glowtime

I just finished scratch building a Airtronics Q-tee from tiled net plans. The engine started as a golden bee but it sports a black widow back plate with screen removed. Other mods include new surestart cylinder, throttle ring, Galbreth-nelson plug- 2 shims, 5-3 ducky and 30% nitro. My question is that it (turns 17000-17250 for the first minute then drops off to 16,500) and settles in for the rest of the 8cc tank. Whats the deal!!!!. Thanks in advance

combatpigg

My Feedback: (3)

Sounds like it could be a worn out piston / liner. With a couple drops of prime, take the piston to TDC and look for bubbles in the exhaust ports. Feel for how long the cylinder stays pumped up, it should hold air for at least a couple seconds. The other thing to look for is radial slop [run-out] in the crankshaft's fit to the case.

I like to start with a lower end [case and crank only] that is fit just right. The prop should spin freely when you flick it, but there should be no radial slop. I clean everything with Hoppes gun solvent. Next is to add the best Black Widow, TD or Killerbee P/L combo you can come up with.

With a 5x3 prop, 30% fuel and high compression head you should get 22,000 rpm or better if you can get enough air through the backplate. I either drill the stock backplate out as far as possible or use a Killerbee backplate.

hllywdb

The stock sure start cyl with the throttle ring is not the most potent combo out there. You said new cylinder, did you use the old piston? CP is probably right as the P/L fit may be off. How about slop in the rod where it seats in the piston? A lot of time those need to be tightened up right out of the package. My sure start with TD P/L set, drilled out backplate will still get me over 20k with the throttle ring.

glowtime

I did not take the time to use the correct new matching piston because the existing piston looked like new. CP was right as i think the fit is incorrect. I should know better than to do a stupid thing like that.I always make sure the connecting rod is spot on even when new or i carfuly reset it. Thanks for your input guys.

controlliner

Drill out the backplate and tank venturi with a # 43 drill. it will give good performance and good fuel draw with small props.

cfircav8r

My Feedback: (1)

One other thing to think about is the Q-Tee will fly superb on a Texaco running a larger prop using full sized gear, and give a much longer run time. Mostly my personal preference, but the Q-Tee is a slower flying design.

glowtime

Thanks controlliner, i will try your mod. Thanks Cfircav8r, i chuckled when reading your post because i just had my trusty Texaco in hand ready to put in the Q-Tee. I just finished resetting the conrod/piston and all new internal gaskets bolted her in. Its been 15 years since i ran the old girl on a cox foam glider. (What nitro,head, and prop do you think will be best for the Q-Tee with Texaco) I weighed in at 18-OZ flight ready. I have to thank you guys again for your help!

cfircav8r

My Feedback: (1)

If I remember right I ran a 7-4 prop and a hot head with an extra brass gasket to drop the compression a little. I always preferred Cox glow fuel in my .049's. I believe that it is about 25% nitro and 20% Castor oil. It has been about 25 years since I had that plane though so I may be a little off.

jetpack

My Feedback: (1)

There was 10, 15 and 30 percent nitro blends. Glow Power Fuel was 10%, Flight Power Fuel was 15% and their Racing Fuel was 30%. All blends carried 20% oil.[8D]

gcb

glowtime,

You might want to check the seal between the front and back of the BW tank at the venturi. It may be sucking extra fuel at first, then air as the fuel level drops making it a bit lean.

George

rrragmanliam

My Feedback: (1)

Heat is the deal. Could be running lean. After you lean it out for max rpm, try giving it a click or two to the rich side.

rrragman

R/C Phile

I second rrragman, plus you may not have enough oil content which will make it run a bit hot and get a little tight. My 049's behaved similarly until I added about 11% castor / Benol to my fuel.

combatpigg

My Feedback: (3)

17,000 is way down on power even before it warms up.

R/C Phile

Roger that CP, both my Black Widows (Std Ventury size / OEM screen) run around 20,000 RPM on a 5 X 3 Cox Prop using a similar 30% nitro , Galbreath Head, Nelson Medium Plug, and 1 shim

trike_flyer

Hello all

I am new to the site.  I see you are talking about differant things to enhance the cox engines.  Recently I have had a strange thing happen to my  049 that I have from the 70's. With the parts getting hard to buy for them, I decided to get a glow plug head for it.  When tried, the rpms seem to be down from the normal for my old 70's head that still works. The needle setting is higher than before as well, five turns instead of the normal 4 turns.  I have no rpm meter to find out what rpm's it is doing, not that far into the hobby again, using engine sound and trust to give me a guide to how it is.

Could the new head have a lower compression than the standard glow head and cause a differance in the performance? I am using the same fuel in it while testing so it should have no effect.  I did the test with a OS#8 and OS#LC3 plug, the LC3 gave worst performance than the #8, as they were the type recamended to use with the head. Are they the right heat range to match a glow head?

Thank you for any light you can shed on this. 

JB

combatpigg

My Feedback: (3)

JB, the head can be the culprit. So can varnish coating the wear surfaces slow things down. If you have a gun cleaning kit and some solvent, you can take care of that.
The other thing that you look at while the engine is apart for cleaning is slop in the ballsocket joint between the piston and connecting rod.
As far as the needle setting is concerned, higher fuel demand because of more horsepower being generated is one cause for opening the needle. Higher compression should increase horsepower, as well as using a small prop like a 5x3.
Changing to a higher nitro fuel also causes the needle to be opened further.
Fuel leaking out the crankcase also causes you to open up the needle to compensate.

trike_flyer

No varnish, test is done same day within minutes only change is head. Off with glow head on with plug head, then back. Prop and all the rest stay the same, fuel and all.  I do have a crankcase leak, I have a few ideas on how to fix that.  Piston ball joint was just done last night and it seems to have removed one turn from before. Reduction in needle valve may have been from my first try to fix the case leak.

The settings again are:

Glow head  4 turns and lots of rpms
plug head  5 turns and less rpms

Thanks for the try combatpigg.
Any ideas to fix the case leak, I already changed the gasket and sanded the case to flatten it. Thinking about an oring instead of the gasket.

Mr Cox

The case should seal once you get the sealing surface flat, unless the tank is damaged. Use fine wet-grinding paper on a piece of glass, the cylinder stands proud of the case and should be taken off.

The heads for regular glow plugs (not Nelson or Turbo) have always been down on performance, it comes from the fact that they seal in the wrong place (above the threads).
That's why cox made their own plugs/heads in the first place.

trike_flyer

I had a hunch the head with a plug had a higher volume than a glow head. To test it I got out the iso alcahol and did a test on both using a dropper. The plug head took an extra drop of fluid. To fix the differance, I gave the head a sanding on glass like most gasket surfaces get to fix them. It worked, in one sanding of about 3 min the volume was low enough to make the head act the same as my glow head and the power was up to the same on the stand. Same number of turns on the needle too.

So if you get a glow plug head for your cox you need to do a test and fix it before it goes into use.

As for my crankcase problem I tried several times to sand the surface flat to no luck. The back plate is the problem. Have a second engine that needs new crankcase due to crankshaft leak. Will use its back plate. Can you fix a crankshaft leak?

Hope this info is good for someone.

SGC

trike_flyer , most Cox engine parts can be found here :- http://coxengines.ca/ , only way to fix a crankshaft leak is a new crankcase and crankshaft , if you plan on useing a cox motor a bit , I'ed recommend buying an anodised C/case, also if your building up a motor for high rpm's use the killer crankshaft as its stronger and better balanced. re your crankcase leak , are you useing the correct crankcase gasket ? , these are available in several different varrieties acording to the backplate type and available from the above webstore.

Mr Cox

Do you have any rpm readings?

There are several threads on how to get more performance out of the heads with regular glow plugs. Typically the compression is too low, best fixed using a lathe as there can be a lot of material to remove, and finding a suitable plug-length. The threads can also be seal with RTV or similar stuff to mimic the Nelson/Turbo plugs.

Personally I have only managed to get somewhere near (within 500rpm in the best case) the power one gets with a proper glow head (or Nelson/Turbo type). Tuning the compression correctly with shims is also important for the proper glow head so there might be more power to get from the non-glowplug head in your case.

Edit: I found the thread I was looking for [link=http://www.rcuniverse.com/forum/m_7973256/anchors_7973666/mpage_1/key_/anchor/tm.htm#7973666]The great glow plug run-off[/link]

Andrew

If your backplate is one of the plastic ones, they will distort if overtightened. Over time, they seem to take on a permanent set and there is little you can do to remove the warp.

Other than replacing the crankcase, I don't know of any remedy for a leaking frontend, other than a high castor content. Even then, if it's worn badly enough, a new case is in order. SGC's suggestion of a new crank/case combination is the best way to go.

andrew

MrGoodwreck

Where did you get these?

Andrew

Sent you a PM.

andrew

trike_flyer

Mr cox nice tread about the heads. His head is differant than the one I got. Mine has lots of room for trim before it will hit cylinder. Differant maker I guess.

Got my case to backplate down to a small leak now.  Still running at 4 turns on the needle so I think it is going to be ok.  Decided to buy a tach and get some readings on it.  I am using a 6X3 prop with old style single transfer port cylinder and tankless - no screen backplate.  Head is old syle hemi glow head low compression.  Fuel is a blend of morgan's called sidewinder race blend 30%/12% oil that has been mod to 20% oil with castor lowering nitro to ~25%.

I got 12800RPM on the tach with this setup on the stand.  It has lots of pull and seems to want to bend the stand.  Does my numbers seem ok or do I need to play with it some more to get extra rpm?

Bought a selection of plugs for plug head and plan to see what differance each will do and choose the one it likes before I burn out the good glow head.  Will keep you posted on the results.