F9F Texan

...Hi All,
I'm building an Avonds F-15 and need to decide if I want to use the supplied bypass or any bypass.

Other than pressurizing the fuselage with ram air inflight, what are the disadvantages of going without a bypass?

I understand there's a thrust penalty involved with bypasses.

Thanks in advance
Johnny

tp777fo

My Feedback: (28)

I have 2 Avonds jets, Rafale and F-104. The Rafale is without bypass and the 104 with. Pros and cons to both but I vote for the bypass. The Rafale I worry about damage to the motor from foreign object injestion from open gear doors, loose wires etc. Also the fuselage drag is increased as the air going in the intakes fills up the fuselage making the gear doors hard to close, and hatches difficult to keep on. The Rafale is very loud compared to bypassed airplane. With the 104 I dont worry as much as anything the motor might eat has to go down the intake, which is far removed from the gear. The 104 is also whisper quiet. These two jets have different motors but the 104 is probably half as noisy as the Rafale. The bypass also may help limit crash damage to the motor (hopefully I'll never find out) and will limit fire damage compared to he Rafale with all its wires hanging out in the breeze. Hope this helps.

Tom Perry

JetflyerJ

My Feedback: (67)

Dont Bypass it John.


regards.............. Johnny Hernandez

JET FX

Johnny (F9F) I am building an Avonds F15 as well and plan to use a bypass as recommended by Philip Avonds. It just makes more sense to me to listen to the experts like Philip Avonds who designed the model! Also aerodynamically the system will run cooler and more efficiently with a "PROPERLY" designed and installed bypass and tail pipe set-up...
I will be using a Gary Muller bypass and bifurcated Tam pipe! also I am adding the Avonds scale louver fuse vents, this I am hoping will also help keep internal fuse temp and/or pressure down as well.
The critical thing hear is making sure you have a matched bypass and tailpipe to suit your particular model and turbine....and also have the relative position of turbine exhaust, bypass and pipe inlet correct.
Johnny, Tam can supply you with the correct tail pipe, bypass, and fuel tanks to suit your model and turbine combination. And also supply more info on the perfect placement of these components for you if needed? within your airframe, as he has flown the Avonds F15 with a similar set-up....

Bypass's- After all if they did not work why are they designed into every full size aircraft design?

F9F Texan

Tom, Johnny & Marty,
Thanks for your input.

Marty, I have a pipe on order from Tam and it was he who asked if I was going to use a bypass or not. He said, if I remember correctly, that there was about a 10% loss of thrust with a bifurcated pipe and another 8% loss with a bypass. He said the vertical performance would be much better without a bypass. I'm just trying to sort everything out before I get too deep into it.

Tom, Maybe I'll see you at Waco in September.

Thanks again to all.
Johnny Adkins

KevinBarr

My Feedback: (27)

Just curious. I have been flying an Avonds F-15 powered by a AMT Mercury for 3 years, why are you not using the Avonds pipe? I have found it to work very well and heat or thrust has never been an issue.

I have just finished a second F-15, with a JetCat P120 in it, the test runs with the Avonds Pipe have proven to run cool...What am I doing different???

Kevin

PS Concering the bypass, I have never flown mine without the bypass, so I can't say how that works, but I know the stock system, with the bypass, has worked fine...Just my 2 cents worth..

HotelSierra

My Feedback: (9)

I like KevinBarr have had only good experiences with the Avonds bypass. Their were two other F-15s in my club and we all ran the Avonds bypass with excellent results, power output, cooling, etc.... Make sure however to create the proper NACA vents on your intakes because they will make all the difference in the world. Hope this helps.

KevinBarr

My Feedback: (27)

I had a sobering experinence this weekend with my Avonds F-15, I thought it worthwhile to share. Avond's supplies a cermic paper insulation that covers both sides of the interior of the tailpipe, to minimize heat radiation into the fuse. He suggest attaching this paper with some light binding wire OR using a aluminum tape.

My experience suggest that you DO NOT use any type of aluminum tape to fasten this blanket. I had a overtemp start on my Mercury (due to my high pressure line poping off during startup, The engine performed properly and shut itself down). This hot start must have produced enough heat to ingnite the adhesive that is on the back side of the tape, and it BURNS VERY WELL!!!

I would suggest using lightweight wire to attach the paper. What I have done is just give the tailpipe two coats of BV heat shield, instead of the paper, works like a dream....

Like I said, only my experince, but if it helps prevent a mishap, then its worthwhile.

Ohh, my plane is fine. One more reason we can't get complacent with these turbines, a fire extiguisher MUST alwasy be present.

Kevin

JET FX

Hotel Sierra re- NACA vents. I am converting my Avonds F15 from D/F to turbine and after reviewing the turbine refit instructions and accessories, I am going to try leaving the D/F inlet in place! instead of re-fitting the supplied Avonds turbine inlet as the only difference appears to be the D/F starter access center ring and the NACA vents cut into new inlet. All the work of changing the already fitted D/F inlet may not be necessary! if the scale Avonds fuse vents are in place! as these would supply more air to the fuselage than the inlet NACA vents anyway. Plus its a scale way of air venting/cooling the fuselage.

Johnny - The Gary Muller bypass is a bit larger in overall area than the supplied Avonds bypass, this may work better if a more powerful turbine is selected for the F15. Tams pipe may also I believe have better flow through than the stock Avonds pipe IMHO... although more testing on I.D./O.D. pipe sizes needs to done for optimum performance on any given turbine. Adding variable exhaust outlet nozzles to the bi-furcated pipe would be interesting here as well???

As a foot note: It would be interesting to hear from Avonds F15 owner/flyer's how their F15 performs with the different size turbines....
As my original O.S.91/fan combo flys so well, and the Dynamax would be putting out no more than 9-10 lb at best... I plan to try my F15 with both a PST600/ 11 lb thrust turbine and a TJT3000/ 27lb thrust turbine.
I have a feeling that 11lb of thrust will be just about perfect...

Topgun2mo

My Feedback: (45)

Why isn't a dual wall pipe used in the F-15 like his F-16? It just seems like it would solve some heat problems. Also does anyone know how that 12V fuselage cooling fan operates? Is it a permanent install or ground support?

Thanks

Mike

KevinBarr

My Feedback: (27)

The nice thing about the DF inlets, at least in theory, is the opening that exists for the old starter probe can now be used to accept the front mounted starter cases on the auto start turbines.

As far as my experince is concerned, there are no heat issues with Philip's pipe...

JET FX

Kevin, do you have any pics of your F15 turbine/pipe installation??? I am very interested to see how you have placed your turbine/bypass/pipe in relation to each other. Also Kevin could you tell me the inlet and outlet diameter of the Avonds pipe???

Cheers-

F9F Texan

I received my Tam pipe yesterday. I was anxious to compare the
OD of the outlets between the two pipes, thinking Tam's might be a little larger, requiring modification to the fuselage former at the rear of the fuselage, but Tam's pipe is actually a little smaller. With the double-walled pipe it ends up with a significantly smaller ID. The other difference I noted was that the point at which the pipe splits is quite a bit farther to the rear than Avonds' pipe.
Philip knows which engine you're going to use when you order a kit, so I assume he sends specific pipe/bypass sets for that application. The two people I've consulted with who fly the F-15 with a RAM 1000(Johnny Hernandez & Chris Zonio) both use Tam's pipe. Chris mentioned this in another thread.

I don't know about the cooling fans, but it seems to me that they are ground equipment only.

Johnny A

JetflyerJ

My Feedback: (67)

Johnny you made the right choice by using Tam's pipe.

Dont modify the pipe at all just modify whatever it is you need to modify in the Jet in order to make it fit nice and snugged. Just so you know My tail pipe does NOT stick out of the outlets if thats what you're concerned about.

Let me know and I'll be glad to shoot you a pic of my setup tail and Engine.


Regards.......Johnny Hernandez

Ian R

I have an Avonds F15, JETCAT120 std Avonds bypass and pipe.

Philip knows what he is doing.

Mine runs well and no significant heat build-up. with a 120 it is awesome.

The reason he asks for the turbine type to be fitted is because there is an inner short length of pipe that I think gets positioned differently or even removed for some turbines.


Ref. the smaller turbine, I think a 12lb output turbine will be a bit marginal with the extra fuel load compared to a DF.
the model will fly (Avond's great design) but a little slow

Hope this helps Ian R

ps not an Avond's rep, just pleased with his products

F9F Texan

Ian R
If I'm not mistaken Kevin Barr is also running a Jetcat 120 and has no problem with heat, but both people mentioned previously plus a local flyer who used a RAM 750 have had temp problems with the pipe supplied by Philip. (Actually the RAM 750 was in an Aeroloft F-15 with Aeroloft's bifurcated pipe)

Maybe there's a specific problem with RAM engines in this configuration.

Johnny (Jetflyer 24) I would appreciate any and all pictures of your setup. I have saved all of Kevin Barr's photos from his marathon thread and I refer to them often. Thanks, Kevin
Johnny A

JetflyerJ

My Feedback: (67)

As soon as i get home I'll shoot my 15 from every Angle possible so you can use it as reffrence, keep in mind that I have ZERO heat problems No bypass whatsoever.


Regards.......Johnny Hernandez

KevinBarr

My Feedback: (27)

It is threads like these that keep me tuned in to RCU. I think we are all lucky to have a great flying, economical airplane such as the Avond's F-15. I will try and snap some pics of the installation if Johnny H can't get to it.

Do any of you guys think you will make it to Missouri Valley Jet Scramble..Johnny, I know thats a long trip for you, but if fly in, there is an F-15 waiting for ya...

KB

F9F Texan

Johnny H,
Please send anything you think I might need. I'll be happy to share with anyone who wants them.
To anyone who hasn't read it, you can also enjoy Kevins thread.

Thanks, All
Johnny A

P.S Kevin, you might want to be careful with your offers. You didn't specify which Johnny you were talking to re:Missouri Valley
I might show up and fly it into the ground

JetflyerJ

My Feedback: (67)

When is the MO jet meet ? I was actually thinking on taking a few days off to attend a meet somewhere up North.


Johnny I'll send you the shots when i get home Bud count on that.



Regards.........Johnny

KevinBarr

My Feedback: (27)

The Missouri Valley Jet Scramble is August 2-4. Check out the website...

www.mvjs.com

It is really fun event, draws some good pilots. The facilities are first rate!!!

Kevin

Ian R

sorry about my previous email

I meant the model's performance is awesome not the temp

The set-up with 120 run's very cool,

Sorry

Ian R

F9F Texan

Johnny H,
I pm'd you with email address.
Johnny A

tamjets

My Feedback: (2)

Hi guys,
I been listen to you guys discussing about pipe.
Here are some of my input about my pipe compare to others.

Most concern is HEAT problem.
Sometime you got the bad wet start or hot start. The pipe are brite red. Even you got ceramic blanket cover. Guess what happen to your paint and your fuselage?

This is why I design double wall bifurcated pipe. My pipe can suck out the heat. Even you got the bad wet start.
Single wall pipe with ceramic can't. The heat remain in the fuselage and cause the paint to lift and bubble. Sometime worst. I withness it cause on fire.

Here is another issue.
WEIGHT
If you guys put my pipe and others brand pipe on the scale.
I bet my pipe come out at least 8-14oz lighter than others pipe with ceramic blanket or any kind of heat protection.

PERFORMANCE
I had done many test to find the best way to get MAX performance.
If you guys look at the split. You notice my are built different from other. I spend many hours designing how to built round shape split. Instead of sharp egde split. The round shape split help reduce noise and better airflow.
Also moving the split farther back help the pipe performance better.
Most of my pipe the split are 40% or farther back. That depend on how wide the pipe.

LIGHT and STRONG
I built my inner pipe with .006 stainless steel and .003 for outer pipe. I built structure frame in between inner and outer pipe.
This structure frame make the pipe really strong and don't need thick material. I notice most the pipe on the market are using .007-.008. But still very weak if there is no structure frame.


PIPE Installation.
My pipe built to be use with bypass or without.
Every pipe I built come with bellmount. Bellmount help airflow if not using bypass.
Also important to install your turbine correctly. Do not place your enigne exhaust to far in to the pipe. Best recommending from 1/4" to 3/4" in to the pipe.
If the engine exhaust go in to far. That cause blocking air draw in to the pipe. That cause loosing power.

BYPASS or without bypass
Some always asking me this question.
Here are my and Ray Davis test result.
I test the pipe with bypass. I lost 3-4lb of thrust at 28lb.
Here the test without bypass. At 28lb of thrust only lost 1.8lb
This test was done with F-15 pipes. Same kind of pipe was on Johnny Avond F-15.
My opinion for bypass go both way.
If you guys flying fast(150 mph over) jet like Bandit, Starfire and ect.
You need bypass to reduce drag.
But if you are flying slow(150 mph under) and drag airplane F-15, F-4, MB339 and ect. I wouldn't use bypass. I need extra booth at slow speed.

Hope my input help.
Brg,
Tam
P.S.
Johny H.
Shoot me your address.
Your pipes is ready.
You almost break the longest pipe record.
Shelias Partel beat you by 4" with his F-86 pipe.

aparchment

As Tam points out, Ray Davis has been flying his F15 for several years, and he doesn't use a bypass. He measured thrust losses with and without a bypass and found significantly less loss without the bypass. Ray was very concerned about performance because he flies off of a short grass strip.

As an aside his plane sounds amazing due presumably to all of the swirling air inside the fuselage. It makes for a very scale sound.

Antony