Options:

1. Tower Hobbies .75
2. ASP .91 four stroke

Thoughts?

Do you own either engine? A 91 4 stroke would be nice

IMO,

The 91 4 stroke or larger.

Bob

I don't own either. I have had the TH .75 on order with Tower for about a month with an expected delivery of end of October. Now their website no longer specifies an expected ship date which leads me to believe they are not getting straight answers from their supplier or having other issues. My options are to wait for the TH, or cancel that order and get the ASP.

The .91 four-stroke is the smallest four-stroke that is recommended for the Big Stik by GP, hence my question. I wanted to ensure it doesn't end up being under-powered with the .91.

A 91 four stroke flew my BS60 very well. If I remember correctly the finished plane weighed 8 pounds, plus or minus a couple of ounces.

This model tends to "build" nose heavy based on everything I have read and that was my experience. With an OS 91 four stroke, tail wheel, and rx pack several inches behind the wing saddle, mine still needed around 2 ounces on the tail.

If you want to use a two stroke to try to save a little nose weight, and do not want to wait for the TH 75, the GMS 76 and SK 90 two strokes are both available for about 100 dollars
http://www3.omnimodels.com/cgi-bin/w...I=GMEG1076&P=0
http://www.atsrcplanes.com/skengines.htm

Carrell,

Good thoughts, thanks. I think the decision was made for me when I called Tower after my original post and they told me they expect to get the TH .75's in the new year.

Quite frankly, I would rather stay with the 4-stroke and from what you guys are telling me the .91 is a good size so I'll just go with that.

Thanks again.

You could go with a SAITO engine, the 100 or 115 or even the 125 would work good. The SAITO engines don't weigh as much as the OS style engines do. A SAITO doesn't weigh much more than the 91 two stroke engine does.

I can tell you a 61fx is under powered a 91 for4 stroke should be just right.flew mine with a 61.needs more power, i love saitos 115 would be my engine of choice

Actually I've flown my GP Big Stick .60 with both a TH .75 and an OS .91 Four stroke.

The Tower Hobbies .75 beats the OS .91 four stroke in terms of power on this plane.

I ended up leaving the .75 on the plane as the performance is much better.

And this with 3800 NiMH batteries in the plane on both instances, to permit me to fly all day long w/o interruption.

It penetrates wind better with the extra loading.

-

BTW: I also have a .91 Four Stroker on my Skybolt, and there is another club member at our field with the same plane and the T.H. .75 engine. He gets MUCH better performance on his Skybolt, though mine sounds more authentic.

opjose what prop did you have on your 91 a 14-8

Thanks guys, unfortunately the TH .75 is out of the picture as current lead time is March of 2010...

Back on the topic: I can get my hands on a Magnum 1.2 Four Stroke, is that too much engine for this plane?

A .61 two-stroke and a .91 four-stroke are the same power. Other than pulling a large diameter, low pitched prop for ultra good takeoff power, but reduced top speed once airborne, the .91 four-stroke has no power advantage over the .61 two-stroke.

If you're not afraid to fix your own engines, go to the Hobby King website and gaze at the prices of ASP engines (Magnum USA parts will fit). There, you can buy an ASP 1.08 two-stroke for less than $100 plus shipping or an ASP four-stroke .91 for not much more than $100 plus shipping. Both are great engines.


Ed Cregger

No, it is not too much engine for this plane, but plan on mounting your servos in the tail and possibly mounting your flight battery in the fuselage behind the wing's trailing edge in order to achieve proper balance. Good luck.


Ed Cregger

A similar size Saito is 35% lighter but 50% more expensive.

Decisions decisions...

Since you have not mentioned the OS75AX or 95AX as possible substitutions for the Tower 75, I am guessing you are not really wanting to spend Saito 115 or 125 money right now. I know my budget does not really fit Saito.

.91 to 1.20 is the recommended range for four strokes on this plane and the Magnum 120 is about the same size and weight as the OS. To compensate for the weight of a Magnum 120, you may need to do some or all of the following
> Lose the nose wheel
> Move the engine as close to the firewall as you can
> Move the elevator and rudder servos to the tail area
> Add a servo on the bottom to steer the tail wheel
> Put the receiver pack as far back as possible
None of it is hard to do. It all takes time though and it means you have to do surgery on a brand new plane.

Carrell,

Yes you are right, I am trying to keep this project within a certain budget.

Although I have been trying to standardize around four-stroke engines, I couldn't pass up the performance of the TH .75 at its $100 price tag which is why I had originally ordered it. Now that I cannot get it, I thought why not go for a ASP .91 FS which is very reasonably priced at $150 delivered. Reading some of the posts however, I started wondering whether or not a larger FS engine would be desirable, so after looking around a little I found a ASP/Magnum 1.2 for around $230 delivered. Problem is, this engine weighs about 1 kg (30+ Oz) and knowing the Big Stik already builds nose heavy, that would mean a lot of lead in the tail. I am trying to finish this plane ASAP so I'd rather stay away from doing surgery to it and moving servos around. The other thing I question is, can the larger prop of the 1.2 FS engine leave enough ground clearance.

As another option, I actually do have a brand new Saito .91 that I'd bought some time ago, but that is already installed on a brand new 4*-sixty and I don't feel like making modifications to that plane.

With all that said, at this point my options are:

1. ASP .91 for $150
2. ASP 1.2 for $230
3. Get a budget two-stroke such at the GMS .76
4. Use my .91 Saito and make surgery to my almost-finished 4*

Shouldn't be that hard a decision and I have already been procrastinating enough, so I'll make a choice today and move on. Meanwhile, anyone with opinions please chime in!

I think the OS 91 four stroke was a perfect match for my plane, so, I am biased and would choose option 1.
For me the only other possibility out of the four choices would be the GMS 76. I use the same 15% fuel in everything so the only "bad" thing about having a two stroke is the sound. I have an ASP two stroke on my Uproar 60. I like the engine a lot but do not like the sound that comes out of it.

If you already have a Saito .91, use it. It's light and powerful and wouldn't take as much moving stuff to the rear to get the CG correct.

I am flying an Ultra Stick 60 with an SK .91 and a buddy has the Big Stick 60. He had a Super Tigre .91 in it until the bearings went, now he has a GMS .76 in it. Both pull it well.

I also have a couple of Saito .91s and a Magnum .91FS. The 4-strokes will make it a nice flying plane, maybe a little better than a 2-stroke .61. To wake it up you need a good .75 or a .91 2-stroke or a 1.20 4-stroke.

Now That is sooo true, not to mention
the difference in fuel consumption.

Bob

Well, ASP .91 it is. I just ordered it but as my luck has it, it is on back order . So, if I don't get it by the time the rest of the plane is finished, my Saito .91 will go on it.

I have a BS 60 with a SK.91. It flew great until two weeks ago when I had a dead stick landing. I was able to land without any damage, but noticed that the prop and spinner hub was missing. No big deal and got a new prop. But upon closer inspection, the engine must have thrown a rod or something. I can spin the crank shaft about 180 degrees and it makes a "clunking" sound coming to a stop. I pulled the muffler for a look inside and the piston does not move at all when I turn the crank shaft. It's stuck in one position. So something is definitely broken inside. I'll have to call Kangkeusa tomorrow and see what they can do. Hopefully they honor the two year warranty. I'm not sure if I want another SK91 or just ask for a refund.

I bought two ASP 1.08 two-strokes for $70 each a few months ago. The price went up $20 a few weeks ago, but it is still a bargain. The .91 is a great engine too. I have one with the Magnum label on it. It's as strong as a bear.


Ed Cregger

Denver,

I would really like to hear how this goes for you. Sorry to hear about your engine troubles.

I am in the process of putting my original TT 91-FS in a Ultra Stick that has been converted to a tail dragger. It appears that the LSN might
be bent a little and is messing up the misture control and carb barrel movement.

James in CO

I tried various props including APC 14x7, APC 15x6 & APC 16x6.

I was not unsatisfied with the overall performance particularly with the larger diameter props, but the .75 ended up being a better match for the plane.