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Author Topic: ASP .21 C/L venturi  (Read 4921 times)
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sigrun
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« on: February 20, 2014, 05:33:58 PM »

Seeking a (substitute) C/L venturi for the ASP .21 as it appears ASP don't actually make one.

Conducted a search here and elsewhere. Nothing fruitful yet except dimensions (from JEN spec sheet for that engine) -assumed correct.

Throat outer is 12mm, throat height is 9mm. Neck internal 4.5mm. Admittedly that's pretty small for a .21, and I reckon one could get away with a bit larger. The rest doesn't really matter so much. ST G34 venturi throat fits, but its neck internal diameter is 7mm (spec) which I think is just a bit large and might well cruel suction on the .21 if not running flat out at the top of its RPM range - which I don't want to do.

Anyone trodden the conversion path before and know the answer as to where I might source a readily available substitute C/L venturi to fit at a fair price? The whole concept is specific performance on a budget. Looking to try one of these in a SIG Skyray 35 as a sub for Brett Buck's highly recommended -in that model for purpose- O.S. 20FPS-S (NLA). Yes I can run the R/C carb in fixed open position, but I'd like to get rid of that chunk of metal for a lightweight venturi if it triages economically feasible.

I am aware a substitute JEN venturi is available from a certain UK engine supplier, but I'll rule it out by saying a price of GBP£22 and silly shipping for the item rules it out when the cost of a venturi and shipping = more than the cost of the engine + (supplied with R/C carb and muffler) shipping !!! Even the retail price of an O.S. .25LA  to .25LA-S conversion kit (spraybar, venturi & o-ring) is only AUD$20 -GBP£9.50!

Any assistance which might be rendered appreciated.
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ffkiwi
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« Reply #1 on: February 20, 2014, 07:47:40 PM »

How many do you want and what sizes? Aluminium or delrin? I'm assuming you're talking about the current 'small' series 3 ASP 21 not the early chunkier model? [doesn't matter as I have both-but no point wasting time and effort on venturis for the wrong one...]

 ChrisM
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sigrun
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« Reply #2 on: February 20, 2014, 09:57:59 PM »

This one, because it's spec'd much lighter and bore/stroke is closer to square. Not buying from there, but used the link as it's a better image. Other than they are Schnuerled ABC and TBR with an almost square bore/stroke ratio which is more to my purpose than the majority of fast reving oversquare brutes of today, I know nothing about them other than the ASP .25 I also saw has the same look as the O.S. FX series or ST current G series and that more knowledgable end user are reports state that run in right and 'fed' right, they'll work just fine and will last at least as long as a LA. The case looks very much a cheap casting of the AX's predecessor SF tech. I'm not after the "most powerful" in terms of peak top end power boasting. Rather I want the more tractable right through the range. As stated, it's for a SIG Skyray 35 with the objective to throw a largest diameter fine pitch prop that it can, fly slower rather than faster whilst maintaining line tension on 60' lines whilst in the vertical or overhead.

Now Delrin or aluminium. Never used a Delrin venturi. What's the advantage disadvantage? If they both do the same job, as it's a budget project whichever cost less sounds just fine. :]

How many? Just one ATM. I haven't bought the engine yet until I find out if I can source a venturi, otherwise -dearer- I'll just go with an Schnuerled ENYA SS25-S (the .20-S is baffle piston crossflow ported still and considerably down on power) although I think that'll be to much power -just- in the Skyray 35 for what I want to do hence the decision to take a punt on trying one of those ASPs. Although I do build/finish light, I well know from previous experience that plain bearing O.S. 15FP-S's fly my 36" wingspan APS (Aldrich) Peacemakers just fine, so at just 44" span for the Skyray 35 the TBR ASP .21 should be up to the task in it per Brett Bucks' report. I run .15 TBR diesels (ST & PAW) and find them overpowering in .15 orientated 36" wingspan design like a 36" Peacemaker or even marginally larger Smousen. I'm, 'fingers crossed' hoping the .21 ASP will prove to be about just right. If not, well, it won't have cost me an arm and a leg. I'm thinking of a .32ASP in a SIG Twister, but I suspect it'd be like kitting it out with a ST G34. Bully engine. Just the way it's ported and delivers its power, not the right one for the intended role the way I want to fly it.
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ffkiwi
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« Reply #3 on: February 20, 2014, 10:15:58 PM »

I was offering to make you one-or several but if you haven't even purchased the engine yet-and haven't yet decided whether it WILL be the ASP 21 then I'll withdraw the offer.......

 ChrisM
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sigrun
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« Reply #4 on: February 21, 2014, 01:13:16 AM »

Thank you Chris. You offer is appreciated if I failed to inflect that it was.   Embarrassed

It is a case of cart/horse. I was searching to ascertain a cost effective suitable venturi was available prior to buying the engine. Once I've established it is, then I'll definitely buy that engine and see how it goes. I tend to plan and do things that way rather then diving in and hoping. No point in buying an engine for $40 and spending as much again just to to obtain a venturi as is the JEN scenario in which case I'd do as well well avoid the issue and just buy an O.S. 25LA or lash out on the ENYA SS25-S instead. both coming with venturi and N/V RTR OOTB.

Just been in and out most of the day, which is why my replies are not immediate. On a positive note, I just sourced and picked ether & DII. YES!  Smiley
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ffkiwi
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« Reply #5 on: February 21, 2014, 02:00:17 PM »

No problem. The ASP 15 is quite popular over here (NZ) for C/L combat, being very cheap (~NZ$70) when purchased in quantity- the other sizes seem less popular-though you do spot the odd 25 and 32. The 15s go very well on a bladder.....AFAIK ASP do not make C/L versions of their engines so (1) people have to make up venturis and (2) we ought to be awash in unused ASP 15 carburetors....!  Actually venturis are not hard to make if you have a lathe-even with my self taught skills. There's a bit more work in a peripheral jet one, but a simple venturi insert for a standard spraybar setup is easily done.  Delrin vs aluminium?  No particular benefit (some claim insulation benefits-which might certainly be relevant in T/R but is largely irrelevant elsewhere) but it IS beautiful stuff to machine-much nicer to work than aluminium alloy. I also use it for repro tanks. Not as cheap as aluminium though-especially in the larger sizes of bar......
   The JEN venturis have always struck me as ridiculously overpriced.................

 ChrisM
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sigrun
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« Reply #6 on: February 21, 2014, 06:36:48 PM »

Concur. £22 -VAT +p&p (and they don't miss you there either) is IMO OTT for a venturi. I buy a lot of stuff out of the UK for my other hobby, and JE are 'having a laff' with their shipping pricing and its included mandatory insurance covering their risk at our expense. A typical .46 engine simply doesn't cube that big or heavy to warrant what they are charging per item even taking into account packing material. Mind, they aren't alone these days as I notice more and more businesses have started value adding with disproportionate shipping. I bought a couple of R/C Irvine .53s (for R/C) from them a decade ago, but they do seem to have lost the plot since. The marketplace has changed whereas they haven't. Whinge mode off.

I saw a couple of ASP .15s in the flesh yesterday. Quite well cast externally. No idea what the internals are like metallurgy and machining wise, though I suspect they've come a long way since the early days of SANYE. I only have Schnuerled FP-S' and baffle piston cross ported 15-III O.S. .15s along with a sole remaining NIB ENYA IV .15 and several tasty .15 TBR diesels. Oh, and how could I forget? . . .my FAI combat motors.

For AUD$50 delivered, I'm going to give one of those ASP .21's a go in a SIG Skyray 35, so I'll PM you re a venturi deal once I've ordered it. Brett Buck reported here that he liked the O.S. 20FPS best in his favouring it over the .25. Looking at that ASP's SF clone design, being TBR I expect it'll perform similar to and probably marginally better than an L.A. if O.S. still made a .20 or the .20 FP-S. I plan to swing a bigger diameter fine pitch prop, so if the FP-S can be made to run OK with its timing and Schnuerle porting, that model ASP should be OK as well, even better with its almost square bore/stroke config which is about as long stroked as any modern sport R/C engine gets. As already expressed on several occasions, I really like ENYA engines. Whilst acknowledging that from the vid I saw of the lain bearing ENYA SS30-S in flight it has power in excess of requirement, from my perspective the combo as it was configured was way too fast for my requirement in the Skyray 35, especially for a gentleman no longer in his reflex prime at the handle. Smiley
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sigrun
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« Reply #7 on: February 24, 2014, 08:26:06 PM »

Hi Chris. Just an update. I have ordered that ASP .21 -from Hobbyking HK. Although the AU warehouse had stock, I wanted some other stuff as well and the AU warehouse is A. always in back order status on almost everything, B. dearer, and C. there's little difference in shipping or real world delivery time frames. So that said, I'll keep you appraised on the venturi situ once I have it in hand.

I'll measure the throat carb throat internal diameter when it arrives. A couple of considerations are that I don't want it to go flat out, and I do want it to suck well on a wedge uniflow, although I will also experiment with a Sullivan clunk and on muffler pressure. In discussion with Jim Thomerson (sp)? running a similar characteristic and capacity unit (not ASP) in a Flite Streak, he found it circulating too fast on a 9x5 prop on 60" lines and went back to a 9x4. I'm surmising I'll probably be running a 9x4 on the .21 in my Skyray 35 as well. Relaxed -sport- pattern is what I want to fly with it to get my eye and hand back in. If I can manage that, I'll be up for a bit of fun with Vintage combat and the Sport Bendix and Goodyear racing classes after a long hiatus.

Sitting tight now to await its arrival. 
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ffkiwi
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« Reply #8 on: February 24, 2014, 10:54:32 PM »

It's no big deal to make several venturis of varying throat diameter-but you can ring the changes indefinitely if you start paying around with spraybar location/venturi length as well on a side mount motor. R/C carb throats (with a few rare exceptions such as pylon motors) are generally sized to give good fuel draw (at the expense of ultimate top end power) in most GP motors-so a venturi with the same nominal ID as the R/C carb bore would be a good place to start from, adjusting up or down in diameter from there..........

 ChrisM
 'ffkiwi'

PS I should have made it clearer in my post above about the ASP 15 that it is popular in NZ for 'speed limited' combat-it certainly doesn't pretend to be an F2D motor. I'm not sure how the ASP 21 is viewed as a stunt motor.......but its light, cheap and available.....one day I must run mine up and see how it compares with the earlier ASP21 model-which was a big heavy beast.............
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NeilR
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« Reply #9 on: April 04, 2014, 08:00:09 AM »

I bought two of the ASP .32's for my boys as their first engines and will need to make some venturis for CL use. I sourced some Enya NV's which I think will work ok. Can I simply drill out delrin and machine it down to suit the same bore as the carby?
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ffkiwi
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« Reply #10 on: April 04, 2014, 03:39:17 PM »

I bought two of the ASP .32's for my boys as their first engines and will need to make some venturis for CL use. I sourced some Enya NV's which I think will work ok. Can I simply drill out delrin and machine it down to suit the same bore as the carby?

Absolutely-you can do a remarkably good job on a venturi with a lathe and a few centre-ing drills (particularly if you get the type with a bell shape profile as opposed to a straight taper). Even normal jobbers drills plus a countersink will produce a half decent venturi.   Depending on your proposed use though-you might have to alter the sizes (R/C carbs generally have a fairly conservative hole size)......check out the table at www.controlline.org.uk  (the Barton site) which gives a range of recommended diameters for various usages .....
   If you haven't used it before-you'll find delrin an absolute joy to work with and machnie...........

   ChrisM
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greggles47
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« Reply #11 on: April 04, 2014, 05:37:56 PM »

Apart from various sized drills to get the venturi bore about right, the final shaping is done with a triangular file ground to become a scraper.

This will give you that very sexy curve that looks so cool - I'm not sure it achieves any other function that just a drill would give.

Here's one I did recently
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Re: ASP .21 C/L venturi
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