NikolayTT

Hi Fellows,

My search over RCU on RPM-readings of WEBRA-15cc did not produce much.
I am especially interested in the latest models of Speed-P5 and plain-P5.

Could you please post your experience, mentioning at least the most
important of the things in the list below:

1) Propeller: Maker, Type, Material, Diameter, Pitch, ...

2) Pipe: Tuned, Wide-barrel, Pits, Standard, or Open exhaust, ...

3) Fueling: Pumping by Perry-pump, Direct Pressure from Crank-case,
Pressure from the Exhaust barrel, ... any Special Regulator on Carb ...

4) Fuel: Oil% and type(s), Blend-proportion%, Nitro%, ...

5) Environment: Temperature, Altitude/AthmPressure, ...

6) How New/Old/Used the Engine is.
7) Did you "tune/improve" the engine and how ?

Thanks,
Nick

Hobbsy

My Feedback: (102)

Webra P5 .91
Fuel==Fox 5% nitro with 20% castor oil
Plug==Fox Miracle plug
Prop==APC 14x12
RPM==8,400
Stock muffler

NikolayTT

Thanks Hobbsy,

It looks that propeller is a bit too "heavy" for this engine,
which seems to be mich higher-rpm-engine, isn't it ?
If I use the calculator of Pe, it gives that this propeller
have only 1.68 bhp, while the engine is advertised to
be able to deliver even more than 3bhp. It seems
I'm missing some point here; please clarify further.

Regards,
Nick

Hobbsy

My Feedback: (102)

Nik, here is a link to the P5, the 14x12 is the smallest recommended prop, the engine is designed to run in the 8,000 rpm range for quietness and to meet European noise rules. I like quiet so I use it the way they intended. Others have tried 14x6 props and were disappointed. http://www.webra-austria.at/motor.ph...r=AERO&lang=EN

NikolayTT

Thanks Hobbsy,
Then I just wander why Webra is telling on that www-page those figures for Power and RPM. Here is my way of thinking and
I wander what is wrong: - Using the Calculator of Pe and assuming APC propeller, and power aim 3bhp (out of 3.25) and
the RPM to be 13500 (out of 16000), and iteractively chaning the DxP of the propeller, in few iteractions I come to the
cases like those:
APC 13x7 @ 13500 gives 3.11 bhp, and speed of 144 km/h, thurst = 7.19kg,
APC 12.5 x 8 @ 13500 gives 3.00 bhp and speed 165 km/h, thurst = 6.84kg,
that is what I exactly would like to have, but it seems Webra is the wrong
engine for this speedy performance, is it so ?
BR,
Nick

RVman

Got my 91P5 recently. After three 16oz tanks i am turning 9300 with a Masteraircsrew K series 15-8 and Omega 15. I expect to get about 9500 when it is more broken in. I will likely run a 15-8 three blade for flying. This thing is a brute.

NikolayTT

Thanks Tom ! It looks still far from what Webra page is telling,
especially the rpm up to 16000 ??? With this propeller you
have got (calculated) power of about 2 bhp and 6kg thrust.
The company tells the engine has more than 3 bhp and if
calculate the propeller and rmp back that would give
for example on APC 14x6 thurst of 7.2kg at 12500 rm
which is about 2.9 bhp; that is about 30% more than
what you have got. Also I wander why Webra is advicing
propellers like 14x12 and 16x8, they seems too heavy
for this engine...

RVman

The 14-6 is way too small for this engine, it is designed to run large props. The carb is the same one as the 55, a 9mm throat so it won't do 16K very well. The engine could easily handle larger props than the 15-8 i used. It is hard to compare to a 'normal' 91. It definitely has way more power than a supertigre 90 I also run.

Hobbsy

My Feedback: (102)

Tom, I tried the 14x12 on my SuperTigre .90 and MVVS .91. THe SuperTigre .90 only managed 7,000 rpm and quickly got hot, the MVVS .91 turned the 14x12 at 8,200 and ran just fine. I don't understand people having such a problem believing instructions. As you say the 14x6 is a complete waste of the Webras abilities. As with all engines the HP ratings are a joke.

CustomPC

Can someone tell me what the exchaust bolt spacing is for the 91-p5.

Thanks

RVman

its the same as the OS 91 but the port size is totally different. A muffler from an OS 91 may still work ok even though it blocks a lot of the port. Otherwise you will need to ask Bisson or someone else to custom make one or buy the webra muffler.

RVman

Graupner 15-8 3 blade, bisson inverted pitts muffler, i am taching ~7300 rpm.

speedster 1919

My Feedback: (3)

NIK Your assuming that the computer prop calculator is 100% accurate- which it is not, and no engine manufacturer max RPM was ever hit by the recommended prop. In case you were to put a very light load or overly small prop on that engine it is warning you to limit RPM to 16,000 so it won't break a con rod or loose a bearing. More and more prop recommendations are done for noise levels and not the most power or speed.

sarpet

pipe lenght from exhaust flange to reflector plate 450mm
fuel 15% mobil glycoule30 3% castor and NO nitro
apc 13x6 13600
apc 13x8 12300
apc 12x10 11600
apc 13.5x12.5 9600
apc 13.5x13.3 9400

CustomPC

I posted this in the "Why not a Webra Engines" thread but thought i'd post it here because it's a more relevant thread.

Anyways.... After wanting one for a long time i finially gifted myself with a new Webra .91 P-5 and started to break it in on the test stand.

I was using 20% castor and 80% Methanol, as per the manual's instructions for break-in. I've still got another 1/2 gallon of the FAI fuel to burn up before i switch to 5% Nitro fuel with a 15/3% mix of Coolpower/Castor.

I put about 60oz of fuel through it on a half dozen or more runs. It was easy to start and did not quit on me once, unless i deliberately shut it off.

I started with a 14x7 as a light load for two tanks before moving up to a couple of different 15x8 props. I was running it deliberately rich and wasn't really concerned about peak rpms so i kept the needle fat just on that verge between 4-cycle and 2-cycle. Occasionally i would pinch the fuel tube or lift the test stand nose high to lean it out slightly and break into a smooth 2-cycle rythm, just to vary the rpms a bit.

I tached the APC at 15x8 at 8,500rpm for a brief moment when i pinched the fuel tube and it settled straight back down to 7,000 when i released it. I forgot to write down the figures but i think the Xoar 15x8 rpms were higher but it didn't feel like it was moving as much air as the APC.

What impressed me most was how consistently it held rpm and how at the end of the day it would hold a reliable idle of 1500rpm.

I was using a Turbo-Jett muffler that i had already. The port on the Jett muffler is a direct match for the Webra's exhaust port. The muffler is pretty quiet (almost too quiet) in the low rpm range and has a good note when the revs get higher. If you order one for the Webra make sure to tell them you need 2" or 2 1/4" muffler bolts.

One thing i've noticed when i got back home is that there is a pool of after-run just below the carb in the webbing on the right hand side of the engine. The carb O-ring looks dry so i don't think it is leaking from there, but it could be coming from the carb retaining pin. Should i be concerned about that?

This engine is slated to go into my Great Planes Venus II to be my main flyer in the Sportmans Pattern contests.

CustomPC

Some numbers from last weekends 2nd break-in session.

I've switched to 5% Nitro, 15% Synthetic and 3% Castor.

Still using the Turbo-Jett muffler.

APC 14x8 10,000
APC 14x10 9,300
APC 15x8 9,200

The compression has increased significantly after approx 12 tank fulls.

Such a great engine.

jnred123

I know this thread is a bit old now but I'll post anyway.
Got this engine for a replica 70's pattern ship so as was a previous post from Finland not really interested in stump pulling big prop torque, these things have to sound right as well as go fast.
Run in on six tanks of FAI fuel on 11x7 at about 11000 rpm rich then switched to 18% KL100 10% nitro.
Baseline with Macs Black muffler which apart from being nice and light is not very quiet and I think knocks the perfomance a bit too, I didn't have a stock Webra muffler.
14x6 MA 11,900
11x9 APC 12,600
I wasn't blown away by those numbers but we'll press on with a Macs 1190 pipe and see what happens, well !
APC 14x8 11,600
APC 13x8 13,200 (narrow sport prop)
APC 11x10 14,200 Yee Hah
APC 11x9 14,300 (the pipe needed to be shorter but I think I would err on the side of loading this engine higher rather than lower).
I didn't have a 12x10 APC with me on this test but my gut feeling is it is THE prop for this engine in a fast 70's style pattern ship like the new Hanger9 Phoenix 7.
This one is going in a Funkey Speeda which is like an MK Blue Angel.
Well done Macs I love your pipes they make serious power, not sure about your mufflers though.
Cheers
Greg Hede
Australia

sarpet

P5 is strong engine,after runing in apc 12x12 11500rpm
ihave this for phoenix7 http://www.webra-austria.at/motor.ph...r=AERO&lang=EN