After a brief discussion with Bob Wilcox at JetCat I was told that it is better to NOT use a bypass in our installations....His reasons were that the turbine can get hot and there is a thrust loss....Tam has recommended to not use a bypass in his F-16 due to thrust losses...

My question is to all of you here is what are your findings???....I thought that the bypass was beneficial in adding top speed to a model. If thrust is lost in a bypassed installation, then the loss in speed would possibly be made up with the bypass due to decreased drag...And vice versa....The thrust gained in an open install, the possible increase in speed would be negated by drag???

Tell me your thoughts...[8D]....

Kevin

PS...I really don't care about top speed as with our jets pretty much everybody can go fast....(In reality, the problem is keeping them under the 200 mph AMA limit in most cases...) What I am interested in is any thrust gained for short field/grass takeoffs as these are the types of fields that I typically fly from...

I quit using them a couple of years ago. I feel like I get better performance without them, but I could never back it up so I quit trying.

I know for a fact though that it is hurting my top end because of drag inside the airplane. But it seems like my vertical is better without.

I have an issue when trying to slow down on a bypassed installation.........high speed air being forced into the engine while decreasing fuel flow and EGT temp = flame out.
I can never go to idle when trying to slow down, which sucks becasue it means having to do more turns to bleed off airspeed.

Not a big fan of bypass myself.

There has been some discussions about " to bypass or not" here. It is, in most cases, better to use a "propely designed" bypass system. a "system" is the intake, the bypass and the tail pipe with great consideration given to the size and power of the turbine.

Most BVM bypass sytems are well designed for bvm's jets and their recommended turbines. The exception is the P70 bypass with a Wren SS, the bypass is too small.

An inadequately designed bypass system will cause power loss and when the bypass is removed it will seem that you have more power (and you do) but it is because the bypass system was not correct to start with.

So to answer your question, it depends on your specific case... For me, I always use a full bypass if at all possible ....

Look at the January 5, 2009 article
http://www.bvmjets.com/Pages/bandit_...ot%20shot.html

I agree....BVM has done their homework pertaining to their bypassed installations....For now, let's not take BVM products into account...

The planes that my buddy and I have that are bypassed are the EuroSport (one is bifurcated and the other is a single exhaust), Dragon, JL L-39, and Cermark/Spark ViperJet....Anyone have any experience with these planes???....Or just continue to tell us your experiences with other planes!!![sm=thumbs_up.gif]

Kevin

I've got a Titan SE in my Flash, with the lower half of the bypass removed i get lower temps, much higher top speed and a very noticeable increase in vertical performance, with a P-70 in there it's not noticeable at all with or without it. on the Flash the boost comes from the turbine getting more air via the nose wheel hole, if your setup has full gear doors i don't think you'll notice as much a difference with or without a bypass.

wohoo whose is that cool looking BARF at the top of the page?

Can someone explain to me what is a by pass and where is located?. I have an F-16 but I think it has no bypass.

Is the bypass the inlet duct that bring air from the air intake in the fuse to the turbine?

Most people know the bypass as the tube that encloses the turbine itself, generally made of carbon fiber, fiberglass or kevlar. The trubine sits inside the bypass which located after the intakes...

Another purpose of the by-pass is, to my knowledge , to prevent turbulance of air inside the airframe during high speed flight therefore improving speed and stability of the flight...

Im getting ready to fly my flash this weekend and im going to try the half bypass, just removing the engine cover and see what that does. I however have never had a problem with the engine idle and the aircraft going fast, I actually like to get high and come down with alot of speed, then idle the motor before pullout and do a fast "silent" pass then spool up and burned out..

I have a half bypass in my 60" BVM Fury. Wren 54 powered, manual start. Seems to work fine, maybe top speed is affected a little, but it seems about right for 12# thrust.

Guillermo Ibanez

Can someone explain to me what is a by pass and where is located?. I have an F-16 but I think it has no bypass.

Is the bypass the inlet duct that bring air from the air intake through the fuse to the turbine?

Thanks Sam

I have seen this enclosure in some models

This may be true because I have an Eagle Tree Telemetry System and the speed sensor that has its static sensor inside the fuse, has sometimes inacurate readings I guess because the negatÃ*ve pressure cause by the turbine intake in the fuse.

Not sure why, but the larger turbine installations often do not take advantage of the extra 5-10% thrust available by using a diverging tailpipe. These are sold by Wren for their smaller turbines and were studied by John Wright, I believe, in an article in RCJI a number of years ago. They work at least in part on a venturi principle, using the high speed turbine exhaust gasses to suction additional air (mass flow) from the fuse out a bell-mouthed tailpipe. Probably wouldn't work with a fully 'bypassed' installation or if there is significant restriction of inlet air.

If your aim for an installation was to improve take off and low speed or high alpha performance, as in a single piped Eurosport, you might get better thrust with lighter weight using a divergent tailpipe without any bypass system. Has anyone out ther tried this?

I gained 3 pounds of thrust on my Titan powered EuroSport using a pipe similar to Wren's with only the top half of the bypass installed.

I agree...Using a pipe such as the one that Wren developed makes sense as the heated expanding gasses are turned into extra useful thrust...Instead of the heated gasses being choked down until they exit the pipe....I wonder why more kit manufacturers haven't included this type of pipe with the kits...Does Wren have a patent on this???

I'm going to try running with the top of the bypass removed and see if I can tell the difference on my JL L-39...

Thanks for all of the replies!!!...If any of you have more to add, please do so!!![sm=thumbs_up.gif]

Kevin

The Wren pipe works incredibly well and produces additional thrust while allowing air to move freely from the efflux of the turbine, thus helping to keep the EGT down slightly.

As far as I know, the design details are not patented and the 'how to' details were published in RCJI so, it is in the public domain.
I am also amazed that others have not adopted this pipe, it works for sure and can be proven on a test stand.

As for bypass, I have used them and if you want extra top end then they are a must due to reducing the internal drag on the model.
However, for most 'sport' applications and sensible installations (keeping as much out of the airflow as possible), I have found them to be unnecessary.

Hope that helps.
Paul

I flew my Flash this weekend with out the bypass cover and reviewed my Avg. EGT, it went from 509C to 508C and the Peak EGT went to 638C to 629C. I also noticed an increase in low end thrust production and spool up times were increased slighty and it was not any slower on top end, heck maybe faster, lol...

Justin, what engine was that again?
I have only flown my Flash with half the by-pass but was thinking of removing the other half too [:-] That half does provide some heat protection though. The wing on the Flash also conforms to the engine so actually even with half off it's sort of a half-assed by-pass [sm=tongue_smile.gif]

Why? the only thing you'd gain is loosing about 1/4oz weight. there is no advantage at all to removing it.

Removing that and the inlet joiner would allow even more air for the pipe and room for smoke tanks.

removing the inlet joiner won't give more air, but will give you more room (i don't use mine either) but removing the upper bypass isn't gonna give you any additional space at all.