Stuka Stunt Thunder Tiger 25

Will anyone who has used one of these for a while report on it? How did you set it up? Do you run it in the 4-2-4 break style? What prop and fuel are you using? In general, how do you like it? Would you recommend it? Any negative comments?

P.S. similiar questions about the Double Star 40...

Thanks!

The Double Star 40.
The two Double Star 40's that I purchased were twins. They looked excellent and workmanship was great.

Break in: I broke the engines in on GMA 5/29 with a Zinger 10-6 prop.
Each engine had a total of 12 ounces on the test bench.

Running: The double Star engine is a direct replacement for a FOX 35 and this should always be foremost on your mind when building an airplane for this engine. Keep the size of the airfrane to 480 - 520 square inches and light.

Kits: I purchase several airplanes and use this engine on them but to no avail. You see, the one thing I did not remember is that this is a direct replacement for a FOX 35 not a OS40FP. Size does matter.
I purchased a Dare Profile Smoothie from my local hobby shop. Built her and installed my DS40, 4 ounce uniflow tank on pressure, tounge muffler, Zinger 11-5 prop and Tru-turn spinner.
This airframe came out to about 38 ounces ready to fly.
Now don't get me wrong I did try several different types of kits but this one kit was the correct for the engine.

Engine runs: I used GMA 5/29 fuel in the summer, ran a good 4-2-4 break. Lines were 60 foot @ .015. This combination would fly the complete pattern plus about 10 laps extra.
When it comes to choosing a plug, use a sig hot.

Engine cranking: The DS 40 would crank on the second or third flip.
after fuel was draw into the cylinder. After a full pattern run if wanted to I could pick up the airplane by the engine cylinder, it ran that cool.

Likes: The DS is a great engine, easy cranking. Low Drag
Dislikes: I don't have any.
Tech support: Tom Dixion out of Georgia.

Mike,
I have a little experience with the DS 40 and found it to be a very nice engine to run. It is currently nestled in a Sig Super Chipmunk that weighed in at 46 oz in the good days and is probably closer to 48 these days. My initial impression of the engine is that it was a little light on power but ran very smoothly. Based on some work that I had done with a Fox 40, I tried varying the exhaust in order to get a little more power, but had no luck (more exhaust opening=more power and more fuel consumption-generally). So I tried the other end, the intake. Since I do not have larger drill bits and a good place to chuck up the venturi, I opted to decrease the diameter of the NVA. I would guess that I went from about .155 to .125, but have never really measured it.

The result was a night and day difference with respect to power. Shortly after I made this modification, I began reading about others who had similar results by increasing the ID of the venturi. The headshim that was included with the engine was also installed. It currently runs with a Zinger 11x5 wood prop with a ground launch of 9100-9200 rpm which generally yields a fat 2 stroke with a break to a stonger 2 cycle. It has a Fox Gold Series RC long plug and I have been using 4 oz of PowerMaster 10-22 fuel to yield a 6:30 or so run time. Other 10% fuels such as 10-20 all castor Sig have been used with succuess. I should also note that Big Art made a custom tongue muffler for me that has the holes exiting at the end (pointing straight at me while flying). Not sure what effect this has on back pressure since the 90 degree turn is not required, but the previous tongue muffler seemed to work okay, I just did not like the oil being dumped back into the cowling.

FWIW

I don't have the TT 25 but did send Len my Magnum GP 25 to set up. Should be the exact same engine (FP clone but ABC). I also have a stock FP 25 and wanted to benchmark the two motors. Lacking a good tach that will be a little difficult.

After one flight of a Sig Skyray 25 and the stock FP 25 - it just seemed FAST! It ran a 2C setting for the whole flight. I forget which prop I was using but it may have been a MA wood 10-5. I switched to the modded TT 25 with the same 10-5 and it was noticeably tamer. The lap speeds seemed much more comfortable and it was decidedly richer but held that setting for virtually the entire flight. The other club members commented how steady the motor ran.

I dorked the Skyray a couple of weeks later (that infamous "one more fight" before you go home) and haven't repaired it yet.

Meanwhile, I've got my Fancherized Twister completed and am using the stock FP 25 but with a smaller 9x4 Grish plastic prop. It's still a low time engine but will hold a nice fat 2C setting for the tank. I'm just sorting this combo out and so far, really like it.

Len's instructions said he didn't have a lot of experience with the 25 schneurle engines so didn't have any recommended prop sizes but the 35/40 engines like larger props.

Sorry I have no more detailed info but hope to get lots more time in the air this year. Last few weeks have been hampered with the usual midwest thunderstorms.

Ron:
I have a TT 25 GP that Leonard prepared for me. Although I have owned it for some time, it does not have much flight time on it. However, it is one terrific little power plant!
Here's its story. It was bench run for about 1 1/2 hours before it was first flown using an 8x6 for a break-in prop and following the short and fast initial runs, then longer runs at a fast four cycle, approach that I understand is appropriate for a motor of its construction and porting. Fuel was Power Master 5/22 (half castor, half synthetic) with castor added to bring total oil content to 24%. From the first runs on the bench I knew it was going to be a good one.
Flying has been done using the same fuel and a Brodak profile oval tank on muffler pressure. First flights were on a 9x4 Zinger; subsequent flights were on a 10x4 Zinger cut down to 9 1/2. All flights were needled for a fast four cycle. I did not tach the motor before flights. Every flight the little beastie just hummed along without a change in its note except for an almost imperceptible break in maneuvers on the 9 1/2x4. I strongly suspect that neither of these props will prove to be optimal, but further tesing will just have to await the return of decent flying weather in the spring. (Call me a wuss, but I just do not enjoy flying when the temperature is below about 45 and we are not going to see that again in Connecticut for some time.)
I can not compare this with other 25's, but I can say that it flew my plane just as authoritatively (a highly technical, aeronautical engineering term) as my Fox 35 on a 10x4.
I am delighted with this motor and highly recommend it.

Pete,
What plane were you flying with the TT .25? Inquiring minds want to know. Thanks.
DennisV

Dennis:
The SSW TT 25 GP has hauled both a SkyRay and a Ukey 35. Both of these smallish, minimal planes are just perfect for my current ability and climb up the learning curve. I used 4" pitch props because my experience with the Fox 35 on these planes was that anything above a 4" pitch made the plane simply too fast on the 61' lines that I was using. The 4" pitch props on the 25 GP provided comfortable speed and good line tension in all attitudes. Unfortunately, I did not time the laps. That, as with all else, will have to await the arrival of spring when I will also try the 25 GP on the Fancherized Twister that is starting to take shape on my building board.

These aren't necessarily 'negative' comments...merely a different point of view...I'm sure I'll get chastised for them, too.

Leonard's engines might very well be good if that is what you are looking for...an engine that has a restrictive venturi and the boost ports blocked in order to 'tame it' and/or run 4-2-4.

I prefer a modern engine that is running as it was designed to run...2 cycle. When I'm running my R/C engines or C/L engines, the engines in either case exhibit no 'runaway' as Leonard mentions on his webpage. 'Runaway', if it ever existed on my engines, could be 'tamed' simply by using the correct prop size/pitch and setting the NV properly. The way I do C/L conversions on an engine is to do calculations for the net opening of the R/C carb venturi for that size engine and I size the net opening for the C/L venturi the same size. When running them I adjust the NV on my engines so they are just breaking into 2 cycle when the plane is pointed straight up on the ground. Once in the air they are running a rich two cycle and have ample power to go through any manuever you throw at the plane. I run a flatter prop...3 or 4 pitch...to slow down lap speed. I use this method for all modern engines that I convert for C/L use. This 'method' obviously isn't for everyone...but it suits me fine and saves me the $40 (plus extra for any parts needed) that Leonard would charge to modify it for me.

...to each his own I guess.

eyho2,
Would you mind giving us the details of your mods on the TT25? Example of the net opening of the venturi, spraybar diameter, fuel type (nitro and oil), glowplug, make and size of prop, line length, airplane, how much fuel consumed per flight, launch rppm, etc. I ask this not trying to be a smart aleck, but would like know more about your set up.

I've run an OS 25FP very successfully and would like to compare your set up with mine.

Thanks,

I haven't fully set-up my TT GP .15, .25 or TT PRO .36 yet...but I have done a TT PRO .46. It had the venturi bored to 1/4" (.049 sq.in.)...being a 'true venturi' set-up the spraybar didn't enter into the picture. I used 10% nitro, 10% castor, 10% synthetic fuel and lit it off with a OS #8 plug. My prop of choice for that set-up is an APC 12.25x3.75. The engine with a factory muffler (baffle removed and tailpipe bored-out) will run full lean with that prop and an R/C carb at full throttle at 12.2K...it does the same with the C/L venturi. Lines used were .018" x 70' stranded (eyelet to eyelet). The plane was a fairly heavy scratch-built 54" WS (~600 sq.in.) flapped stunter. The tank was a 6 oz Dubro (I forget how long it flew...it's been a while). Launch RPM's were never checked...I adjusted the NV to just barely break into a 2 cycle run when the plane was pointed straight up...I'm guessing a level plane launch RPM would be ~10.5-11K. The reason why I say 'was' a lot is that the plane has been re-kitted:(

Guys, you have strayed very far from the original thread. I would like to reserve this forum for product reviews only. Even questions that you have about other products should be directed to the main forum so all may join in. Let's leave this for reviews only so we don't have to look all over the place for the rest of the stuff

LAST EDITED ON Dec-09-03 AT 06:33 PM (CST)
 
Sorry Leonard. You're right.