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Author Topic: Brodak 40 on a Skyray?  (Read 2521 times)

Offline Darryl W

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Brodak 40 on a Skyray?
« on: December 05, 2020, 10:43:12 AM »
Hello All,

Is a Brodak 40 too much engine for a Skyray 35? Or is an LA25 a better choice? I plan on using this plane on 60 ft lines, as a trainer to practice wingovers and loops.

This is my first post on SH, thanks Sparky for letting me in!

Darryl W

Offline Brett Buck

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Re: Brodak 40 on a Skyray?
« Reply #1 on: December 05, 2020, 11:51:14 AM »
Hello All,

Is a Brodak 40 too much engine for a Skyray 35? Or is an LA25 a better choice? I plan on using this plane on 60 ft lines, as a trainer to practice wingovers and loops.

This is my first post on SH, thanks Sparky for letting me in!

Darryl W

   A 25LA is a better choice, but the Brodak is certainly not too powerful for it, based on helping a bunch of different people with them. Some of them seem to be only marginally stronger than a 25LA once you get the venturi to a usable dimension (some of which are .308 - far too large - on depending on when you got it), and the LA allows you to run a better prop.

   If you have a Brodak 40 that you know runs well, the I would say use it, instead of seeking out a 25LA.   Either combination is perfectly adequate for primary training.

   I would also note that the straight-out-of-the-kit Skyray will fly well enough if you have the right engine on it, but is both heavy, and *extremely fragile*. All that plywood and spruce is a little stronger than balsa, but much heavier. So in any given crash, the forces are much higher, and thus much more prone to self-destructing. Mine originally had a 20FP, and weighed 36 ounces, which is heavy, but flew extremely well. It just shattered to irreparable bits in the first significant crash.

     I rebuilt it (in a single afternoon...) with all balsa parts in the wing, very small balsa spars, etc. and all I had on hand was 5-lb wood. So it ended up 7 ounces lighter. This made little difference in the performance, but it subsequently survived upwards of *40* crashes , minor and major, and has only required significant repair once - when the monokote shattered like glass due to extreme age and UV exposure over 20 some odd years.

    I don't wish you ill, but reality is that you are very likely to crash multiple times if you are pushing yourself to learn. What you don't want is to be at a dead stop for a month afterwards. I would suggest that as soon as you finish your first airplane from the kit, *start another one*, using the kit plans as a guide, replace the spar with medium balsa, replace the lite ply ribs with medium 3/32 balsa, and the half ribs with full ribs, also of 3/32 medium balsa. The rest is OK as is. I would also replace the single-wheel gear with two-wheel gear on all of them, far less prone to disaster on takeoff.

    Take them both with you to the flying field every time. Fly one and repair minor damage on the spot but when it gets too bad, just grab the other airplane out of the car and *keep going*. The worst thing you can possibly do is encounter one problem, give up, and go home to try and fix it for a week. It's the old "get back on the horse" plan, don't lose time doin a few flights, then leaving, just grab the other airplane and keep going. It's not like they are expensive, you can probably put a Skyray together for $20 worth of material.

     Brett

Offline Darryl W

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Re: Brodak 40 on a Skyray?
« Reply #2 on: December 05, 2020, 04:30:46 PM »
Thanks for all the great advice guys!

I already have a Skyray kit and a newly broken in Brodak 40 on hand, ready to start building, so that is why I was asking. And actually, as Brett suggests, this will be a back-up for my existing Skyray with a Fox 35 that I built last year and has so far survived my awkward loops and tip-over landings. I am hoping the Brodak engine will be a bit less cantankerous than the old Fox.

This will be my 3rd Skyray build, number one succumbed to a crash and yes those ply ribs do shatter into shards on impact. I was too frustrated at the time to try rebuilding but in hindsight I should have replaced them with balsa ribs instead of throwing the whole airframe into the dumpster. Live and learn I guess.

If it runs as good on the Skyray as it did on the bench, next home for the Brodak 40 may well indeed be a Banshee.

Darryl

Online Dan McEntee

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Re: Brodak 40 on a Skyray?
« Reply #3 on: December 05, 2020, 09:42:35 PM »
   I'll second what Brett suggests, and when building Skyray .35's for training purposes, build them in batches. Use the plywood parts for templates. The first one I built I used some decent 3/16" balsa for the ribs and used the same number of ribs. This airplane was powered by a Fox .35 and suffered much abuse but still survives today! The problem with the Fox.35 and it's operation on this model as built stock, is the fox is a real shaker of an engine, and there isn't sufficient structure in the nose to dampen that out. At certain RPMs, you can actually see the nose shake from side to side like a tuning fork, and that makes getting a consistent needle setting very difficult at best! You can replace the motor mount stock with new ones that are as long as possible, and put a doubler on the in board side that is made from the hardest balsa you have, even if you have to laminate it with epoxy to get some thickness. This will help stiffen the nose. Balancing props will help also. I find that if you run a 10-5 prop instead of a 10-6 you will have to lean out the needle a bit more, and the higher RPM tends to smooth things out also.  The other cure, as mentioned , is to use an LA.25 or an FP.25. I think I remember Mike Pratt saying at one time that e flew the prototype with a FP-25. The .25 size engines may be easier to find used. I also prefer the two wheel landing gear for normal operations. A simple finish of a couple of coats of thinned finish cure epoxy that is well sanded, and then spay painted a solid color along with an iron on covering will get you in the air pretty quickly and is easy to repair.  The Brodak .40 can be tamed down with smaller venturi like Brett says and smaller props.

  From your description of previous flights, you are making the same mistake that I think we all did at first when attempting simple loops, and that is making them WAY to tight. Stand at the middle of the circle and look up, and all around you. You have ALL of that sky to fly in, so learn to use it! No need to do a loop under 20 feet high!! Make sure your controls are not too fast and the elevator does not need to deflect more than 30 degrees or so. You may have to use a
 longer elevator horn to achieve this, and a handle with adjustable line spacing helps also. Narrower or closer together line spacing will slow your control movements down and make the model not so sensitive. Most of us of a certain age were under the impression that we wanted a LOT of control REALLY FAST if needed to avoid a certain crash, but did not realize that having controls like that more often than not usually cause crashes! We have all been where you are at one time or another so don't think you are the only one to have these problems. We can help you flatten out the learning curve a bit! But sometimes, the best lessons are the hardest ones learned!
   Type at you later,
   Dan Mcentee
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Offline Darryl W

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Re: Brodak 40 on a Skyray?
« Reply #4 on: December 06, 2020, 10:23:57 AM »
Hey Dan, about the Fox 35 shaking, yes that was my experience exactly. Especially with the first Skyray, it shook like crazy! I had chalked it up to maybe an out of balance crankshaft and after the crash I took that engine off and put it on the shelf where it remains to this day. I wonder, maybe there is nothing wrong with it, it seems to run fine on the test stand. My current Skyray also has the shakes but not as bad and I found I could smooth it out by leaning it in to run faster than I think a Fox 35 should be run. I have never used anything but a 10-6 prop on these engines and so yes I will be definitely be trying a 10-5 on the next flight (which will have to wait till spring, as we are up to out eyeballs in snow and sub-zero temps up here) I checked the elevator throw on this one and it is +/- 30 degrees with the outermost hole in the horn.

As for the new Skyray, I am now thinking an OS LA25 might be the way to go.  My Brodak 40 just has the stock venturi that came with it. And I will be incorporating the suggestions you guys have given in the new build

I do enjoy building, as winter season is very long in Canada, and I have a fleet of some other planes but most of them, except with the Skyray and an old Corehouse Texas Slow, I have never attempted anything but flying level laps. I have been trying to open up my inside loops, and I think it was Charles Carter on the video chats who said his main impediment to learning maneuvers was fear of crashing. This is something I have to work on to get over.

Darryl

Offline Brett Buck

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Re: Brodak 40 on a Skyray?
« Reply #5 on: December 06, 2020, 12:19:23 PM »
The thing about the B40 is AAC so it tends to run cold unless you push it. On a little plane you will be grossly over powered so you'll have to do things to de-tune the engine to get stunt speeds. Smaller venturi, richer needle valve, low nitro fuel and lower pitch props could run cold enough to make ignition inconsistent.

     It will not be "grossly overpowered" with a Brodak 40, as long as you use an appropriate (not the stock .305- .308) venturi. The stock venturi, as far as I can tell, just leads to flight after flight where it is sagged off lean. I watched profile stunt at the NWR, one flight after another, about 40% Brodak 40's either full tilt lean or sagged off lean, either case was fairly fast in level flight but died in the maneuvers as it sagged off. Most people did not realize that there was any problem, but almost no one could reliably needle it, and on a profile the pressure drop  just killed it.

  In this case it is far more important to get an airplane of some type in the air ASAP, with whatever equipment is available, nit-picking it is not required - rather than come up with some ideal match. A Brodak 40 with a low-profile tank, like a Sullivan SS4 with the flat side up against the fuse side, is more than sufficient for the stated purposes. Would it fly better with a 20FP or "new" 25LA, yes, but they don't make those any more and most of the ones I have seen have already been butchered up with ST spraybars, fixing that is not the best way to get an airplane in the air ASAP.

    Brett

Offline Brett Buck

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Re: Brodak 40 on a Skyray?
« Reply #6 on: December 06, 2020, 12:28:13 PM »
Hey Dan, about the Fox 35 shaking, yes that was my experience exactly. Especially with the first Skyray, it shook like crazy! I had chalked it up to maybe an out of balance crankshaft and after the crash I took that engine off and put it on the shelf where it remains to this day. I wonder, maybe there is nothing wrong with it, it seems to run fine on the test stand. My current Skyray also has the shakes but not as bad and I found I could smooth it out by leaning it in to run faster than I think a Fox 35 should be run. I have never used anything but a 10-6 prop on these engines and so yes I will be definitely be trying a 10-5 on the next flight (which will have to wait till spring, as we are up to out eyeballs in snow and sub-zero temps up here) I checked the elevator throw on this one and it is +/- 30 degrees with the outermost hole in the horn.

   It was not an "out of balance" crankshaft, unless ALL of them were out of balance - which, in a sense, they are. My Skyray partly shook apart on a few runs with the Fox, too, and had to be extensively repaired when I did just as you did - run it at speeds that no Fox should ever be run. 9-4 Rev-Up and whatever setting it took, which was very fast. It not only destroyed the airplane, it also ate through the stuffer backplate anodized plating and about halfway through the backplate itself in 3 runs.

      I actually beat David Fitzgerald in that particular contest, as he was doing similar screwing around with the "brand new for 1994"  PA40. Unfortunately we both lost to Bill Howe who was *not* experimenting with engines, and a well-set-up ST46 on a Genesis 46 MK II disguised as a Macchi 202!

   When Frank Williams discovered the fix to the burp, I took it back out with the engine fixed, and while it now managed to run through outside corners, it was shaking the nose off again, so I gave up. Later I got a 20FP from a local hobby shop, put it on the Skyray, and after flying it with the Fox a few weeks earlier, it was like gravity had been cancelled and it was smooth as silk.

     Brett

Online Dan McEntee

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Re: Brodak 40 on a Skyray?
« Reply #7 on: December 06, 2020, 02:21:26 PM »
   Yeah, I think all production Fox .35s are not balanced at the crank as well as they could be. It's damn hard to almost impossible to balance a single cylinder two stroke engine. On high performance motorcycle engines, it is possible to get close but takes an elaborate set up and some people can do it in their sleep. There is a way to do a bench top type of static balance of the Fox .35 crank that I have done numerous times and it has some effect. Another thing to try is to swap ends on the prop. Take it loose and turn it 180 degrees and test that. Some props don't have even pitch on both sides which can shake things up, and that needs to be checked if possible. You just do what you can within your means or seek outside help if available, and make the nose of the airplane as stiff and strong as possible.,
  Type at you later,
   Dan McEntee
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Offline GallopingGhostler

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Re: Brodak 40 on a Skyray?
« Reply #8 on: December 06, 2020, 04:39:55 PM »
Interesting talk, thanks for the inputs on the Brodak .40, sounds like a really nice sport motor, might be worthwhile for me to pickup next time I am around to it.

RE the Fox .35 Stunt, given it is a 70 year old late 1940's design, do notice the observation on counterbalance not as refined as later, seen it on Ringmasters, Skyrays, T/F Flite Streaks, Clowns, etc. but still gather it is still one heck of a sport motor. But given the fact that it shakes a bit more lends credence to why some also ride Harleys. ;D

Online John Skukalek

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Re: Brodak 40 on a Skyray?
« Reply #9 on: December 06, 2020, 05:58:56 PM »
For what it's worth, I have been able to set a Brodak 40 to run in a straight 4 cycle on a Brodak Clown(profile). I use a plastic tank set up for uniflow and a 10x5 or 10x6 prop. Runs beautifully and a great trainer.

The same set up on a larger profile stunter runs beautifully in a 4-2-4.

Offline RandySmith

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Re: Brodak 40 on a Skyray?
« Reply #10 on: December 06, 2020, 09:16:43 PM »
Hello All,

Is a Brodak 40 too much engine for a Skyray 35? Or is an LA25 a better choice? I plan on using this plane on 60 ft lines, as a trainer to practice wingovers and loops.

This is my first post on SH, thanks Sparky for letting me in!

Darryl W

The Brodak 40 is  fine for that model, even though the 25 will  pull it, Just use low nitro and a 10 x 4.5  prop, it will be  a great combo  for you

Randy

Offline Mark Mc

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Re: Brodak 40 on a Skyray?
« Reply #11 on: December 07, 2020, 10:08:05 PM »
Darryl,
I did the batch build thing.  I scratch built three identical Skyray 35s at the same time.  Each has a .25 LA-S on it. I originally had an APC 10x4 prop on each, then tried a 9x4.  But in another thread here somewhere someone said they found an APC 9.625x3.75N prop worked well for them on their .25 LA-S.  I ordered a couple of them to try and found I like this prop on the Skyray better than the APC 10X4 AND 9X4 props I tried.  Granted, I'm still just a beginner.

Mark


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