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

RE: Need Help with Fox 15 Davis Conversion
 

"Fiery" posted his findings and rpm numbers on several differents props here; [link=http://www.rcuniverse.com/forum/fb.asp?m=11078702]Fox .15 DDD head[/link]
Those numbers look very reasonable for a .15 engine;

APC 9x4; 12000rpm
Robbe 9x6; 9000rpm

RE: Need Help with Fox 15 Davis Conversion
 

A very simple solution no charts no tables get a Berkley digital fish scale about $25 and attach to tail wheel of aircraft very easy way to check a range pf props in a
short time martin

all you really need to know is thrust under real conditions

Note do not use the old spring type not accurate enough and hard to read

RE: Need Help with Fox 15 Davis Conversion
 

Martin,

I like charts and tables,

and I get a shiver of ecstasy up my spine at the thought of being able to plot a real Horse Power v/s RPM graph for a motor just like Peter Chin.

:D

RE: Need Help with Fox 15 Davis Conversion
 

Gazimoto no doubt the charts and tables are the road map but each airframe is different would be interesting to chart out and cxompare to the pull test for thrust
not going blind does give the HP based on RPM and the prop(s) that achieve it

martin

RE: Need Help with Fox 15 Davis Conversion
 

I have no experience with Fox 15s, so if Ray says it's believable then I'm willing to believe it.

Even so, it's a pretty good .15 that will do much more than 10000 with a 10x4. I'd struggle to squeeze 11000 out of an APC 10x4 with a good PAW 19TBR, so 10600 from a 10x6 would be very impressive indeed.

RE: Need Help with Fox 15 Davis Conversion
 

So there is a DDD head doing 9,000 rpm on a 9-6 Robbe prop. in post #41.  Add another inch and lose some more.  I think 10,600 rpm is a dream or misprint.  It is way too big for anything I can think of anyway.  A fishing scale can tell static thrust well for comparison, but a flight is the real test.  As soon as a higher pitch prop unloads the rpm's go way up and the blades dig in better.  The pipe could even kick in and who knows what could happen?  Maybe ecstasy shivers.

RE: Need Help with Fox 15 Davis Conversion
 

Let me clarify.

The Fox 15 would have to be putting out 0.41 HP if it could turn an APC 10 x 6 at 10500 RPM. That sized prop is so calibrated in the prop absorption curves done by the noted UK model diesel designer Gordon Connell.

Many of the modern 0.15 sized diesels will put out over 0.5 HP by the same or similar set of calibration curves at higher revs.

My point was that it was (just) within the realms of possibility that a good Fox 15 BB could attain 0.41 hp at a much lower rpm given that they were the basis of a high performance glow C/L combat motor in the late 1980's.

I must say that my PB early glow version bought nib is a hunk of garbage! I'm prepared to concede that the newer versions have improved quality.

I come from a c/l perspective where relative engine performances are easily and accurately measured.

I notice that Davis doesn't quote a propeller brand when he claims 10500 rpm on a 10 x 6".

Some brands are notoriously "fast". I once bolted a Master Airscrew on to a hot Oliver Tiger 2.5cc diesel and got something like 12000.

This was ridiculous so either the tacho was crazy or the individual prop had depitched.

There are now effective methods of determining actual airborne unloaded rpm without using a tacho.

Perhaps the Davis figures were obtained in flight?

Ray

RE: Need Help with Fox 15 Davis Conversion
 

Hi Ray,
are your 'modern' 0.15 diesels running mufflers and using hot fuels?

And conversly, is the Fox?

Food for thought.

RE: Need Help with Fox 15 Davis Conversion
 

Without mufflers!

I guess just about everyone just uses variations of Oliver Tiger brew. Additional additives (eg as used in F2C) can have nasty side effects.

I don't know anything about where Davis got his figures nor what fuel he uses, just speculating as usual.

Ray

RE: Need Help with Fox 15 Davis Conversion
 

As I thought, I would expect you not to run mufflers mate just as much as I would expect the Fox to do so - makes the figure even more spectacular don't it.