Fire Bomber FAA Gear Down?

[climber314]

Why does the FAA require some aircraft to perform drops in a "Gear Down" configuration?
Aerodynamically it would seem a "cleaner" plane would have better performance.
With a significant number of fires in the USA this year, I've noticed several photos in news articles similar to this MD-87:

https://cimg4.ibsrv.net/gimg/www.gmforum.com-vbulletin/730x673/firebomber_3c9d297ca187d4b0b28908fd6c0e1c481d640108.jpeg

[bafanguy]

I can't speak to why fire drops are done in a particular way.

As for the MD80s, if flaps are beyond 26 degrees without gear down/locked, you get a non-silenceable warning horn. I can't tell the configuration from that picture but a normal landing flap setting is 28 degrees so maybe the fire drop was trying to get a particularly slow IAS by using more than 26 degrees so had to lower the gear to prevent the horn ?

[climber314]

I can't speak to why fire drops are done in a particular way.

As for the MD80s, if flaps are beyond 26 degrees without gear down/locked, you get a non-silenceable warning horn. I can't tell the configuration from that picture but a normal landing flap setting is 28 degrees so maybe the fire drop was trying to get a particularly slow IAS by using more than 26 degrees so had to lower the gear to prevent the horn ?

It's an FAA requirement but I don't quite understand how GEAR DOWN is supposed to prevent stalling.
Seems counterintuitive to me?

https://fireaviation.com/2017/09/16/the-faa-requires-ericksons-md-87s-to-drop-retardant-with-landing-gear-down/

[Flexable]

Interresting comments below

[havick]

Having the gear down would help make the aircraft more stable as far as airspeed goes when dealing with updraughts etc. think having the drag to help prevent flap overspeeds etc. not to mention the un-silenceable warnings not having the gear down

if an emergency occurs then it’s simple to drop the water and instantaneously improve your performance and then clean up.

im not sure about the FAA reason but having flown quite a few fire seasons as a bombing pilot (albeit in the rotary wing world) and now a jet pilot, that would be a practical reason for it.

hopefully someone who actually flies that jet in the role can post on here with a definitive answer

[bafanguy]

It's an FAA requirement but I don't quite understand how GEAR DOWN is supposed to prevent stalling.
Seems counterintuitive to me?

https://fireaviation.com/2017/09/16/the-faa-requires-ericksons-md-87s-to-drop-retardant-with-landing-gear-down/

314,

Interesting. I don't know it's related to stall characteristics. Probably have to know more about certification testing in the 40 flap configuration. I have no idea where to look for that. The comments at the end of the article are interesting.

So much to know...so little time ! :confused:

[plhought]

It's really simple - with gear down engines run at a higher N1 = better engine response (less spool up etc).

Same reason the BAe 146's/Avro RJ bombers usually dump with the speed brake open.

Don't have the instant power response of the big piston/turbo-prop jobs out there.

[bafanguy]

It's really simple - with gear down engines run at a higher N1 = better engine response (less spool up etc).

The MD80 has a dial-a-flap system that allows plenty of flap to be selected (between 15 and the setting causing a non-silenceable gear horn...the number escapes me at the moment) keeping N1 up if that's a consideration in this firefighting operation.

[tdracer]

It's really simple - with gear down engines run at a higher N1 = better engine response (less spool up etc).
Not necessarily - depends on the aircraft. Many Boeing aircraft run high idle off flap position - there is no gear down input.

[ehwatezedoing]

I’ve been told one of the reason for dropping retardant gear down on the MD is to prevent load injection into its engines.
But don’t quote me.

[bafanguy]

Not necessarily - depends on the aircraft. Many Boeing aircraft run high idle off flap position - there is no gear down input.

The MD-80 has a flight idle set up where N1 is bumped up (I think I remember) about 6-8% in flight based on NLG extension. Don't bet the rent money on those numbers but I'm pretty sure of the higher flight idle.