quepasa

Hi all!
I'm thinking about bashing a C/G Falcon III and converting it to a twin.
My current Falcon III has a LA-.40 and flys great. I have no experience with twins, so am needing to know what size the engines would need to be to duplicate the performance of a single .40 sized engine in the same plane.
Is there any rule-of-thumb to figure this? Thanks in advance. Q.

Ram-bro

My Feedback: (101)

what is the smallest size engine recommended for the falcon? I am sure two 25s would be more than enuff. I know of no rule ....

quepasa

Thanks for the quick reply.
Weight is 4.5# w/.40, & kit calls for a .35-.45 2-stroke.
I guess my question is...does 2, .20s = 1, .40?

Ram-bro

My Feedback: (101)

for the falcon,I think you would be fine.

Ed_Moorman

My Feedback: (1)

I'd get another LA .40.

If you get 2 plain bearing .25s, you'll be low on power and your weight won't change very much. The nacelles will weigh the same. You can use 20-40 engine mounts from Great Planes and 4-6 ounce tanks.

Use a little out thrust so you won't have as much yaw when one engine quits. One .40 will keep you flying a lot better than one .25.

quepasa

Not to argue Ed, but 2, .40s on a 5# plane sounds kinda wild to me. I was thinking maybe 2, .15s would do it. The current Falcon with one LA-.40 I have is "high-drag" with wing struts, 3" wheels, (tail-dragger) & a radial cowell, and its still pretty fast for me.(SLOW is better)
I wouldn't even consider twice the power on this plane at my skill level as a pilot. As you have probably gathered by now, I'm a builder and would like to build a twin that I may be able to handle some day soon. I actually already have 2 nib LA-40's so it would be nice to not have to spend the money for a couple new engines. If you or others could recommend a KIT that would take 2, .10s I'd be grateful as I have a couple on hand. Thanks for the advice on the thrust angles tho. (If I put 2, .40s on this airframe I'd scatter airplane clear to Phoenix!)

jaka

Hi!
Two OS LA .15 or FP .20 will be just fine. Anything bigger and it will fly too fast.

Wayne22

My Feedback: (2)

Actually your power requirments are more closely related to the disk area of your propellors.. I presume you are running a 10" prop now, which has a swept (disk area) of 78.5 square inches.... two 7 inch props would give you the same disk area which a .10 to .15 engine would spin... All other things being equal, in level flight, this would give you approximately the same performance as the single .40. However the climb will be slower because the smaller engines combined have less torque than the .40 (and less displacement) More importantly, in the event of an engine failure, you would likely be unable to maintain your altitude and the plane would be heading downhill. So to give yourself some reserve, go up a notch or two in engine sizes to a .20 or .25 ...........

cyclops2

I love and build multi-engined planes.
Unfortunately, I PANIC when a motor conks. A knife edge, and out comes the body bag, again.
All my fuel planes use big engines to be able to be hand glided in deep grass.

NO LEAD! It is toxic to models on 1 dead engine.

Build the plane completely without any engines in it. Add equal weights to each engine mounts area. When the plane balances with hand glides. Buy 2 engines that are the same weight.

Works everytime. About a little less than 2 X the rated sizes of the kits reccomendation.

All the engines are side mounted. Exhaust pointed down.

quepasa

Well, looks like I nead a couple new engines.[],,,,,
Or maybe a smaller .20-.25 sized plane to bash and use the .10s I already have. (Wife would like that option alot better I bet.)
Thanks so much for the info. to all of you.

Wayne, that explination told me what I needed to know.
Cyclops, side mounted is my prefered method, but is there a reason this better than mounting uprite or inverted for a twin?
Jaka, seems like you all agree on engine size. The part where it would fly too fast may not be a big problem for some,,,but for me it would make a huge differance in the size of pieces I would have to pick up.

Thanks again! Q.

Wayne22

My Feedback: (2)

If you want slow...why not kit bash a Bird-of-Time or something like that??

quepasa

Wayne, I have a kit of a Gentle Lady ready for a bashing with an LA-.10. After that in the glider stable is a 102" Breguette 902 with a Fox .29 vintage engine slated for power. I don't wanna go that slow with this one. I'd like a twin engine airplane that flys like the Falcon. I'd think maybe an old Pilot QB-20-L might be the ticket for 2, LA-.10s but haven't found a kit yet. Thanks tho! Q.

cyclops2

Side mounted gets rid of the engine out the top of a plane. It blows the wet stuff down away from most of the plane that is seen. A muffler looks better. The engine starts and idles just like straight up. Chokeing the engine DOES NOT FLOOD IT.

You may have to make up new engine mounts or use a firewall mount. You can even go past sideways to another 45 degrees down and still be OK on a great running engine.

Put a junky glove on and tilt the engine to see how it runs and idles. 2 screw carbs do best past the horozontial.

quepasa

Wayne22, from what I understand from your post is that 2, .10-.15s would fly this plane about the same as 1, .40? (YES, I'm using a 10-6 @ about 12,500 rpm on the .40) I guess from others replys, bigger is always better, but are you saying that 2, .10s w/7-4s @ 16,000 would do the job as the single .40 does? If so, this is good news. I also wonder why I'd be in any deeper Ka-Ka if one engine on a twin quit, than I'd be if the engine on a single quit? Either way I'm gonna land deadstick. Other than the torque differance, I would think that having one small engine quit, would only make the plane handle better than if a more powerfull engine quit on a twin?
SO,,,the quest remains...ED says "go big or stay home", You say 2, .10s would do it, but that 2,.20s would be better, I'm thinkin that maybe the 2, .10s I have might work? I'm confused what would be the best choice for a ROOKIE twin pilot on this plane.

I respect Ya'lls opinions and value all the advice you guys offer. Q.

Ed_Moorman

My Feedback: (1)

Let's talk about a twin Falcon 56 again.

As for 2 40LAs being too big, that's what the left stick is for, I think.

Having built several twins ( my buddy and I are on our 24th twin), I can say with some experience that when you bash a single into a twin, you usually come out heavy. Your wing loading will be greater and the landing speed will be slightly higher. We figure on adding 3 to 4 pounds with .46 size engines.

You already have a 1/4 ply firewall in the nose of the plane. You aren't going to remove it so you'll end up with 3 1/4 ply firewalls. You are going to cover the nose with balsa, probably, but keep the nose gear. You are going to add 2 nacelles (firewalls, top, bottom, sides), an extra tank, extra servo and pushrod, extra engine, prop & spinner. All this adds up. I originally calculated that we could do it with 2 lbs extra and it turned out to be 4! We also went to 3/16 wire gear because the 5/32 one kept bending.

You should do a little better with an LA 40 since it's pretty light. You won't save much with a 25 LA and when one quits, you have one little plain bearing engine to get your plane back.

One other thing I recommend is out thrust on both engines. 8 degrees is ideal, but 4 or 5 is better than nothing.

quepasa

Thanks for the advice Ed!

edit; reckon I'll just order a couple .25 LAs and then I won't have to worry about one engine quittin!

mosert

If you have some 10's left over then use 4 10's
this bigstick 410 as I call it runs great on 4
steady on 2 and I'm landing if only on 1.
flown countless twins going to Bigscale multi
got distracted by jets .
video @ www.baxterfield.com

quepasa

Ed, I've re-read your explination about 10 times and it's making alot of sence! I honestly don't think that 2, .10s would be enough, but 2,.40s sounds like too much to me. (Atleast at my flying skill for the forseeable future anyway.) I really don't know what to do as almost none of you guys agree on what size would be best for a 1st. time twin pilot, or even if it needs thrust offset in the engines. This twin will be built from a new kit. Not from an exhisting plane. It will also be a taildragger. I'm leaning toward 2, .25LAs as I've got everything except the engines already. (I know that an LA anything ain't what alota guys think is the best choice in engines, but for the type of flying I do, they are, and the plain bearing has nothing to do with it. LAs are the most reliable, easiest to tune engines I've ever had period!) I plan to use a couple HS-55s for throttle servos as contrary to popular belief, they are fine as a throttle servo on my .10 thru .40 sized planes anyway. Between the smaller mounts, nacels, tanks, servos, etc, I'm thinking that an additional 2# of weight over the 4-4.5# projected weight for the single, oughta be close? What do you think?

Please be advised that I'm not argueing with any of ya!
Like I said before, I value ya'lls opinions and it helps me make the decision. I'll just have to live with it![X(]

Mosert, Thats cool! No thanks Pal! I actually was thinking about a tri-motor with .10s, but I blinked.

teammaico

Mosert,
Can you tell me the weight and wing span of your plane? It looks like about 45"X 8" wing. The reason I am asking is because I am planning to build the guillow series 2000 B-17G. I wanted to use 4 .049 engines but it appears they are hard to find and there is limited throttle control. If your plane is about the same size and weight it looks like I could move up to the .10 engines and get everything I want.
Thank you if you respond.
Jim

mosert

Its a great planes bigstick 40 Arf converted to 4 os 10's
each engine pod has 4 oz tank, remote glow, and seperate mini throttle servo
I placed the battery on the normal engine mount to balance my weight
is about 8 lbs dry

My plan was to learn to fly multi -engine cheaply and scale up to
B-17 or 29 with 4 g-26's or bigger. Being distracted bt jets lately
next build F-100


specs from gp web site
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SPECIFICATIONS
Big Stik 40 ARF
Stock Number: GPMA1220
Wingspan: 58.5 in (1485 mm)
Wing Area: 770 in² (49.7 dm²)
Weight: 5.3 lb (2.4 kg)
Wing Loading: 15.7 oz/ft² (48 g/dm²)
Fuselage Length: 51 in (1295 mm)
Engine Required: 2-stroke .40-.51 cu in (6.5-8.5 cc) or 4-stroke .60-.80 cu in (10-13 cc)or four .10 cu in
Radio Required: 4-5 channel w/5 standard servos