Mr Cox

I've been playing a bit with an old Queen Bee engine and an RJL head. Seems quite promissing, I'm getting about 10000rpm on a cox 8x4 prop, will try a lower load too. Here is a short bench run;

http://youtu.be/y0vgOAR7tac

fiery

My Feedback: (2)

Nice!

I have often wondered how the cox 'ball-and-socket' little end holds up to diesel use.

I have a couple of Pee Wee .020's in good shape; but they appear far too delicate to consider as candidates for 'dieselisation'.

Mr Cox

The Pee Wee runs very well as a diesel too. The important thing is to avoid small props and too high compression settings. And stay away from the Teflon discs, they are very dangerous, they leak a little and will trick one into increasing the compression further so if/once they fire the compression is too high.

Here is a short movie of a Pee Wee (with a modded DDD head for proper operation). I'm now flying it in a J3 cub. It flies much better now as the thrust is much higher compared to with the engine screaming on the stock prop as a glow engine....

On diesel you also get very reliable runs, it will always run out the tank even if the settings are not absolutely perfect. With glow it was like buying a lottery ticket each time...

https://www.youtube.com/watch?v=mMJlI0rgXVo&list=UUo_tYY3Qvzd8t7I9k18YJVg

ffkiwi

Good effort Mr Cox-you've gone ahead and done what I've talked about doing for several years but never actually gotten around to. 10,000 on an 8x4 is quite respectable-and typical of a sport plain bearing 1.5 'conventional ' diesel on that size prop (DC Sabre, Frog 150, ED Hornet, ME Snipe etc)-now drop down a size to 7x3-7x4 and tell us how it goes. I suspect-given that on glow they were a bit of a disappointment-that dieselising might prove to be the answer for the sort of sport/vintage slow flying models the original was intended for-and prove superior in that role compared with the glow. The good throttling (about the only attribute of the original Queen Bee superior to the 049 alternatives) appears unaffected by the conversion.....

On the Pee Wee-what exactly did you do the Davis head to modify it? I tried one about 30 years ago-but found it indifferent running on the bench and never persevered with it. Aeromodeller-in the late 80s or early 90s IIRC, published an article on converting a Pee Wee to diesel, using a 'puck' style contrapiston and a domed alloy disc as the head combustion surface-so similar to the Davis system, but with a less fragile and frangible seal.

ChrisM
'ffkiwi'

Mr Cox

I ran it today with smaller props, it does about 12400rpm on an APC 7x5 and about 13800rpm on an APC 7x4. Throttle response is faster but there is a little noise at full throttle (might be vibrations) that I could not get rid off by tuning, it was running smoother at full throttle on the 8x4 I think.

Here is a little movie on the 7x4 prop;
https://www.youtube.com/watch?v=Hc-Kd3W9b1A
On the Pee Wee I reduced the size (height) of the counterpiston, to enable a low enough compression setting. I also replaced the Teflon disk with one made from a brass sheet. This gives a much better seal and will last for many runs as well.

qazimoto

My Feedback: (1)

This one? Anyone know which Aeromodeller issue the image was in? A rescan would be good.

Mr Cox

You can also make a counter piston with an o-ring and not have to bother with the discs. AndyW showed some time ago how it can be done, this was on a .049 (if I remeber correctly);



I took a look inside the QB engine today, it looks very clean even after the smaller props, and the counter piston is spot on in terms of height (with one shim on the head).
The power on the 7x4 prop is quite good actually, it is certainly stronger than a PAW .061, so it seems to be delivering power that is proportional to its engine size, finally....

Godsey

Must resist urge to spend more money for conversion........

ffkiwi

That's the one I had in mind-I think the author was a Pete Meleg? who for a time was offering head conversions for those who couldn't do it themselves. I may be wrong but 1989 sticks in my mind as the year the article appeared in AM.

ChrisM
'ffkiwi'

Lou Crane

Mr Cox,

Thanks for the very interesting info about the RJL dieselized Queen Bee! I like the idea of easy use and useful RPM on props "way too large" for the engine in its stock, glow form.

... checked the MECOA site to see if they had conversion heads for the QB, (or the .09 engines if they are the same size.) I didn't see any there... They keep busy enough that they discourage calls asking questions - and I respect that if I possibly can. Cox Canada might be another source - I'll check there, too.

Is the QB head the same size as the Cox .09 heads? (I have a Cox .09 around somewhere, finding it might turn into a project...)

If not, did RJL ever offer the .074 QB heads?

If none of the above, where did you get yours?

How was the economy?

Final thought... the "little noise at full throttle" might suggest checking that the rod ball socket is properly snug.

Thanks again!

ffkiwi

Without pre-empting Mr Cox too much Lou, I can confirm that the Cox 09 and QB 074 glow heads are interchangable in both directions-so the RJL 09 diesel head will certainly fit. You should find the 09 head on the Mecoa site-look under the 'accessories' heading-they list it at $26.99. There's also a downloadable instruction sheet...

ChrisM
'ffkiwi'

Mr Cox

Yes, the heads are interchangeable between the Cox .09 and .074. The head shown above is the RJL .09 head from Mecoa, I have not modified that in any way.

The only mods I have done are to the RC carb. For a better (leaner) idle I have added an airbleed, but it was a little too small I think. I have now enlarged it and also opened the carb a little above the throttle barrel. Both these things should give a leaner low-end.

I have a testbed for the engine now too, a TT Scooter, should be able to fly it soon.

Mr Cox

Oh, about the noise. I think the revs are not high enough for any slop in the conrod to be any problem. I have run this engine up to 18000rpm on glow fuel before...

The 8x4 prop should be enough for the TT Scooter I think, so I'll start with that.

Mr Cox

I have flown the engine today. It is plenty of power for the "Scooter" and I will have to add a bit more of downtrust to the engine. I also surprised/shocked two older gentlemen at the field today by the easy starting and quiet flight. They told me about their own past experiences about flipping diesels for hours etc. Their comments where; "Wow, that's more quite than electrics"

Here is a little video with an APC 8x4 prop and inflight settings, recorded on the ground;

https://www.youtube.com/watch?v=KLFfH1vQKSY

ffkiwi

Nice work Mr Cox-and nice rpm figures. What a pity Cox never realised they had a good candidate for a diesel...! Could you take a closeup shot of the carb and annotate it to show where you've added the airbleed -and size details etc. Sounds like it might be a worthwhile mod to do to mine. In any case, complete carbs are available from cox Int'l if I mess it up (admittedly for about the same price as a complete second hand Queen Bee....!) The geometry of the carb body doesn't lend itself easily to fitting an adjustable airbleed, mores the pity... again it's not beyond the realms of possibility to scrap the Queen Bee carb and retrofit the TD 050 carb which does have an airbleed....

ChrisM
'ffkiwi'

PS-having just been on the Cox In'tl website to check out prices on the above carbs I notice something very interesting-both the OEM ($39.95) and the current Cox Int'l Queen Bee carbs ($29.95) have airbleeds -my Queen Bee engine carb does not. I bought my Queen Bee from Tower many years back, when they first became available on the market. Now Martin Hepperle's site shows the Queen Bee as being available/manufactured over the period 1987-1996-so somewhere along that timeline Cox decided that an airbleed was an improvement..... I'm guessing I would have bought my Queen Bee ca 1987or 88...

fiery

My Feedback: (2)

Chris

The bottom L/H photograph in post no. 7 above shows the location of the air bleed hole quite well.

ffkiwi

Quite true Derek-I hadn't looked at it closely-but what it doesn't show is the size-and that will no doubt be quite critical-which is why most airbleed carbs-excepting the very crudest like early AM, OS Pet, and some PAW - are adjustable.....

ChrisM
'ffkiwi'

Mr Cox

There are two mods that can be done to lean the low end. One is to enlarge the hole above the throttle barrel such that it closes after the opening below the barrel (this is how the OS .10FSR was made). On my stock version it was almost the other way around, before modification. The second mod is to add an airbleed, I only eyeballed the position at first and it ended up a little too high, after that I have added a second one, a little lower than the picture shows above.

There is a guide to these mods that I saw somewhere here on RCU, not sure who wrote it. It explains the principle and gives the dimension. To me those numbers sounded a little too aggressive, and both mods will lean the low end, so I have started with smaller changes and then increasing in steps, but I may very well end up with similar numbers in the end though. The newer carbs sold by Bernie does indeed have an airbleed, I haven't checked the dimensions of it, or looked for the intake mod, but I think I have one in a drawer somewhere.

I'll try to attach the guide to the mods below.

ffkiwi

That's useful info Mr Cox-thanks for the post...

ChrisM
'ffkiwi'