nicov1978

Hi,

This post is still highly activated!

As far as I'm concerned, mine is equipped with an OS FS91, and it is already rather "front" balanced naturally, so I don't really know what would happen with a 120...
If I had used a 120, I would have positioned the glow battery far behind the COG and not at COG as it is now, but i'm not sure that it would have been sufficient.

I don't know what the others think about it, but my plane is not very wing loaded, and I think that adding 50 or even 100 g in the tail, so in total 300g (200 for the engine + 100 in the tail) would not be a problem, I think that with 300 more gramms the plane would remain "gentle", stable and not too difficult to fly...

It also depends on if you want to do smooth or hard aerobatics; in first case, a 91 would be more adapted in terms of power and weight... otherwise, if you want to go up to infinity and beyond, a 120 is needed!

Nico

cmoulder

Hey, snomobila!

Like Nico, I am running mine with an OS .91 4-stroke and it is a very good choice.

I agree with Nico that this plane would still fly well with a 1.20 FS because an extra 2-300 grams is not going to increase the wing loading that much.

No matter what engine you use, however, this model cannot be slammed around too much (such as, a pretty high drop into a violent blender[X(]) because of the wings. You will notice that the wing tube goes in only up to the second rib, and if you look at the shear web (the sheeting between the spars) you will see that the grain of the wood runs parallel to the spars and not perpendicular.

Which means you still want to keep it reasonably light. If yours weighs 300 grams more than another model, that translates into an extra 3000 grams (6.6 lbs) during a 10-g maneuver, so that might eventually cause problems with the wings.

FAST-J

I am running the o.s. fx 91 also, i have tried several props and the one i really like is the apc 14x4w, vertical is unreal, i agree the the 91 is plenty of power and if a larger engine is used then have to add wait, it's not really a huge gain in my opinion.

FAST-J

Also, don't use anything less than a 91 not unless you just want to fly. I had problems with other brands of engines not wanting to run correctly with the motor mounted at 45 degrees, so far the o.s. fx 91 has given me no problems mounted at 45..

stevo revo

If you are looking for fun......... go with a .90. If you are looking for stupid fun, give it a 1.20!!!!! Usually stupid fun is greater than or equal to doubling the size of the smallest recomended engine!!!! Enjoy!!!

snomobila

My Feedback: (1)

cmoulder, you mean wing proplems, you mean wing breaking in flight problems, correct?

cmoulder

Of course it's possible, but I'm not trying to be alarmist or exaggerate the issue. Just a couple of things to keep in mind when stirring the sticks. However, if somebody were to dive it in fast and do a hard parachute, I wouldn't be surprised if this were to happen.

I haven't been keeping up with the thread for a while, so I don't know if anyone has had such an experience. I have not, but then I've kept this in mind from the start.

snomobila

My Feedback: (1)

just curious, what are you powering yours with?

cmoulder

OS .91 FS

Some changes I made:

1) Cut 2" off the back edge of the cowl
2) Used LG from a Fliton Extra Freestyle (stock gear is HEAVY)
3) Made an elevator joiner with 3/32" piano, using one elevator servo
4) Rudder servo in tail, with pushrod
5) Dremel-ed out the canopy deck
6) Used a more scale-looking Great Planes pilot
7) Added yellow Monokote trim (sticky trim sheet stuff)
8) Using plastic bolts for canopy hold-down
9) Reduced wing incidence by raising back edge 3/32"

AUW 7 lbs 0.7 oz as weighed on a digital postal scale.

nicov1978

Hi guys,

I also powered my extra with an OS 91 FS.

I'm not keen on 3D, and I prefer quite smooth acrobatics, this is the reason why I powered it with this engine rather than with a 1.20...

So I'm happy with my plane powered that way, but, to be honest, I would have thought it would be a little bit more powered all the same... and therefore I am getting wondering whether this is normal or whether my engine is not well optimized...

Can you guys, who have powered it with an 91 FS, raise up vertically for a long time before if gets stopped?
I know my question is unprecise, and difficult to answer to, but please try to describe as well as you can its behaviour...

Thanks a lot
Nico

cmoulder

Nico,

How old is your engine? (valves may need adjusting)
What fuel (% nitro) do you use?
Which prop?

snomobila

My Feedback: (1)

What size prop are your running, My 120 running a 15 or 16, what kind of clearance do you have?

cmoulder

Right now I am running a modified Zinger Pro 13x8 and it has pretty good vertical, although I plan to try a 14x6 APC that I found in the attic this morning, and perhaps try a 14x8. Clearance is of course great with the 13x8.

The Zinger was sanded a lot to smooth out the leading edges and feather the back edges, then painted. Lot of work for a prop, but the result looks nifty and sure works a lot better than stock Zinger props, which have a deservedly crappy reputation. The reduced noise and increased efficiency are starky better after re-working.

I also have the 1.20 FS on a pattern bird (Venus II) and it has very good all-around performance with a 14x10 APC.

What pitches do you use with the 15- and 16-inch props? I have a 15x6 which I reckoned was too much prop, but if you're getting good results I may try it.

snomobila

My Feedback: (1)

I think it is a 16/6 or a 16/8, they both should work great. Just ordered the plane yesturday, should be here soon. I think a 16 prop should have enough clearance. I hope.

nicov1978

Hello Everyone,

Cmoulder, you're right, of course I should have precised the details you ask for...
The engine I use is new, is fed by a 10% fuel and it runs a 14x6 MASTER AIRSCREW propeller.

What do you think?

Thanks a lot,

Nico

FAST-J

Hey cmoulder, what changed (in flight) when you reduced the wing incidence by raising the back edge 3/32" ?



Thanks, Jay

FAST-J

Hey nicov1978, I have tried a ton of props and the best one is the APC 14X4W, RUNNING 10%, The vertical want stop, it will go out of sight before you know it.

Jay

Crashtruk

snomobila here is the answer to you question.


I found the ST2300 was too much engine for the pilot. Quite scary actually. I have a ST91 now still plenty of power.
People should read the whole thread. There is some good info in here.

cmoulder

Thanks much! I will give those a try.

Normally a 16-inch prop would be a problem on the Venus II, but I am re-building mine and re-designing some stuff and re-covering it as my winter project, and I plan to use a taller, stiffer gear than stock.

cmoulder

Hi, Nico:

Okay, IMHO you may see an improvement with 15% or 20% nitro (Yep, more $$$$ or Euros) and a stiffer prop such as APC, Xoar, etc.

The MA props have an incredible amount of flex, as you can see if you stand off to the side and slightly behind (a safe position!) as the engine spools up. I've got to think that there is also tortional pressure on each blade that reduces the pitch. The "old school" wooden props such as Zinger and Top Flite are also pretty bad because of their squared-off edges. But if you take the time to sand the leading edges to a more aerodynamic shape and feather the trailing edges, they can work quite well.

cmoulder

Jay, I found that with the correct CG the plane looked funky flying - nose high and needed more than a touch of down elevator to maintain trim. Inverted flight still required quite a lot of push, as if the CG was way too far forward. (I used the stock engine bolts, built-in thrust line with no shims on the engine mount.)

Anyway, the overall way it handled suggested reduced incidence would help, so I made a very un-scientific WAG and raised it a little. Flies much better now, in every attitude!

FAST-J

Yep, mine is the same way, no matter where the cg is i always have a little down trim to make it fly level.
I might try that.
Did it make the plane more stable?
On mine if you give it a slight to hard up it will drop the the left wing, im not crazy about that.
So are you at zero on the incidence?

Hey cmoulder, what changed (in flight) when you reduced the wing incidence by raising the back edge 3/32" ?



Thanks, Jay
[/quote]


Jay, I found that with the correct CG the plane looked funky flying - nose high and needed more than a touch of down elevator to maintain trim. Inverted flight still required quite a lot of push, as if the CG was way too far forward. (I used the stock engine bolts, built-in thrust line with no shims on the engine mount.)

Anyway, the overall way it handled suggested reduced incidence would help, so I made a very un-scientific WAG and raised it a little. Flies much better now, in every attitude!
[/quote]

cmoulder

Jay, I found the plane was always very stable, even without the wing incidence modification. It is the least snap-happy of any model in this size range (.60-.90) that I have ever flown.

If yours is dropping a wing, maybe check to make sure washout is the same on both wings, or no twist in one of the ailerons?? [sm=confused.gif]

nicov1978

Dear All,

All that you explain about the wing incidence is very interesting because I also onserved this phenomenon with my extra. I had thought it was due to a bad down-thrust angle but maybe it is actually due to what you say...

Cmoulder, you're totally right about the MA prop spooling up, I saw that a few days ago... I agree with you, considering such a flexibility, one can guess that there could also be some torsional efforts applying to the blades and leading to a pitch modification... I think I have to try a stiffer prop.

Do you think using a 15 or 20% fuel would really improve the power? What would be the effect, more RPM at full throttle, wouldn't it? With same prop of course...

What do you think about trying a 14x4 as Fast-j proposes? What would be the effect? Could it improve the vertical rising?

Thanks a lot for all your advices.

Nico

cmoulder

Nico,

Concerning the wing incidence change, to arrive at my solution I just played over all the factors in my head (considering especially how much down elevator trim was needed) and figured that just a little incidence change wouldn't hurt. And if it did, it wouldn't require a major operation to change it back. Thus far, I'm quite happy.

I think 15% or 20% nitro would help, especially with a 4-stroke since the plug ignites on every other stroke. Also, your engine is new and you're probably running it quite rich, as most new 4-strokes should be run. As it breaks in and you gradually lean it out, the power will improve.

Remember that Fast-j is running a 2-stroke .91, so IMHO a 4-stroke will probably be underpropped with a 14x4. I would run at least a 14x6 or perhaps 14x7 or 8 when the engine breaks in a bit more.