O.S 55AX vs. 61FX?  
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O.S 55AX vs. 61FX? - 5/23/2008 9:37:32 PM   
Tony Gag Jr.



Posts: 605
Joined: 1/21/2002
From: Terryville, CT, USA
Status: offline 		How do these two engine compare in terms of power? If I put an 11X7 or 12X6 prop on both, how many more RPMs will the .61FX produce over the 55AX? I am looking for an engine for a .60 size plane with a 58" wingspan that should weigh around 8lbs. Just wondering if the 55AX could handle it with no problem, I really like the AX line.

Thanks,
Tony
       Post #: 1

RE: O.S 55AX vs. 61FX? - 5/23/2008 10:06:07 PM   
asmund


 

Posts: 1902
Joined: 11/20/2005
From: Floroe, NORWAY
Status: online 		By all means go for the 55 AX!
The 61 FX is a heavy dog of an engine (I used to own one) The 55 weighs about 550 grams and the 61 weighs 700 grams. My 61 FX would only swing the APC 12,25-3.75 at 13100 rpm when stock and I think the 55 AX will beat this with a good margin.

If you want the 61 FX you might just as well pick the 91 FX at only 70 grams weight penalty

< Message edited by asmund -- 5/23/2008 10:07:12 PM >

(in reply to Tony Gag Jr.)
       Post #: 2

RE: O.S 55AX vs. 61FX? - 5/23/2008 10:08:11 PM   
XJet


 

Posts: 3452
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: online 		Caveat: I've not owned either of the engines you're talking about but...

I suspect the 55AX is more of a torquer and the 61 more of a rever.

I would not be surprised if the power levels were similar but the 61 will be significantly heavier which can be important if it means that you'd have to carry a bunch of lead with the 55.

The 55 is a highly regarded engine, being powerful, tractable and mild-mannered. The 61 has been regarded as an "okay" engine but was largely eclipsed by the OS90 which pretty much weighed the same but put out more power. Unfortunately, the early 90s had their share of problems that may (or may not) have also affected the 61.

If I were you I'd weigh up these factors:

1. which engine will require the least lead (in the nose or tail) to balance the model?
2. will you be using this engine on another model later and if so, will it be a model better-suited to the .55 or the .61?
3. do you need torque or revs?
4. is resale value important? (it's easier to resell the 55 than the 61).

But as I said at the start, I've not had either engine so my comments are worth what you've just paid for them.

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RE: O.S 55AX vs. 61FX? - 5/23/2008 10:22:37 PM   
Rcpilot


 

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From: Arvada, CO, USA
Status: offline 		I used to have a 61FX.

I have a student who built a Kadet Senior with the 55AX. I did the break in on the motor and I've done all the tuning on it so far.

I like the 61FX better.

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RE: O.S 55AX vs. 61FX? - 5/23/2008 10:33:08 PM   
Ed_Moorman



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From: Shalimar, FL, USA
Status: offline 		Just for information, in the Model Airplane News .61 engine shootout, the only prop the OS .61FX out turned the OS .65LA was an 11-7.

I have 2 of the OS .55AXs and they are excellent engines. Lots of torque and they will turn fairly well. Jett Engineering has tested their tuned muffler on the .55 and gotten good results. Their favorite prop is the 11-6. I tached the 11-6 APC on my bench with both the stock and the Jett mufflers and showed a 1,700 rpm increase (12,800-14,500). This is on 10% Omega castor blend fuel. I gained 1,500 on an 11-7 APC. The sweet spot for the 55 seems to be in the 14,000-15,000 rpm range and not up in the 16's. I only gained 800 rpm on a 10-6.

The 55 was really made to over power a .46 size plane or fly a small .61 sized plane. For a true .61 sized plane, forget the older .61FX and get the newer .75AX. All the FXs will be gone sooner or later just like the SFs were. The engines will last a long time so you really should go will the newer model.

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RE: O.S 55AX vs. 61FX? - 5/23/2008 10:33:29 PM   
Ed Cregger



Posts: 7736
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From: Ringgold, GA, USA
Status: offline 		As Dubb Jett explained to me, it is better to think of the OS .55AX as a glorified (my word) .46 than as a .61. The gas passages are too small for it to compete head to head with a larger cased (larger bypass) .61 sized engine. Dubb seemed to hold the .55AX in high regard, but did not feel comfortable comparing it to a full size 10cc engine.


Ed Cregger


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RE: O.S 55AX vs. 61FX? - 5/24/2008 2:23:15 AM   
Tony Gag Jr.



Posts: 605
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From: Terryville, CT, USA
Status: offline 		Thanks guys. Maybe I will just wait a little and see if O.S. releases the .61 in the AX line. The plane should weigh around 8lbs, it is a Sig King Kobra, a true .61 might be the better choice.

Thanks,
Tony

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RE: O.S 55AX vs. 61FX? - 5/24/2008 3:21:30 AM   
XJet


 

Posts: 3452
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From: Tokoroa, NEW ZEALAND
Status: online 		Why not go with the 91? Most 91s these days weigh the same as a .61 but put out more power. Remember, the throttle can be used to reduce that power to whatever level you deem suitable :-)

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RE: O.S 55AX vs. 61FX? - 5/24/2008 3:22:19 AM   
Harry Lagman


 

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Tony,

Take Ed's advice (see below)....

quote:

ORIGINAL: Ed_Moorman

The 55 was really made to over power a .46 size plane or fly a small .61 sized plane. For a true .61 sized plane, forget the older .61FX and get the newer .75AX. All the FXs will be gone sooner or later just like the SFs were. The engines will last a long time so you really should go will the newer model.


For an 8lb model, the approximately 22-24oz weight of a ".60 block" engine will most likely be required to balance the model. To get sparkling performance from an 8lb model, you'll need at least a .61-.75 or maybe even a .91. The .55 just seems like it'd be too small from what you describe.

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RE: O.S 55AX vs. 61FX? - 5/24/2008 4:17:59 AM   
Tony Gag Jr.



Posts: 605
Joined: 1/21/2002
From: Terryville, CT, USA
Status: offline 		Thanks for the advice guys. I won't be building the plane anytime soon so I will wait to see if O.S. makes a 61AX. If they don't maybe I will go with the .75AX.

Thanks again,
Tony

(in reply to Harry Lagman)
       Post #: 10

RE: O.S 55AX vs. 61FX? - 5/24/2008 7:05:27 AM   
draftman1


 

Posts: 409
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From: Strathmore, CA, USA
Status: offline 		go with the 75 ax. I don think there will be a 61 ax, I think it will prob be a 65 ax. all of the ax are oddball sizes, expt the 46. OS is releasing a 35 ax next. 35's havnt been made in a long time. but it will take the place of the 40. I think os is going with smaller displacements and making the same power.

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RE: O.S 55AX vs. 61FX? - 5/24/2008 4:10:25 PM   
Daryl Martel



Posts: 595
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From: WinnipegManitoba, CANADA
Status: offline 		In reply to Tony who said - "Maybe I will just wait a little and see if O.S. releases the .61 in the AX line."

I concur with draftman1 - I don't see OS releasing a replacement .61. The new .75AX fills that gap. The introduction of all these "bored out/super light" designs has changed everything. .32s based on .25 size cases. .55 based on .46 (which were based on .40 size to start with!), and .90 size engines based on .60 size cases... why would they introduce a replacement for the .60? I've got a couple of O.S. .61 FSRs in good condition - I love 'em, but a new .46 has almost the same power.

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RE: O.S 55AX vs. 61FX? - 5/26/2008 10:24:16 AM   
suzonka


 

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quote:

ORIGINAL: asmund

By all means go for the 55 AX!
The 61 FX is a heavy dog of an engine (I used to own one) The 55 weighs about 550 grams and the 61 weighs 700 grams. My 61 FX would only swing the APC 12,25-3.75 at 13100 rpm when stock and I think the 55 AX will beat this with a good margin.

If you want the 61 FX you might just as well pick the 91 FX at only 70 grams weight penalty

Hi asmund, I have the same os 61 on a 3D type plane, will it handle a APC 12x4 without overhheating or over Reving?

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RE: O.S 55AX vs. 61FX? - 5/26/2008 5:11:36 PM   
Kweasel


 

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From: fort worth, TX, USA
Status: offline 		Your King Kobra will need a 60-90 for any kind of performance. A 61 will need a tuned pipe and high rpm. A 75-90 with a muffler will come close in power depending on rpm range. I would use a muffled 75 with a 12-6 or 11-8, if noise is an issue then a 90 with 12-8 for non-competition flying.

(in reply to suzonka)
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RE: O.S 55AX vs. 61FX? - 5/26/2008 6:16:51 PM   
asmund


 

Posts: 1902
Joined: 11/20/2005
From: Floroe, NORWAY
Status: online 		Your 61 FX should swing APC 12-4 at about 13500+ and it will not harm the engine at all. Overheating is usually because people use too big a propeller, let the engine work light and let it rev and everything will be fine.

For more power in the 61 FX, remove the baffle in the muffler and drill the outlet of the muffler a size or two bigger. That brought mine up from 13100 on APC 12.25.3.75 to 14000 rpm on that prop and made a world of difference in the air

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RE: O.S 55AX vs. 61FX? - 5/26/2008 8:38:33 PM   
suzonka


 

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From: calverton Long Island, NY, USA
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quote:

ORIGINAL: asmund

Your 61 FX should swing APC 12-4 at about 13500+ and it will not harm the engine at all. Overheating is usually because people use too big a propeller, let the engine work light and let it rev and everything will be fine.

For more power in the 61 FX, remove the baffle in the muffler and drill the outlet of the muffler a size or two bigger. That brought mine up from 13100 on APC 12.25.3.75 to 14000 rpm on that prop and made a world of difference in the air



So I really can use the 12X4 APC on my 61 OS as long as I don't abuse it . Right now I have an 11x7 and it wont slow down at idle coming in for a landing , its just to much pull at Idle

(in reply to asmund)