Hi guys

I have always preferred a full bypass in my jets and is faced with a bypass ducting on a new ARTF that will only allow me about 3 to 4 mm allround my AMT Pegasus M2. I would have been happier with about 10mm, but maybe I don't need to worry.

Please comment.


Springbok Flyer

3 or 4mm isn't much. I have a tight installation like this on my F-106. I'd run it on the ground and see if the pipe runs hot. In flight, the air is going to stack up in front of the bypass. You might need to cut a few vents in the front to dump excess air around the outside which wouldn't hurt cooling.

I would think the answer to your question has a lot to do with the size of the inlets your Arf has. For instance if you have a F15 with big inlets you might do well to have a bigger gap around the engine but if you have small inlets like on a S.M Hawk you might get away with a smaller gap.

This bypass size, tail pipe distance/size Augmenter gap is a bit of a black art. No one really seems to know what's best and manufacturers seem to promote their set-ups on the fact they run cool and not what thrust they loose or gain.


Jason

Mike

I must admit, my thinking coincides with yours. I have actually cut two 40 x 15 mm (1 3/4 x 3/4') narca vents into the intakes just as they start curving inwards. Very much like we use to do with the fully ducted, ducted fans, ala BVM. I believe this will allow the air pressure to drop enough in front of the turbine during flight and thereby also reduce the drag it may cause.

Jason

I agree with you too. The intakes are not large, but not particularly small either. I was thinking I'll run it on the ground and then decide on whether to cut a further two narca vents on top of the tutbine in the bypass, should the bypass run too hot on the ground. This I hope will allow hot air, directly around the turbine, to be sucked out from the bypass - by the air coming in from the two narca vents up front.

Anybody else with experience of a small gap around the turbine in a bypass?

Cheers

Springbok Flyer