ameyam

Ok, so I am most likely taking the H9 Showtime 50. Reading through the dedicated thread, I am wondering as to which engine to take

1) OS 55AX: it doesnt seem to have sufficient pullput from hover. But everyone said the same when I took the Reactor 46-70 and I am quite OK with the 55AX on that airplane. It is also the cheapest of the lot and I can source it locally. Costs about $150 landed

2) OS FS72A: It weighs same as the 55AX and can swing a bigger prop. But power is less than the 55AX. I can also source it locally. Costs $330 landed

3) OS FS81A: It weighs more, is damn expensive. But most people are recommending this size. I cant get it locally, having to import it so will cost a packet. Costs $369.99 + shipping-discount

4) OS FS91SII: Its a bit larger than recommended for this model and will require some modificaton in the firewall. However its an old tried-&-tested design (I have one already in another airplane). Again its expensive but cheaper than the os81. Costs $324.99 +shipping-discounts

5) Saito 82AAC: Its actually cheaper than the OS81 by $60 (so should cover the Tower discount) and lighter than the OS 81 at 17.6oz. I should get a good deal ordering it with the ST50. However, there are few saitos on our field. It costs $299.99+shipping

6) Saito 91AAC: It weighs about same as OS FS91SII. Again, I should get a good deal ordering it with the ST50 but there are few Saitos at our field. It costs $309.99+shipping

I have listed the relative weights of the candidates below.


OS 55AX: 18.52oz (525g)
OS 91FS SII: 22.6oz (641g)
OS 72A: 18.7oz (530g)
OS 81A: 20.11oz (570g)
Saito 82AAC: 17.6oz
Saito 91AAC: 20.6oz


Can you suggest which one is better choice

Ameyam

ThumbSkull

My Feedback: (57)

The new YS70 has more power than all those choices. I think the weight is similar to a Saito 82. If you can get it. Here they go for $329 shipped.
If you are going for a 20oz. engine, I'd get the Saito 100. Weight is similar to the 91. If the all up weight is near the 7lb. end of the scale, you'll need the 100.

FrankFuss

I had a Showtime 50 with a Saito 91. It was OK for a sport flyer at my 5000' altitude, but lacked good vertical for IMAC style aerobatics. It would probably be much better at your altitude, having 15-18% more power. The stock engine mount was too flimsy for a larger engine, so I used a Dave Brown 90FS mount. You need to be aware of the engine length dimensions if you want the designed firewall to spinner spacing. The Showtime 50 has excellent flight characteristics, by the way. I also made other modifications as posted in other related threads.

Frank

ro347

My Feedback: (13)

As Frank said, use the DB mount. They are my faves now. Had one with a Saito 91 and loved it. Had good power. Thumbskull brings up a good point. I would go with the Saito 91 or 100. My Showtime weighed in at about 6.5lbs. Anything less than the 91 isnt fun, unless you are doing strictly sport flying - my opinion.

ameyam

I intend to use a GP adjustable mount that I recovered from a crashed Reactor. That way, I hope I dont have to redrill the firewall. Whether I use the 55AX or FS91 or 81A really depends on what is available.

Ameyam

ro347

My Feedback: (13)

If I remember correctly, even trying the GP adjustable mount...you will have to redrill. If youve never done it before...its a very simple process as long as you have everything needed to make it so.

FrankFuss

A Saito 82, one of the engines the Showtime 50 was designed for, would probably be adequate at sea level, if you don’t want to make modifications. I would imagine that more power would be best for 3D, but 3D is not my thing. In my case when I re-drilled the firewall, it was a good thing. I found that the original blind nuts were not glued in as well as I would have liked.

ameyam

Was actually comparing the advertised HPs of the engines. Basically, I took the advertised HP and divided by the engine wt in oz. Results are below

OS 55AX: 1.73HP, 18.52oz- 0.093
OS 75AX: 2.37hp, 26.46oz- 0.089

OS 72A: 1.18hp, 18.7oz- 0.063
OS 82A: 1.3HP, 20.11oz- 0.064
OS 91sII: 1.6HP, 24.2oz- 0.066

Ok, Ok I know it is wrong to compare 2C and 4C directly and that the given HPs mean nothing unless specified at the same RPM (so will vary based on prop size). That is why there is a gap between the 2C and 4C ratings. Firstly, the 2c ratings are both at about 16000rpm so we can compare them. The 4C are at 11000rpm so we can compare them seperately.

But arent these figures surprising? There isint much difference in the HP/oz for the two 2c engines. Similarly, there isnin't much difference in the HP/oz between the three 4C engines either. I read this as the hp/oz remains fairly constant with increasing engine displacement. For 3D, where wing loading should take precedent, it is a good idea to take the lightest engine possible with the maximum thrust. Would that imply that I should go for the 72A in 4C or the 55ax in 2C?

Just a footnote, the 91SII is the cheapest of the three 4C engines. Given a choice (and discounts not playing a part) I would definately go for the 91SII. My only concern is, being an old engine, would parts still be available sometime down the line?

Ameyam

ThumbSkull

My Feedback: (57)

Advertised HP is a worthless number for 3D. The only time that matters is at full throttle, full speed.
Most of 3D happens at half or less throttle. What matters is thrust, and how quickly an engine can make it.
The OS91 is overweight for it's power (as it pertains to 3D).

Get a Saito 100 at 21.2 oz (with muffler). It will be lighter and more powerful.
Remember that airframe needs to be kept light. Ignoring this will give you very poor 3D.

ameyam

ThumbSkull,

remember, I am still talking regarding the ST50, so the airframe component is out of the way.

You are suggesting to put a 1.00 size engine on a 50 size airframe? I would really consider that overkill unless you are flying at a higher altitude. I fly at sea level (in fact just across from the sea) and I really dont need that kind of power. Besides, a bigger engine needs a bigger fuel tank and more ballast and this in turn increases weight.

Based on the reviews, most people had better results with a 81 sized engine. That makes sense because that engine weighs similar to the 55 size 2C and produces more thrust at part throttle due to larger props that can be used. But if you go to the next 2C size it weighs more than a 91 size 4C. From the economics point of view, its either 55AX or 91FS

Ameyam

ThumbSkull

My Feedback: (57)

You did post in the 3D flying forum. Power/weight ratio is almost everything.
The AUW of this airframe is 6-7 lbs. If you are anywhere near 7lbs, a 55 will barely hover, let alone pull out.
The 91OS is way too heavy and will surely put you over 7lbs.

The 50 size is a rating for sport flying with a 2-stroke. In the 3D arena it will be WAY underpowered with a 55AX.
The 55AX is good for 3D under 5lbs maybe even 5.5lbs but no more. Trust me on this.
The 91FSII is 24.2oz with the muffler. The Saito 100 is 21.2oz with muffler. That's why the Saito 100 is a better choice.

Do what you want, it's your plane but you asked for advice and I have flown all the engines in question.
In my avatar is a Saito 82 hovering a 5.1lb 3D bird. It's just enough to pull out well from a hover on 20% fuel.

ameyam

Actually, I cant get the Saito[&o]. Thats why I am only discussing OS. I know Saitos are lighter. Which in OS would you suggest?

Ameyam

ro347

My Feedback: (13)

If you want 3D the 55ax will not work!!!! I have a profile that weighs about 4.5lbs. with a 55 and its great! The ST at almost 7lbs wont work(in my case 2.25lbs more- my ST AUW was 6.75lbs)!!!

As someone who has had the ST with a Saito 91 - its the way to go. I havent flown the saito .82, but I personally would think twice about it as I thought the .91 was perfect - I was attempting 3D at this point, not hardcore yet.

In regards to OS, just find something comparable to the saito .91/100 and you should be fine.

ThumbSkull

My Feedback: (57)

If it must be OS, the new Alpha series is the way to go. The 20.2oz [link=http://www.osengines.com/engines/osmg0981.html]81FS-a[/link] would be minimum.
The 21.5oz [link=http://www.osengines.com/engines/osmg0990.html]110FS-a[/link] is probably a better choice. I know someone that has that engine in a 7lb profile that is very happy with it.

Steve N

I had a Saito 82a in my ST50 and for me it just didn't have quite enough oomph, certainly not enough for 3D. I don't know if you fly with lots of nitro in India so it might not be too bad. I think this model deserves unlimited performance which is delivered by the OS 75AX I now have on the front. The Saito, being quite light necessitated quite a lot of lead to get a comfortable balance point, I didn't need nearly so much with the OS (that powerbox muffler is pretty hefty).

ameyam

After a lot of thought, I explored through the possibility of electric setup for the ST50. Since the ST50's manual does not give an electric reference, I used details from the Reactor Bipe's manual which is similar. The details are as below. I worked out in an excel sheet for the landed price in INR which I converted to USD for easy comparison.

RimFire 0.80size motor: $89.99
Mount: $19.99
60A ESC: $99.99
lipo (2x3.2Ah Electrify 11.1v in series): 129.98

Total landed cost: $390.68 (incl shipping & customs)

Alternative engine cost (OS FS91SII): $369.3 landed

Now this is actually higher (if not equal) to the cost of the FS91SII & 81A. And there is the added issue of field recharging (for which I have no means right now). As against this, putting in a glow engine means, if I run out of fuel, I can borrow fuel from anyone and just continue flying. I can also use the same engine on my other airplanes

OK, I know some will suggest to get a cheaper motor, esc and battery from a alternative site. Most of the reputed brands cost similarly. Admittedly, I am not too much into electric flight so I am not sure of what replacement motors in other brands/ makes will be. But I am not too sure it will dip much below the $300 landed price. Also, there is risk of fire from the Lipo batteries and I am not too comfortable with that right now. Electric is good from various points of view, but I think just not cheap enough for me right now.

Ameyam

ro347

My Feedback: (13)

If you go electric...do alot of searching and research. You can find cheaper alternatives at much less...should you be decide to go that route