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Acrowot with laser 80

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GrahamWh18/03/2019 18:41:52
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Tim is there a danger that at high speed a venturi effect around the carb intake side scoop could drop air pressure to the carb?

Tim Flyer18/03/2019 19:06:26
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Hi Graham I don’t think so. It would need really massive speed if anything. I have a similar arrangement with the carb in my LA7 where the carb is actually in the main cowl air outlet. I also have the carb right in front of the wing and directly in the airstream on on Wot4 powered with a laser 80. The carb comes out right into the airstream and it is absolutely fine. I guess if one were at massive speed there could be some turbulence effects but I have found most carbs fine being in airflow in fact it’s much better than them getting hot!

Tim Flyer18/03/2019 20:17:43
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This one I fly a lot has carb on laser 80 right in the airstream. 598ca135-4b31-4e69-8335-22be913b7c18.jpeg

Tim Flyer08/04/2019 12:44:04
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Here is the cowl now fitted. I put a small aluminium scoop on the bottom to cover the bulky exhaust bracket and for aesthetics. I also added a bit of internal baffling so the air doesn’t bypass the cooling fins and be drawn out of the bottom exhaust scoop . Here is the front side view . Hopefully I will get the rest finished and maiden fly it this weekend 😊c9340909-0b6f-4278-9987-2d1ed80ba2b6.jpeg

GrahamWh08/04/2019 21:17:35
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Very neat work Tim and thanks for answering about the airflow around the carb as it is something I have often thought about in the past.

Tim Flyer09/04/2019 11:13:25
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Cheers Graham. I can honestly say the slipstream airflow has never yet been a problem on the carb. One thing that is bad though I have seen is when a carb is enclosed in a cowl and too near The firewall. If it gets warm and restricted air that’s a problem. I think the main thing is just having a decent flow of air around it . Petrol carbs are much more prone to overheating as the fuel quantity used is less than in methanol engines plus as Jon mentions often the latent heat effect of methanol keeps the carb cooler. That’s why petrol engines need plastic insulator blocks on their carbs.

Tim Flyer10/04/2019 16:02:40
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170 photos

Did 3 “maiden” flights today . It’s a superb plane..the Laser 70 is a real screamer . The vertical on this plane seems unlimited and the high revving engine really helps. The wind was 25mph and gusting and this light plane was buffeted around especially when I was landing. Even so it’s aerobatics were great. I got two good landings and one cartwheel after getting caught in a gust so called it a day after that! The damage was only very minor though and I look forward to flying it at the weekend.

Tim Flyer10/04/2019 16:05:58
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2270d84a-3b36-4e20-b492-6657bebef278.jpeg

Paul james 810/04/2019 16:13:19
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Great news! Makes me want to get on with my new one

Percy Verance10/04/2019 16:26:41
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A Laser 70 screaming Tim? You may not be getting the best from your Laser if it's screaming. What prop are you using? I think a 13x6 or 7 is about par for the course for a Laser 70.......

Percy Verance10/04/2019 16:27:17
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A Laser 70 screaming Tim? You may not be getting the best from your Laser if it's screaming. What prop are you using? I think a 13x6 or 7 is about par for the course for a Laser 70.......

Tim Flyer10/04/2019 17:49:04
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Hi Percy that’s what I have . It is using a 13x6 APC and it really goes ! I’m “just running in “ at the moment but full throttle is quite something. Maybe it’s my custom “tuned header” 🙄. Anyway it’s certainly a great fun plane . It’s a great little brother for the big Acrowot and I do find the smaller planes more convenient and quicker and easier when to set up when I’m pushed for time .

Tim Flyer10/04/2019 18:19:25
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1009 forum posts
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By the way Paul I had to add10g of lead on the tail. If I did the build again with the 70 , I would have put the throttle servo next to the rudder servo as per instructions. I did also replace the heavy wooden elevator pushrod with a light weight carbon one . That may have also affected it a bit. 

Edited By Tim Flyer on 10/04/2019 18:20:52

Paul james 810/04/2019 22:47:15
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Posted by Tim Flyer on 10/04/2019 18:19:25:

By the way Paul I had to add10g of lead on the tail. If I did the build again with the 70 , I would have put the throttle servo next to the rudder servo as per instructions. I did also replace the heavy wooden elevator pushrod with a light weight carbon one . That may have also affected it a bit.

Edited By Tim Flyer on 10/04/2019 18:20:52

That is a bit of a surprise as my old one, with a Saito 82 up front has a big slab of lead on the firewall. Balances perfectly and flys well for an old un. I've got a Kyosho spitfire to sort out first then maybe on to the new Acrowot.

ASH.10/04/2019 23:34:01
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298 forum posts

Looking good Tim. Could you give some more details on your flexi pipe arrangement. Is there any brazing involved and how is it affixed to the engine?

I have a Laser 70. Will like to use it one day without the muffler if I can.

Also, the AUW on your model? I use a 14x6 APC on my Saito72, gives good thrust, torque and flywheel effect. No "flameouts" ever. Tried lighter Graupner 13x6 and 14x6 wood and found engine cut on the down verticles coming out of a loop. 

 

 

Edited By ASH. on 10/04/2019 23:41:51

Jon - Laser Engines11/04/2019 08:25:11
4765 forum posts
179 photos

Our 70 is/can be a screamer if you so choose. Its good to 14000rpm if you really want. I personally wouldnt use it over 10000 or below 9000 in general use. 13x6 gives you around 10k, 13x7 around 9k. 12x7 sits up near 10 again. 14x6 is likely to be a little to much if you want maximum performance.

Tim Flyer11/04/2019 08:51:37
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1009 forum posts
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Hi Jon I agree it’s interesting the characters of each of your engines. This one can really rev so definitely can go fast . 😊. I’m getting all I need on the 13x6 but may have a go just for info on a 12x7or 13x7. On the 13x6 I don’t need much more than half throttle for all the aerobatic stuff. It’s very good on fuel too. I’m getting close to 15min on my 10oz tank and coming in with spare fuel. Hi Ash the AUW is about 2.85kg or 6.28lbs. It feels very light to me vs my heavy kit built Acrowot which I built like a truck😉.

Regarding the exhaust it is a stainless flexi-pipe with a brass sleeve (7/16” or 11.1mm diameter) silver soldered on the end which slides into the exhaust outlet with a fairly tight fit. I did put a dab of high temperature red silicone on it to ensure a total seal(the standard manifold uses o rings). The end of the SS flexi pipe has a smooth tapered section which fitted nicely into the brass sleeve for silver soldering. The standard laser exhaust clamp holds the sleeve in place . I used the cut out under the plane to mount a home made simple aluminium exhaust bracket. The pipe is held to the bracket with a steel jubilee clip with red silicone on the inside. That allows some flexibility whilst still gripping the pipe. Exhaust systems should not be totally rigid as cracks can develop longer term as the engine does shift slightly when running. I’m out today but happy to post more info.

Edited By Tim Flyer on 11/04/2019 08:58:40

Edited By Tim Flyer on 11/04/2019 09:01:42

Jon - Laser Engines11/04/2019 10:27:13
4765 forum posts
179 photos

The character of an engine is everything. Some are fussy, some are laid back, some are vicious, and some even seem bright and happy to see you start them up. Its quite remarkable really and can make quite a difference to the enjoyment of a model.

Tiger moths etc call for a laid back sort of engine that really couldnt give a rats about anything you throw at it, where as the acrowot demands an engine that likes to get up and go. Swap them around and the two models just would not feel right. It should be noted though that many engines have dual personalities as a prop change on our 180 can make it laid back (20x6 etc) or pretty lively (17x10 or 18x8).

Running our range on the test bench is always a fun time and the 240v is one of my favourites as i slap a 16x8 on it and wind it up to near 10k. Having a 40cc twin screaming away at those sorts of revs always brings a smile to my face

I dont recommend flying it at those revs though, might be a little loud

gangster11/04/2019 10:49:39
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Posted by Paul james 8 on 10/04/2019 22:47:15:
Posted by Tim Flyer on 10/04/2019 18:19:25:

By the way Paul I had to add10g of lead on the tail. If I did the build again with the 70 , I would have put the throttle servo next to the rudder servo as per instructions. I did also replace the heavy wooden elevator pushrod with a light weight carbon one . That may have also affected it a bit.

Edited By Tim Flyer on 10/04/2019 18:20:52

That is a bit of a surprise as my old one, with a Saito 82 up front has a big slab of lead on the firewall. Balances perfectly and flys well for an old un. I've got a Kyosho spitfire to sort out first then maybe on to the new Acrowot.

Interesting that I have an asp70fs up front and also have a sizeable chunk of lead at the front. The RCME review also spoke of a few ounces of lead. So have they changed them in any way.

Tim Flyer11/04/2019 21:36:06
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1009 forum posts
170 photos

Cheers Jon ...that bit of the engine testing sounds fun! I must admit I do enjoy engines it’s all about the right engines the right application. Obviously there are good and bad quality engines but engines are always suited to a particular purpose depending on torque and rpm cubes. There are lots of combinations of stroke bore and capacity ...matching props to all that and it certainly becomes a bit of an art getting it right . Obviously experience is the most useful! .

Re the Acrowot weight . 10g on the tail is just a slither. The engine thrust seems very well above the 6.28lb all up weight. However up front I did add reinforcement plus baffles and aluminium scoop in the cowl. I also used my own beefy laser engine mounts as the kit ones were missing. The other thing I customised were the cowl fixings. I have an aversion to wobbly threaded screws in fuel soaked holes in the cowl . I used glued in stainless steel threaded inserts in the wood with plastic m3 cowl screws . The plastic screws do not vibrate loose like metal screws do . . Kits and wood do vary so it’s possible that my tail would light but as I mentioned my hollow carbon tail rod is a lot lighter than the wooden kit one too.

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