Jet engine cowlings

Sounds like blow in doors to me. essentially those are doors that open during take off to allow more air into the engine during that critical stage of flight. Once the aircraft is aloft, those doors are closed tight.

On the ground, those doors are usually closed to avoid foreign objects from getting inside the engine duct. they are, depending on what's being done, opened during ground maintenance.

Blow in doors, also called auxiliary air inlets are very typical on jet aircraft

Do the doors on your model open inward or outward fro mthe model's surface, and do the openings face forward into the airflow or backward away from it? If you answer that, I can give you a better answer.

In the case of prop aircraft, the movable cowling sections are more to do with radial engined aircraft (such as the P-47) and the movable section is those little flaps at the back edge of the cowling. Those are part of the exhaust system and govern how quickly exhaust is expelled from the engine, basically the faster the engine is going, the wider those flaps are open to allow the exhaust to disipate faster.

The doors on the Mig open outward and perpendicular to the centerline of the aircraft. If you look closley at this pic, you'll see the two on this side. They hinge at the top.

Dana F

Thats a really difficult call now that I see them.

They could be blow in doors but considering the larger air inlets around them, I suspect they are emergency access panels on spring hinges for fighting engine fires while the aircraft is parked. the idea being that ground crew could simply stick the nozzel of a fire extinguisher through the opening the door seals off and fill the area with fire retardant.

I suspect the larger, fixed scoops in the general area fill the purpose of auxiliary air inlets as the doors you are pointing out are rather small for that purpose.

Actually, let me clarify. There are four doors on each side. Here is a pic showing the four on this side open.

Dana F

In the first picture they appear to be "D" shaped doors that are clustered together in pairs above each other. These spring loaded doors are part of the bigger rectangular access panel. It does not seem likely that they would have 4 fire suppresion doors that close together for the same compartment. Maybe there are sight guages, system service ports or some sort of ground maintenace switches behind there. Or a combination of all these answers including fire suppression.

As for the cowl flaps that upnorth spoke of I would like to clarify a bit.

They are found on both radial engine and horizontaly opposed (modern day piston aircraft engines). Most complex aircraft today at your local airport still have cowl flaps. They are not part of the exhaust system though. They are actually part of the cowling, hence the name cowl flaps. They can be located at either the inlet or outlet of the cowl. Their purpose is to control airflow through the engine compartment. Aircraft engines are air cooled and rely on air movement to dissapate the heat.

When the cowl flaps are closed the airflow is slowed and the engine temp increases ( cylinder head temp and oil temp. Exhaust gas temp is unchanged). They are normally closed during a decent when power is reduced. If not the engine temps would decrease too rapidly. Repeated rapid heat/cooling cycles can harm the cylinders. This process is referred to as SHOCK COOLING. Also oil temps can fall below the point at which moisture is boiled off during normal operation. Moisture is deadly to an aircraft engines health. Corrosion will develop on high stress surfaces such as cam shaft lobes, piston rings, cylinder walls and crankshaft bearings. It could also develop in the hub of a constant speed prop.

When cowl flaps are open they allow increased airflow to cool the engine. Normally during ground operations and takeoff the cowl flaps will be full open. Once in flight after reducing power you can partially close them to keep the temps up. Cowl flaps will not prevent overheating while on the ground. Particularly during the summer months. The pilot must be careful not to run at high power settings on the ground even with cowl flaps full open. With out the aircraft moving forward through the air there just isn't enough airflow through the engine compartment. Taxiing will help keep the engine cooler as opposed to just sitting there not moving at all.

Thats all for today class

Darren

Sorry for the unintentional misinformation on the cowl flap bit there[:0]

I'll go along with what Darren said regarding the doors on the MiG. Now that I can see clearer the area they cover altogether, my guess about blow in doors is still a possibility as well.

Thanks alot guys! Very interesting info and exactly what I needed to know. Thanks again!

Dana F

The aux air doors are spring loaded out, not in. The are used for aux air when the engine is running on the ground and whenever the aircraft is on the ground parked, without engines running. Once airborn, outside air pressure, as well as the intake pressure will suck them closed.

Jet engines require a large amount of air to operate. On the ground, the engine has to suck in air through the intakes. It still can't get enough air, so aux air doors help supply that air to the engines. Once airborn ram air will keep the engines operating, thus the aux air doors will close to prevent too much air from getting to the engine. In case of excessive air or pressure in the intake, air will be vented overboard to prevent stalling the engine.

So basically, if the aircraft is on the ground, the doors are always open?

Dana F

QUOTE: Originally posted by Bones-coa So basically, if the aircraft is on the ground, the doors are always open?

All reference photographs I have show the aux air doors open on the ground. They are also open with engines running on the ground. All but one inflight shots show the doors closed. That photograph also had the gear down, so landing gear position may also play a part in the position of the aux air doors.

A good reference is "MIG-19 Farmer in action" and "Modern Fighting Aircraft, MIG's" Vol 9.

Darren

Cowl flaps are also good for bugging pilots (especially if they're operating an old radial)

With buddy in cockpit, place several shop rags and hand tools in cowl flaps at bottom of engine. Hold in place while buddy closes cowl flaps. Leave aircraft and wait on pilot. when he appears, move to aircraft and offer to help preflight. Point out to him the cowl flaps need to be open for preflight and he needs to do it. If possible, get picture of his face as cowl flaps open, dumping rags and tools on ground. Pilots love this too, as long it isn't done to them.

I did have that happen me once but on a jet. pre-flight says to open certain panels and doors to check everything. I opened the door for the o2 and hydrolic guages to check for good pressure and two old guages, some tubing, nuts bolts etc went everywhere. I had to pay a pretty penny to get the photos and negatives back. Your right Q, it is funny if it isn't you. But I do laugh about it, only 10 years later.