I just got done flying mine... What a blast... I have a new Magnum .70 4s in mine... Have probably 5 tanks through it... The plane and engine are both doing great.... Question.... I have a 13X6 APC on it now for breakin.... In the air this setup will fly the plane fine at half throttle in a mild scale like fashion... If I open the engine up I can hear it roar to life but am not seeing any change in the planes performance... Is anyone else flying this combo and if so have you found a good prop for it... I want to get a coulpe more tanks/flights on it and then I am thinking of going to a 14X4 for pull.... Vertical is not that great now... This plane weighed out at 8 pounds with the Magnum and it is spinning the 13X6 APC at 9700 while still on the rich side for breakin....

Thanks
Roger

Hi Roger.

I'm not following you around. I'm not......Really.... I'm not!

OK I've got one of these, but freely admit to not being a four-stroke afficionado. Mine's fitted with a .61, as the suggested .46 flies them (having seen one initially powered by same) with all the aerobatic 'performance' of a Tiger Moth. The .61 is about right IMO, allowing decent RC like performance or scale like performance. I'm not looking for pattern like performance. If I was, it needs more because of all that bloat.

A nice enough design in every other respect, the Seagull Decathlon's singular failing is that weighs in like Pavrotti. I know..I know it has a generous wing area and decent section, but 3.63kg (8lb) and I presume that's your dry aka zero fuel weight spec (?), is a LOT of weight on a 70 4 stroke to expect any vertical other than courtesty of kinetic, let alone ½ decent vertical we expect in the RC sky.

Once run-in, propped appropriately and tuned to peak, your 70 should fly it scale like. But that's about all. The real McCoys either Standard or Super Decathlon aren't exactly performance powerhouses. If you can squeeze a single vertical roll out of them and exit into a hammerhead or stall turn before inadvertantly tailsliding (non-approved maneouvre 'cos you can't hold the large empennage surfaces rigid with cables) you're doing well. And they have constant speed props which we RCers don't.

Just about anything will fly it on that wing, but the moment you point the nose skyward altering the balance of forces to rely predominently or wholly upon thrust vs weight instead of lift vs weight, well just do the "thrust required" arithmetic.

To have any hope at all with that 70 in this model, tuned to deliver its peak power potential is the byword. A gurgling rich run-in setting isn't it. And IME&KO you'd want a climb prop. ie: Pitch it down, 5" is good, and go for a diameter with that pitch which will allow it to achieve circa its peak power curve RPM. If it won't achieve what you want it to do on a 5" pitch of appropriate diameter, then you need a more powerful engine. With the unavoidable characteristics and limitations of fixed pitch, the flight envelope simply narrows too much below 5" unless 3D is where you want to 'play' or you want to putter at low power settings around like a Cub.

Someone like Minnflyer who has fitted his with a 70 Surpass will offer you a more favourable pro 4 stroke bias perspective towards propping your Magnum 70. His flies nicely, and rather scale like.

Me - I just reckon you need a pumped FS-90 Surpass II! [8D]

Otherwise, your key to vertical is pre manoeuvre dive entry for speed is your friend given that KE=½mv².

sigrun
"Castor oil is cheaper than synthetic so if someone is bragging about castor, then you know what they are selling."
- DJ

You sure your not following me :-]
Your close to right... I do think I can improve on it a little though... Thinking of a 14X4 or something like that... This does weigh in right at 8 pounds dry.... Nice thing about the .70 though is a .91 will bolt right in... Same case etc and the weight is almost the same... I still have half the throttle left which isn't producing much change in speed etc... This tells me there has to be a better prop for this setup... I can do a big loop etc no problem. Stall turns run out of verticle rather quickly though.. Maybe I am just used to overpowered Extra's....
Take Care
Roger

Nice report! I've got a Saito 82 going in mine.

.82 might be closer to what it takes... Can't believe they call for a .46 in this... Maybe they have some real potent .46's in Nam now... I have the Global Decathlon which is smaller and lighter... It flys great.. I have a Saito .72 in it which is kind of overpowering that one... Maybe I need to swap engines...

I've got an OS 70 in mine with a Graupner 12x7 prop. EXCELLENT combo!

PS this is the combo I used in the RCU review which will be published sometime this winter.

MinnFlyer
Looking forward to that review.... I will try a 12X7... My thinking was a bigger diameter for more thrust... The engine is running great. Probably not quite as much power as a Saito .72 but not that far off either...
Thanks
Roger

IronCross

Forgot to mention. Your other best friend when it comes to improving vertical or swinging more prop is Cap'n nitro.

'sigrun von Braun'

PS: Larger diameter = greater propeller efficiency at lower flight speeds (high drag airframe) ipso facto increased thrust.

Not knocking Magnum as indisputable bang for the buck, but a 70 Surpass performance equivalent? In Sanye's 2007 dreams mayhaps.

Thanks for the info..
I don't have a .70 supass to test against the Manum but I do have a couple of Saito .72's.. The Magnum is swinging the 13X6 APC around 500 rpm less then the Saito's do... But like I said it is only on it's 5th tank and still set rich to break in... Word from others with Mag's and Surpasses is the Mag puts out somewhere between the OS and the Saito's... Biggest question in my mind is how is it going to hold up..

Which version have you got? Their AR or RFS suffixed 70? I suppose we should be sure we're comparing apples with apples.

I understood from non-anti OS prejudiced reports here that the current model Surpass II certainly kicks the AR's arse, and is still more powerful than the RFS as well? I know from personal experience that whilst it looks impressive on paper, IMO&E the 61AR is sick when compared with an OS 52 Surpass, and the low end carburation issues OOTB simply make it not worth the trouble. The 70AR performances I've witnessed are at best described as "ordinary". We haven't seen the RFS here as they've only just started distributing them. The 70 is the only RFS capacity currently available locally, presumably wanting to exhaust remaining stocks of ARs in all other capacities prior to importing RFS's.

Longevity wise, I don't think current Magnum P&L longevity will be any more of an issue than current OS models. Oil education and run-in procedures are the problem with so many RC flyers today, so many observably lacking the acquired knowledge and basic skills derived of an apprenticeship necessarily served as aeromodellers in the hobby demanded of a bygone era. Certainly not seeing any evidence of reduced longevity due manufacturing issues this side of the pond. Only reason I can think of in terms of value not to buy a Magnum over OS at this juncture is simply their hit or miss carburation issues with some models. eg: XLS52A, FS-61AR.

On that power comparison between the RFS and Surpass II, I'd only be too happy to be wrong, and freely admit to not being interested in researching it further to establish 'the irrefutable argument' either way, as its all of merely academic interest to me at this juncture. Even the vanilla Surpasses certainly made the ARs look sick. But I digress. Suck and blow. Anything more complex is superfluous affectation.

Just a point of note, using a silicon exhaust deflector will significantly effect a reduction in power available from two strokes in vertical. They act as a choke under load. Unsure of how detrimental their effect upon mechanically timed and valved four strokes.

I have a couple of the RFS versions.. As I said I have no OS's to compare it too... Ouput between the Saito and Magnum are close enough to make it an easy choice for me... Saito shines because it is a much lighter engine then the OS or Magnum... Transistion is excellen in the one .70 I have fired up... Guess if you a "balls to the wall" engine you go with YS :-]. If the weather ever straightens up here and I get that Mag broken in I will be able to get some more realistic numbers....

Post us some piccies of your Decathlon. [:-]

Ok, here's a pic from the review:

MinnFlyer
Nice looking (plane :-]). How did you get that gloss on it ?....

SigRun
Here ya go

[img][/img]

And another....
Now it is your turn...
[img][/img]

SigRun
Check this link out for more data on the engine... Not bad for 129.00 USD
[link]http://www.rcgroups.com/links/index.php?id=4450[/link]

I think so too. Even the older AR's were good value. Continual improvement of ASP (UK) or Magnum (US & Australia) brandings from Sanye are the best news in RC this decade.

That 70 RFS is circa AUD$250 over here. Where are you buying them for USD$129? Tower has them listed at USD$169, down USD$10 from when last I looked (last week). At $129, that's almost irresistable. [sm=spinnyeyes.gif]

We are in agreement there.... I got them from Tower... Magnum had them on sale for 149.00 a while back and then Tower was doing there 20.00 off thing... Same with there .91's, got them really cheap through Tower, same sort of deal... I was waiting for the .61's to go on sale again but it appears I missed the boat on those... They seem to be out of production... Guess I can still get the ASP version though from Paul across the pond...

So MinnFlyer
What did you use to shine that one ?... Looks like it goes beyond wax ?..
Thanks
Roger

SigtRun
I believe some pictures are in order from your end here.... :-]
The weather is lousy here.. In the 50's but low clouds (sometimes reffered to as fog) and drizzle .... Yuck
Haven't been able to try different props yet...

That is the stock covering right out of the box. I didn't even clean it.

The shine must be the reflection of my beautiful coworker who's holding it.

Actually, it's from the combination of a bright sunny day, and the fact that she's sitting in the shade of a large tree. What you're seeing is the reflection of the sky coming through the trees

Your coworker certainly adds to the glow, no doubt about it... I'm going to have to move back to Minn.. Seems you have access to an endless supply of these "coworkers" :-]. The plane in that picture on this screen looks like it has a gloss on it a mile deep... Strange effect....
Thanks
Roger

IronCross

Apol 'bout no pic yet. Happy to comply ASAP. Unusually, Decathlon "one of the few" for me yet to zap with the Nikon Coolpix. My most recent build and fly.

Been distracted between work and uncharacteristically local rainy wx exacerbated by 2 eager new R/C students keen to opportune every R/C wx flying window, so Decathlon hasn't been to the field for a couple of weeks. Wx here right now is uncharateristically unfavourable for flying this time of year. When it hasn't been storming with heavy rain, it's been alternately 38 deg C (100 fahrenheit), 85-90% humidity, zero breeze and the field a tidal duckpond. Think Corpus Christi, Miami or New Orleans in high summer without the sea breeze.

I understand the w%$ word... Gets in the way of life a lot... Weather here is lousy too... Sounds like you get a lot of humidity during your summer... We spend a good portion of our summer in the 90-110 range also but it is more of a dry heat... Not all that bad... Much better then what we have now... At least for flying...

I'm thinking of getting one of these, but trying to figure out what engine to use. I like the idea of a running a 4 stroke, such as an OS 70, and know where I can get one, that's almost new, for a really good price. However, I happen to have a K&B .61 twister that's looking for a home. I think the twister would be nice, same weight range as the OS 70, but more power. However, I'm not crazy about having the big muffler sticking out. Anyone have any thoughts on picking one engine over the other for this plane?