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T 2.5 by Dave Owen.

Old 12-10-2014, 05:52 PM
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Default T 2.5 by Dave Owen.

Picking mine up tonight and boy am I looking forward to it!

Any chance of a "Club Taipan" thread?
Old 12-10-2014, 07:05 PM
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fiery
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Go for it! But call it "Club Burford" as a tribute to GB and so we can include Sabre's and Gee-Bee's, as well as the post retirement specials ...


I am thinking of starting a "Club Deutsch" thread in the New Year.

Why?

So forum frequenters can show off their WAF's, WILO's, EGA's, Krick's, Eisfelds, FOK's, Jaguars, Schlossers etc as well as the better known Webra's, Profi's and Taifuns. We see plenty of UK and Aussie product but not so much of the german product. It will also get some more non English first language speakers visiting and hopefully contributing.
Old 12-10-2014, 07:22 PM
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Ok, but I am probably not the best qualified to comment beyond having two Taipans.
Old 12-10-2014, 11:53 PM
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I'm sure you'll be pleased and impressed with the quality.
I've had my T2.5 for about 3 months now and its absolutely superb.
I did actually run it in with David, so the running in was a bit more "hurried" than my usual, but it's a superb engine!
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Old 12-11-2014, 04:02 PM
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I was privileged to be present during some of the construction of the T2.5 and was mightily impressed as to the care he took at each step.
Even though 200 examples were made each one was treated as a one off special.

Little design tips that I picked up on were -
the cup shaped contra piston design that gets installed from the top of the liner that is far lighter than the solid disk type and fits better,
hollowed out crank pin, again a reciprocating weight saving,
heat treated alloys every where,
a precision matching of liner to crank threads that should prevent cylinder unscrewing during running,
differing spraybar diameters to suit different applications,
at least 3 years of field testing that I know of,
and Oliver style porting that is the best type of reverse flow known.


I have known Dave for about 20 years and all of his designs are about improvement rather than copies - and it shows.
Old 12-15-2014, 05:16 PM
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Received my T2.5 diesel yesterday, Dave's attention to detail towards the whole package is outstanding. Far to nice to use I think.

Steve.
Old 12-15-2014, 06:03 PM
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Methinks that the quoted "0.30hp" is very conservative and the early T 2.5 that I saw in the field really looked to pull like it was half as big again.

Had a good talk with Dave Owen upon pickup and he mentioned that the venturi was verging on too large and so he has the option of a thicker spraybar for some applications like CL stunt.

But yes, it is a jewel to look at indeed.
Old 12-15-2014, 06:07 PM
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Originally Posted by fiery
Go for it! But call it "Club Burford" as a tribute to GB and so we can include Sabre's and Gee-Bee's, as well as the post retirement specials ...
Problem is that a club "Burford" would simply have to include glow engines and placing that inside of a Diesel section seems incongruous.
Old 12-15-2014, 07:29 PM
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Originally Posted by Recycled Flyer
Methinks that the quoted "0.30hp" is very conservative and the early T 2.5 that I saw in the field really looked to pull like it was half as big again.

Had a good talk with Dave Owen upon pickup and he mentioned that the venturi was verging on too large and so he has the option of a thicker spraybar for some applications like CL stunt.

But yes, it is a jewel to look at indeed.
Chris, where is '0.30hp' quoted? I didn't think Dave was going to make any performance claims for it, and I'm surprised if he's gone for something as low as 0.3. From what we've consistently seen, I'd say it'd be comfortably in the 0.35 - 0.40 range.

I've had a play with both spraybars, and to be honest, I didn't think it made that much difference. The bigger one knocks off a couple of hundred rpm, but fuel draw is still fine with the smaller. The main thing if you want to use it in a stunter is to go for a sidewinder mounting.

"Far too nice to use"? Well, they're certainly very nice, but it's a shame not to use them.
Old 12-15-2014, 07:55 PM
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Originally Posted by steve111
Chris, where is '0.30hp' quoted?
You got me doubting myself now Steve, but I am certain that its written on the instructions that come with the engine along side Bore/Stroke/weight/power etc.

Side winder mount, agreed.
Old 12-16-2014, 12:38 AM
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Originally Posted by Recycled Flyer
You got me doubting myself now Steve, but I am certain that its written on the instructions that come with the engine along side Bore/Stroke/weight/power etc.
I don't think so, my "Operating Instructions" sheet makes no mention of power...
Who cares? It's just a super engine that Rolls Royce would call "of adequate power"...

I might do some rpm checks if I get time.

Last edited by brokenenglish; 12-16-2014 at 12:40 AM.
Old 12-16-2014, 01:34 AM
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Um, brain snap guys - of course there is no power quoted.

And I have no idea why I thought there ever was or where I got that into my head - weird!
Slinking off to hide under the nearest rock now, bye.
Old 12-16-2014, 08:08 AM
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Why is a sidewinder mounting of a diesel better for stunt? Jack
Old 12-16-2014, 10:49 AM
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The power out put was quoted in Dunkin's second edition engine book bottom of page 12, .359 bhp @ 15200

Hwm 77
Old 12-16-2014, 12:30 PM
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Centrifugal force, narrow stoichiometric operating band, and violent maneuvers all play havoc with the need for lower speed consistent stunt runs for diesels.

Placing the combustion chamber on the outside of any maneuver, as in invert or upright mounting, will cause an immediate transient stutter from flooding. The residual charge that condensates in the transfer ports is thrown loose and into the head, the engine misfires for a split second until that extra charge is ejected and then its back to business as usual.)

Whereas mounting side ways places the chamber in a neutral position when using a radial ported engine (side bypass or schnuerle diesel engines still suffer from the 'gear change phenomenon'.)

Side mounting also enables one to clear the engines sinuses more readily if flooded.

All of this is well proven with Tony Eifflienders Freebird PAW 40 and 35 series of stunters, he started out with an invert mount, suffered readily from inside maneuver stutters and shifted to side mount as a cure.

Side mount schnuerle diesels used for stunt are not symmetrically ported as thus still suffer slightly from the effect.

All of this has been my observations both by personal experience, from many years of talking to others who fly stunt diesels and from reading about the same.

Cheers.
P.S. Unsure whether or not side mounted stunt engines should be restricted to outboard only, inboard has been tried with glow engines and in theory may be better as they tend to lean out better when needed but with a diesel consistency has to be the key.

(Just don't ask me about power outputs!)

Last edited by Recycled Flyer; 12-16-2014 at 01:08 PM.
Old 12-16-2014, 01:42 PM
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Thanks for the info Recycled Flier. In the late 1950's and early 1960's I had full size Flite Streak light in weight with no landing gear powered with an O. S. .15 diesel. It flew great and would do the whole stunt pattern. Later around 1967 to 1969 I had a Flite Streak with a Webra Mach II diesel and it flew well also. I put the Webra in a Veco Brave no flaps and it did not fly as well with the up right engine. I did not know why back then. Jack
Old 12-16-2014, 05:40 PM
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I agree. "Club Taipan" will draw in more viewers and therefore possible contributions.

Let's call it "Club Taipan", but welcome diesel engines from those like David Owen who have been inspired to re-create a past classic, and others like the AAMotive S.66 repro, which clearly draw inspiration from a Burford design.

Diesel Gee-Bee's, StuntMota's, Sabres and no-names from the early years and later limited run 'specials' like the CIE and Deezil repro's would also be most welcome! Also, of course, the exquisite pb .33 ..
Old 12-16-2014, 06:40 PM
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Originally Posted by steve111
.......The main thing if you want to use it in a stunter is to go for a sidewinder mounting.

"Far too nice to use"? Well, they're certainly very nice, but it's a shame not to use them.
So Steve, what model would you recommend?
I was thinking one of the early Aeroflyte warbirds, but none of those are sidewinders. The Montgomery Stiletto was s/w but I would think a bit small for such a powerful engine. Maybe times 1.25??
Old 12-16-2014, 08:44 PM
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Originally Posted by greggles47
So Steve, what model would you recommend?
I was thinking one of the early Aeroflyte warbirds, but none of those are sidewinders. The Montgomery Stiletto was s/w but I would think a bit small for such a powerful engine. Maybe times 1.25??
Hi Greg, a scaled-up Stiletto sounds like a really nice idea - maybe about 38-40" span? Alternatively, you could look at Geoff Pentland's Kookaburra designs. I've found his Ki-61 (as kitted by Browny) really good with the T2.5; there's also a Spitfire, Me-109 and profile P-39. All sidewinder mountings. Otherwise, something like a Junior Flitestreak would work well, but personally I like the idea of having the T2.5 in an Australian design.

Steve
Old 12-17-2014, 01:46 AM
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Steve,

Like you the idea of an Aussie design really appeals. The Stiletto at 34" is about what I'd use for a 1.5, in fact mine has a Tyro in it. I'd increase it to 125% making it 42.5" and probably add wing flaps as well.

On the other hand a lot of the Pentland models are appealing too, and you can never have enough Spitfires.

Luckily Dave hasn't burdened me with the task of deciding yet - my T2.5 is in the next batch, so I can change my mind any number of times.
Old 12-17-2014, 03:14 PM
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A few thoughts on scaling up or down an existing design....

Remember that the wing area changes by the square of the change of dimensions. Say, what?? Say you start with a 400 sq in profile. For example, call it a nominal 10" by 40" plank wing... (This method works for any planform, btw, if you know the span and wing area.) (I'll use traditional inch numbers, but of course it works in metric, too.)

If you want to enlarge it to 500 sq in area, that's a 25% increase. Span increases to square root of 1.25 * 40 or 1.118 *40 = 44.72". Chord goes to 11.18".

Vice versa, if you want to reduce size to 300 sq in, dimensions change by square root of 0.75, or 0.866. Span goes to 34.64", chord to 8.66".

If all other dimensions are changed in the same scale, and weights are in proportion to other models of the same area, performance should be similar.

Another thought for the discussion of upright or inverted mounting for diesels, vs. sidewinder, for high performance stunt or combat CL use...

Relative tank height: An early fortuitous accident may have caused decades of confusion and frustration. The Fox 35 stunt engine ran very well with a 1" tall tank mounted on the same engine bearers as the engine, in upright and inverted configuration for inside and outside maneuvering. The wedge tank fuel pickup was 1/2" above bearers, and so was the Fox NVA spraybar.

Not all engines ran that way; still it became a rule of thumb to set up a stunter this way. Some good engines were considered useless because the engine ran too rich (or too lean) when flipped over.

In recent decades, stunt fliers have taken note of the facts that not all engines like the same "relative tank height" to yield an equal run both ways. This became even more critical with the general adoption of uniflow vented tanks. The initial over and under vented tanks required a rich enough initial needle setting to survive the leaning-out that developed during the course of a flight. Uniflow tanks run very consistently down to the last bubbles at fuel exhaustion, but they establish a reference height point that must be matched closely to the engine in the model.

Diesels are somewhat less finicky about relative tank height, particularly when the engine is mounted sidewinder. The effective g-loading on the fuel in the tank includes an approximately 3g or greater component outward (centrifugal), a 1g vertically downward component regardless of the model's attitude (gravity) and varying components in varying directions from maneuvering.

With a sidewinder (profile) mounting, and the tank relative height about centered on the crankshaft (or venturii, if that's offset like some older ST engines?) net vector variations in all attitudes and loadings start pretty much centered, and vary proportionately to each side. The fluid variations and 'churning' actions inside the crankcase have a very small vertical range in which they operate.

With an upright or inverted engine that 'churning range' may be significantly larger, and sloshing or dumping collected fuel may affect operation. Still, it may be possible to find a "tank height" that cancels, or greatly reduces, the effect. I've done some experimenting with profile mounted PAWs, on a special engine stand that allows simulating the directions of resolved load vectors for a model in flight, but, of course, not the magnitudes of those loads. Even working with the lesser loads on a bench, the effects of the crucial tank height relationship can be clearly observed. Adjustments follow seeking equal RPM and run character for both upright and inverted flight. These help set the initial tank positioning for a new model, or an engine I'm not familiar with.

Added:
It has worked quite well! Except for PAWs, on the bench, so far. Glow engines tolerate considerably richer settings, so sloshing some excess around inside one of them is much less noticeable. Diesels MUST run at near optimum compression and mixture settings, and do not tolerate flooding at all well.

Last edited by Lou Crane; 12-17-2014 at 03:21 PM.
Old 12-17-2014, 08:28 PM
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Originally Posted by steve111
Chris, where is '0.30hp' quoted?
Well ......... here.

Only problem is, it was the wrong plain bearing Taipan Replica!

(Knew that I saw it written somewhere recently.)
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