Does cheater holes make a jet faster?

[JieZ]

Hi, I have a question in mind.

Does cheater holes make a edf jet fly faster?
Where do people usually cut the cheater holes?

[joe yap]

Nope. They slows down the plane. They are used to compensate for the lack of ram air at or near static condition, when the fan unit is more likely to starve from air going through the intake. Once the model is moving, the ram air will supply more air into the intake and the total air intake from the inlets and cheater hole will be excessive for the fan unit, thus creating additional drag.

The most common place to cut cheater holes is just before the fun unit itself. This hole was also common used as an access to start the glow engines on old gas powered duct fan designs.

I've seen a clever ducting design on at particular EDF model before. Just behind the inlet cheeks, the designer incorporated a few small auxiliary air inlet doors, with a lightly spring loaded doors. When the fan is starving at or near static conditions, the negative air pressure in the inlet plenum will overcome the light spring load and cause the doors to open, allowing additional air in enter into the plenum. When the model starts to accelerate, the pressure in the plenum will increase due to ram effect and the doors will spring shut.

You can see the same design used on the full size Harrier jumpjets. The A380 hydraulic system air-cooled heat exchangers uses similar design.

[JieZ]

Nope. They slows down the plane. They are used to compensate for the lack of ram air at or near static condition, when the fan unit is more likely to starve from air going through the intake. Once the model is moving, the ram air will supply more air into the intake and the total air intake from the inlets and cheater hole will be excessive for the fan unit, thus creating additional drag.

The most common place to cut cheater holes is just before the fun unit itself. This hole was also common used as an access to start the glow engines on old gas powered duct fan designs.

I've seen a clever ducting design on at particular EDF model before. Just behind the inlet cheeks, the designer incorporated a few small auxiliary air inlet doors, with a lightly spring loaded doors. When the fan is starving at or near static conditions, the negative air pressure in the inlet plenum will overcome the light spring load and cause the doors to open, allowing additional air in enter into the plenum. When the model starts to accelerate, the pressure in the plenum will increase due to ram effect and the doors will spring shut.

You can see the same design used on the full size Harrier jumpjets. The A380 hydraulic system air-cooled heat exchangers uses similar design.

I see...I'll research on that.Thanks!
Was actually thinking how to increase speed of my EDF instead of just upgrading my setup

[mirage2k]

cool, wondering any cool pics or technicals on the spring cheater holes? amazing

[wireless]

J-35 stock plane come with 12 cheater holes...

[darenlsl]

Joe is correct. Cheater holes improve your thrust but does not improve your speed. It actually slows down the plane creating drag and air turbulance both inside and outside the plane. It does however, aid your take off. Especially for hand launching. As it increase the static thrust of the plane.

Nope. They slows down the plane. They are used to compensate for the lack of ram air at or near static condition, when the fan unit is more likely to starve from air going through the intake. Once the model is moving, the ram air will supply more air into the intake and the total air intake from the inlets and cheater hole will be excessive for the fan unit, thus creating additional drag.

The most common place to cut cheater holes is just before the fun unit itself. This hole was also common used as an access to start the glow engines on old gas powered duct fan designs.

I've seen a clever ducting design on at particular EDF model before. Just behind the inlet cheeks, the designer incorporated a few small auxiliary air inlet doors, with a lightly spring loaded doors. When the fan is starving at or near static conditions, the negative air pressure in the inlet plenum will overcome the light spring load and cause the doors to open, allowing additional air in enter into the plenum. When the model starts to accelerate, the pressure in the plenum will increase due to ram effect and the doors will spring shut.

You can see the same design used on the full size Harrier jumpjets. The A380 hydraulic system air-cooled heat exchangers uses similar design.

[JieZ]

Joe is correct. Cheater holes improve your thrust but does not improve your speed. It actually slows down the plane creating drag and air turbulance both inside and outside the plane. It does however, aid your take off. Especially for hand launching. As it increase the static thrust of the plane.

Oh.If i were to make my jet faster,The only option is to upgrade the powerplant?

Wow 12 cheater holes! Thats alot

[joe yap]

Oh.If i were to make my jet faster,The only option is to upgrade the powerplant?

Wow 12 cheater holes! Thats alot

Or minimise losses. I also believe choosing a good airfoil should allow the model to cruise at lower angle of attack, saving a lot of drag.

12 cheater holes, probably much more structural sound than cutting a big hole on the thin moulded fuselage. Save the need for beefing up the structure.

[darenlsl]

Or minimise unimportant weight, reduced drag, try different fan design, play around with thrust tubes, smooth the outerskin, smooth the intake, round the intake corners, use he intake ring, stop air from colliding in the intake, so many things to do for EDFs! that why I am hooked! ke ke EDF!

[randomtask]

Oh.If i were to make my jet faster,The only option is to upgrade the powerplant?

Wow 12 cheater holes! Thats alot

Actually there's 14 holes hehe. It's the "holiest" plane I've seen. Yet it's a speedy little devil.

Ok, got that out of my system. Sorry for the OT.

Cheers,
Adnan

[JieZ]

Or minimise unimportant weight, reduced drag, try different fan design, play around with thrust tubes, smooth the outerskin, smooth the intake, round the intake corners, use he intake ring, stop air from colliding in the intake, so many things to do for EDFs! that why I am hooked! ke ke EDF!

Wow, so much more things for me to learn

[JieZ]

Actually there's 14 holes hehe. It's the "holiest" plane I've seen. Yet it's a speedy little devil.

Ok, got that out of my system. Sorry for the OT.

Cheers,
Adnan

That's gonna be my next plane.
I feel the need, The need for speed!

[blueangel]

Or minimise unimportant weight, reduced drag, try different fan design, play around with thrust tubes, smooth the outerskin, smooth the intake, round the intake corners, use he intake ring, stop air from colliding in the intake, so many things to do for EDFs! that why I am hooked! ke ke EDF!

Does it really improve or butt dyno ? Full scale plane maybe, but we are flying a small model and air density doesn't reduce correspondingly to our scale.

Just like sailing ship / boats.. for any reduction is scale size, the waves are still as big..

[jansonfinn]

Does it really improve or butt dyno ? Full scale plane maybe, but we are flying a small model and air density doesn't reduce correspondingly to our scale.

Just like sailing ship / boats.. for any reduction is scale size, the waves are still as big..

Bro, i think if u r talking abt waves for sailing ship / boats, it will be wind for plane.

In this case, it is more abt the air intake of the plane. Dun forget it's scaled down model with scaled down powerplant too. It will be directly proportional in this case. That is y during designing stage of a plane or a car, the designer will first use scale model to do testing in the wind tunnel first before constructing the 1:1 scale

[joe yap]

[QUOTE=blueangel;428069]Does it really improve or butt dyno ? Full scale plane maybe, but we are flying a small model and air density doesn't reduce correspondingly to our scale.

[QUOTE]

I don't really get what you mean by butt dyno here, but our ducted fan system for models are simple designs that only allows relatively small envelope for performance. The system designs can only strike a compromise between maximum static thrust and velocity and at a certain flying speed. Operating at any speeds or ambient conditions will result in losses somewhere. But we don't fly our models at one fixed speed only, thus we are always running the system at a loss. For that reason, our ducted fan systems have relatively poor efficiencies.

With enough knowledge and skill, you can always incorporate gadgets to enhance the efficiencies by taking care of the airflow in the ductings and changing ambient conditions.

If you want me to explain more, I can go into the details, but it'll probably be too much to swallow for most.

The most obvious difference in operating models these size versus the fullsize, is that our models need to fly at much higher speed than scale to fly well. As for performance wise there is still a lot of things that can be done although the size and weight is the limiting factor. Simple theory from Bernoulii's theorem still applies and you will get the penalties if you don't follow.

Just to give a simple example. Most EDF models in the market, have (excuse me) very poor ducting and fan design. Many decades ago, Mr Bob Violet and Scozzi had done a wonderful job of explaining and designing the most ideal and yet practical ductng system. Even the lower end Cox TeeDee 0.049 engine powered Axiflow unit from Midwest also follow the design as much as they can. Today's powerful brushless motors and Lipo packs have made designers and manufacturer becoming complacent in thier designs. Folks are still getting away from the poor designs by pumping gobs of power to the units, which often ended up with some damaged components, in order to achieve the so called spectacular performance. Poor ducting designs often robs the useful work away from the system, although I do not have any figure, is plenty lot.

A good understanding and simply by minimising the losses, you'll get a big boost in performance. I remember reading an article from a Magazine, describing the improvements in the ducting system of the old Kyosho T-33, will turn this dog into a chilli pepper, even on stock motor.

If you are still there, give me a hint before I go on.