RL F-15 structural imperfections (specifically the radome)

[mvsgas]

I have been reading aircraft accident reports in the last couple of days, I don't know why, and on several F-15 mishaps cause by out of control conditions the mention the Radom as having "imperfections"

 

One example of a report mentioning the radom;

this is a direct pdf link

F-15C 80-0041 From Nellis AFB

 

another example;

http://www.airforcetimes.com/story/military/tech/2015/03/13/f15-lakenheath-crash-report-radome-cap/70265748/

 

Has anyone ever read or heard of more info on this or other aircraft with similar problems?

How common is this on the F-15?

[Monkey21]

I spent the day with an F-15 pilot at RIAT last year, and we talked the dangers for a while. One of his friends had had to abandon an Eagle because of this exact thing; the nose had been slightly damaged by something (he didn't know what) and that even the small difference in shape had disrupted the airflow so much at high speeds as to make the jet uncontrollable. I suppose it makes sense, since basically the entire jet has to fly through the hole made by the radome. This is purely anecdotal of course, but it does seem to be something the Eagle suffers from.

[Bushmanni]

Imperfections on nose have high impact on handling in F/A-18 at high AoA. Pilots inspect the tip of the nose for scratches and bumps before flight just for that.

[pr1malr8ge]

My cousin told me specificly back in the 80s that patches done on the raydome cause major issues. Ill upload the txt he sent me about it later tonight.

[Capn kamikaze]

Imperfections on nose have high impact on handling in F/A-18 at high AoA. Pilots inspect the tip of the nose for scratches and bumps before flight just for that.

 

Imperfections like this....

 

 

J/K, I know it was a mid-air.

[Darkbrotherhood7]

Imperfections like this....

 

 

J/K, I know it was a mid-air.

What happened? lol

[Necroscope]

What happened? lol

 

 

He sneezed. ^)

[winchesterdelta1]

What i'm more amazed about is, how can some aircraft keep flying with half or their entire wing gone. But if there is a imperfection on the nose it crashes and burns (figure of speech). That is interesting stuff. I thought the nose only difficulty to get right is the aerodynamic shape and how it lets radar beams pass (still don't know how i solid nose like that can make the radar beams pass). So many questions.

[joey45]

What happened? lol

 

2 hornets kissed midair... both landed safe.

[Darkbrotherhood7]

2 hornets kissed midair... both landed safe.

 

:lol: Nice that both landed safe.

[Bushmanni]

What i'm more amazed about is, how can some aircraft keep flying with half or their entire wing gone. But if there is a imperfection on the nose it crashes and burns (figure of speech). That is interesting stuff. I thought the nose only difficulty to get right is the aerodynamic shape and how it lets radar beams pass (still don't know how i solid nose like that can make the radar beams pass). So many questions.

 

Imperfections cause trouble only at high angle of attacks. If you look at the accident reports mvsgas posted both accidents happened when pilot made hard maneuvers ie. pulled lots of AoA and the plane spinned.

[pr1malr8ge]

Here is that img I promised.

 

Back info, I had asked how hard/easy was to get the f15 to depart controled flight.

Edited July 15, 2016 by pr1malr8ge

[=Panther=]

Although this one has a laundry list of things that went wrong, they still had radome imperfections listed as one.

 

[ame]http://usaf.aib.law.af.mil/ExecSum2008/F-15D_Nellis_30Jul08.pdf[/ame]

[mvsgas]

I think the radom is mention on every F-15 accident report where the aircraft departed flight. Never as a leading cause, but mention. I did not see any mention of radom causing problems on F-16, I did not look at other aircraft.

[GGTharos]

The cause was uncommanded yaw due to essentially two things:

 

The pilot had spiked the AoA very high and may have already had yaw input due to blended controls, and at the same time to imperfection on the radome caused a high hinge force at a time when the aircraft is not directionally stable (ie. high AoA). This caused the yaw to increase to the point where it turned into a spin.

 

It's a collection of factors, but basically without the imperfection this would probably not have occured.

 

That's my understanding of this. In any case, they're talking about this imperfection combined with very high AoA - we're talking on the order of 40+ units (the spike was 54).

 

It's possible that this is reasonably unique to the F-15, but I have my doubts. For the F-16, I suspect the strict control of the AoA by the FBW masks such issues - you basically may never reach an AoA where this becomes an issue.

[Capn kamikaze]

What i'm more amazed about is, how can some aircraft keep flying with half or their entire wing gone. But if there is a imperfection on the nose it crashes and burns (figure of speech). That is interesting stuff. I thought the nose only difficulty to get right is the aerodynamic shape and how it lets radar beams pass (still don't know how i solid nose like that can make the radar beams pass). So many questions.

 

The nose is usually made of something like fibre glass or some other non-metalic material, and the radar will have little trouble passing through such materials, there may be some slight distortion of the beam, but it will be incredibly small, and during design of the radar itself it will be accounted for.

[mvsgas]

I wonder if other aircraft with large radom (Mig-25/31, Su-24, F-14, F-4, etc.) have same issues?

[strikeeagle]

Even if the metal nose cap that's about the size of an US $.50 piece is installed incorrectly or misaligned can cause airflow issues. QA would often check measurements during QVI's. PITA...