Pond Skipper

http://www.bolly.com.au/book/Book.ph...er=6&Section=4

This link to Bolly chart may help..

Racing engines commonly have exhaust timings of say 175 to 195 degrees.
Other high performance engines (ducted fans or free flight etc), have timings of say 160 to 175 degrees.
‘Normal’ engines have timings of 145 to 160 degrees.
Engines below 140 - 145 degrees are often difficult to operate correctly on a pipe.

rcguy59

My Feedback: (8)

Thanks, Skipper. I'd never been to that site before. I need to find my degree wheel.

aspeed

I put it on bookmarks. It took a minute to figure out the lengths were MM. I would not go past 180 degrees, as it makes it hard to adjust the needle. Shimming the liner is good for the timid or nickel liners. Just noticed your reference to Jeremy Clarkson. Isn't he unemployed now?

rcguy59

My Feedback: (8)

First thing I did was bookmark it. Yes, Clarkson is unemployed for the moment, but I'm sure it won't be long before he lands another gig. I'll watch anything he appears in. I cut another 1/4" from the Demon's header last night. I'll take the tools with me to the field next weekend so I can cut it some more if I need to. I'm not only chomping at the bit to fly the Demon again, I'm also looking forward to getting to know my Twin Mustang. The maiden went without a hitch, which is usually a good sign for me. I had one just like it 7 or 8 years ago that had Saito .62's on it. Between the weight of the Saitos and the tail weight they required, the airplane was about 2 lbs. overweight. It flew fine, but landings were dicey. It's a bit nose-heavy even with the .32's, according to the manual, but it flew fine and slowed down better than I'd dare hope. I need to measure the exhaust duration on the .32SX. I wonder if the heli versions were any different in timing. I have three distinct versions. Airplane, Heli and ringed Heli. There are also two different styles of Heli carb, as well. The Heli versions were all front-needle types. The earlier carb looks like the one that was on the .32F. The later ones look just like the Airplane carbs, only they are front-needle instead of remote-needle. The earlier Heli carbs have noticeably smaller venturis than the later ones. The Demon has the large-bore Heli carb and the ABN P/L.

combatpigg

My Feedback: (3)

180 is the magic number if you want to see the explosive jump. Also make sure that the intake closes at 60 ATDC.
You might find that the hole going through the crank is too restrictive to process enough fuel mixture to support a huge jump in power.
The other problem is running out of header length to hack off to make a higher revving prop compatible with the higher timing.
If you get the chance, look at the Nelson .36 internals to see how a .25 - .36 case engine needs to be designed to make serious power.

MJD

My Feedback: (1)

Is it more like a .25 block than a .40?

aspeed

When we ran the old Rossi .15, we used 135 degrees bypass, 180 degree exh., 40 opening and 60 degree closing. I don't think much has changed since 1980. I have noticed the Russian stuff seems to flare the crank hole to each side of the pin/counterweight, as well as combine the bearing to the crank rather than have a regular bearing. The car motors like the "Turbo scoop" thing, but I don't know about that. Saw a pic of a Jett with a slot milled on the face of the crank. That was different, but similar to the Russian idea. The Russian flare keeps the hole the same small diameter but still allows the mixture to get around the rod. I think crankcase packing and opening the crank hole might be the ticket for piddly mods at least. I don't have a Nelson to check out, maybe there are some pics somewhere. I picked up a couple .32 heli motors and an F Heli motor to check out. I am not sure the one .32 SX is worth the trouble. The rear bearing is gone, and the very top of the cyl. is flaking. Must have run too lean. I think I paid $20 for that one. One was $2. Oddly enough the $20 one seems like a ripoff?

BiggerDanno

When you guys change the exhaust timing are you changing the opening or the closing point?

I'd like to try this, but need more info.

Thanks, Dan

rcguy59

My Feedback: (8)

Horror stories about OS liner peeling abound but I've yet to have it happen on one of mine. Lucky, I guess. I just ordered a couple of sets of .32 bearings from Boca. I've not had good luck with bearings in my 32SX's. As noted, they were all purchased second-hand, mostly from Feebay. OS bearings from that era are crap in my experience. Maybe it's the popularity of all-synthetic fuel and the fact that they were poorly stored. I've run Wildcat Premium for the last 15 years or so and never had bearing problems with engines that I either purchased new or replaced the bearings in. The "Premium" version has a bit of real castor in it. Our LHS buys Wildcat by the pallet and has by far the best prices around on fuel. In case anyone is curious, I'm running 10% nitro in my .32's and everything else except my YS .45. That one gets "YS 20-20" fuel. My Norvels get 30% Heli fuel spiked with 6oz/gal Sig castor.

combatpigg

My Feedback: (3)

Yes, the typical BB .40 has 1.40" between the beams and the .25 to .36 BB class is 1.25"...generally speaking.
Nelson used a very thin rear bearing to accommodate the larger than normal diameter crank.
He also uses nothing but UCON LB 625 lubricant [20%] when he goes flying.

MJD

My Feedback: (1)

I imagine he did a fair job on the needle settings. On the flip side, getting parts at cost might have sealed the deal?

MJD

My Feedback: (1)

Just did a backyard shakedown run on the old Demon fitted with the Evo 60NX/Jett pipe combo (that has about 15 sport flights on it but squeaky fresh). Fitted a carefully balanced APC 9x10, I figured it would load the engine in to an appropriate rpm range for the pipe. I expect a small block (and light case) .60 to shake a bit more than average in a light airframe, and it is no exception but I believe it within "spec". First thing I found of course was two bolts that were not as snug as they should be. I had fit some alien 270cc clunk tank from an ARF long forgotten, because it fit nicely. Interestingly, the manufacturer thoughtfully supplied nice color coded silicone fill, vent and fuel lines, but forgot to use fuel proof material for the stopper.. duh. So the first start quickly became a diagnostic run (but a first flip start at least).

Replaced that.. torqued the muffler bolts properly.. ah there we go. Rich and not fully staged, my concerns about static thrust on that prop turned out to be unnecessary. After cooldown I'll go out and run one more time and tach the peak.

Survey says: 15% Omega, APC 9x10: 16,600rpm

Might be 100-200 left.

So I suspect this is a 165-170mph package ($1.30/mph), soon to find out.

aspeed

If you raise the exhaust port, say about .030" or 1/32" it will make the total open time longer. That means the # of degrees is the sum of both ways from BDC (Bottom Dead Center) It is the same both ways. The crank timing is different each way because it is the window in the crank. The closing time is the most important.

combatpigg

My Feedback: (3)

If you want 180 timing, measure from the top of the cylinder to the piston dome when the piston is at TDC then take a similar measurement when the piston is at BDC.
180 degree timing is exactly half the distance between the TDC and BDC points.
Chrome or nickel is hard to mark, so use tape to mark for your cut.

rcguy59

My Feedback: (8)

I just replaced the 4oz. tank in the Demon with a 6oz. A few more minutes of fun before I have to land!

MJD

My Feedback: (1)

Jett 6oz shorts fit nicely if you ever want to use a bladder tank. I've been meaning to order some smaller Tettra tanks but haven't yet. I have them all drawn up in CAD for fit check.

iron eagel

With the .25 version a 28 mm HET or similar inrunner brushless would work great. The HET 2W-23 is small light and cheap will take 700 watts peak 650 or so continuous. For higher power applications figure on a 30 or 35 mm diameter motor do you need the measurements of lengths and alike?
For the 28 mm motors you want a forward mount for the 30 and 35 mm ones you want a rear mount. Power levels with the 28 MM go upwards of 2 KW, for the 30-36 mm 8KW setups can be had it you have the cash and enough wing to carry the battery.
The real PITA is you need the room about the COG for the brick that substitutes for fuel.

MJD

My Feedback: (1)

As a design target I'd aim for 1.0 - 1.5kW systems allowing the builder to do whatever more they want.

One challenge is a good front mount for 28mm - I'd rather find something commercial but compact enough it doesn't end up with a 2" square nose. Laser cut ply ain't the best idea for front mounting. Any ideas?

Hyperion had a couple of perfect motors in their high rpm outrunner series, until I tried to order one and found out a whole whack of motors were discontinued.

MJD

My Feedback: (1)

BTW with a minor thickening of the root rib airfoil, the Demon will hold a 6S 2500 on the CG.

I already have the open CG bay idea drafted out - i.e. the spar isn't centered on the CG on this one, similarly to the RIRE version with CG tank. The motor mounting is not my forte, as an electric dabbler. For a buddy I built one with a 2" square firewall for an X style outrunner mount. So if I can lock into the motor mount method, I can move on to finishing the design. Anything you have to suggest is most welcome - bear in mind it needs to be suitable for the "masses".

iron eagel

I progressively thickened the airfoil to the root from the last balsa rib before the ply to about 8%at the ply rib location to fit a 4500 90C 4 cell on my SD. For the motor mount/cooling intake I used 3/16 th ply mounted to the front of a balsa tube to mount the motors into the space between the last two ribs using spacers on the sides. The balsa tube was a pain but it is needed to keep the airflow tight to the motor case for cooling. I built the tube inside of a 1/2 chrome drain pipe for a sink as a form an mounted the intake/mount to it. For the HET (high End technologies) 28 mm Typhoon motors the intake looks like this.

Send me your email in a pm and I can send you the DXF for it.
Here is a good choice for a het http://www.highendrc.com/index_eprod...roducts_id=304
For the SD I am using a Ammo 28 mm brushless and it has a different mounting pattern but the same idea for the mount. As you can see there is a cowl added to finish it off.

iron eagel

By the way you may notice that the intake and cowl were turned on a lathe for shaping. I'll try to figure out something that may be more suited for the masses I tend to go to extremes when building as the frame for the stingray illustrates.

MJD

My Feedback: (1)

Not hard to repro with concentric 1/4" rings.

iron eagel

Cool didn't think of doing it with rings, to darn hard to cut that out with an exacto.
This is how I mounted the tube in the airframe.

iron eagel

Don't forget the cooling outlet.

MJD

My Feedback: (1)

It would be a rectangular or flush outlet at the rear of the battery/radio bays. Ooh, laser cut NASA flush inlets/outlets.