Ice Protection - Large vs. Small Aircraft

[Flaps]

I've come across the following statement in a book on aircraft systems:

"On large transports, only the outer portion of the wing leading edges or slats and the engine cowl lips require protection but the air flow requirement can be similar to that for airconditioning."

The author then goes on to say:

"Smaller aircraft, such as the BAe 146, also require protection of the tail surface leading edges, and when operating ice protection can take three times the flow for air-conditioning, for the short time that ice protection is required."

The author gave no additional reason, and cited no proof to validate his statement. So if he's in fact correct, my questions are:

1. With the second statement, the author seemed to imply that only small aircraft require icing protection for the tail. Is this true, and is so, why?

2. Why would the airflow requirement to protect "large transports" from icing be equivalent only to the flow required for air-conditioning, but for smaller aircraft, be three times the amount required for air conditioning.

Thanks in advance!

 

[firstthird]

1. I've been flying the B737 for the Navy for 6 months and our tail is not de/anti-iced and I presume all 737s are the same way. Also, on the wings, the part between the fuselage and engines is not de/anti-iced either, although the 3/4s of the wing from the engine pods out are excepting the very last panel near the tip, which is not. Basially, if you divide a 737 wing up into 5 sections the middle 3 are anti-iced.

2. I'm thinking because big planes have big motors that put off lots more bleed air so it is a much smaller percentage of the air bled off to deice the wing. pure speculation there.

I've also wondered about why our tail isn't deiced, the best answers I've gotten said something about the AOA and ice won't attach to the empennage therefore we don't need anti-ice back there. Our books say nothing about it though.

Anyone that has a better grasp of why swept wing pax jets don't have emp deice want to help us out?

 

[tarp]

I think your author may be showing a little bit of "generalization" fever and may not have flown that many "small" jets.

Tough to generalize any airplane design.

On the one point - the BAE146 is larger than the CRJ but the CRJ does not have tail de-ice/anti-ice either. For the CRJ, our "secret" may be found in the limitations section talking about the wing anti-ice function and in the tech manuals. Basically, the engineers feel that the wing is "aerodynamically clean" and will not accrete ice at speeds over 230Kts. From our classroom work and the doubting people such as myself that came from the Dork Jet (which has tail systems), we were told that this "clean" effect was exhibited in the tail to much lower speeds and that the tail would not accumulate appreciable amounts of ice unless basically flying slower than normal approach speeds.

Note: our operations manual still requires us to use wing ice systems anytime we receive an "ice" message from the ice detector system but "supposedly" wing anti-ice over 230kts is a redundant system.

The word "airflow" is a context thing, but the author in my reading of your blurb is talking about "bleed airflow". The bleed air requirements for the anti-ice systems are huge compared to airconditioning. In the CRJ again (my only point of reference since the Dork had boots), bleed air is tapped and sent down tubes in the leading edge of the wing to be just ported overboard - basically throwing bleed air right over the side of the airplane instead of in contained systems. If the Bae146 does the same thing with its tail systems, that would take a substantial amount of bleed air to heat the vertical stab and leading edges of the tail and then throw it (the bleed air) away. (Air conditioning uses far less bleed air to run the air cycle machine - with a certain amount of bleed air thrown away for "heating" purposes).

I would say that your author took liberties in his generalizations but for the most part tried to present icing systems. It's hard to be an expert in everything and if your guy seems well rounded in other points, maybe you can forgive some poetic licence.