Has anyone improved the Brodak Buster 40 inch? Im sorta new what can be done to improve it? Anything?..bigger elevator and stab? or Just leave it alone? HR

Make it 2" longer between the wing and stab. Use a 4" bellcrank and carbon fiber push rod. Leave off the plywood nose doublers and use .025 carbon fiber plates on both sides. How far down the rabbit hole do you want to go?


MM

Let's agree on the CF stuff then head for the rabbit hole.  It was a long time ago but I had several Busters. They were fun sport fliers but really not stunters by today's standards.  Applying what I know now, I would increase the stab span by about 4" 2 on each side but not make the fuselage any longer.  The reason for a 4" bellcrank is leverage but at the Buster's size and weight a 3" is probably OK.  It is inline which means that you don't have much tank room.  Personally, I would increase the nose an inch because they build tail heavy, and it will give you more tank room.  If you are not a purist and are building from plans rather than a kit make the airfoil thicker.  About 3/8" at the high point.  Tip weight box and adjustable leadouts are "duh" additions and make a part of the rudder adjustable.

Had a lot of fun with the Buster and it's sibling the Shoestring.

Quote from: Harry Rountree on March 26, 2025, 05:54:25 AM
Has anyone improved the Brodak Buster 40 inch? Im sorta new what can be done to improve it? Anything?..bigger elevator and stab? or Just leave it alone? HR

   The choice of engine has far more to do with the performance than anything you can do aerodynamically. A modern high rev/low pitch engine will *drastically* improve the performance compared to, say, a Fox or McCoy. Something like a "new" 25LA, 20/25FP, etc, swinging a 9-4.

     Brett

Quote from: Harry Rountree on March 26, 2025, 05:54:25 AM
Has anyone improved the Brodak Buster 40 inch? Im sorta new what can be done to improve it? Anything?..bigger elevator and stab? or Just leave it alone? HR

     Just what do you wish to improve on it?? What skill level are you flying at? The Brodak kits are just re-engineered versions of the Goldberg, Shoestring, Cosmic Wind, and the Buster. The word on them back in the day was that most thought the Buster was the best flying airplane of the three, so you could have that going for you.  From what I have seen of the Goldberg kits compared to the Brodak kits, they already look to be a  bit better wood quality wise, and have a different type of wing structure, so should build lighter.  The room for a typical tank has always been an issue with the Goldberg models and will be in the new ones also, I would guess.  Making the tail surfaces a little bigger would not hurt. I would say that even built stock it would fly as well as any beginner or intermediate level pilot could fly it  And as mentioned, the power plant choice is part of the recipe also.
   I have collected the Goldberg kit and the Brodak kits, with the intention of building them and flying them just for giggles and grins. Along with the Midwest War Bird Series airplanes!! I guess I had better get to that soon!!.

  Type at you later,
    Dan McEntee

My Buster was stock with a Brett Buck OS Fp 20 and she flew great.  Would do anything in the book that I could do and the engine ran great.

John

I have a couple plans built Goldberg Busters here we used to train basic aerobatics.   I added about 3/8" around the outline of the stab/elevator.  Other than that just left them alone.  The design has a long track record of good service for thousands over the years.  I covered them in silk to help them survive.  Both have broken loose at the wing/fuse joint so you might reinforce the joint with a little cloth and epoxy.  Both mine have McCoy .35s. It's not a sophisticated airplane so I wouldn't overthink it and try to make it one.  When you can fly better than the airplane-move on to a better airplane.

Dave

As Dave says the Goldberg/Brodak  Buster, Shoe String and the third plane (brain is not quite awake yet) were great fiers for first time or second  to build and fly.  I used them mainly for racing, balloon burst and fun type events.   I know this is a stunt forum but the Shoe String has even been used in scale events.

Quote from: John Tomlin on April 05, 2026, 04:22:14 PMMy Buster was stock with a Brett Buck OS Fp 20 and she flew great.  Would do anything in the book that I could do and the engine ran great.

   Glad it works out for you - the better engine makes all the difference!

   And just to be entirely crystal clear (and to head off the email) - a Brett Buck 20FP actually means a OS-20FP with an extremely radical and controversial setup - absolutely stock as it comes from the factory with no modifications at all!

    Brett

Quote from: Brett Buck on March 27, 2025, 02:26:14 PMThe choice of engine has far more to do with the performance than anything you can do aerodynamically. A modern high rev/low pitch engine will *drastically* improve the performance compared to, say, a Fox or McCoy. Something like a "new" 25LA, 20/25FP, etc, swinging a 9-4.

    Brett

I've seen time and time again where an OS 20/25 FP swinging a 9-4 prop is highly recommended for models of similar size to a Buster or Skyray.

But to be clear, OS FP's originally had an iron/steel P/L version and upgraded to ABN. So, are you recommending the older version, ABN version, or does it matter?

Colin

Quote from: Colin McRae on May 01, 2026, 10:05:44 AMI've seen time and time again where a 20/25 FP swinging a 9-4 prop is highly recommended for models of similar size to a Buster or Skyray.

But to be clear, OS originally had an iron/steel P/L version and upgraded to ABN. So, are you recommending the older version, ABN version, or does it matter?

Colin

   It needs to be an FP version. The older OS MAX .20 steel fin is not the same. The early FP series engines were all iron piston/liner engines I believe but not for very long before the change over. There is some difference in the case that can tell which is which. Some used to think that the iron/steel versions were a bit better, but that's just another discussion topic.
  Type at you later,
  Dan McEntee
 

Quote from: Dan McEntee on May 01, 2026, 10:39:36 AMIt needs to be an FP version. The older OS MAX .20 steel fin is not the same.
  Type at you later,
  Dan McEntee
 

I am talking about the FP series, not the OS Max's

Time and time again people discuss the OS 20/25 FP engines, but fail to mention if they are talking about the older iron/steel version vs the ABN version.

I would think for the same displacement the older iron/steel version would be less powerful simply due to the OS recommended oil content of 25%, vs 20% for the newer ABN version.

Colin

Quote from: Colin McRae on May 01, 2026, 10:54:28 AMI am talking about the FP series, not the OS Max's

Time and time again people discuss the OS 20/25 FP engines, but fail to mention if they are talking about the older iron/steel version vs the ABN version.

I would think for the same displacement the older iron/steel version would be less powerful simply due to the OS recommended oil content of 25%, vs 20% for the newer ABN version.

Colin

  I think there are actually 3 different engines being discussed here, and it needs to be very clear what we are talking about, because is makes a huge difference. Just talking about OS 20/25 engines

OS 20/25S - 70's vintage baffle-piston engines. The very first engine I bought with my own money was an OS-20S. This is a baffle-piston engine with an steel liner and iron piston, just like a Fox, etc. This is an small upgrade to the old steel-fin OS 15/19 (Max I, Max II, Max-III 15). It runs like engines of the day, more power than an baffle-piston 15, it uses props like an 8-5 or 8-6. Much less effective power than the Fox 29/35. These engines are minor upgrades to 15s in the "Jr." models - Jr. Flite Streak, Junior Nobler, etc. You *cannot* run them at higher RPM, the crank will break before you get enough power,  you cannot use with any decent success on "35-sized" models like the Skyray 35, Flite Streak. You might be able to coax them through patterns in ideal conditions but they are clearly far too large for these relatively weak engines. The 25 is exactly the same as the 20, but bored out slightly.
   These engines came with, unfortunately, two venturis - a "small" and a "large". It was more-or-less out of the question to run either engine on the large for stunt using suction, however, *many* people tried, and then threw away or lost the small venturi, so they would "burn down" flight after flight. The small venturi is 5.5mm with a *3 mm* spraybar.

OS-20/25FP-S "Iron Liner" - These are the first FPs, which were all initially released with iron/steel construction. There were also a 10, 15, 35, 40, and 60(!). These are schneurle-ported engines with the liner rotated ~45 degrees to the normal way for some reason. They can be identified by looking for an obvious bulge in the casting just to the right of the crank as viewed from the front. They come with an OS-862 muffler.

 These engines are perfectly viable for using in 35-sized airplanes if you are careful with the needle and use the right fuel - 50/50 or more castor, 20%+. Note that SIG Champion or Powermaster is not quite enough, you can get away with it for a while, but they are both ~17% 75 synthetic/25% castor. I have very little experience with these engines, if it was me, I would run it with the right fuel and the e20-30 muffler from the 20/25FP ABC and 25LA. This engine WILL allow you to use the proper 9-4 APC prop and reasonable RPM, and aside from  breaking it in, I would run it exactly like the ABC version until something bad happens. I am told, and it makes sense, that it runs better with the E2030 muffler.

OS-20/25FP-S ABC - Second, upgraded version of the iron-liner version. Smooth case as opposed to the "bump" for the bypass on the iron-liner version. This comes with the E-2030 muffler - WHICH YOU MUST USE TO GET THE CORRECT PERFORMANCE . ABN construction, which is superior for our application to ABC - breaks in faster and lasts longer than you will ever fly it. All my (exasperating long diatribes) are about this engine, it was the one used in the "Small Engine Experiment" from the early-mid 90s). The 25 has a lot more power, almost to a fault. The 20FP runs better for stunt for these sorts of airplanes, and is *far far better* than a Fox 35 for these smaller profile airplanes, with *vastly* better performance.
    The last batch of these engines were released with a rear-needle arrangement, mounted to the backplate with a metal metering block (the core of a OS R/C carburetor) on a metal bracket and a spray nozzle through the venturi. These work more-or-less identically to the front-needle version and there is no performance reason to switch it to a front-needle setup. Choking it is a bit more tricky on a typical profile mount.

    The 20FP-S ABC was far and away the best runner of any of the engines tested in the Small Engine Experiment. Subsequently, the "new" version of the 25LA-S ABC showed up, and I think it is slightly more stable than the 20FP with similar power. The 25FP has *way* more power than either of them but it much harder to tame in these smaller airplanes.

    This engine can run regular fuel and extra castor does not help you, if anything, it causes progressive power loss as it varnishes up.

  Those are the different variants.

    All of this assumes the *unmodified* stock engine as delivered from the factory. If someone has "improved" it, my temptation is to tell you to throw it in a wood chipper so neither you nor anyone else has to deal with it any more, but failing that, get any of the above engines in as close to stock configuration you can, because you, your buddy, almost any "name" reworker, do not know how to improve it significantly, and anything they do will make it worse. This includes the spraybar, venturi, head screws, head shape, head shims, or anything else.

Brett

Quote from: Colin McRae on May 01, 2026, 10:54:28 AMI am talking about the FP series, not the OS Max's

Time and time again people discuss the OS 20/25 FP engines, but fail to mention if they are talking about the older iron/steel version vs the ABN version.

I would think for the same displacement the older iron/steel version would be less powerful simply due to the OS recommended oil content of 25%, vs 20% for the newer ABN version.


   They are significantly different engines, really, just share displacement size. They run well, and were used a lot in a lot of construction articles for sport C/L models in their day. Different porting and timing.
  Type at you later,
  Dan McEntee
Colin

Quote from: Brett Buck on May 01, 2026, 12:28:51 PMThe 20FP-S ABC was far and away the best runner of any of the engines tested in the Small Engine Experiment. Subsequently, the "new" version of the 25LA-S ABC showed up, and I think it is slightly more stable than the 20FP with similar power. The 25FP has *way* more power than either of them but it much harder to tame in these smaller airplanes.

   
Brett

Thx Brett. That is the info I was interested in. i.e.: The small engine experiment was based on the OS FP (ABN) version. If that was stated in a past post, I must have missed it.

I recently acquired a Medic in great condition. The previous owner had an OS 20 FP (Iron/steel version) on the model. I have no idea how well that worked out.

I put on a stock OS 25 FP (ABN) with stock muffler on the model w/ APC 9-4 sport prop and gave it a try the other day. BTW, the Medic ready to fly is at 35 oz. Running the 25 FP engine where it likes to run I had trouble getting it above 5 seconds on 62' lines. So, as you say the 25 FP is pretty powerful. I switched to a MAS 9-4 prop and that helped a bit. 5.2 sec laps but with a somewhat hard break in maneuvers.

I don't own a 20 FP (ABN), so I will try a stock OS 25 LA as a comparison next time I am out flying. I know others have had success with a 25 LA on the Medic.

Colin

I believe the FP liners were rotated 45 degrees (ish) so that the cylinder walls would be solid where the wrist pin travels up and down, so that the wrist pin could use pads rather than circlips. With a "normally" aligned cylinder, the wrist pin would travel across the schnuerle ports, and to keep the end of the wrist pin from getting into ports, circlip retainers would be required. More expensive to make, potentially more to go wrong.

  I have a Buster that was given to me years ago. It came without an engine. I had an OS 40 and it fit so I used it. Since it was an R/C engine I used the throttle by adding the lightest servo, receiver and battery I had.
  It is NOT a great stunt plane. It will do acrobatic maneuvers that do not require square corners.
  As as a sport plane it is exceptional! It excels at High/Low events like carrier. It is quite stable and should do well at balloon bust. It will hover but I'm not brave enough to try a sabre dance maneuver. It is more fun than my similar Ringmaster.
  It is a definite keeper but there is no sense in trying to make it fly a pattern. I have a third hand ARF Nobler for that.
Oh, and with a 10x6 prop it will tow a 75'+ streamer, just for fun. Don't try that with a small engine.
Jess