss,Groovy. etc.
also I am using a 2500 MAH Eneloop battery

RE: Need Help with Fox 15 Davis Conversion
 

That is a cool idea for public events.
Yeah one has to rinse out even new fuel tanks and flush out the fuel tubing too. Use a filter if possible on the fuel filler device as little tiny bits of crud can get in there for sure.

Are you using muffler pressure? You could probably move the fuel tank back a little farther with muffler pressure.

RE: Need Help with Fox 15 Davis Conversion
 

Some folks do not like them but i use a 2pc aluminum filter with a wire mesh (cleanable) before the carb martin

RE: Need Help with Fox 15 Davis Conversion
 

A good old "crap trap" from Sullivan on the feed line saves a whole lot of headaches. Not a lot of surface area, but the double mesh really traps the nasties, and I like that you can see through it, so you know when it is time to back -flush it clean.

I tried one those pretty anodised two-piece filters with the removable nylon mesh element. They work great with gl*w fuel engines. Unfortunately diesel fuel dissolves the element.

Went back to the Sullivan :eek:.

RE: Need Help with Fox 15 Davis Conversion
 

FIERY I use the " sully" too works well easy to clean the wire mesh filter

PS got the teflon discs for OS10 thx, they can be reduced to fit with little effort THX THX regards martin

RE: Need Help with Fox 15 Davis Conversion
 

Not a good day, engine still not running right, spray bar clogged again, think it is the sealant I tried to use to seal the exhaust, I’m going to remove the engine, disassemble, and clean it, and try and get things sorted out on the test stand. I did attempt a flight plane got airborne and was climbing but engine sagged and I ended up in a juniper tree, no damage that silk is tough stuff.
Tweedy

RE: Need Help with Fox 15 Davis Conversion
 

Tweedy I do not think it is your exhaust sealant pull the engine I would just clean the carb, put on stand and run no need to take engine apart, think you have an issue with junk in your tank and or fuel lines martin
I also use a one way pressure fitting on the line from the muffler pressure tap to the tank, I had a tank too low in one of my planes solved the issue

whoops wrong pix will try again

HA finally pix on right OS10 in minnie telemaster you can see the pressure fitting right off the nipple in the muffler

RE: Need Help with Fox 15 Davis Conversion
 

I was pretty skeptical as well, but I finally found Brian Hampton's spreadsheet tool with the data extrapolated from real model propeller power absorption curves.

An APC 10x6 turning at 10500 rpm would need 0.44 HP and give 42.54 inch ounces of Torque.

This is at the upper end of what I'd expect from a Fox 15 but believable.

Ray