Scale F-16 Intake

[BayDesigns]

I abandoned my scale F/A-18D project because of CAD limitations, but I found a lovely F-16 with the internal structure modeled enough for RC use. However, I'm not totally sure that the intake design will work.

So there's the normal intake plus 2 extras, not sure if they're cheater holes, but they'll give me more airflow. Assuming the intake is adequately sized, will the squashed duct in between the inlet and EDF be an issue? Only the internal part matters, the landing gear bay is just mounted on that and the inlet ring that extends backward is purely cosmetic.

 

[telnar1236]

That intake design will be a real problem for any EDF unless you add cheater inlets closer to the fan unit. A good rule of thumb is that you need at least 100% fan swept area for the entire length of the inlet duct. To me, that looks like a supersonic diffuser, which is not well suited for our very subsonic EDFs. If you add cheater inlets leading to the outside of the airframe, you would almost certainly be fine, and most EDF F-16s make use of those, so you could probably use the inlet, but it's pretty far from optimal. If you see the squashed section, increasing the height of that would fix a lot of the issues with this design. From a structures standpoint, I would also be worried about the location where the gear is being mounted. It looks like a single hard landing could cause the inlet structure to buckle.

Edit: I checked and the F-16 uses a normal shock -> subsonic diffuser. I am not sure why the inlet in the CAD model is designed that way.

 

[BayDesigns]

That intake design will be a real problem for any EDF unless you add cheater inlets closer to the fan unit. A good rule of thumb is that you need at least 100% fan surface area for the entire length of the inlet duct. To me, that looks like a supersonic diffuser, which is not well suited for our very subsonic EDFs. If you add cheater inlets leading to the outside of the airframe, you would almost certainly be fine, and most EDF F-16s make use of those, so you could probably use the inlet, but it's pretty far from optimal. If you see the squashed section, increasing the height of that would fix a lot of the issues with this design. From a structures standpoint, I would also be worried about the location where the gear is being mounted. It looks like a single hard landing could cause the inlet structure to buckle.

Edit: I checked and the F-16 uses a normal shock -> subsonic diffuser. I am not sure why the inlet in the CAD model is designed that way.

Is it possible to have more than 100% FSA at points in the inlet without performance decreases? That would make my life easier.

 

[leaded50]

the squashed duct in between the inlet and EDF is an issue. it need here at least be 5 (?) or more times wider at squashed point to get closer to 100% FSA by picture . On picture it seems not wider than at EDF... then the intake restrict intake air.

 

[telnar1236]

Is it possible to have more than 100% FSA at points in the inlet without performance decreases? That would make my life easier.

It depends on how much you want to optimize for speed. The short answer is that it won't be a major issue most of the time unless you do something really dramatic. If possible the duct should be area ruled, going from a max size at or above FSA at the inlet to the FSA at the fan surface, but in practice, almost every duct is above the FSA right before the fan. Good advice is to avoid sharp corners and sudden area changes since those cause large pressure losses. Otherwise, you should be fine.

 

[BayDesigns]

I’ll cut out the squashed section and replace it with a smooth transition duct of the appropriate size. Then, if you don’t mind, I’ll upload an image to get your input.