What size bipe for a 70 engine

[MODE 1]

Got an old 3dub 70i single with maybe 10hrs runtime on it and have decided to build a small ultimate from scratch for the thing.
I've got 5 mono wing projects on the go right now but I fancied something different for a change of scenery.

Any ideas on the max size plane for this engine with good 3D performance?

Weight wise I know the engine is fine for hauling up to 22 pounds with a purpose and since I build very light I can go larger than normal....just need a starting point in size or scale as I'm not a huge fan of bipes. I never really absorbed much info about em.

[MODE 1]

Bumperty bump

[WangoTango]

Pete,
I have a set of Bowen 30% Ulti plans here in the archives. Same size as the Goldberg 30% that is no more. The cowl, pants and canopy are still available.
WT:198::198:

[MODE 1]

Thanks Terry ........but whats 30% in inches? I wanna try to go as big as possible for that size engine....Like i said I dunno diddly about bipes. All the 50cc sizes look too small in span for what I was hoping for.

[smokin]

that goldberg bipe would've been a great one for your 70.... if you can build off of the plans mentioned above and use the goldberg fiberglass etc... that would make the build alot easier. the span on that plane was 70.5" i believe.

[WangoTango]

that goldberg bipe would've been a great one for your 70.... if you can build off of the plans mentioned above and use the goldberg fiberglass etc... that would make the build alot easier. the span on that plane was 70.5" i believe.

Yep,
70.5"
WT :198::198:

[MODE 1]

70.5 huh....Appreciate the offer Terry.
I think I may opt for a little larger now that you've given me a reference size to work from. Guess I'm saying if i was to go ahead and take the time / effort to build I would want to have more model at the end...or as big as I could go without loosing performance.

Wonder how an 80" would work with this engine if it didn't exceed 20lbs.?

[brycesteenburg]

I think a Chip Hyde double vision bipe would be a good platform to follow. 75" w\s and around 15#s.

Bryce

[MODE 1]

ok thanks I'll just go look that up

DIMENSIONAL SPECIFICATIONS
Wingspan: 75.00 inches
Wing Area: 1600.00 sq. inches
Length: 82.00 inches
Weight: 17.00 Lbs.
Engine: 3W 55i or Similar
Airfoil: Fully Symmetrical


Hmmmmm I may be in with a chance of shooting for 80" then.
Now I'm getting interested.

[WangoTango]

I have my old Brishagella Skybolt that is 78 inches span. They were built like a tank from his plans back in the late 70's-early 80's. Mine was 22 pounds and was pretty lively on a Sachs 3.7 back then. I have stripped the covering and sanded everything. I've re-glued all the joints and put in a new firewall. It always needed more power and I now have a new Quadra Aerrow 75 (ignition version) hanging off the front of it. (That would be 4.4 ci!) Since I stripped the old Coverite and K&B paint job and will be replacing it with Ultracote, I'm hoping for 22-23 pounds and this ought to have a lot of "YEEHAAA!" factor built in! I'll keep ya posted!
WT :198::198:

[MODE 1]

Now ya talkin......Good info thanks

I was thinking this over last night and thought that I may be able to stretch the size to 85". I figured an 85 mono weighs 17 pounds ...ish so an extra wing, servos and a few additions shouldn't add more than 2.5 pounds

Cranked up the CAD already :200:

[mrbigg]

It's not just the extra weight with a bipe, it's the extra power needed to overcome the extra drag of the cabanes, struts and extra wing. Cox Pitts 12 that comes in at 17 to 18 pounds. They recommended a 50 to 70cc engine. Since a Super 80 doesn't weigh much more than a G62, I went with that.

Your estimate of adding 2.5 to a mono is low in my opinion. That's going to have to be a super light 85" wing to hit that weight. The weight of the cabanes, struts and mounting hardware to go with adds up quick.
The best deal out there in this size plane is the PAU Ultimate. Can't beat it for the price. Check it out.

[ULTIMATE1]

Here ya go a 77" Ultimate from Precision Cut Kits! Quite doable around 20 to 22 lbs!
http://www.precisioncutkits.com/301.htm

Ultimate 10-300s
Kit # 301
http://www.precisioncutkits.com/ultimate.JPG

Specifications

77" Wing Span
1848 Square inches
81" Length
20 - 25 Lbs. Flying Weight
4.2 - 6.4 2 stroke

[MODE 1]

It's not just the extra weight with a bipe, it's the extra power needed to overcome the extra drag of the cabanes, struts and extra wing. Cox Pitts 12 that comes in at 17 to 18 pounds. They recommended a 50 to 70cc engine. Since a Super 80 doesn't weigh much more than a G62, I went with that.

Your estimate of adding 2.5 to a mono is low in my opinion. That's going to have to be a super light 85" wing to hit that weight. The weight of the cabanes, struts and mounting hardware to go with adds up quick.
The best deal out there in this size plane is the PAU Ultimate. Can't beat it for the price. Check it out.

Thanks for the info. I still think 2.5 is plenty with an extra wing coming out at 40 oz covered one piece no tube ...easy enough.
For the cabanes (spelling) My plan was to use CF tubes with aluminum end caps inserted in the tubes and all would then be sandwiched between soft balsa. Aluminum tags from the wing roots would fit into the tube ends and held in place with pins. Each cabane shouldn't weigh more than 3 oz.

Just finished a mid wing CAP 87 span after talking with Tom from Wildhare it gave me some ideas to try one of my own. With a DA50 it came in at 15 pounds 6 oz, 24 oz WL so the bipe should be well under 18 pounds....my max is 20.

The point you made on drag is an interesting one.....Now I've read many times in FG that drags not a factor for models when they run small engines on big frames. I would have thought this incorrect. Drag has to have some input on the model. Maybe someone could comment.
I should have stayed awake during biplane class.

[MODE 1]

Thanks Brian ....20 pounds huh.......LOL maybe I should do a build thread on an ultra light Ulti :200:

[mrbigg]

"The point you made on drag is an interesting one.....Now I've read many times in FG that drags not a factor for models when they run small engines on big frames. I would have thought this incorrect. Drag has to have some input on the model. Maybe someone could comment.
I should have stayed awake during biplane class."

Bipes are well known to have more drag. The sink rate when power off is alot more than a mono wing plane. That's why you using have to have a little power on when bringing it down to the runway. As for small engines in a big airframe, you can look at any type of power vehicle and it's pretty much the same result. Let's take a 350 chevy, same exact build-horsepower and torque. Then we'll take a pickup truck and a corvette and use the engine in both. Let's say they both weigh the same ready to go. It's not hard to see which one will cut through the air easier because it's more slippery. The truck is like a brick wall trying to force it's way through the air while the vette is like a knife slicing through.

I still say you'll have a hard time doing an 85" Ulti coming in at 18 pounds, but give it a shot. Some of us like real build threads, not ARF "build" threads.

[MODE 1]

Yep your analogy makes sense and I would be the last to argue with it. I had the same thoughts but for some inexplicable reason several other builders of note here in FG disagreed when the same question was popped to them. Wish i had kept the links now.

Hmmm gotta think this out more. As for weight I still have no doubts about the eventual outcome. Without sounding like i'm blowing my own horn i can build lighter than many arf's and some builders I've come across....have been doing so for many years even though I have never done a build thread on FG to prove it....but the darn drag factor is making me re think. Dont wanna spend all that time and effort to achieve a good weight only to find its going to need a bigger engine in order to perform to my expectations.

Thanks again for your input ....appreciated.
And yep i hear ya on the build thread v ARF comment ......my sentiments exactly.

[Geno]

Would you maybe consider the 50cc Aeroworks Ultimate? From the videos i have seen, i dont think a 50cc is enough power, if you like lots of power,your motor would a good combo. JMO

[Geno]

I used to have a Greatplanes ulitmate with a DA 50 and the power was perfect. The aeroworks ultimate is bigger the gp one. Thats why i would suggest that plane for your motor

[pipercub123]

I have a Great Planes Giant Aeromaster 72" wing and 20 lbs with a US Engines 41cc. What a dog this thing is on the vertical side, but surprisingly it still performs fairly for a sport plane. Not the best but enough to still be fun.

So you should have no problem getting the size wing you want with a 70cc. The Aeromaster is not built light weight.

[MODE 1]

I have a Great Planes Giant Aeromaster 72" wing and 20 lbs with a US Engines 41cc. What a dog this thing is on the vertical side, but surprisingly it still performs fairly for a sport plane. Not the best but enough to still be fun.

So you should have no problem getting the size wing you want with a 70cc. The Aeromaster is not built light weight.

A 41cc huh?....Well then maybe your right about the 70 being plenty.
How do you find the drag factor when flying a bipe compared to a mono? Are we talking a little difference or loads??? Its been over 10 yrs since I last flew one I cant remember what its like and videos dont help.