Checking installed thrust at the field today
 

Wayne Lane brought out a digital fish scale today and we tested our jets to see what the installed thrust was. The temps were 97d+ and i was surprised with the results. Can the heat really rob this much power?? I placed a 6oz lead weight on the scale to see if its calibrated correctly and it was right on. We also figured in the thrust loss to move the jet.

My BVM 60" F-86 with P-60 (170k) full bypass 11lbs

Rons Euro (with intake and Tams bifurcated pipe) Wren XL-200 22lbs

Waynes Flash P-120 18lbs

RE: Checking installed thrust at the field today
 

Vin..
See summer is started to show up.
Semper Fi
Joe

RE: Checking installed thrust at the field today
 

The purpose of water injection on many of the acft in the early 60s (P-3As & some P-3Bs). If not that, then adding a movable cambered inboard leading edge slat (in addition to the outer slats) a la TA-3B & EKA-3B. Without the CLEO wing on the EKA-3B, takeoffs (from land bases with runways shorter than 11,000 feet) had to be done early in the morning before the temp got above 80.

RE: Checking installed thrust at the field today
 

Some of that loss is in the pipes.

RE: Checking installed thrust at the field today
 

I'd be interested to see results from the GSU connected as well, maybe include thrust measurements and the EGT's at those measurements.

In full scale jets - older designs, smaller engines - we can sometimes see certain ambient temps bringing the engine to EGT limits before being able to set takeoff thrust, depending on the health of the engine. 97 degrees is cetainly not an extreme temp, I've seen this at the 120 degree mark and such.

With model engines I would not be suprised to see something like full thrust being limited by EGT, rather than the engine being dynamically limited to those thrust levels based on density altitude. But I don't have lots of experience running my model engines in test conditions like this, I'll be the boys at JC would know with all sorts of test cell runs over the years. In a Jet Cat, for expample, if the EGT max limit is reached momentarily and can be controlled by the ECU, will the engine thrust setting simply be limited / brought back, or will a flameout be commanded by the ECU.. I wonder.

I'm sure the pipe is at play on those readings too as said above.

RE: Checking installed thrust at the field today
 

woops, double post

RE: Checking installed thrust at the field today
 

what was the method of measuring the thrust ? did you guys just put a scale on it's side and push??
Kevin

RE: Checking installed thrust at the field today
 

Digital fish scale holding it up against the nose at full power. We figured in the rolling weight of the jet as well.
V..

RE: Checking installed thrust at the field today
 

That's why no jet should have anything less than a Titan!! [&:]

So, at full throttle, you might still get double digit thrust...:eek: [:o]

Raf

RE: Checking installed thrust at the field today
 

Last weekend here in Virginia we had 100F temps and I decided to fly my Reaction with a P-60 at our local field which I had never done before. Even though it's about 500'+ grass which is plenty for the Reaction, it is surrounded pretty closely with trees and I just didn't feel comfortable flying it there until last week for some inexplicable reason. The Reaction usually gets up easily with no flaps in about 300' on grass. I did have a slightly canted wheel which casued some drag but I never had a problem getting enough speed up to rotate until last Sunday. After using up around two thirds of the runway and pinning full up elevator for what seemed an eternity, she wasn't close to lifting the nose. At that point I could have dropped the throttle and hit the brakes but probably still would have ended up in the high grass and probably had wing/gear damage so I just held the full up elevator and hit the flap switch to full flaps and she got off probably fifteen to twenty feet before the end of the runway[X(]. During the flight the plane seemed slower than normal at full throttle and I definetely feel it was due to the heat and humidity.

Marty

RE: Checking installed thrust at the field today
 

Maybe the oil companies are "watering" down the kero with all these high oil prices! [sm=drowning.gif]

Raf

RE: Checking installed thrust at the field today
 

Raf
Don't you have to Pass Gas somewhere:D:D

Semper Fi

RE: Checking installed thrust at the field today
 

I'm in clinic. So I don't have to pass gas until tonight. Thank you very much. :D

Don't you have a picture to take? :)

Raf

RE: Checking installed thrust at the field today
 

Ambient humidity actually has little bearing on the thrust of our engines...though it's air density of course that affects them....and that is primarily determined by OAT and elevation. Figure a loss of thrust around 3% for evey 10-degrees F above 59F......and another 3% for every 1000' above sea level. At 4000', then, on a 90-degree day, you might be losing some 21% of thrust relative to standard conditions (STD, that's how the mfgrs' should be listing them). Additionally, of course, your lift is similarly affected....you can see how easily poor model performance gangs up on you at altitude on a hot day! Below sea level, cold weather.......more power.

Split (bifurcated) pipes usually cause a few pounds loss as well.....singles up to a pound. 'Fairest' way to test is to measure the model's slow rolling friction (engine off, level ground) and add that to the max thrust taken during a steady-state slow roll forward....i.e., no fair pushing back...which will inflate figures.

Ray

RE: Checking installed thrust at the field today
 

All right then, why haven't mfgr's picked up on and started exploiting the "thrust augmenting" tail pipes? Instead of loosing anything, you GAIN thrust (something like 3-5%).

It's not like they're difficult to build or a mystery or patented (I believe the inventor posted the formula in public forum/GTBA). Heck, there's no more material involved...

Even Gary Baker made one. :-) I don't know at this point if anyone's figured how to apply the theory to bifurcated pipes yet though.

What's a good thickness stainless for pipes? 0.007"?

RE: Checking installed thrust at the field today
 

Wren's pipes do augment the thrust.

RE: Checking installed thrust at the field today
 

Well...touche'. Since it was one of their founders or associates (I think) that discovered it...

Yup! Always liked Wrens business ethic/strategy and products.

Have they patented the pipe or something?

RE: Checking installed thrust at the field today
 

Chuck,

Pipes are like props....Everyone has their opinion and every defferent model is best suited with a different, particular size/shape. How long has it been since an engine manufacturer made props?...50+ years?? I believe that if we raced jets or competed in aerobatics with jets then we would see some improved tailpipes. Not just ones "that work" as we have presently. How much cutting edge prop design do we see among the scale crowd? Same with pipes on the turbines...Buy what's available and use it. That's what I do. I have been using Wren pipes for 5 years. My 25 lb. A-7 flies fine with the 18 lb. Super Sport and Wren pipe.

No patent on them though. In fact, John Wright (the "W" in MW) published the design with dimensions a couple years ago....no one bought into it...............Just install a bigger engine to get the performance..............


Tailwinds,

John

RE: Checking installed thrust at the field today
 

Who is he????

And I was able to get 29# of thrust out of my Titan after I got the thrust augmenting pipe fine tuned (The Titan only put out 26.5# on the stand without the pipe).[:@]

I just built another one for my YA F-18. Can't wait to see how the Merlin pushes the big bug around!

RE: Checking installed thrust at the field today
 

Ahh, he's some dude I've seen once in a great while in the PAST - rumor is he's still flying somewhere, but I can't confirm that...

You made a bifurcated pipe for the bug? Did you try and diverge the volume like the Wren pipe?

RE: Checking installed thrust at the field today
 

No, it's another straight pipe. I'm not brave enough to make a bifurcated pipe yet.

RE: Checking installed thrust at the field today
 

Gary,
Maybe its just the pic but that former the pipe is secured to looks like its 1/2" plywood !! :)
V..

RE: Checking installed thrust at the field today
 

What is the theory (in layman's terms) behind the thrust augmenting tailpipe? Is is simply a divergent duct increasing the exhaust pressure? if so, there is always a penalty to be paid and surely this would be in terms of exhaust gas velocity (and hence top speed).

I am still a believer that you don't get something for nothing.

Also, the thrust that is being measured by most people is static thrust. Does anyone know the magnitude of the benefit these "augmenting" pipes actually have in the air?

RE: Checking installed thrust at the field today
 

It is!! Two 1/4" ply laminated together. What you can't see in the pic is that there is another 3/8" ply laminated on there also. I didn't build thus one, I just refurbished it.

RE: Checking installed thrust at the field today
 

I had test both design of the pipe in the same model.
This while back with the Ram 500 in BVM ultra viper.
The taper pipe had much higher efflux velocity and the speed is much faster than the pipe with more static thrust.
I had test the taper pipe at 12 lbs of thrust only lost 1/4 lbs. That is the bellmount pipe set up. The bypass set up loose up to 2 lbs. The reason is the bypass not allow cool air to draw in the pipe. That why recommending put some hole in the back of bypass to help get cool air in to improve thrust lost.

In the last 2 years I been doing a lot R&D with high performance E-power fan system.
Everyone is after high static thrust for marketing interested point of sale.
I going for high efflux velocity design.
Sure enough. My tiny little fan had 30% less static thrust can out fly any bigger fan that had more static thrust with low efflux velocity.

There is no secret to pipe design.
If you want more static thrust. You will had less efflux velocity.
If you want more efflux velocity. You loose little bid on static thrust.
You can't had both.