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Auster AOR 9 engine advice

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andy paterson23/12/2017 12:34:41
60 forum posts

Hi all,

I have a Trablet plan of Auster AOR 9 1/5 scale 81" wingspan I was thinking of putting a Saito 62fs engine, the plan recommends 40 to 61 two stroke .Would Saito be to under powered for this plane.


Denis Watkins23/12/2017 12:56:50
4335 forum posts
104 photos

Equivalent power to a .60 stroke, the top end recommended

Would be a 90 - 120 four stroke

The 120 would be more comfortable to fly

The Saitos are powerful for their size, but the .61 would be very marginal

Edited By Denis Watkins on 23/12/2017 12:58:41

andy paterson23/12/2017 13:04:36
60 forum posts

thanks Denis

kc23/12/2017 13:05:23
6427 forum posts
173 photos

Well actually the designer ( Keith Humber) said in his article on this design " A four stroke of around 60 capacity would power this aircraft adequately "

The article was in RCModelWorld March 1986 when four strokes were a little less powerful than now so the Saito 62 would surely be quite OK. Also the model is a little tight for space in the cowl so a large engine might be difficult to conceal.

Of course it used to be Traplet and now these plans are from Sarik Hobbies.

Andy send me a PM if you need a scanned copy of the article.

andy paterson23/12/2017 13:56:08
60 forum posts
Message sent kc
Engine Doctor23/12/2017 16:19:13
2469 forum posts
39 photos

Andy . Is your Saito an older version with a thin exhaust pipe and no silencer ? or the newer version with a muffler? If its the older less powerful model then its power will be equivalent between a 40 and 46 two stroke and will fly the model in a scale like manner but wont have any fun factor/ get out of trouble power . The later version has more power with a different cam and bigger valves and will fly that model easily. Its not an aerobatic model so shoehorning in a big engine will be a waste of time for scale like flying.

Geoff S23/12/2017 16:24:05
3590 forum posts
14 photos

Just a quick correction. I think the aircraft you mean (or mis-typed) is an AOP 9 (I think the initials stand for Air Observation Post). I have a part finished quarter scale version (which hasn't been touched for longer than I care to remember but certainly 3 years).

I think the quarter scale called for a 120 four stroke and I was originally going to fit a Zenoah 26 but couldn't get it to fit the very narrow cowl. I think kc may be right and the 62 would be adequate but perhaps not startling. If I were to continue my build I would probably go electric.


andy paterson23/12/2017 16:53:44
60 forum posts
Engine doctor , thanks for the reply ,the saito is the newer one with muffler
kc23/12/2017 17:39:47
6427 forum posts
173 photos

One of the reasons for keeping to the 62 is that the design uses engine bearers and it avoids ( probably! ) altering the bearer spacing which then can need other alterations.

This design has lots of attraction as an atmospheric type of plane but it was too large for me. Keith Humber also did a 45 inch AOP6 for Traplet (Sarik) in RCMW Oct 2004 plan No MW3091 but that was a little too small!    However there is also a 54 inch AOP9 version which would make a nice electric model.........if only I had the time to build it......  The 54 was a free plan in RCMW Nov2006.

Andy, the article has been scanned and sent to you.

Edited By kc on 23/12/2017 18:11:29

Jon - Laser Engines23/12/2017 18:06:57
5422 forum posts
263 photos

I agree with ED completely. Its a gentle model and excessive power is not required.

For the slightly larger DB auster I usually recommend our Laser 80 which gives a good performance with plenty in reserve. As this is a slightly smaller model I would say a 60 will fly it scale and a 70fs would probably be the sweet spot.

andy paterson23/12/2017 20:35:37
60 forum posts
Thanks all for the help , thank you Keith for the email
David Ovenden23/12/2017 21:26:14
357 forum posts
17 photos

Andy, if it helps, the bearer spacing is the same for saito 62 ; 72 and 82 engines. So if you use yor 62 and find the model would benefit rom a little more power it wouldn't be difficult to upgrade to either of those 2 larger Saitos.

andy paterson23/12/2017 21:37:46
60 forum posts
Thanks David , that is handy to kniw

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