Author Topic: Hot Fox 35 Restarts (Read 1289 times)

Stan Bidowski · « **on:** May 03, 2008, 01:00:14 PM »

Anyone have some good tips on how to get a Fox 35 Stunt engine to restart quick for racing
use? What's the most important areas of attention? The fit, the tank, the technique, etc.

Thanks for sharing!

Stan Bidowski

Alan Hahn · « **Reply #1 on:** May 03, 2008, 06:21:28 PM »

Stan,
Mine always start great when hot---things go south if you let them cool off to the "middle" zone (not hot, not cold). So I say, get it on the ground asap, and to your pitman to minimize cool off. Also train your pitman to be fast!

Stan Bidowski · « **Reply #2 on:** May 03, 2008, 08:19:41 PM »

Yes, I guess that can be the ticket. Sometimes a pitted Fox 35 will fire right off.
However, many pit men aren't 'always' quick. So, any more tips for starting
in this medium area of hot restarts? What about dousing? Are the Fox ABC units
considered to be a stock Fox by anyone? I have a couple ABC P/L' ers, but
have never used them for racing, not legal as far as I know and easy to check.

Stan

don Burke · « **Reply #3 on:** May 04, 2008, 10:30:27 AM »

My FOX racer had a pinch-off on the uni-flow vent. I directed the overflow to hit the head and provide some cooling. Seemed to work OK.

BTW finally I cured all my FOX restart problem by going to plain-bearing 25s! LOL

Alan Hahn · « **Reply #4 on:** May 04, 2008, 05:27:02 PM »

Well if I were to squirt something on the head, it would be water,not fuel. I remember watching Jerry "Who"'s monocote simply melt away in an invisible alcohol fire after his fuel caught on fire after he squirted the head trying to shrink the outside.

don Burke · « **Reply #5 on:** May 04, 2008, 07:06:23 PM »

I haven't had a pit fire from doing the overflow squirt, but I have certainly had too many when using an exhaust prime tube on my TQR and BTRs.

It appears to flame up if I contact the hot glove points before I finish fueling. Not a lot of fun!

don Burke · « **Reply #6 on:** May 04, 2008, 07:08:18 PM »

And to answer the ABC question, definitely not OK for FOX race. Nor, as it appears the new ceramic P/L assys from FOX.

PaulGibeault · « **Reply #7 on:** May 04, 2008, 09:02:16 PM »

HI STAN,

Excellent Question! First off, the more castor oil in the fuel the more tolerant the engine becomes. I think it really helps to break-in a new Fox on 25-29% castor oil fuel for the first litre of fuel anyway, & bonus if you have a whole gallon. After that, it doesn't matter very much what you run, as long as the oil content is 20% of which 10% must be castor. My break-in is not on the bench, but in the air. I use a 9 X 6 prop & a 1 to 2 oz stunt tank. Start off rich, & do some lazy eights to get the engine to lean out in the manoeuvers, then fly a few level rich laps to get the engine to cool & then back to manoeuvers / level flt & so on. Gradually lean the needle mixture until the engine holds a setting & doesn't sag. Now, you can start racing & can pitch up the prop using a 9 X7 & finish with an APC 9 X 8 which is the max load I've found so far...
Hot starts (w/ a Fox) need attention to a few items:

1. THE FIT: A decent piston/cylinder fit is needed. This is obtained from the process just described. Once in a while, a poor cylinder fit ecapes the factory & will never be a good hot starter & will need replacing... All good starting engines will have good cold compression. ANY vertical score marks on the piston or cylinder make for a poor starting engine. (The high castor run-in fuel helps prevent that).

2. THE TANK: A narrow ( 1"), uniflow tank is a MUST. Narrow uniflow tanks prevent a great deal of rich to lean running throughout the run. This is very important for good hot starting, as a std. vented wide stunt tank going rich to lean, causes the engine to be freakin' hot on landing & this makes it A LOT harder to get an instant re-start.

3. THE TECHNIQUE: As much as I've read about it, I've never seen the need to pour raw fuel on the cyl. during my pitstops. On re-fueling, as long as the fuel line is full, the Fox will re-start in a flip or 3. (I think if you have to quench the cyl for the engine to restart, the "fit" is no longer good for racing, but it will get you through that last race, once you've discovered the fit is gone) $20 sent to Todd Ryan will buy you one sweet running tank for Sport Racing. I find that my "Kwik-Klip" attached AFTER fuelling works just fine.

BOTTOM LINE: Racers have been hot starting Foxes for 30+ years & so can you! It's cheap fun, & with a bit of care & attention, you can do it. It's not hard & not certainly not rocket science.

Hope to see you in a Fox race sometime, Stan.....( how about the NW Regionals??)

K

Paul Smith · « **Reply #8 on:** May 05, 2008, 05:18:50 AM »

I my experince, the biggest problem is when the contest management furnishs the fuel, thus preventing you from using good high-castor stuff.

In two major contests last season, the house brew was low budget RC sport fuel with no lube at all, probably donated by a local toy store that couldn''t otherwise give it away.

The above does not refer to the DCT, AMA Nats, and Beanfield contests where the fuel was good and so were the restarts.

If they don't let you use shutoffs, (as stated by Mr. G), a tank that quits clean is a must.

Stan Bidowski · « **Reply #9 on:** May 05, 2008, 05:27:52 PM »

Good info here. Yeah, I ran at Sig and the fuel supplied could of been better,( at least when
I was there ) seeing as they make the good stuff! That was a suprise. I really need to make
or get a better tank... I just threw on something quick, just to get it done, after I finished
building. It ( the tank ) has been on there for a couple of years now!

Stan

Mark Scarborough · « **Reply #10 on:** May 06, 2008, 08:23:30 AM »

As Paul said, contact Todd Ryan about a tank, he is a very precise crafsman and has been playing the racing game a while, and may I add is pretty succsesfull at it as well. Not only that, hes a great guy, and one of the younger ones in our branch of the hobby. He has my tank sitting on his bench now,, All I have to do is finish my sport racer, then were ready to rock (or get rocked?)

Alan Hahn · « **Reply #11 on:** May 06, 2008, 04:04:14 PM »

Hi Stan,
Were we using the 50-50 oil mix at Sig? I was assisting in running the Fox Race, but don't recall right now what fuel we were provided (it was already there when I asked for it).
Around here (Chicago area), the fuel seems to pop back and forth between all castor and the 50-50 mix (typically we are running a Sig fuel though).

I could ask tomorrow at the Tree Town Meeting what people prefer (as well as here for those who think they may attend the Sig Contest this summer). With a consensus, we could ask Mike Gretz to give us what we want. The obvious options are 20% oil (50-50), 20% Oil (100% Castor), and 25% Oil (100% Castor) since they are all Sig standard mixes. Also I believe we are using 10% nitro. I don't recall using the 25% castor in the Fox racing events. I think "true" racers and speed types (seems an oxymoron to combine "speed" and Fox 35 in same thought!) tend to want the 20% oil--(50-50) (I think Glen Lee likes that), but Stunt retreads prefer more castor.

Stan Bidowski · « **Reply #12 on:** May 07, 2008, 06:26:19 AM »

Alan, I recall the fuel served up was 20% oil ( 50-50 mix ) and 10% nitro? I would of thought 25% all castor 10%
would of been a better Fox diet, since the 25% oil would run cooler, and maybe help with the restarts. The 50-50
will run cleaner over time, and also a bit faster too with less oil, but speed is not really the objective in the event.
I don't think only 10% castor would do a Fox 35 much good in a lean run, the extra 10% klotz will help cool it down
some, but not provide the bean oil buffer a mechanite piston likes. This is a good topic to explore opinions on.
I know what a Fox likes for fuel in stunt use and good longevity, but perhaps for Fox 35 'racing' use, the best fuel is
different?? It would be good to hear some more thoughts on what works well for a racing application. A Fox is not
a ball bearing ABC motor, if it was, then a 20% 50-50 mix, at 10% nitro should be great for sport racing.
I'm sure Glenn Lee knows his stuff! He told me that as soon as fuel hits the hot piston, it shrinks away from the
liner, and that drops the compression. The best method was to get fuel just up the line, and then try for a start.
Made sense to me, it's getting the theory to work in practice thats the tricky part. The motor doesn't always pay
attention to what it's supposed to do!
The Sig contest is a good one!

Stan Bidowski

phil c · « **Reply #13 on:** May 11, 2008, 08:28:41 AM »

Stan, another trick is to flip the prop as close to the shaft as possible. You can double, or even triple, the speed of the flip by catching the prop in close. Hitting it out in the middle of the blade gives the shaft a very leisurely hit on compression. Just flipping closer to the prop nut will often start a motor.

johnt4051 · « **Reply #14 on:** May 15, 2008, 02:08:59 AM »

I have always had good results getting hot Fox restarts by following this sequence: When I catch the plane, the first thing I do is douse the head with fuel to get it cooling while I'm fueling. Contrary to worries stated above, I have never had a fire while doing this. Then just fuel up (do not prime) and give the prop a hell of a whack. I find that if you don't douse the head right away, it doesn't do any good. The other thing is to practice enough to figure out just exactly when to let go the uniflow pinch. Do you squeeze a bit after the tank is full with the vent open, or stop squeezing before you let go the uniflow, or simultaneously, etc.? Your results may vary, and some trial and error will reveal the proper sequence. Once you figure it out, the restarts will become predictable.

--jt