hi,

For the moment i'm building a Robbe Diamant no Limit.
This is my firs 3D plane
It has 150mm span, 2200gr without engine.
Now i was planning to get an Irvine .53 in it but somebody
warned me that it would barely have climbout power...

The Irvine.53 with muffler has a weight of 510gr.
The Irvine..60 without muffler 600gr.
IMO that would be too much.

So i got the idea to put a Saito FA-91S(only 540gr) in it who's homelessfor the moment.
But this thing has tons of power. Would it be too much
for this kinda plane?
Did anybody use a that powerfull engine in a comparable
plane?

Really need some opinions on this one!

Thanks,
Wouter

In my opinion there is no such thing as too much power, just excess power!!!

Their is such a thing as too much weight.

With 3d flying it is vertical thrust and acceleration that saves me most of the time I screw up. That is why you should go with a saito 91. I know of a guy who has a YS 63 on a No Limit and it does fine. Some argue that the YS has almost the output of the Saito so it should be great!!

Make sure you build the firewall very well though, but don't add weight.

the firewall is build with like on the plans but
i added some triangular strips on the inside, just to be sure.

Another thing: will it land without having to cut
the engine? And will the plane hold up with the
vibrations?

It has been my experience that in a 3D plane, anything over 2:1 thrust to weight is a waste. With 2:1, you will punch out of about anything pretty fast. If you can get more without a weight penalty, go for it, but that is often difficult. You can get light weight power plants in about any size, but if you go too big you end up adding weight to reinforce the airframe. There come a point where more power is not not better because of the side effects of supporting that power in the airframe.

Man, my brain doesn't work well in metric. From my calcs, were talking a total weight of 2.7Kilo with engine, or about 6 pounds total. If the Saito 91 can turn a 15x8 (in inches) prop at 8000 RPM (just guessing), that is a thrust of about 10 lbs, or 4.5 kilo. That is 1.7:1 or close to the 2:1 ratio. I'd say you would be set up just fine with that combo.

Comparable plane? My 2M pattern ship weight 10.5 lbs (4.8K) and I am spinnig a 17x10 at 9200 with a YS140DZ, that equates to 17 lbs of thrust, or a 1.7:1 ratio. My 35% carden has a ratio of 2.1:1. I have had ~2 meter fun flys at 2.2:1. Had a 40 sized fun fly a little smaller than your setup with a 2.5:1 ratio. They all fly well at these power to weight loadings.

Your concerns about airframe are probably justified. Softmounts go a long way to reducing stress. I guess just use your best judgment in deciding if the airframe needs to be reinforced to handle the engine. Might also check the tail feathers as vibration can often weaken them.

Probably won't need to kill the engine for landings. Just keep your prop diameter large and pitch low and you will slow down just fine.

light weight and low wing loading is one of the key elements to a good 3d model, keep it light and it'll fly right!

Wauter,
I fly a Madness of 2200grams with motor. I have flown Madnesses with an OS46FX, and OS50SX, and currently the YS63. You will probably come closer to 3000 grams with motor installed so I would highly recommend the YS63.

Here are my results on the 2200 gram Madness with three different motors.

While the OS46FX was enough to hover, touch the tail, and then climb away, the OS50SX gave much more confidence. It did not shoot skywards, but it was completely respectable running 20% nitro Coolpower. Now, I have not owned an Irvine .53, but I'd match the OS50SX against it as being the same or a hair more power.

The YS63 on 30% Coolpower makes the airplane into a yo-yo. Up, down, up, down like it weighs nothing, and that is with the YS overpropped. I'm using the APC 14x4W, but I plan to switch to the 13x4W which should give much more umph.

You airplane should have no trouble with the YS63 on the nose. Also, the YS63 with the little muffler weighs about the same as the OS with its larger muffler, so you will not experience any trouble with too fat an airplane.

One more thing...my club in Havay is having a show on the 23rd and 24th of this month. We will have some great pilots there and some great airplanes. The Madness II shall make its Belgian debut at the show, 3 meter Extras, bipes, Spits, club Pheonix will bring their awesome show to include a very intense combat show with lots of crashing, and, just perhaps, Benoit Paysant-Le Roux will be there.
Come on out and enjoy the day. Saturday is Vol Libre, Sunday a more organized program with Belgian F3A champions of yesteryear and today.

Regards,
Mark

If in doubt, go for more power.

Therefore go for the Saito 91 as the weight penalty is not big.

Prop to use should be 15x6 on that engine

thanks for the input.

I'll start out with the .91 and if it goes too hard i can
always install a .72, right?
I mean, are the dimensions the same? i need to know
if i want to mount them on the same mount.

The only thing that i'm afraid off is that the engine
would vibrate the plane apart...

Greets,
wouter

No, not the same mounting dimensions.

I doubt you would want to go down an engine size once you have tried the bigger one.

another question:

i'm using a protech motormount, similar to them dubro
plastic-like mounts...

anytips on how i can reduce vibrations?