Mini Delta Foam Rocket Glider Conversion

[Crawf56]

From time to time, I have wondered about taking an existing radio control model, and converting it into an RC ROCKET GLIDER. [Insert maniacal laughter: BWA-HA-HA-HA-HA ]

But I haven't had time, or I had other projects, or Frank at Dynasoar Rocketry comes out with a new kit that I simply had to have. However, I decided to take the plunge, before I get back into my large RC scale projects.

So, for your consideration: the Mini Delta. This was an RC delta wing foam model, with a pusher prop. It had poor flight performance, which I think was mainly due to control horn location on the elevons (more about that later).

 

[Crawf56]

The Mini Delta was made by Great Planes, at least 5 years ago (maybe more like 10 years ago.....).

Wingspan: 19 inches
Length: 15-1/4 inches
Current weight (no servos or electric motor; just the foam body): 55 grams

Tried to attach manual...???

 

[Crawf56]

More views. There is an existing front compartment, which would be good for storing receiver & battery. Servos were designed to be near the tail; I plan to relocate the servos closer to the center of gravity [CG].

 

[Crawf56]

And here is the butt; or the tail; or the aft fuselage. The electric motor was removed some time ago, and there appears to be space for a D motor. Very interesting.....

OK, I need a better picture.

 

[Crawf56]

Here is a better look at where I am planning to put the motor. Here is a D motor. Note that I would modify the fuselage so the motor won't stick out the back so much.

 

[Crawf56]

Which brings up the second reason for doing this build: all my old D motors.

I have gone through the experience of a $2 motor destroying $150 of RC model. But, in this case, I have an expendable model and expendable motors.

 

[Crawf56]

I am very open to comments and criticism on this build.

In general, I am planning to set the Mini Delta up so that, with a D12-0 plugged rocket motor, it is balanced on the CG. And will hopefully be able to glide back down.

I will be launching from an abandoned airfield/soy bean farm. Woo-hoo.

 

[Crawf56]

To get things started, I need a D-size [24mm] motor mount. Ordered one from Apogee:

https://www.apogeerockets.com/Build...m/Motor_Mount_Kit_24mm_29mm?cPath=42_166_168&

 

[burkefj]

Should work, may need a bit of downtrim to compensate for the drag of thethe th fins on boost, make sure the thrustline is straight...

 

[neil_w]

I know jack squat about RBGs but that looks pretty cool to me. Would D12's be a bit thrusty for such an airframe?

 

[Crawf56]

Should work, may need a bit of downtrim to compensate for the drag of thethe th fins on boost, make sure the thrustline is straight...

Yeah, getting the rocket motor situated will be THE challenge here.

 

[Crawf56]

I know jack squat about RBGs but that looks pretty cool to me. Would D12's be a bit thrusty for such an airframe?

Maybe. But the RC model was made to be a bit speedy. I am hoping I can get away with it, as long as I don't make any sudden course changes while the rocket motor is blazing.

 

[Crawf56]

Well, while I am waiting for parts, doing a little work.

I believe one of the problems with this aircraft was the location of the control horns for the elevons. They were located on the inner edge of each elevon; due to the 'softness' of the foam used for the elevons, the elevons did not respond well to my controls. So, I snipped off the existing black control horns. (see pic)

I am planning to locate my control horns much closer to the middle of the elevons. The middle section of the elevons is more rigid, and should provide better control.

 

[Crawf56]

OK, my box of goodies from Apogee Components arrived today. Including my motor mount kit.

 

[Crawf56]

Got the motor mount assembled. For D (24mm) motors.

 

[Crawf56]

OK, quite a bit going on here. Drew a line down the middle of the fuselage, and use this to align the motor.

The wings have a flat bottom, so I arranged the model so that the bottom of the wings were level. I then used a level to make sure the motor mount was parallel with the bottom of the wing.

I glued the motor mount in place with 30 minute epoxy (which gave time for adjustments). Once the epoxy has dried overnight, I will go back and fill in gaps with hot glue.

 

[burkefj]

Looks good, you may get a bit of pitch up with the low thrust line compared to the drag of the wing/vertical stabs, may want to put in a touch of down trim or be ready on boost. I like the color. I'll be curious to see how well the elevons work in nose heavy burnout mode, they look small to me in width...but they are full span.

 

[Crawf56]

Looks good, you may get a bit of pitch up with the low thrust line compared to the drag of the wing/vertical stabs, may want to put in a touch of down trim or be ready on boost. I like the color. I'll be curious to see how well the elevons work in nose heavy burnout mode, they look small to me in width...but they are full span.

Which brings up a question: Where to locate the elevon servos?

As stated earlier, one of the problems with this model was the location of the elevon control horns. Being located on the inner edge of the elevons, the control horn location did not provide good movement.

So, my thought is to change the control horn location to the middle of the elevons, or at least 1/3 the length of the elevon. But if I do this, where should the servos go. Should I put the servos out on the wing? Or put the servos next to, or even into, the fuselage? And run a pushrod to the control horn at an angle?

The elevons are a bit flimsy, but I think I can overcome this issue by changing the control horn location.

 

[burkefj]

Centering the horns may help, but if the hinge is stiff, if it is a live hinge it may be easier to remove/cut the hinge and re hinge them with blenderm tape so they move freely.

 

[Crawf56]

Here are some of the parts I am using for the elevon work.

 

[Crawf56]

Marking the servo location. The line on the wing is the Center of Gravity [CG].

 

[Crawf56]

Cut out foam with an xacto knife.

 

[Crawf56]

Pushrods made from .047" wire.

 

[Crawf56]

Install the servos.

 

[Crawf56]

Installed the servos in the fuselage, then the control horns on the elevons. Bent the pushrod to fit, and assembled.

 

[Crawf56]

An overall look.

 

[Crawf56]

At which point, I had an attack of "build fever".

"Build fever" is when you get moving on a project, and you don't stop to review what you are doing.

Instead of measuring my pushrods to make sure the have the same shape, I sort of 'eye-balled' it. The result is that my right pushrod was bent at a different location than the left pushrod. The elevons would probably function ok, but I need to make the pushrods match.

 

[Crawf56]

OK, pushrod on right is a little better. Maybe....

 

[Crawf56]

When you take a model, and starting putting parts in places where they are not supposed to go (like the servos), you create new problems.

When I moved the servos to the mid-point of the fuselage, their new location interfered with the 'hook' on the canopy/cover. (See where the pencil is pointing.)

I also had to widen the compartment a little for the receiver.

 

[Crawf56]

The fix for the canopy/cover was pretty simple: cut away some parts of the hook.