fizzwater2

My Feedback: (61)

Don't they all?

hsukaria

We budgeted so much money each month for my hobby to match what the wife spends each month to do her hair. At first, I thought that I got a good deal, but then I realized that we didn't factor in all her other expenses like makeup, hair goop, etc... I think I got gipped!

I knew about MECOA, but I am not familiar with them as much as Fox. My wife is from Arkansas, so I have a certain affinity to Fox. I plan on taking the kids (and myself) someday and visit the place.

All my other engines are foreign, I'm afraid: Super Tigres 40 and 51, Thunder Tiger 75FS, Irvine 40, Norvel AX-40, Magnum 52RFS, and I confess, OS 55AX and 70 4-stroke. So I have some experience with breaking in an engine from some of these. Maybe not as long a break-in as a Fox, but at least I know what lies ahead.

Konrad

You are doing better than I. Those beauty expenses go on my budget! She claims that the results are for my benefit and therefor I should pay for them. I'm starting to see why the idea of a dumb blonde is often so popular

It takes some guts to admit you have those 0.55cid and 0.70 cid engines.

All the best,

Konrad

hsukaria

The .70 came with a used plane I bought, so maybe I can be forgiven for that? The .55 I bought for a plane I built for my son's birthday and I thought gettng an easy out-of-the-box engine would be more encouraging to him. Unfortunately, he lost interest anyway.

Konrad

All kidding aside the OS 70 four cycle engine is a good sport engine. Too bad Duke was too wise to try to bring a four cycle engine to market.

All the best

hsukaria

Like you mentioned before, Fox engines are under-rated and if they hired some slick marketing types like the other engine manufacturers, they might sell more. I for one have been noticing the increase in foreign-made engines (ST and TT, plus the already high price of the OS) and Fox and other American made engine are starting to look price-competitive. If the monetary exchange rate with China is freed up, the price of the Chinese engines will go way up and Fox might start selling more, if they get themselves prepared for it.

fujiman

My Feedback: (133)

konrad, i never measured the choke area of the perry vs. the ST. and yes i did know of the delivery discharge slot adjustment on the ST carb. not too many guys do. i really don't have any thing bad to say about the fox or ST carbs. i guess i just like the perry. kind of like soup veg. vs. tom. they all seem to get the job done. some years ago i had a fox hawk (no mods.) in which i ran a perry carb. and installed it in a EZ pilot FW190 arf w/retracts. i used a cut off fox tuned pipe header and used a copper 90 degree plumbing elbow and the pressure nipple on the header and if i remember i was using a fox plug and powermaster 15% nitro cast/syn fuel. looking back on that plane/eng. combo and tyme it has to be one of my favorite planes to date. good power to weight ratio, looked very cool w/ gear up full throttle veerryy LOW flybys just over the grass or weed tops and that hawk singing a lovely song. the hawk with that combo i could get the hawk to just tick, tick, tick, over and it took the trottle, i mean right now!!!!! been lovin' the perry's ever since. and i must add have bought up as many hawks as i can find!!!!!!

hsukaria

Speaking of choke area, if the engine is converted to a diesel, do you have to reduce the carb size? I read that some of you guys have converted your Fox engines to diesel. Did you keep the stock carbs and mufflers?

Konrad

That is the goal, to have an engine that allows us to have such fun.

All the best,

Konrad

I do. I like to use the Mk X "A" sized carb ( 0.290) or maybe the "B" (0.312) carb on the 10 cc engines. This is because we use very large props we don't need that much flow capacity. I recall that much to my surprise the Diesel engine actual tracked better with a smaller load prop. This was because it allowed higher CR than the slower heavier large props. Normally you would think that the bigger prop would idle better because of the added flywheel effect. In the case of a diesel it often isn't so. Now I have been known to use a heavy prop nut to give the added fly wheel effect and still allow the use of a higher CR of the smaller loaded prop.

All the best


P.S.
I think there is a diesel conversion form on this site. You might get a better answer there.

NM2K

My Feedback: (14)

The problem with Fox engines is the same problem that OS is experiencing, although I do believe that OS finally began to solve their problem, after a fashion.

The shared problem with both companies is that the founders passed on. This left a heck of a vacuum in both companies. I haven't seen anything really new in the vein of what Duke would have done, since Duke's passing. Ditto OS. But, OS did have some talent lurking in the background with the introduction of their new series of four-stroke engines and some of their later two-strokes. If Fox did something similar and it got by me, please forgive me.

Now I know that Fox has/had some really terrific people working for them and I'm not trying to make them feel badly at all. I just haven't had my attention pulled in their direction with new product introductions.

Duke always favored the control line flyers. I had heard that he really wasn't enamored with R/C, but produced those engines in order to stay afloat. What I heard could well be wrong, but the feeling felt accurate.

The large gas engines sold by Fox of late never really caught my attention because of their high prices. However, now is a time for Fox to get on the 20cc and smaller displacement gas engine fad. I do get the feeling that the popularity of this size of engine is going to be with us for quite a while.


Ed Cregger

hsukaria

And Fox just came out with the .50 gas engine, looks nice but is expensive compared to a glow. Maybe the price will come down eventually.

Hobbsy

My Feedback: (102)

H, since the rc carb is a variable venturi carb it is not necessary to change to a smaller carb, some of us like to simply because "we can", as the old cliche goes.

hsukaria

I was looking for the Davis Diesel website, but when I click on the front page to enter, I get nothing. Davisdieseldevelopment.com. Has it moved?

Hobbsy

My Feedback: (102)

http://davisdieseldevelopment.com/diesel/index.htm

Try this one.

Konrad

No, we change the carb because it is the correct way to accomplish the task, proper fuel draw with the minimal pressure loss.

I beg to differ most of our model carbs and the Fox carb are NOT variable venture carbs but rather variable orifice carbs.

Lets see if I can explain this in 2K words or less.
Using Bernoulli’s principle http://en.wikipedia.org/wiki/Bernoulli's_principle that as air increases in velocity the pressure drops. And using venturi theory http://en.wikipedia.org/wiki/Venturi_effect we can get this velocity at the narrow point in the throat and by the time we exit the venturi have regained most of the pressure. While our carbs at full throttle are short they are rather crude venturis at best yet they work rather well at giving us good fuel draw with little loss of crankcase pressure. Now if we hold the throttle of our carb at say some partial throttle point (see attached drawings) we loose much of this venturi effect as we have in effect added a plenum or expansion chamber (yellow area) if you like. This expansion chamber surrounding the spray bar can drastically reduce the effect from Bernoulli’s principle causing a pressure rise. Exactly what we don’t want at the spray bar to help with fuel draw.
Also because of turbulence there is little recovered pressure at the exit of the carb.
Now in our engines if we are at part throttle it is assumed that we don’t desire the full power potential of the engine so this is not too much of a concern. Now at full throttle we are very concerned with the pressure recovery at the exit point of the carb and at the same time demand good fuel draw.

An oversized carb throttled back to the same size choke area of a properly sized carb CANNOT achieve these seemingly opposite requirement. The oversized carb suffers from poor fuel draw along with lower power output. There are also some less tangible points in favor of a smaller carb. A smaller carb will allow for much better throttle transition and overall tractability of the engine. This has huge benefits for adverse attitude work (aerobatics).

Now the only variable venturi carbs I know of for our toy engine are the H&H (?) carb and the slide valve type, like that found on the Picco 45 (7.5cc). The H&H carb had what looked like an upside down water drop suspended above the inlet. This kept that expansion chamber from developing as the throttle was closed (this is a good carb design for the “carb design thread�).

And if none of this makes sense remember what Mark Felt (AKA Deep Throat) said; If it doesn’t make sense follow the money. Just think how much money the OEMs could save if they only had to make one size carb for all their engines from say a 2.5cc to 20cc engine. Since they do make various sized carbs there must be a reason.

All the best,

Konrad

P.S.
Sorry for the various arrow sizes, these are just artifacts from my drawing program.
Yep, I think I went over the 2K limit!

P.P.S.
While not as effective as a properly sized cab many OEMs will supply a choke insert. This is to control the size of that plenum. I think OS and Saito still often do this.

earlwb

The problem with a model diesel engine is the air fuel mixture is much different than with a glow engine, a diesel runs a much leaner mixture ratio, which is where they get their frugal fuel consumption from.  Granted one can change the ratio easily enough with the needle valves. But with a model diesel engine, if you use a large prop on the engine and have it turning lower RPMs, the carb being too large has fuel draw problems. So you install a smaller bore carb on it, that reduces the venturi bore size a lot and the engine now runs good with bigger props. Now if you ran smaller props the larger carb would not normally be a issue (there are always exceptions of course). I remember trying some engines with a big bore carb as a diesel and with larger props, you could not go WOT throttle as the engine couldn't take it. But putting on a smaller bore carb corrected the problem.
If you look at a lot of model RC diesel engines, not the conversions either, you'll notice they tend to use some really small bore carbs on them, downright tiny in comparison to a equivalent glow engine. But they run just as well as a equivalent glow engine, even with the tiny carb on them. The easiest to convert glow engines to diesel engines are those that have smaller bore carbs on them already. Engines like the OS40FP, OS40LA for example, make good diesel engines. Many regular glow engines work well, but if the carb is too large, you may need to install a smaller one. But you won't know for sure until you try it first and see how it goes, especially with the prop you want to use. Now then the european combat diesels or racing diesels (mostly control line)  have big bore venturis on them as they turn small props and can turn up really high RPMs, so they do well with big bore venturis. Plus if you use bladder fuel tanks you can go to a straight bore and have a huge venturi if it is needed.

Konrad

Good point about the air to fuel ratio. Now the old Fox Mk X carb allowed you to custom profile the low speed needle to maintain that proper relationship across the whole rpm band. The fixed fuel transition slot of the 'Easy Adjust' carb does not allow this (well you can only make it richer and if you mess up you need a new rather expensive barrel). Nor is it practical for the average Joe to change the slot in the asian tube over slot design carbs.

All the best,

Konrad

Hobbsy

My Feedback: (102)

Well Konrad, Mr. Wikipedia never actually ran a Diesel to see, first hand experience says that you're dead wrong.

Konrad

Wikipedia was reference to explain concepts, not the application of these concept to our toy engines. Now not only does first hand experience support my stance so does actual test data with measured pressure drops at the spray bar. (I have run those tests) Now I will say that these tests were not accomplished to optimize the performance with diesel engines. (I had problems with the first OS long strokes with their way oversized carbs) The carb and its airflow have characteristic that are not effected by the engines ignition source. Now the air to fuel ratio is and was addressed later by Earlwb.

Please note, I did not say that your technique doesn't work. I tried to show that a proper sized carb is much better than an oversized carb that is throttled back, be it glow or diesel ignition.

Or was your concern about the term variable orifice?

Al the best,

Konrad

Sport_Pilot

You are mostly correct. I think you did go wrong in the following statement.

While this does reduce fuel draw, it is not correct to say that the carb CAN NOT overcome this. Some carbs clearly can, some for example are not oversized enough to overcome this. Some have more muffler pressure than others or larger capacity needles. For example that condition exists at idle yet the fuel draw at idle is greater which helps to overcome the lower muffler pressure at idle.

Konrad

My point was that the throttled back oversize carb does NOT have as good a fuel draw nor does it exhibit the pressure recovery one gets from a properly shaped and sized venturi (no plenum). I think I stated in a throttle condition we ignore this efficiency loss as we assume we are not striving for full power in the throttled back position.

I'm I wrong in thinking that at idle the fuel draw is actualy worse (less flow therefor less pressure drop at the spray bar). I seem to recall I could not raise a collum of fuel as high at idle as I could at full throttle. I have to admit performace at idle was never much of a concern to me .

Now a slide valve carb like the that found on the Picco 45 (not the dynamix type found on the Webra or CMB) does maintain the venturi as the throttle is moved. So much of the pressure loss is recovered. Now fuel flow with pressure fed systems was outside the scope of my discussion.

All the best,

Konrad

controlliner

My new Fox .60 Eagle (reliving the past) new in box from 1971. I got it from Bob Boumstein. Unfortunately I have to wait for Christmas to run it.[:@]

hsukaria

So because it is so special you only run on Christmas? Only one day a year? That engine will certainly last forever!

earlwb

Those are great engines. Not as powerful as our more modern Schnuerle engines. But they still run really good. But at their time way back then, they were quite powerful in comparison to the other engines at the time. You had to get a Clarence Lee PDP ported .60 (K&B or HB) to beat it out.
I thought I had a video of when I ran mine last, but I guess I didn't make one. Or I would have let you watch me run mine to tide you over until XMAS.