What Is a "Blip" Switch?

[Roadhog]

Dear fellow Forum members, What exactly is a "blip" switch and what did it do? It is my understanding that this device was used only on rotary engine aircraft. Would a Sopwith Camel and a Siemen's Schuckert D-III/D-IV have them installed?

Thanks for any help, Roadhog "Memento mori."

[se5a12]

Hello,
It is my understanding that rotary engines tend to run constantly and the only way to slow them down is to cut the ignition.This is achieved by a blip switch that cuts the ignition to some of the cylinders.There are dangers however from overdoing this as the fuel tends to still flow and when the ignition is reapplied there could be a small explosion and fire....

[Makhpiyaluta]

Roadhog,

SE512 is right since a rotarie runs full power because you can only set the air and fuel mixture you need a device to go down on power. This is indeed done by cutting the ignition. Once someone said about rotaries 'It's like driving your car with the pedal down and stop for a trafficlight by switching of the ignition when the light go's green you just turn on the ignition still having the pedal down' Here you can see our one running although it's a short video.
http://www.luchtvaartnieuws.nl/video...gels-deel3.asp

Willem

[Maxim08]

Well, I'm no great authority on rotaries, but I have started and run a 110 leRhone in a triplane replica. The owner/pilot, Fred Murrin, showed me how to balance fuel and air for the start and how to throttle up and down. So yes, a leRhone does have a throttle and yes, it controls engine speed.
Not having flown the airplane I can not comment on how the blip switch is really used but I can state that it's a hell of a lot of fun to sit there going bbbrrraaaapppppppp brraapp braapp bbrrraaappppp!!!!
Regards,
Maxim08

[TomVrille]

One of the principal uses of the "blip switch" involved ground handling. The early rotary engines that had no throttle capability at all were particularly challenging. Cecil Lewis wrote a charming little piece about taking off in an Avro 504, with a 100hp Monosoupape that had only two speeds, on and off. He wrote:

"So the 'vital actions' in the cockpit were simple. You turned on the petrol and opened a 'throttle' needle valve which supplied juice to the crankcase. The mechanic then 'sucked in', that is to say, he spun the propeller, so that petrol vapour would pass up through ports in the cylinder wall into the cylinders and there combine with air drawn in through a little suction valve on the cylinder head. This valve was uncontrolled and just sucked air as long as the piston moved down. The resultant mixture was explosive only if the correct amount of vapour had got into the cylinder__ and everything was designed for this to work only when the motor ran full out. So, after 'sucking in' till most of the cylinders were full of mixture, the mechanic called 'Contact!' The pilot switched on, the mechanic heaved on the propeller, there was a roar as the engine caught and you were immediately ready to take off!

But as this was usually impossible straight off the tarmac, it was necessary to taxi. To do this the engine had to be switched on and off and indeed a bellpush, or button switch, had been carefully fixed on the top of the mahogany joystick for this very purpose. So no sooner had the engine 'caught' than you 'pressed the tit', as we used to say, and stopped it again and then kept bursting it 'Brr-rp! Brr-rp!' as you waved away the chocks. Put the rudder hard over: Brr-rp Brr-rp, and the tail was thrown round. Reverse rudder: Brr-rp Brr-rp, and it was straight again. So in a series of Brr-rps you proceeded down wind, swung round, took your finger off the button and let her go!"

The above passage from Farewell to Wings describes the original blip switch. Later development allowed ignition to be cut off for specific cylinders, providing a degree of throttle capability.

[Lufbery]

Originally Posted by TomVrille

The above passage from Farewell to Wings describes the original blip switch. Later development allowed ignition to be cut off for specific cylinders, providing a degree of throttle capability.

Thanks, Tom, for that passage.

There's been a lot of discussion over the years on this board regarding whether rotaries could be adjusted and to what extent.

The simple answer, as Maxim08 indicates, is that rotaries generally did have controls for adjusting the fuel/air mixture and RPMs.

The blip switch cut all power to the ignition and caused a rapid slowing of the engine while it was held down. It allowed for very quick changes in engine speed, and was most useful during landing, while diving, and while taxiing.

Even those planes that could adjust the ignition to take more than one rotation to fire all the cylinders (like the Camel), had a blip switch.

Regards,

[retread]

At least one of the later rotaries ( I want to say the 160hp Gnome 9N) had a dual option as regards its blip switch depending of which magneto you were running off of. With the selection of one magneto you were either full power or off, while the selection of the second magneto gave the pilot a choice of 1/2, 1/4 , 1/8 power or off. On the 1/2 power option every second cylinder was fired, on the 1/4 power every fourth cylinder and so on.

[timjnf]

This old thread from this forum has lots of info. An references some even older ones.

http://www.theaerodrome.com/forum/sh...ad.php?t=17121

[Taz]

Fred Murrin has a great article on rotary eingine operation in the summer 05 OTF which answers just about all the question asked in this thread. The throttle on the Le Rhone would allow rpms from about 600 to 1200 on the ground. In the air, however, the idle position gave 800 or so rpms on approach because of windmilling of the prop, and this was too high for landing. The blip or coupe switch then allowed engine revs to decrease enough for landing and fine tuned them for taxi.

The early Gnomes did run unthrottled and had a tendency to pool unburned fuel in the cowling if the fuel control was not retareded during power off descents (ignition grounded with the blip switch). The 160 Gnome, as retread stated, had a five position switch to prevent this. One position was off, and the other positions fired all the cylinders at different rotation rates. One would fire all the cylinders on each 4 cycle rotation, the next all the cylinders at half that rate, and so forth. This prevented the plugs from fouling with unburned petrol.

The blip or coupe switch, depending on whether you were British or French trained, fine tuned the results. read Fred's article for way more information. It is the best treatment on rotary engine operation I have read.

Taz
Terry Phillips

[greatwarpilot]

I have to agree with Taz. Fred has one of the best understandings of how these engines operate, and his article addresses many of the persistent rumours circulating about rotary engines.

One of those very rumours has just been raised by Retread, and addressed by Taz. Namely the belief that only some of the cylinders fired on the Gnome to slow down the engine. As Taz correctly points out this was actually achieved by firing ALL the cylinders, but only after a set number of revolutions of the engine (depending on the switch position).

In any case, Lufbery is correct. Blipping should really be used if necessary at start up, taxi, approach and landing. In a dive shutting off the fuel was still a valid practise even with later rotaries, as opposed to blipping.

Also noteworthy is that excessive blipping at full power, however interesting it might be for an assembled crowd, is in fact rather nasty to the engine and as such should be kept to a minimum. As I found out when given the chance to run a 120 LeRhone on the ground, the fuel and air levers really do give a significant amount of control. Blipping should really only be done from a low power setting if one wants to avoid damaging the engine.

Sincerely

Edward