I rebuild a well used and abused OS FS91 Surpass I.

It turned a APC 14x4W 11200 rpm.

Fuel: 18% oil 10% nitro synth/ castor blend

ooops, thats scary. Almost the same as my 91 twostroke. Isn`t that too high for its own good? I don`t think a fourstroke should rew much past 10k on the ground. A 15-4 would be better I think

As long as the valves don't float, why not? Sure it would last longer on lower revs, but most of my engines last too long anyway.

The engine worked in a Madness fun flyer. In this kind of model you can peak the engine to the best ground rpm because you need thrust at low speed and you don't want to fly very fast. This is the reason for the low pitch prop.
The OS Surpass 4-strokes rev up to 13000 with no problems. If the prop is to small they just dont turn more rpm.
I have yet to break one of these engines.
They are designed to turn in the range from 9000 to 13000.

oh, can todays surpass 2 also take that kind of rews?

They are almost the same like the normal surpass series. They only use different carbs and the ventilation is connected to the intake.
A friends Saito .91 has the same reading like my Surpass 91 but with 20% nitro (11000+).

Engine: YS 91AC
Prop: MA Scimitar 15x8 S2
Fuel: Powermaster YS 20/20
Plug: YS
Tach: TNC

RPM: 10,200 peak

O.S. .91 FS (I)
10,200 rpm
12x8 APC
15% MP
#F
90 degree F
45% Humidity
Sealevel 0

Magnum .91 RFS
WC 10% Extra premium + 2 oz's castor.
OS F plug.
After (6) 16 oz tanks.
All rpms are backed off by 300 from peak.
14-6 Master Airscrew S2 10,250.
15-6 Master Airscrew S2 8,200.
I am very impressed with this engine so far.

YS 91FZ
8200 rpm - 15x8 Zinger
9400 rpm - 14x7 Master Airscrew
11,100 rpm - 14x6 Master Airscrew
Cool Power 30% Heli
Altitude - 4300 ft (Yeah, that sucks)

Hello

I have just been given an old Thunder Tiger .91 FS.

The reason I got it was that the pre owner was "sick" of it. He could get it to run just fine on ground and everything was ok. During flight it suddenly stopped. This happend over an over until he got tired of it and gave it to me.

Any ideas what is wrong with this TT .91 ?

Any help will be highly preciated.

Regards from Gandalv.

This is just a guess but most often when you have that problem the mixture is too lean. On the ground after you get the perfect setting, move it rich just a very small amount. Maybe this will help, Good Luck!

I always take a test lap around the field after tuning an engine, and I listen to how it runs.

Also, weather changes will change your tuning too. You may have to get to know your engine throughout the year, summer, fall, winter, etc.

OS 91 surpass (I think Surpass I)
cool power 10%
MS K series 14x6
10,600 peak

Operate at
10,200-300

O.S. 91 Surpass II-P MODIFIED
30% nitro Heli fuel Powermaster
o.s. F glowplug

APC 15X4W 10900 rpm (11K peak), idles at 2300, (my Saito FA-100 never got more than 10600 same fuel same prop).
Master Airscrew 15X4 12100, idles at 2500

Regards.´.

OS 91 Surpass II

Still in the break-in (rich-peak-rich) cycles. 15% Nitro, 15% Klotz, 3% Castor

Peak readings
Bolly 14x6 Carbon 10,300rpm
MA Schimitar 14x8 8,800rpm
APC 14x6 9,300rpm

Today i tested my OS .91 Surpass II with MA 15x6 Schimitar running 20% Nitro, 16% Klotz, 2.4% Castor.

Peak reading was 9,760rpm
Idles at 2,100

Magnum .91 APC 13"x8" 9800 RPM 10% nitro.

I was having trouble getting my Magnum to run consistantly so I looked into it further and found a leak on the intake manifold from when I adjusted the valves so I resealed it and tuned the engine again. Now it runs very smooth with a solid idle at 3100rpm but it was peaking at an amazing 11800rpm with a Master Airscrew 13"x8" K series prop! Looks like I need a bigger prop.
Note: Tach was a TNC

OS 91 FSII

apc 14x8 with 15%omega @8900.

ASP 91

MAS 14x6 classic> 9930 RPM
MAS 14x6 S2 scimitar> 1.0030 RPM

Engine has no more than 15 tanks through.

Altitude> 2500m ASL
Fuel> Omega 10%
Glow Plug> OS F

Ihave neglected this thread long enough.
OSSurpass I 91FS
9400 rpm
Merlin 2009 plug
15% Sig Synpower fuel
Master Airscrew 16X6 Classic

ASP FS91
Custom Blend fuel 10% nitro 20% oil
on ground
APC 13x7 10500 rpm
APC 13x8 9900 rpm
Bolly 12.5x8 10800 rpm

This is the Video http://www.youtube.com/watch?v=FTGcJMnuqJw

a ys 110 on 20% turning a 14x10 at 14,000 rpm I DO NOT Believe that at all. maybe a 13x10N it would have to be a Master Airscrew plastic prop and more than 20% nitro with mods to the engine. most guys with modded 110's will turn a APC13x13N prop at 11,800-12,000 on the 110 with 65% nitro. the 13x13N is = to a APC 13x11 full blade prop. My OS 120AX will spin that prop at 11,400. the 14x10 prop at 10,600. with a pipe maybe get another 700-1000 rpm is set correctly so let say 11,600 with the 14x10 prop and what kind of HP is that maybe like 4hp.

So i call BS on that 110 spinning a 14x10 prop at 14,000 rpm[>:]

I think Harry was being ironic there in order to make a point about the unreliability of tach readings and numbers, a bit like the weight of a fishermans catch...