Hi folks. Have a plan build Astro-Hog that needs some power on the nose. I've got a new OS .55AX and a new OS .75AX sitting on the shelf without "homes". The .55 seems a bit small and the .75 a bit large as I'd always put a .60 on the nose before. Which one would you choose for my new tail-dragger version with the old 6 degrees of dihedral style wing? Weights not a problem as she's building up nice and light (I got to pick out the wood).

Comments and selection choice? Drum roll, please.......

Joe

It will fly with either but the 55 will be disappointing

Go with the 75AX

Well, it would sure seem like that would be a natural choice but as I remember flying the .60 size around at half throttle or so most of the time I just wonder at the idea... I'd be "shocked" to find my nice Astro-Hog having a "Sabre" look on landing after that first flight .

Joe

Joe:

I have a Lanier Mariner 40 and a Mikulasko Arrow with the 55AX. They both scream. The 55AX seems to like a 11x7 MAS 3 blade and the MAS Scimitar 12x7 two blade about equally. Isn't the Astro Hog an old design? If so, the 55AX is likely a lot more powerful than the 60s of that day. I'm going to use one on a Super Kaos. I just got the plans from RCM and the short kit from a cutter.

We're in NJ at the moment awaiting the birth of grandchild #7. We were in VA a few days last week, and I got to maiden my TF P-51. Lovely airplane. I lost a lot of sleep for nothing, worrying about how it would do since completion last Oct.

If I had my druthers I'd put a 4-stroke on the Astro Hog. This plane just "sounds" right with a 4-stroke "putting" along. However, I do realize that is not the question you asked. Go with the 75 on it. This plane is a 60 sized plane and I think you'll find yourself lacking with the 55 on it. I'm sure the plane will fly with the 55, but you won't have any "extra" power with that engine on it. The 75 is actually going to be almost overkill for this plane, however this is definitely a case of better to have too much than not enough.

That's my 2¢ worth

Ken

A four stroke would be nice, that's for sure. The only 4 stroke I own is an OS .52...and that's not going to do it. In todays economy I cannot justify purchasing another engine for the Astro-Hog when I have two new engines sitting on the shelf. I am leaning towards the .55AX the more I consider the givens as I believe it will fly the plane nicely without the "overkill" aspect as you bring up, not to mention I can use a shorter prop on the nose, too. In my younger R/C days (daze ) I'd have gone for the "straight up" factor...now I go for the fly for the fun of it.

Joe

Hi, Bob! Hope all goes well with mother and new grandchild in NJ. We had a new one in December (number 4) and are expecting number 5 in September and our first Great-Grandchild in September, too!! My younger daughter Becky and her first child, my first grandchild, are both having babies near the same time!! Man am I getting old or what???

Have a safe trip, my friend.

isnt the 75ax the same phyisical size as a 60? thats what OS was advertising about. at least the mounting was the same. 75AX all the way!

I would probably use the .55 myself, especially considering that you are not looking for a speed demon or a vertical climber, BUT, if you end up needing a bunch of lead in the nose to balance, you might as well put in the bigger engine.

Likewise, if you use the .75 and need a pound of lead in the tail, then you might as well go with the .55.


Good luck

I have flown an Astro Hog with an OS 70 Surpass and it had good performance. Nice big loops, would not go vertical, lots of 2/3 throttle flying.
I have also flown an Astro Hog with an OS 91 Surpass and it has excellent performance. Loops as big as you want, almost unlimited vertical, lots of 1/2 throttle flying.

Both engines you have should do a very good job, if you want the vertical capability go with the 75, but if the vertical is not required the 55 will pull it through big loops.

Joe:

Put the 55 in it. My Mariner weighs at least 8 pounds and is a rocket with one. Your Hog specs at 7-7.5 lbs. With a 13x5 prop, you'll have all the airspeed and thrust you can handle, and a strong vertical.

Well, guys, after considerable thought (I don't DO that too often) I have decided to go with the O.S. 55AX; plenty of power for the design, I have built the framework light, can use a smaller prop, the engine weighs less with the O.S. metal motor mount I'm using and the tank for it is reasonable and fits nicely in the compartment.

You have all offered some good thoughts and comments on the selection but I believe the O.S. 75AX will be a better fit for the plan build FlyBaby (RCM plan) that I also have on the "board". Thanks for taking the time to present your thoughts.

Soft landings.

Give us a flight report when you have a chance.

I'll do that, Charlie. Right know we have snow piles up to my a....er..... Well, we'll have to wait awhile to find the flying field in this neck of the woods. We don't get much chance to fly until mid April or later.

Soft landings.

Tech details:
55AX - weighs in at a svelte 18.5 oz. and has the same foot print as the 46FX and 46AX siblings - hp 1.7 (hp/oz .092)
61FX - hits the scales as 23.6 oz with a bigger foot print that is shared with the 75AX and 91FX brethren - hp 1.9 (hp/oz .081)
75AX - em, 8 more oz. of nose weight over the 55AX at 26.5 oz - hp 2.4 (hp/oz .091)
91FX - 24.3 oz - hp @ 2.8 (hp/oz .115)

75AX gives you a bunch of hp at the cost of 8 oz of nose weight. A 91FX is lighter - go figure

for comparison
Saito 100 shares the foot print of the 61/75/91 platforms - wt. 20.9, hp 1.8, hp/oz .086
OS FS91 shares the same foot print as the 61/75/91 - wt. 24.2, hp 1.6, hp/oz .066

All of these numbers came from respective manufacturers.

Btw, the 61FX group and Saito 100 share the same size mount. I just mounted the Saito 100 on a Hog Bipe with a Hayes AL60 mount. The mount fits nicely. Allows upright, side or inverted using the same blind nut locations. If I get a wild hair (or hare) I can grab another AL60 and toss one of the OS 2-strokes (61/75/91), new throttle control & tail weight - just to see how it goes.

SeamusG, last night I reviewed the O.S. tech data (at least on the 55AX and 75AX) to help make my decision. If I was building the Hog Bipe I'd put the 75 on it in a heartbeat. It just appears to make more sense to me to go with the lighter 55AX, on the Astro-Hog, to fly this model in a nice manner. We'll see how she does in the Spring. Thanks for sharing what you found....I should have posted those numbers myself.

Soft landings.

It must have been in 2001 but a guy came to the field with a new tri-gear Sig Hog with a MECOA 46, It wouldn't lift off the first few tries but eventually a little puff of wind came and away he went. He flew it full throttle and didn't do too bad up in the air.

Your welcome - just copied this stuff out of a spread sheet. Now if I could just apply the information

I just finished adding up the weight (used a nice electronic postal scale) of all my Astro-Hog components, minus the Monokote covering and Spectrum DX7 onboard radio gear, and came up with exactly five pounds so far. I believe the .55AX will work fine.

Soft landings.

I had a Thunder Tiger .61 in my Hog... (Check my Avitar) More than enough power !
Ugo

I have the G.61 super tiger,hope that is enough muscle for the hog.I do wish now I would have gone for a .91 4 stroke,but mabe down the road I could convert it over to 4 stroke,what would I have to do take out the blindnuts fill the holes and redrill?

FWIW,

Here's my current project. I finally
decided on my Saito 82 over a older
K&B 61 that was NIB. The 61 will now
go to my 40 size Stik.



Bob

Man - that looks a whole lot like a Astro Hog Bipe [:@]

Blind nuts are pretty easy to dislodge. I use a nail set and a tack hammer (kind of a kid's sized claw hammer - not too much force). The nail set that I use is just fat enough to rest solidly on the blind nut but slender enough NOT to hit the firewall plywood. I give the nail set a crisp tap (not a WHACK) and that's usually enough to unseat the blind nut that has been epoxied in. Then I tap as needed to remove the nut. If the blind nuts are 6-32 (I think that they need a 3/16" hole) I get a dowel the same size, cut it to length so that a bit stands proud of the firewall and glue it in. Flush sand when dry.

Btw, check the alignment of the original mount so that you can recreate the thrust line when you mount the new engine mount.

HTH,

Since a 70 Surpass flies the plane with authority I am surprised that a 46 bb two stroke had so much difficulty getting it off the ground.
Even though a 46 two stroke and a 70 four stroke are similar in equivalent power that power is definitely delivered differently.
While I have not flown an Astro Hog with a two stroke engine I still think the 55AX will fly the plane well.

My friend, Dan, has an Astro-Hog with a .46 on the nose and another Astro-Hog with a .91FS on the nose; they both take off and fly nicely. No problems with either plane.

Soft landings.