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Question about Model Airplane Weight Limits

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Question about Model Airplane Weight Limits

Old 12-23-2013, 08:37 PM
  #26  
jester_s1
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I'll address an attitude that I'm seeing here that many newbies have, which is making decisions based on what is cheaper or easier instead of simply getting what the plane needs. You're flying a scale WWII bird; they aren't cheap. It's a flying art project, so go ahead and do it right. I know it will cost you some money, but it's going to be a nice plane once it's all done. At 9 pounds and 700 inches of wing, you'll be at 29 oz per sq ft of wing loading. Certainly that's flyable, but it's going to require some skill. If you're suffering from sticker shock from the OS 95 AX (great engine) have a look at the Super Tigre G90. I bought mine used and put it on an ugly stick. It's a torquey engine like all .90 engines are, and swings a nice big prop to pull the plane really well.
In case you didn't know, nearly everyone's .90-.95 is a bored out .60. They still have the .60 porting and intake and the .60 bottom end with the bigger cylinder and piston. That design lowers the power band by several thousand RPM, making them suitable for .60 size planes where you want to turn a bigger prop. They are not the same class of engines as the typical 1.00-1.20 engines that have considerably larger ports and intake to make big power with that displacement.
Old 07-24-2015, 08:41 AM
  #27  
gregoryshock
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I can tell you guys that a .75 OS AX won't fly my 10 lb Corsair 60. I tried it yesterday, the plane got about 4 or 5 feet off the ground and wouldn't climb any higher.
Old 07-24-2015, 10:25 AM
  #28  
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Originally Posted by gregoryshock
I can tell you guys that a .75 OS AX won't fly my 10 lb Corsair 60. I tried it yesterday, the plane got about 4 or 5 feet off the ground and wouldn't climb any higher.
Were you able to get it back on the ground in one piece.?

Did you have to make a circuit. ?
Old 07-24-2015, 01:07 PM
  #29  
gregoryshock
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Originally Posted by j.duncker
Were you able to get it back on the ground in one piece.?

Did you have to make a circuit. ?
It's got some broken stuff but the majority of it is in one piece. It nearly wrecked my retracts, broke something in the tail that works the rudder. And the Rudder is broken. I won't know what is broke until I cut in.

No. The plane only managed to make an unwanted turn away from me and headed straight out. I had to ditch it in the tall grass.
Old 07-24-2015, 08:00 PM
  #30  
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Gregory sorry to hear of your incident and glad the airplane was not totaled. I did get your PM yesterday requesting photos of my Corsair after I made the engine change from from the Webra fourstroke .91 to the two stroke O.S. 1.08. Keeping in mind mine is not a Topflight but just an unknown generic sixty size ARF from somewhere on the pacific rim. Also keep in mind I do not use in cowl mufflers but prefer stock ones and do not hesitate to cut a simple tunnel when needed.

So dug these pics up today of the same airplane with the current OS 1.08.

As far as the .75 AX not flying your airplane I feel there is something not right with this picture. That engine should certainly fly your ship if flown with care, of course its not going to fly like some sport plane but fly it should. have used a .75AX on one of my cross country airplanes on floats (actually and old sixty size pattern plane) about the same wing area and at up to 12.5 pounds and the 75 was quite sccessfull.

OK I am going to hazard just one question, what size prop and please don,t tell me it was a three or heaven forbid a four blade?


John


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Old 07-27-2015, 02:50 AM
  #31  
gregoryshock
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Originally Posted by JohnBuckner
Gregory sorry to hear of your incident and glad the airplane was not totaled. I did get your PM yesterday requesting photos of my Corsair after I made the engine change from from the Webra fourstroke .91 to the two stroke O.S. 1.08. Keeping in mind mine is not a Topflight but just an unknown generic sixty size ARF from somewhere on the pacific rim. Also keep in mind I do not use in cowl mufflers but prefer stock ones and do not hesitate to cut a simple tunnel when needed.

So dug these pics up today of the same airplane with the current OS 1.08.

As far as the .75 AX not flying your airplane I feel there is something not right with this picture. That engine should certainly fly your ship if flown with care, of course its not going to fly like some sport plane but fly it should. have used a .75AX on one of my cross country airplanes on floats (actually and old sixty size pattern plane) about the same wing area and at up to 12.5 pounds and the 75 was quite sccessfull.

OK I am going to hazard just one question, what size prop and please don,t tell me it was a three or heaven forbid a four blade?


John


John, You do a good job at taking pictures, and giving advice. After looking carefully at your firewall, and the way you have your batteries mounted. I'm curious what is the diameter of your firewall? I measured mine and it's 7 1/8th inches.

To Hazard an answer to your question: My Dad and I contacted TowerHobbies, OS support, Master Airscrew, Wrote in the Forums etc. The result of this information caused us both too much confusion. (The biggest problem was how the OS manual didn't agree with OS support BTW: What OS support suggested didn't seem to pull the models weight on the ground) Nobody fully agreed with anyone else. At the end of the day all we could do was just experiment. We set up our model with the heaviest battery pack (5 volts, 4200 MAH) and drove the Airplane around the field. I bought 5 different propellers and did RPM and Thrust tests on them all. I tried 3 2 Bladed Propellers of various pitches and sizes. and 2 3 Bladed Propellers with various pitches and sizes. At the end of that we found that the largest 3 bladed propeller pulled the model the best on the ground. However with the Large Battery Pack the model acted too heavy. So we tried to switch it back the 5 volt 2000 mAh battery pack. But once I went down that size, I couldn't balance the model without adding some more weight. We was scared to add more weight since the model already weighed 10 lbs with the small battery pack. (It was around 10.5 pounds with the bigger one) We tried various heavy spinner nuts and locknut combinations and couldn't get the CG right. But on the 14x7 3 bladed propeller the CG came out right without adding any extra weight. Plus that propeller pulled the model the best on the ground.

I'm hoping that with the 95AX engine I'll be able to add the weight needed for balance and use one of my 2 bladed propellers. Someone Else in the forums on RCgroups commented to me:

That same round cowl requires a large diameter prop to clear enough to produce efficient thrust. Based on weight alone the 75 would meet the requirements and would work fine on a narrow-nosed plane of the same weight. With that cowl you may need more diameter prop than it can swing to any effect. In fact, you state you already tried a few different props with differing results.

The problem is that 2-strokes have a rather narrow peak power band and anything that prevents it getting there will drastically reduce power output. Too large a diameter and you can lug down the RPM just from drag. One that large would require such a low pitch you may not get enough thrust to fly, etc.

That's why all my warbirds of this class get 4-strokes. Sound more scale, but more importantly they can swing a much larger diameter prop.

* I don't want to use a 4 stroke. But it does appear to me that when I have a big enough propeller to pull the plane, it makes the engine turn too slow. (On a 75)

Last edited by gregoryshock; 07-28-2015 at 01:21 PM.
Old 07-28-2015, 10:57 AM
  #32  
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Is this the same plane that you were asking
about the propeller? If it is, my guess is
that you went with the propeller your dad
said is best instead of what the experts
(including Bax) recommended.

The AX 75 should have enough power to
actually fly at 10 pounds. Try the right
propeller.


Jenny

ps. I've seen a Gee Bee racer that had
the propeller barely wider than the cowl
and it flew fine.

Last edited by Jennifer Curtis; 07-28-2015 at 11:03 AM.
Old 07-28-2015, 11:15 AM
  #33  
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Last edited by gregoryshock; 07-28-2015 at 01:07 PM.
Old 07-28-2015, 01:50 PM
  #34  
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You need to use the propeller that flies the plane.
You use lead to balance the plane, As much as
it takes, and as far forward as you can get it.

Using a bigger battery puts the weight farther
back than a chunk of lead all the way up in the nose,
so it doesn't do as much for balance. This makes t
he plane heavier than it needs to be. Use the right
size battery, and use lead to balance the plane, as
far forward as you can get it.

You can use really long screws on the engine
mount and put the lead under the engine on
the extra length of the screws. You can screw
it to the front of the firewall.

Don't select the propeller because it is heavy
and helps balance the plane. Don't choose the
propeller that gives the most thrust on the ground.
Select the propeller that translates the engine torque
into the most thrust at flying speed.

A 14x7 three blade is way WAY too much propeller.
Sure it will blow a lot of air on the ground, but the
engine will not get up to its proper running speed.
The engine MUST run fast enough to produce its
maximum power. PERIOD. Running it with too
much propeller is like driving a loaded truck uphill
in high gear. (In the truck you need to downshift
so the engine runs faster and produces enough
power).

On your plane, a 14x7 two blade propeller will
turn faster and produce more thrust at flying speed
than the 14x7 three blade. A 14x6 two blade will
turn even faster. A 13x7 propeller will turn faster still.
You don't want to get too light, though. The engine
will have a "sweet spot" where it performs well. You
need to try different propellers IN THE AIR to find
the sweet spot.

About the weight issue, the plane can get pretty
heavy and still fly with a reasonably small engine.
Planes fly at half throttle quite often. A heavier
plane will have a higher stall speed, which is
really only an issue in landing, They also need
a bit more power for climbing aggressively.

The biggest problem with weight is pulling it
through grass on the takeoff run. Since your
plane did get off the ground, it will probably
be OK once you get the right propeller on it.

One plane I have started off weighing 9
pounds, Now after modifications and repairs
it is up to 12.5 pounds. That is over a 25%
increase. It still has the same engine, which
was on the small end of the scale when I
installed it. That plane still flies great.

That said, losing unnecessary weight always
helps. Light wheels are an easy first step,
especially the tail wheel. Removing the
retract servos and locking the retracts in
place should be possible. Removing any
wheel covers could also help. The pilot figure
can be removed if it isn't too difficult. (It may
be easy to cut it out from the bottom of the
cockpit.) You might be able to remove 1/4
pound of weight this way. Its not a lot, but
it could be noticeable.

Jenny
Old 08-01-2015, 04:27 PM
  #35  
DGrant
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Originally Posted by gregoryshock
I can tell you guys that a .75 OS AX won't fly my 10 lb Corsair 60. I tried it yesterday, the plane got about 4 or 5 feet off the ground and wouldn't climb any higher.
I would say too much prop. If the engine were propped correctly, it would fly fine.

This was a response to an earlier post to a question the OP made... concerning just this issue...

Originally Posted by Bax
To get optimum power out of your O.S. Max .75AX engine, you'll need to run it near 12,000 RPM or a little more. You have too much propeller on it. The RPM range O.S. states are the limits to RPM that they have gotten during testing. With some propeller, they could idle as low as 2,000 RPM, and with a different propeller could get it up to 16,000 RPM before they decided that more will cause the engine to come apart. Don't expect that RPM range to happen with one propeller. Won't happen.

We'd like to run the engine with a two-blade prop to get good power and efficiency, so a 12 x 8, 13 x 6 or 7 or so. Get the engine between 11,000 and 12,000 RPM for max power with whatever propeller will fly the airplane. Perhaps even running between 10,000 and 11,000 RPM will give you good flight performance. Going below 10,000 RPM will most certainly put you well down on the power curve.

"Scale" propellers are good for display, but almost never good for actual flight. They will be too large for the engine to turn properly.
I'm curious what size prop gregory shock was using.... honestly now.

Last edited by DGrant; 08-01-2015 at 04:29 PM.
Old 08-04-2015, 12:18 PM
  #36  
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I spoke with Ken the moderator about closing this thread down. The reason being that I feel really embarrassed. I realize that when you look at this from the outside it appears that I didn't listen to the experts. This is not entirely true. This is the first time I've had to contact a product support or seek help online for model airplane issues of this kind. In the past I always just followed the instructions and only had small problems with my airplanes. All which were either remedied fairly easily or continue to be a slight annoyance. But nothing as major as this.

The Bottom line is I didn't know who I could trust. This kit never suggested a propeller for me. Most don't, I know, but it would have been nice if they had, at least for the Engine they said they ran on the prototype. The propeller sizes listed in the OS manual are all incorrect. Product support is correct. Product support tells you what size will give you the needed RPMs. None of the propellers, except for maybe the smallest listed in the manual will give you those RPMs. Some people online told me that in Japan they run bigger propellers to reduce noise. That doesn't make a whole lot of sense to me but "Ok" Maybe they put large engines on smaller airplanes?

I had a big problem with my CG, and weight. What the kit tells everyone about weight is incorrect. Almost everyone is telling me that 10 lbs is pretty average for this type of model. The kit boasts 7 lb - 9.5 lbs. I was scared to add enough weight to the nose to balance the plane. However the largest 3 bladed propeller 14x7 gave me just enough weight to balance the plane. The next reason I chose to use that propeller is because, after testing several, it pulled the model on my grass runway the fastest. I didn't realize that this meant nothing to what the model would do in the air.

Just remember what I said before. I was trying to obtain good information, but there was so much misinformation that I didn't know who the experts were. It's fine with me if you want to say my inexperience got the better of me. But what is a newbie to do when the manuals don't agree with product support. And others don't agree with either of them!

I see no reason to continue this thread. I learned my lesson. Hopefully you've learned something too.

* I'm going to run .95AX Engine because early in this thread some other modellers suggested going to a 90. Since I'm trying to take off a heavy airplane from a Grass runway I the extra power is welcomed. I'm going to run a two bladed propeller. I don't know exactly what size yet. But I'm shooting for 11,000 RPMs. If a propeller doesn't give me that high, I'm not using it. Also it is noteworthy to know that this airplane will probably won't be taking to the air this year. There is too much damage for how much time I have left to fix it all.
Old 08-04-2015, 07:03 PM
  #37  
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It was good that you came back with the report even when the outcome was less than optimum.

BTW getting an underpowered warbird witn an aft CG back on the ground in repairable condition IS A RESULT. Mostly they go home in a trash bag.

Here is a RCU thread on the 95 discussing props. http://www.rcuniverse.com/forum/glow...s-95-ax-4.html

IMHO it is a toss up between the 13 x 6 and the 14 x 6 in APC for your model.

When you have it on the bench look to see if you can move stuff forward. With short nose models I would often have all servos as far forward as possible up against the bulkhead at the back of the tank. The throttle servo can go on the side of the engine. The battery would get mounted on the engine bulkhead I have even fitted a small engine mount with long arms to the bulkhead and moved it to the front of that. [ Fokker triplane ] I really HATE having to add lead. Because light models fly better.

But better to have to add lead than to fly with a rearward CG.

Last edited by j.duncker; 08-04-2015 at 07:14 PM.
Old 08-05-2015, 12:56 PM
  #38  
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Hi!
I have a GEE BEE R-2 (Great Planes ) model powered by a MVVS 15cc (.91) engine, that has a much bigger cowl then a Top Flite Corsair and using a 15x4 APC which flies the model real well at 5kg (around 10-10,5 Pounds). I tried several other prop sizes (14x6, 14x5N and 15x6) but the APC 15x4 woks best and gives that model rather good aerobatic performance.
It's very important the choose the right prop brand and not just use the prop that looks "good on the ground"!
I fly from sea level and mostly use 5% nitro in my fuel and I can say from experience that never ever should you use a white tipped MA prop on any cale (or sport plane ) if you want good performance. The props to use is always APC, RAM or Graupner G-Sonic. And of course only two blade props should be used . If you know how to carve and modify a wooden prop, of course it could be used with good performance too.
My 40 year experience tells me that a .60 size warbird like the Top Flite Mustang or Corsair powered by a .91-95 two stroke at sea level could well be flying with a 15x4 prop. Any 12 or 13" prop has to little diameter! And don't shot at a particular rpm .in this case 11000rpm. A much better way of obtaining good flying performance is trying some props and see which works best.
For instance my GEE BEE R-2, I tried several props and choose the one that worked best giving no though to how much rpm the engine delivered
.
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Last edited by jaka; 08-06-2015 at 12:00 AM.
Old 08-05-2015, 02:04 PM
  #39  
flycatch
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http://www.bolly.com.au/book/Book.ph...er=2&Section=2

Read this to answer your questions.
Old 08-06-2015, 06:59 AM
  #40  
gregoryshock
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Thank you for the link. I will print and read it.

One question keeps coming to my mind. Everyone says you need choose the right propeller for you Airplane and Engine. It appears to me that is a balance of the two. But nobody has come out and explained to me how you choose the right propeller for your Airplane. Many say you need to experiment. Experimenting can be really dangerous. You need to have something that works for your model or it isn't going to fly for the first time. It's the first flight you got to get right. After that I could see someone experimenting. Please tell me: how do you figure out which propeller is going to take your model up for the first time?
Old 08-06-2015, 08:08 AM
  #41  
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Hi!
It's simple! You choose the "right" prop from experience! That means you know what prop brands that are best (gained from experience ) and what prop sizes that works best for a certain size/type of plane, knowlegde gained from experience from flying a lot airplanes during a many years.
Old 08-06-2015, 09:08 AM
  #42  
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If you don't have experience, you start by
looking at the engine manual, and asking
others with experience. You get several
propellers in the range that is recommended.
You try each propeller on the bench and check
the engine rpm. Of the ones in the correct
rpm range, pick one that gives the plane a
good tug at full throttle while you hold it. That
one will probably get the plane off the ground
ok. Then after a couple of flights try one of the
others. If the plane needs full throttle all the time
to keep up flying speed, maybe a little more pitch
and less diameter. If it seems like a rocket try more
diameter. If it doesn't climb well try less pitch.

There should be at least 4 propellers of various
diameters and pitch that will fly the plane acceptably.
One of them will be the best for what you want to do.

Jenny
Old 07-04-2016, 11:13 AM
  #43  
gregoryshock
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Originally Posted by j.duncker
It was good that you came back with the report even when the outcome was less than optimum.

BTW getting an underpowered warbird witn an aft CG back on the ground in repairable condition IS A RESULT. Mostly they go home in a trash bag.

Here is a RCU thread on the 95 discussing props. http://www.rcuniverse.com/forum/glow...s-95-ax-4.html

IMHO it is a toss up between the 13 x 6 and the 14 x 6 in APC for your model.

When you have it on the bench look to see if you can move stuff forward. With short nose models I would often have all servos as far forward as possible up against the bulkhead at the back of the tank. The throttle servo can go on the side of the engine. The battery would get mounted on the engine bulkhead I have even fitted a small engine mount with long arms to the bulkhead and moved it to the front of that. [ Fokker triplane ] I really HATE having to add lead. Because light models fly better.

But better to have to add lead than to fly with a rearward CG.
The manuals wasn't any help, which is why I had to try "google" "youtube" and the "forums"

I like sharing my results. I think sharing my results might be helpful to someone searching for answers. However last year I got really tired and even a bit mad at my threads. As a beginner to war birds I never encountered the kinds of issues I faced building this plane. Often times the discussions caused me lots of confusion and frustration. People often disagree with each other. That kind of disagreement is fun for those who already have experience. But for those of us who are just stepping into something for the first time it's a mess.

I was surprised to learn that 3 bladed propellers don't work on 2 stroke engines very well. I was even more surprised to learn that the max size 2 bladed propeller size that OS mentions in the Engine Manual doesn't turn the RPM that the OS support says the engine needs to turn in order to have the power it needs. Those three things right there messed me up big time. Then add in the fact that it's extremely hard, if not impossible, to build the fu4 within the weight range that Top Flite says it can be built in. I didn't know who to believe anymore, my Tach and Taxi pull results wasn't adding up to everything I was reading in manuals, support, and forums. I had to crash my plane in order to learn the truth.

* In case anyone misses the point I'm trying to make: Due to the difference between OS Manual and OS Support. I couldn't know who the "experts" really is. Only the crash told me. Another way to say it: If the "experts" don't agree then who do you believe? I can say the same thing about Top Flite telling you that you can build it for 7-9.5lbs, when everyone I talked too online ended up 10 lbs and over. Even when I emailed top flite directly and asked them how they managed to build their prototype at 7lbs, they didn't answer the question. Instead they avoided a direct answer and just said "depends on how much glue you use" Well duh! But you need to have enough glue to hold it together.

I don't know for sure if I'll ever get this bird in the air. For the time being I decided to move onto another War Bird. Something that looks easier to build and hopefully easier to set up and operate. My Dad and I might work on the Corsair during the winter. Depending on how things turn out for us will determine if the plane lives or dies.

Last edited by gregoryshock; 07-04-2016 at 11:36 AM.
Old 07-04-2016, 07:35 PM
  #44  
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Don't you know by now that everyone on the forums are experts?

There is one guy that has posted on this thread that I trust without reservation (besides me of course). His depth of knowledge and experience is second to none. It is your job to figure out who.
Old 07-19-2016, 06:08 PM
  #45  
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Originally Posted by JohnBuckner
OK let me see if I understand, Forget what the manufacturer says for just one second. So far the airplane is to be powered .61FX so far so good great engine. But the airplane currently weighs 10 pounds and it is not even covered yet much less all the little tid bits that we all miss when doing those kinds of projections when we are at the same stage?

John
most planes tend to be tail heavy, if you put in a larger engine that will help balance the plane and give you some extra power.

I would not try and fly a 10lb plane with a .60 size engine, every,never, no way!!!
good luck and save up some money for a new plane!

sticks
Old 07-19-2016, 06:28 PM
  #46  
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Good grief Stick 40 perhaps your advice would serve a better purpose if you actually addressed the original poster, the owner of the subject airplane instead of singling me out.

John
Old 07-19-2016, 08:43 PM
  #47  
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Originally Posted by Stick 40
most planes tend to be tail heavy, if you put in a larger engine that will help balance the plane and give you some extra power.

I would not try and fly a 10lb plane with a .60 size engine, every,never, no way!!!
good luck and save up some money for a new plane!

sticks
Okay, what do you base that tail heavy comment on? Experienced builders routinely find a way to remedy that issue prior to covering. When I build a boat, in my case sport and scale hydroplanes, I have to balance them to within a very narrow window to prevent blow overs or plowing. Balancing a plane isn't any different, other than the fact that you can place the engine as far forward as you want where I can't in a boat.
Old 07-19-2016, 09:50 PM
  #48  
TFF
 
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Props in the OS manual are props that can fly various airplanes and not destroy the engine. I have a friend who has done the same thing for electric saying "the book said." I have had three planes that I stuck old OS 40 FPs on. My son's trainer, a WW1 parasol, and a 3D profile. All different props. Trainer 10x6 wood, WW1 11x4 wood, 3D 12x4 APC. The simple answer is the biggest diameter with the most pitch you can put on and not lug the engine. Your AX probably needs 1 13x6. I doubt it can spin more. The type of plane you have needs some pitch for speed as the plane will want to fly fast to not stall. A plane like yours may need 100 feet to take off and the initial climb might be 20 ft of altitude for a 100 yards of flight until it gets leveled off and speed built up. Back through the early 80s airplanes at contests could not use an engine bigger than a .61. Plenty of 60 size planes, back then, at 12 pounds were flying then wishing for a 90. What you really need is someone at your club to give the plane a look over for CG and other stuff. It can save it the next time and hopefully get some hands on explanations. What type of planes were you flying before you started the Corsair?
Old 07-20-2016, 05:39 PM
  #49  
Stick 40
 
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Originally Posted by JohnBuckner
Good grief Stick 40 perhaps your advice would serve a better purpose if you actually addressed the original poster, the owner of the subject airplane instead of singling me out.

John
I did not think I was going against you. , I thought I was backing you up. your statement about more weight being added, means more power. That is to me, it means more power.
I would not fly a 10 lb. cub j3 with a .60 even if it could be done , sorry if I came off wrong.
I did go back and read the original post, the question was about using a smaller engines in planes, I tend to go with the larger engines and use the left stick to limit how much power I put in.
Old 07-20-2016, 06:04 PM
  #50  
Stick 40
 
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Originally Posted by gregoryshock
I have read that model airplanes tend to have more power per weight/size then a full size airplane. For an example I read that a 40 size trainer plane like eagle 2 was originally powered by a 20. If a person is using the smallest engine stated by the kit specs, how much over the weight limit can one go? My kit says it should weigh between 7 and 9.5 pounds.
more power/ weight /size. do we need more power for weight, yes to a point. most planes are tail heavy and a larger engine could balance a plane with out more dead weight. I use the left stick and limit how much power is used, its just my personal idea.
we can generally find a engine that puts out more power with less weight " YS".
and the answer is we in the RC community are going toward larger engines for planes, that is a fact and I tend to like it. MORE POWER Lol
sticks

Last edited by Stick 40; 07-20-2016 at 06:09 PM. Reason: correction

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