18mm engine in 18mm tube - Hi-Flyer vs. Yankee methods

[SolarYellow]

The Hi-Flyer uses a conventional steel engine clip inserted through the outside of the tube with an over-ring to secure it. This adds aero drag and also a slight weight imbalance to the rocket. The ring is particularly pernicious, potentially, in that it trips turbulent flow around the whole body tube, potentially reducing the effectiveness of the part of the fins closest to the tube. This might be a small contributing factor to the Hi-Flyer's stability challenges. The method also adds mass behind the c.g., which reduces stability.

The Yankee uses masking tape wrapped around the engine to make it a snug push fit into the tube. This is lighter, cheaper, and creates no additional aero drag on the outside of the tube. I'm tired of winning (not really).

Thoughts about recovery:
With the Hi-Flier system, as the rocket comes down, it's likely to land on the engine. Having the engine clip possibly hit first drives the impact right past the engine up against a concentrated portion of the engine block. Given how far the bent tang on the engine clip protrudes past the engine, this is likely to occur. One way it wouldn't is if the rocket was swinging far enough to be angled the other direction and catch the side of the engine without the clip. In that case, on level ground, the force would also be distributed significantly laterally into the tube, but you might also be hitting fins. Could also happen that way with less wing due to uneven ground, a rock, whatever.

The Yankee's fins will hit first, and I guess having the engine held into the tube only by friction may allow it to slide out a little on impact, reducing the forces tending to damage the fins. But if you used this method in the Hi-Flyer design and landed on the engine first, the heaviest and toughest part of the rocket which is about to be discarded anyway would get the impact, and it would be distributed to the rest of the rocket on the whole surface of the engine block and through the ring of masking tape to the tube.

Both work well. Surely tens, maybe hundreds of thousands of Yankees have been built and flown successfully, so it's certainly safe and effective. If it made you feel better, I could see using tape wraps in two locations to ensure more perfect parallelism of the engine and tube.

I can't figure out why you'd use the Hi-Flyer method with the extra weight and drag.

Anyone else know something I haven't thought of regarding this?

 

[tsmith1315]

Quick and easy to pop a motor in and out with a hook. Some folks are a little apprehensive about friction fitting with tape.

Both are valid techniques, IMHO.

 

[Back_at_it]

The Hi-Flyer uses a conventional steel engine clip inserted through the outside of the tube with an over-ring to secure it. This adds aero drag and also a slight weight imbalance to the rocket. The ring is particularly pernicious, potentially, in that it trips turbulent flow around the whole body tube, potentially reducing the effectiveness of the part of the fins closest to the tube. This might be a small contributing factor to the Hi-Flyer's stability challenges. The method also adds mass behind the c.g., which reduces stability.

The Yankee uses masking tape wrapped around the engine to make it a snug push fit into the tube. This is lighter, cheaper, and creates no additional aero drag on the outside of the tube. I'm tired of winning (not really).

Thoughts about recovery:
With the Hi-Flier system, as the rocket comes down, it's likely to land on the engine. Having the engine clip possibly hit first drives the impact right past the engine up against a concentrated portion of the engine block.

The Yankee's fins will hit first, and I guess having the engine held into the tube only by friction may allow it to slide out a little on impact, reducing the forces tending to damage the fins. But if you used this method in the Hi-Flyer design and landed on the engine first, the heaviest and toughest part of the rocket which is about to be discarded anyway would get the impact, and it would be distributed to the rest of the rocket on the whole surface of the engine block and through the ring of masking tape to the tube.

Both work well. Surely tens, maybe hundreds of thousands of Yankees have been built and flown successfully, so it's certainly safe and effective. If it made you feel better, I could see using tape wraps in two locations to ensure more perfect parallelism of the engine and tube.

I can't figure out why you'd use the Hi-Flyer method with the extra weight and drag.

Anyone else know something I haven't thought of regarding this?

Nope. You are right on track. Having a motor clip with a retainer outside the tube makes no sense and looks like crap. I've built a few Hi-Fliers and have never even considered using the clip and ring. Throw them directly in the parts bins every time. Come to think of it, I have never seen one in person that used that method. Nobody I know builds them that way. Only seen them here on the forums.

Only recommendation I can give you is to be sure that the motor block that you put inside the Hi-Flier is glued in WELL as you are correct that the motor hits first and it shocks the motor block. I have seen them some loose.

 

[mh9162013]

I agree that the motor hook is an inelegant form of motor retention (as well as high-drag). But it's potentially more secure than the friction method. So it's one of those "pick your poison" type of decisions.

 

[neil_w]

I'm in the camp that hates friction fitting, and puts hooks or retainers on all my rockets.

However, an external hook on a minimum diameter rocket is indeed kind of ugly, and I couldn't fault anyone for using friction fit in such situations. MD motor retention is always a fun topic.

I do think you're way overthinking things like off-center mass of the hook and effect on landing, though.

 

[mh9162013]

an external hook on a minimum diameter rocket is indeed kind of ugly

Understatement of the day.

Before building a minimum diameter rocket that uses 18mm engines, I always consider the possibility of launching it off of 13mm mini engines and using a retainer screw system from the Bandito.

I wish they made a 13mm "B" engine that used composite propellant...

 

[dhbarr]

If you refly a Yankee a bunch of times, even if it's sealed and painted the tube does give up. Presumably the spring clip would be a bit more durable.

Source: my kid flew one 15-20 times at NARAM for some reason.

 

[mh9162013]

even if it's sealed and painted the tube does give up.

Are you referring to the fact that the main body tube stretches out over time due to the high number of launches?

 

[lakeroadster]

Some folks build for looks, some build for durability, some build for simplicity.

Friction fitting is an acquired skill and thus there are risks associated with the technique.

Using a motor hook = no risk. Well, for sure minimal risk.

 

[Back_at_it]

Generally speaking. Most BT20 rockets get lost long before the body tube stretches out of shape or ruptures. I do absolutely agree with MH that many of the common small rockets like the wizard, Yankee, hi flier will give great flights in13mm motors.

I have more than a few that have been built that way. In fact I think both of my current wizards are 13mm and they fly well out of sight

 

[mh9162013]

In fact I think both of my current wizards are 13mm and they fly well out of sight

Have you ever launched them with an altimeter?

My "napkin" calculations would put a stock Wizard/Viking/Yankee at b/w 325 and 375 feet using an A10-3T or A3-4T

 

[dhbarr]

Are you referring to the fact that the main body tube stretches out over time due to the high number of launches?

More of the layers of the tube separating from being taped and retaped and landed on and motor-in / motor-out over and over.

 

[mh9162013]

More of the layers of the tube separating from being taped and retaped and landed on and motor-in / motor-out over and over.

Oh, ok, thanks for the clarification.

I won't be doing that with my minimum diameter rocket for that very reason (as well as the fact that I don't want to ruin the paint job).

 

[beeblebrox]

Understatement of the day.

Before building a minimum diameter rocket that uses 18mm engines, I always consider the possibility of launching it off of 13mm mini engines and using a retainer screw system from the Bandito.

I wish they made a 13mm "B" engine that used composite propellant...

There used to be... AeroTech made the B7... I still have about four of them. Early 1990's vintage. I am now making C26 motors, 13mm x 70mm

 

[mh9162013]

I am now making C26 motors, 13mm x 70mm

Can you provide more info?

 

[beeblebrox]

Can you provide more info?

Note: These are EX motors, I cannot sell them...

 

[bjphoenix]

In the old days there were a lot of 18mm rockets and everything used friction fit. Friction fit is a little bit of a hassle but it works, however I like the clips when the main airframe is larger than the motor mount. I noticed that earlier clips just came to the back end of the motor, newer clips have a piece that projects beyond the end of the motor. I've wondered what this does when it impacts the ground and whethere there is any advantage to removing that part.

 

[mh9162013]

I've wondered what this does when it impacts the ground and whethere there is any advantage to removing that part.

Reduced weight and a higher CG, at the very least. But it's a little harder to insert or remove an engine with that part removed. And the edge/end of the hook might be more likely to scratch or otherwise harm someone.

 

[Back_at_it]

Have you ever launched them with an altimeter?

My "napkin" calculations would put a stock Wizard/Viking/Yankee at b/w 325 and 375 feet using an A10-3T or A3-4T

Only one flight on a Wizard with an altimeter. They don't fit well and I only had a partial ejection. Broke a fin on landing so I never did it in a BT20 after that.

On an A10-3T I recorded 581ft.

 

[mh9162013]

Only one flight on a Wizard with an altimeter. They don't fit well and I only had a partial ejection. Broke a fin on landing so I never did it in a BT20 after that.

On an A10-3T I recorded 581ft.

Impressive!

What altimeter did you use in that flight?

 

[dhbarr]

Have you ever launched them with an altimeter?

My "napkin" calculations would put a stock Wizard/Viking/Yankee at b/w 325 and 375 feet using an A10-3T or A3-4T

The Yankee did ~200 feet on a C6-7...

... CATO, according to our FlightSketch mini.

 

[mh9162013]

The Yankee did ~200 feet on a C6-7...

... CATO, according to our FlightSketch mini.

But the FS Mini was ok, right?

 

[Back_at_it]

Impressive!

What altimeter did you use in that flight?

FS Mini