STUKA STUNT ENGINES
Power on a Budget

(Last updated September 19, 2008)

This is not your Momma's Engine!

Most engines in use today for controline stunt by the sport flyer or budding contest flyer are engines originally designed for RC operation. They are designed to run at high speed with small propellers and meant to be controlled with a carburetor. Many manufacturers, if they even make a controline version of their engine, will simply replace the carburetor with a venturi and plain needle valve, and call it that. To keep the engine from running away, they may resort to one or a combination of the following: 1. Use a small venturi to choke the engine down; 2. Decrease the compression by adding additional head gaskets; and/or 3. Use a restrictive muffler. All of these reduce the available power of the engine, with the result that instead of turning a 10-6 prop at 15,000 rpm, they will now turn the same prop at 10,000 rpm while being called upon to act as a stunt engine.

But most modern Schnurle engines treated this way are still plagued with "runaway". One way to solve the "runaway" problem and make the engine more suitable for controline stunt is to change the timing by raising the bypass ports on the engine. Although this allows a longer period on each intake stroke for the fuel mixture to work its way into the combustion chamber and helps to keep the engine from going lean, too much reduction in blowdown time also serves to reduce the available power of the engine. When this reduction in timing is also accompanied by a lowering of the compression at the head to soften the break, the result is a further reduction of power. Although opening up the venturi and using a less restrictive muffler will regain a portion of the power that was lost, these engines may not be running at their full potential!

On our Stuka Stunt series of engines, we take a different approach. We boost fuel flow at lower speeds through an increase of crankcase compression by blocking off the boost port in the case. (Interestingly, the boost port was not a part of the original Schnurle design, but was added to boost the high RPM range of the engine, which, for our purposes in CL stunt, is precisely what we do not want or need.) Blocking off this port keeps most of the available power of the engine and allows it to produce this power at lower speeds closer to the torque range of the engine, which is what we are after.

Everything is fully measured and blueprinted. The deck height is set to our design specs, lowering the sleeve as necessary. (This can vary from engine to engine because of tolerance allowances of the various parts. We measure first and then set to optimum.) We then set head clearance for optimum power and stunt friendliness, fit an appropriately sized venturi to the engine which enables us to take advantage of its power, and the engine is now capable of turning a larger prop at the slower speeds that are necessary for controline stunt while maintaining that precise extra boost in power that is needed when the plane enters into a maneuver or goes up "on top". The engine is cleaned and reoiled before reassembly, and it comes with an extensive set of break-in and operating instructions.

(Note: The factory muffler that comes with most engines is quite heavy and usually needs to be opened up or replaced in order to realize the full power that the engine is capable of delivering. For those wishing to replace their muffler with something more suitable, we have custom tube and tongue mufflers available for all of our engines and most others as well that are both lighter and less restrictive, allowing for an even greater power output.)

STUKA STUNT 35 OS FP (Strong enough to haul a Magnum.)

This is the engine that we have been flying for a number of years on our planes in practice and competition and is the engine Matt flew at the '96 through '98 Nats, and the '97 FAI Trials. With it we have used a variety of stock 12-6 wood props (Zinger, Rev-Up, and B Y & O.) that produce an enormous amount of thrust for the weight of the engine. And power to weight is the name of the game. Recently we have turned to carbon fiber props in search of even more thrust, and have found the 12.5 x 5.5 Bolly prop to be nearly ideal for this engine. Remember, this engine is turning a prop that is normally used on .46, .51, and even some .60 size engines without carrying either the weight penalty or requiring the heavier line sizes demanded by the larger engines. And it does it with only 5% nitro in the fuel, and using only a little over 4 ounces for the complete pattern, making it not only economical to buy, but to run as well. These engines are normally fitted with a standard, front mount OS needle valve, but will be fitted with an ST needle valve as a no cost option.

STUKA STUNT 40 PROFILE SPECIAL

The OS 40 FP and its "clones" (such as the Tower 40) have a larger bore than the 35, and wider bypass slots cut into their sleeve. When modified in the same manner as our 35 FP, and mounted in a "normal" (upright or inverted) position, these engines allow an excess amount of fuel to be thrown on the plug in certain maneuvers (such as the intersections of the eights) which causes a momentary "stutter" or "burp" in the engine, making them unsuitable, in our opinion, for an upright installation. This problem does not exist, however, when the engine is mounted sideways, as on a profile. When mounted in such a manner, these engines operate with much the same characteristics as our well proven Stuka Stunt 35 FP, but develop even greater power. We have one mounted on the Profile Stuka, and use it exclusively in that configuration. After modifying several of these engines for other modelers to use on their profile planes, we decided to offer the engine as the Stuka Stunt 40 Profile Special.

First offered as a modified OS 40 FP, we have since begun to offer the Stuka Stunt 40 Profile Special as a modified Tower 40. The Tower 40 is a "drop in" replacement for the 40 FP, but offers the advantage of a better balanced crankshaft and a true chrome plated ABC piston/cylinder assembly. These engines are fitted with our custom Delrin venturi and your choice of a standard front mounted OS needle valve, an OS remote needle valve, or an ST needle valve assembly.

STUKA STUNT 46 MAGNUM GPA  (Check for availability before ordering.)

Although the case is 1/10 inch wider and the shaft length about 1/8 inch longer, the bolt pattern on these engines allows a drop in fit replacement for the FP engine in many installations. Weight, without muffler, on these 46 GPA engines is a reasonable 9 3/4 ounces, and the power increase, when modified in the way that we do, is substantial. When fitted with our custom (oversize) tongue muffler, the total engine package is less than 10 1/2 ounces. When you need that extra power for that larger (or heavier) plane, this could be it. This engine is fitted with our custom made "true venturi" and an OS needle valve.

OUR MOST POWERFUL: The Stuka Stunt 53 (Magnum 53 XLA and ASP 53)

This could be the power plant you were looking for to power that "60" size plane. The case width and mounting pattern is the same as the 46 GPA, but the needle location and extended shaft allows for easier choking. This is a ball bearing engine weighing 10.7 ounces, less muffler. Custom oversize tube and tongue mufflers are available, weighing .1/2 ounce for the tongue and 1.3 or 1.6 ounces for the tube. This engine has proved capable of turning a wide range of props of around a 5.5 pitch including a 4-blade 12 inch and a 3 blade 13 inch. These engines are fitted with our custom made "true venturi" and an ST type needle valve assembly. The .53 is the engine used in Matthews Stuka 2000, which he first flew in the 1999 contest season. NOTE: the ASP .53 is a part-for-part copy of the Magnum 53 XLA and the engines are interchangeable.


 

STUKA STUNT ENGINES
Price List

STUKA STUNT 35 FP
Modified .35 OS FPS . . . $105.00 US Funds plus shipping.
User supplied engine modified for $40.00 plus the cost of any needed parts.

These engines are on again, off again available from the distributor, so please check on availability before ordering. We fit the modeler's preference of a standard, front mounted, OS or ST-type controline needle valve and custom venturi on the engines we provide. Needle assemblies and custom venturis are available for customer provided engines at extra cost. (NOTE: Please state your needle type preference at the time of ordering.)

STUKA STUNT 40 Profile Special
Modified Tower .40--RC converted to CL . . . $105.00 US Funds plus shipping.
User supplied 40 FP, Tower 40, or TT 40 modified for $40.00 plus the cost of any needed parts.

The Tower 40 is part for part interchangeable with the 40 FP and we fit these out with a standard OS or ST-type needle valve assembly and a custom venturi as with 35 FP. Please state your needle type preference at the time of ordering.
We will modify your .20 - .40 FP or Tower 40 engine for $40 plus the cost of needle valve and proper venturi if not included with your engine.

STUKA STUNT 46 Magnum GPA
Modified Magnum .46 GPA--RC converted to CL . . . $115.00 US Funds plus shipping.  Short supply.  Check for availability.
User supplied Magnum 46 GPA modified for $65.00, including the cost of NVA and true venturi.

Although discontinued by the manufacturer, we are still occasionally able to locate new engines for resale. Please check on availability before ordering. We fit a standard, front mounted, OS controline needle valve and custom true venturi on all engines.

STUKA STUNT 53 
Modified ASP .53--RC converted to CL . . . $150 US FUNDS plus shipping

NOTE: We will modify your ASP, Magnum XLA, or Thunder Tiger type ball bearing engine for $45 plus the cost of needle valve and proper size venturi if not included with engine. (Note: the included venturis on Thunder Tiger CL engines are generally too large and will need to be replaced.)

We will modify other engines owned by the customer for CL use, but specialize in the Schnurles, notably the OS 20- 40 FP, Tower 40 and 46, Thunder Tiger .20 - .42 plain bearing and .36 - .46 ball bearing, plus the ASP and Magnum .40 - .53. We also supply venturis and needles for older OS, Super Tigres, Foxes, and some others, including the new PA pipe style engines. If you have an engine that you wish modified, contact us for prices and suitability before sending it to us.

ADDITIONAL ENGINES

The following engines are, also available, and operate in a similar manner to those listed previously.

Thunder Tiger 25 GP-25
Plain bearing engine. $105.00 US Funds plus shipping.

These are a near part for part copy of the 25 FP except for the use of a true venturi.

User supplied engine modified for $40.00 plus cost of any needed parts. (Add $23.00 for venturi and needle valve)

Thunder Tiger 25 Pro
Ball bearing version. $115.00 US Funds plus shipping. (while supplies last)

User supplied engine modified for $45.00 plus cost of any needed parts. (Add $23.95 for venturi and needle valve if needed.)

Thunder Tiger 36 Pro
Ball bearing version. $125.00 US Funds plus shipping. (special price)

This a ball bearing engine, but is actually 2/10 of an ounce lighter than the FP 35. These engines fit in the mount of a Fox 35, but have a half inch longer shaft and a true venturi.

User supplied engine modified for $45.00 plus cost of any needed parts. (Add $23.95 for venturi and needle valve if needed.)

Thunder Tiger 42
Plain bearing engine. $105.00 US Funds plus shipping.

These are the same physical size as the 35/40 FP, except for the slightly lower needle valve location. These engines run fine when mounted sideways or upright/inverted, and are a fine choice for planes the size of the Nobler or Thunderbird.

User supplied engine modified for $40.00 plus cost of any needed parts. (Add $21.50 for venturi and needle valve if needed.)

Thunder Tiger 46 Pro
Ball bearing version. $140.00 US Funds plus shipping.

These are similar in outside dimension to the Magnum and ASP 53, but are a little smaller displacement.

User supplied engine modified for $45.00 plus cost of any needed parts. (Add $23.95 for venturi and needle valve if needed)

 

Add shipping charges. 
US = $4.80 for one pound shipped Priority Mail, with additional charges if over one pound.. 
(Note:  Most engines in their box will be over 1 pound in weight.)  
We will bill at cost to foreign addresses.

These remarkable engines are available from

THE STUKA STUNT WORKS
Leonard Neumann
8710 Winding Ridge Road
Indianapolis, IN 46217

E-MAIL
MrStuka@CLStunt.Com

PHONE
(317) 497-1487

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