Author Topic: O.S. Stunt .30 vs..35 engines? (Read 4801 times)

frank mccune · « **on:** June 29, 2016, 04:27:23 PM »

Hello All:

How much power difference is there between the two? I have read engine reports where there is much less power to be gained from the .30 as compared to the .35. For .05 cu in. displacement, I can not see how there would be a huge difference in power.

What parts will interchange between the two engines? For examples, case, cylinder, crank, head etc.

I have both and they both run very well.

Tia,

Frank McCune

EddyR · « **Reply #1 on:** June 29, 2016, 05:00:18 PM »

I ran both in a Ares back in the late 70 and do not remember any difference between them.
Ed

Brett Buck · « **Reply #2 on:** June 29, 2016, 06:36:38 PM »

Quote from: frank mccune on June 29, 2016, 04:27:23 PM

Hello All:

How much power difference is there between the two? I have read engine reports where there is much less power to be gained from the .30 as compared to the .35. For .05 cu in. displacement, I can not see how there would be a huge difference in power.

It's 17%, to first approximation.

Brett

frank mccune · « **Reply #3 on:** June 29, 2016, 06:54:09 PM »

Hi Brett:

The figure of 17% seems to be too high. I remember back in about June 1953, MAN tested the Fox .29 and Fox. .35 and the results were about 500 rpm in favour of the.35.

I aint very smart so would be kind enough to elaborate on your post.

Tia,

Frank McCune

RandySmith · « **Reply #4 on:** June 29, 2016, 07:16:22 PM »

Frank

The 35 has a small amount more power, both will fly a Stiletto and Nobler very well
they both run an excellent 4/2
The use the exact same parts except for piston sleeve head and wrist pin, and of coarse the head shims

Randy

Brett Buck · « **Reply #5 on:** June 29, 2016, 08:43:42 PM »

Quote from: frank mccune on June 29, 2016, 06:54:09 PM

Hi Brett:

The figure of 17% seems to be too high.

35/30=1.17, it's not magic.

Brett

Manuel Cortes · « **Reply #6 on:** June 30, 2016, 12:53:55 PM »

It seems the piston and liner in OS 30 last forever......not as in the big brother. I´ve had good results with both in classic size ships.
Obviously the 35 havin a slight more torque.

Kind regards from Spain.

Bill Little · « **Reply #7 on:** June 30, 2016, 07:16:52 PM »

Hi Frank,
I got with Randy and the guys. Not a whole lot of difference! In the past, many years ago, I ran both and would occasionally swap them for fun and giggles. One thing that was good was if i was having trouble putting enough fuel in for the .35S, it might be just right for the .30S. I got to really like the .30S in the profiles like Goldberg and Sterling where the case was usual that you could not use big (4 OZ.) tanks. I love them both!

BIG Bear
RNMM/AMM

Air Ministry . · « **Reply #8 on:** June 30, 2016, 11:43:25 PM »

Unbelievable , but thepiston / liner for the 30 S is the H29R one . Timings 130/110 in the 30 , lower than the 35 , just .

Chris Wilson · « **Reply #9 on:** July 01, 2016, 09:02:52 PM »

The only variable given is displacement so the only valid answer is based on that, unless this post 'evolves' Brett is again correct.

RandySmith · « **Reply #10 on:** July 01, 2016, 09:28:34 PM »

Quote from: Chris Wilson on July 01, 2016, 09:02:52 PM

The only variable given is displacement so the only valid answer is based on that, unless this post 'evolves' Brett is again correct.

Maybe so maybe NO .. it depends on IF the CR , timing, is all the same, I have not checked a 30 vs 35 , but I can tell you every 30 vs 35 I have built and check, the 30 has a much better/tighter P/S fit, and all of the hundreds of 35s I have built and rebuilt, the P/S were not tight, most you can push the piston right out of the top sleeve
But bottom line is they are both great motors and I will pull the sleeves and check both soon

Randy

Chris Wilson · « **Reply #11 on:** July 03, 2016, 04:28:45 PM »

Well the only documented test that I have ever seen with reliable numbers is -

http://sceptreflight.net/Model%20Engine%20Tests/OS%20Max%20S-35%20and%20S-30RC.html

With the 35 having 76 bhp per litre
and the 30 having 70 bhp per litre (but it does wear the RC type throttle)

So 76/70=1.085 or 11% so the smaller engine (regardless of its size) is actually a less powerful design that weighs 1 ounce more due to its thicker liner (and of course the throttle)!

Air Ministry . · « **Reply #12 on:** July 03, 2016, 06:20:35 PM »

Pity its Not a Litre , then ! .

The Crank is the SAME part no ( & Timing ) The Lower Sleeve port tops on the 30 Could ? make it about as good * on a 10 x 6 , considering
its only useing 6 /7 of the silencer or has a 7/6 advantage there over the 35 , the silencer being the same ( i before e , except after B $:-\$ )

* stunt wise .

frank mccune · « **Reply #13 on:** July 03, 2016, 07:07:08 PM »

Hi Matt and Chris:

I too was aware of the results posted on sceptreflight re. the OS .30 vs.35. It I not a fair test due to the .30 having a RC carb. I have seen other tests where the .30 had a higher b.h.p./litre than the .35.

I was taught that the h.p. diminished as a result of the increase of the size of the engine. The smaller the better. This took on many parameters but the end result was the same. Oh yes, the number of cylinders limited the total output of the engine. Of course the engine that was used as an example was the old John Deere 2 cylinder engine. It could only be made so large before the rule of diminishing returns lowered the total output of the engines.

Perhaps someone who is trained in engine design will chime in and refresh my memory of engine design. Likewise, motor car racing seems to have gone the way of a few cylinders up to and beyond 16 cylinder racing engines.

Matt. how do you think of these thing? Lol

Be well my friends,

Frank McCune

Chris Wilson · « **Reply #14 on:** July 03, 2016, 08:45:03 PM »

Quote from: frank mccune on July 03, 2016, 07:07:08 PM

I was taught that the h.p. diminished as a result of the increase of the size of the engine.

Perhaps you mean that you were taught that "h.p. per litre diminished as a result of the increase of the size of the engine?"

Maybe Top Fuel dragsters will dispute that theory though with something around 1000 hp/ litre.

Trostle · « **Reply #15 on:** July 03, 2016, 10:47:51 PM »

I do not have my book on engine specs right now. However, the OS 30S will be heavier than the 35S, using the same venture arrangement, because of its heavier (as in thicker cylinder liner).

Keith

frank mccune · « **Reply #16 on:** July 04, 2016, 06:06:09 AM »

Hi Chris:

That is what I wanted to say but I failed.

I will bet that you know a bit about this subject.

Thanks for the correction!

Be well,

Frank

Avaiojet · « **Reply #17 on:** July 04, 2016, 12:40:14 PM »

Frank, "The Real" Mccune,

I'm glad you started this Thread. Makes me rethink I should keep my NIB OS Max 30S. I did have it on ebay for 10 days but there was no interest. Not even a question.

Is your's R/C or CL?

I might have an extra venture if you need one for the change.

Charles

RandySmith · « **Reply #18 on:** July 04, 2016, 12:47:20 PM »

The OS 35-S weighs 6.7 ounces
The OS 30-S weighs 7.1 ounces
The timing on the sleeve is .005 thou lower, or more duration ,by about 2 degrees, in the 30, both intake and exhaust, are slight more duration
As I stated the 30s always seem to have a tighter piston fit, Turning the same prop, it is about 5% differance in power.
And No you can't compare the venturie version to one with a carb

The additional weight is of course in the sleeve, both will fly a Nobler or Stilleto very well

Randy

frank mccune · « **Reply #19 on:** July 06, 2016, 01:38:40 PM »

Hello All:

Thanks for the replies.

Charles, I think that I got the OS .30 from a friends trash bin. Prior to discarding it, he stripped the venturi and nva. I bought a replacement venturi and a ST clone nva. I thought that the engine looked new, so I took a chance with it. I have been very pleased at how well my .35S and .40S OS engines ran so I thought that the .30S may also be a keeper.

I installed the engine in some type of airplane and was very impressed how well it ran. For some reason, I am stuck on the 70's as far as engines are concerned. I have been advised to get with the modern times and get newer engines as they are much better. My old tech engines start first flip, unless I flood them, needle easily and have great runs.

One of my better engines is the Fox .40 Stunt circa. 1972. The one with the huge crankcase and is quite heavy. It does not have the power of the .36 pb from the same era but is a great running stunt engine. Throw an 11-6 prop on it and set it for a 4 cycle and have a great stunt run.

Nest project is to get out my old ST G21/.35 combat engines and put them in a stunter. How does an 11-4 prop running in a wet 2 cycle sound for a stunt engine? The engine should last forever being blueprinted and chromed. Lol

Be well my friends,

Frank

Chris Wilson · « **Reply #20 on:** July 06, 2016, 06:32:53 PM »

Quote from: RandySmith on July 04, 2016, 12:47:20 PM

And No you can't compare the venturie version to one with a carb

Randy

With all due respect, isn't that a paradox?
(The fact that you have even come to a decision points to the fact that you would have had to compare them at some stage.)

Anyway from what I have seen of RC throttles compared to a 'stunt' orientated fixed venturi is that a wide open throttle will always given a higher rpm and thus more top end power compared to the partially throttled and limited stunt type.
And yet the RC equipped 30 still suffers in comparison?!

Perhaps someone could swap an RC equipped engine's throttle to a 35 and check the figures?

RandySmith · « **Reply #21 on:** July 06, 2016, 07:10:37 PM »

Quote from: Chris Wilson on July 06, 2016, 06:32:53 PM

With all due respect, isn't that a paradox?
(The fact that you have even come to a decision points to the fact that you would have had to compare them at some stage.)

Anyway from what I have seen of RC throttles compared to a 'stunt' orientated fixed venturi is that a wide open throttle will always given a higher rpm and thus more top end power compared to the partially throttled and limited stunt type.
And yet the RC equipped 30 still suffers in comparison?!

Perhaps someone could swap an RC equipped engine's throttle to a 35 and check the figures?

Yes I have compared same engine with carb and throttle, NO it is not accurate, even the same engine most times give differance in RPMs
In the case of the OS 35S the carb is smaller than the venturie, so NO it gives less top end power not more, at any rate its better to compare apples to apples. Many times the carb is larger than the CL version, but in the OS 30 35 S it is not the case

Randy

Chris Wilson · « **Reply #22 on:** July 06, 2016, 07:20:16 PM »

Thanks, I understand now.

Steve Helmick · « **Reply #23 on:** July 07, 2016, 03:56:41 PM »

"Nest project is to get out my old ST G21/.35 combat engines and put them in a stunter. How does an 11-4 prop running in a wet 2 cycle sound for a stunt engine? The engine should last forever being blueprinted and chromed. Lol

Be well my friends,

Frank"

The ST G.21 .35 was used in a stunt plane way long ago, in a design published (AAM or MA) by Bob Barron. I believe it was called the PA-8, and the prip was a 10-4 wood TF.

Steve

Steve_Pollock · « **Reply #24 on:** July 07, 2016, 05:59:36 PM »

Close, Steve -- it was the PA-6.

Steve_Pollock · « **Reply #25 on:** July 07, 2016, 07:51:23 PM »

In his article on the PA-6, Mr. Baron summarized his engine set-up in the paragraph below.