Mr Cox

Seems alright for a .07 engine, but some 10krpm less than predicted...?

Pond Skipper

Yes per the Static Thrust Calc software incorrectly used to reach "unloaded" numbers per post #824:

"If unloaded" numbers come from plugging in props keeping close to the hp base line manufacturers spec data of .065hp at 31K"
http://personal.osi.hu/fuzesisz/strc_eng/

APC power charts per post #835 provided good static data as previously mentioned.
https://www.apcprop.com/v/PERFILES_W...tDatafiles.asp


So I now have a static base line from the brief preliminary tests using the APC power charts and Static Thrust Calc.
Vertigo .07
APC 5x3 / static 25,227 / .24hp / 179w / 18oz / 72 mph
APC 4.75x4 / static 24,739 / .225 / 168w / 14.5oz / 94.6 mph



Norvel .061

aspeed

When I checked a bunch of .049s I used the 4 1/4" - 4", and the TD .049 went 22,900 rpm. So you are doing a bit better than that, with a bigger motor.

Mr Cox

I think in general one can have around 1800-2000W per cubic inch, from sports engines with regular mufflers and smallish props.
With tuned pipes one can get better, up to around 2400-2500W/cuinch.

Pond Skipper

Norvel on the pipe got that prop to 25.5k static.

Yes this is looking great good boost in power in a .05 size engine frame and the engines can still be bought new for $44.95
I think the 4.5x4 should scream and make reasonable thrust will test that prop next.
The 4.2x4 may be too small thrust wise but could work may try it after a few flights with the Skorch II.

Mr Cox

The Norvel .074 makes around 160W already at around 17-18krpm (spins the APC 6.3x4 at around 17500rpm), and that's with the stock muffler. That sort of set the standard in this engine class I think. Even the TT 07GP will be close to that with a proper head (i.e. Turbo plug).

Pond Skipper

Only already do to load. APC chart shows 148w at 17k and 164w at 17.5k.
But flight speeds would be way too slow for the Skorch.

Mr Cox

The power of the engine will go up with rpm if the torque curve is reasonably flat. I haven't really tried it at higher rpms but according to engine reviews it makes the most power (0.38hp) at around 22krpm.

For higher airspeeds one would choose a larger pitch and smaller diameter prop, while keeping the rpm at where the engine develops the most power. A 5x5 prop might be suitable for instance.

Pond Skipper

APC power chart states .194hp / 144.7w with a 5x5E at 22k static. I will test the engine to compare with the 4.75x4



Will have to break in the engine its never been ran yet will do with a APC 6x3
.181hp / 135w if at 19k

Pond Skipper

Okay ran 2 and half 2oz tanks thru the new Norvel .074 with the 6x3 then did the 4.75x4 with the remaining half tank so 6oz all together the engine was purring along great throttle nice engine most of the time I ran at 13k rpm and rich thirsty engine in rich
mode 20% all castor.

I took the standard plug adapter off and use the stock Norvel plug to keep things fair. I measured the exhaust nipple ID is 4mm and added a 6.5mm ID exhaust deflector on it to keep from getting sprayed it is 2.5in long made for 1/16th 1/2A size cars it didn't make any noticeable change in rpm so great goo control.

Here is the best peak I recorded a video and took the still shots to display the readings.
Note the engine did start to warm up and settled in at 22,771 rpm.
Ran on the same 25% nitro and both ran without a pressure line / tuned pipe has a 3mm exit.
Vertigo was not set up for best peak as mentioned before preliminary test and no pipe tuning.

Norvel .074
APC 4.75x4 / static 22,852 / 129w / .173hp - using the APC power chart
86 mph / 12 oz thrust

Vertigo .07
APC 4.75x4 / static 24,739 / 168w / .225 hp - using the APC power chart
95 mph / 14.5oz thrust

Mr Cox

That sounds a bit low, even the .061 Norvel will do around 22krpm on 10% nitro on that prop...

The Revlite engines are a bit special, they can be very tight and need lots of running on pure castor before they perform. Looks like you need an engine stand, and to give it a proper running in. Head shims are important too, I've started with 2-3 during running in and then use 1-2 shims on 10%nitro. I would drop the stinger on the outlet too.

Pond Skipper

Both where tested in the hand so that was consistent. I gave the Norvel 4.5oz the crank to case fit isnt tight like the .061 was the piston was tight prior to running now flips over much better after 6oz in total. If you have a .074 and willing slap a 4.75x4 on it and test to compare. Note both engines where not ran with pressure lines another constant. Both had stingers but yes could do another
test without it could get the engine past 23k it was warmed up at 22.77k

I think the .074 on a solid test stand with another 6oz of fuel could eek out a bit more rpm. I do have one extra shim to try but for now looks like the Vertigo is the best choice for the Skorch II.

Norvel .074 / 22,852
Vertigo .07 / 24,739

Some past 4.75x4 specs with the Skorch:
Cox TD Cox RC carb - Cox High Comp plug
APC 4.75 x 4
19,380 rpm in the hand 25% nitro

Killer TD .049 3rd flight
APC 4.75 x 4
20,873 rpm in the hand 25% nitro

Other data from others with the Norvel .074
MAS 5.5X4.5 / 20,700
APC 5X5 / 21,100
APC 4.7x4 / 22000
GRAUPNER 5.2X5.2 /19,000
APC 6X2 / 25,300
COX 5X3 / 24,600
5.5x4 - ask CP
APC 4.75x4.75 - ask CP
8x3 /13,000
APC 7x3 19,300 / tuned pipe
Cox 7x3.5 19.1 / tuned pipe
4.75x4.75 EC carbon prop

combatpigg

My Feedback: (3)

Even though the Norvel .074 is one of my favorite 1/2 A engines, it's not a great choice for speed applications.
I've given it a fair trial a few times with various speed props.
It does what it is supposed to do so well [turn a 7x3 or 6x4 prop] that it just isn't worth the accelerated wear for this relatively expensive engine.

Pond Skipper

The test came about to discover .07 size hp output with the same prop and compare it to the Vertigo the Norvel was a good choice to go head to head with it. The Norvel was singing quite happy with the 4.75x4 being rated at .39hp at 22k spinning it to a warmed up state at 22.77k wasn't pushing it too hard.

The .049 /.061 and .074 Norvels are meant to be a good RC sport engines ideally any speed application should be with a true ABC style engine fitted with bearings for longevity. The Vertigo seems to be a good fit for a boost in power. Very special being in the same car engine .05 frame / weight still sold new for 45 dollars with parts support.

combatpigg

My Feedback: (3)

With the right motivation and free spending attitude, you might be able to give the "AME treatment" to a .074 Norvel for higher rpm breathing capability. The motivation just isn't there from what I can see. Norvel might have even tried but never marketed it..?

Pond Skipper

Yea for fun I dug up your thread with the .074 effort cut down 6x4 to 5.75x4 the plane was a SWR and you didn't like the all up weight the plane wasn't climbing out as hoped. No mention of rpm. I think the carbon APC 4.75x4.75CE would be worth a go but hey I have three Vertigo's so the search is over really. The .074 will be reduced to a dust collector if not careful. It does look good with that 4.75x4 as shown in the pic with a sportswerkz header pipe should breath great and up the power. If I didn't live in hot arse TX I would trim them fat fins to match the dia of the aluminum head. Perhaps 23.8k with the near open exhaust 90 mph static

170deg timing and such great numbers on a in the hand preliminary test has me already resting easy.
I may pony up some cash for the carbon props after I do a flight test with the standard 4.75x4.75E my guess is two fold based on the thinner blade but with an aggressive pitch near the hub perhaps 24.5k static with the NV set on the sweet spot. 14 oz thrust / 110mph static should have it doing about 118 mph in actual speed unloaded in theory 128mph. Not bad for an 14 dollar ebay buy. Who knows if the pipe is on point I may squeak past 120. Plenty fast for the plane size and will be hard to follow if allowed out more than 300ft.

Pond Skipper

1/4th wave pipe is only 9.8g stock muffler 6.7g but just the header pipe a mere 3.4g

combatpigg

My Feedback: (3)

I recall trying APC's 4.75 x 4.75 on the .074 and the results must have been underwhelming or I'd see more of those props sitting in my tackle box..

Mr Cox

Why not try the tuned pipe on the Norvel .074 then, when you have all the parts...?
AndyW had some good results with that...

With the very few car engines that I have converted, there is very little gain in terms of power over weight. Sure you can get near .15 power from a .12 engine but you also get the weight of at least a .15 engine...

combatpigg

My Feedback: (3)

The tuned pipe hanging out the side increases drag more than the power gain if you are flying in the 90 mph+ range already with open exhaust. A side exhaust to increase aerobatic performance makes sense to me, though.
The only tuned exhaust that interests me for 1/2A speed is behind the shadow of the engine.
As far as I know, Andy never submitted any "before and after" airspeed results between open exhaust and piped.

MJD

My Feedback: (1)

Good point. 2 ounces of pipe plus almost double the frontal area and all kinds of parasitic drag.

combatpigg

My Feedback: (3)

What I said might sound hypocritical because I've run pipes on larger side exhaust engines that weren't timed for high speed.
I did it to learn, to have fun, to see the rpm improve over the stock muffler, to hear the nice sound.
It's all part of the hobby.

Pond Skipper

The pipe is not 2oz in this case 11.3g if you use a Profi + 3.4g for the header less coupler.
Frontal drag with exposed engine and pipe for reference stock carb is dominating

You can set up a pipe for better torque and throttle response rather than rpm for fun fly type planes.

Of course we can have oil spray over the plane increasing the Reynolds number "in effect"
along with weighing down the plane when fuel burn should equal lighter plane.
Or have 80% of it diverted with a pipe, smooth surfaces left to help keep the craft fast.
Less time wiping the plane clean after each flight is worth its 11.3g weight / drag alone for me.

I like the header pipe on the .074 to at least up power and point the oil spray in one direction at the expense of the extra noise. Timing looks to be around 160 deg Andy may have modded to 170deg



4.75x4
1.4w per gram or 3.43g thrust per gram
1.5:1 thrust ratio max weight 9.7oz

5x3
1.5w / per gram or 4.25g thrust per gram
1.5:1 thrust ratio max weight 12oz

Frontal with pipe

MJD

My Feedback: (1)

Bling plus cool sound is okay with me! The can muffler makes drag too, wonder how much difference there is. I suspect the pipe is far worse. There's probably a MAN article somewhere on the subject.

MJD

My Feedback: (1)

One day someone will develop a series of really small and light RC carbs that have useful throat area but are smaller than the cylinder and contain less metal than the crankcase.

Looks pretty gnarly!