Lengthening noses on nostalgia designs?

[chlee]

Hi everyone,

I am studying the wreckage of a well-made Mirage (112" span design by Blaine Rawdon). The builder had stuffed the nose with 3-4 ounces of steel bolts in addition to his standard servos and full-size Rx pack. With my modern equipment (HS-81, 555 Rx, NiMH pack) and fair building skills, I'm afraid I'll require a huge amount of nose ballast for this same design.

This is probably a common challenge when building classic designs that were intended for full-sized equipment. What are the costs of lengthening a nose by two or three inches? Would there be more drag (more sluggish air dumped over the wing center section?) or less yaw stability? Would it still be worth the weight savings?


Thanks for your opinions/advice,
- Chung

[xtc]

Hi everyone,

I am studying the wreckage of a well-made Mirage (112" span design by Blaine Rawdon). The builder had stuffed the nose with 3-4 ounces of steel bolts in addition to his standard servos and full-size Rx pack. With my modern equipment (HS-81, 555 Rx, NiMH pack) and fair building skills, I'm afraid I'll require a huge amount of nose ballast for this same design.

This is probably a common challenge when building classic designs that were intended for full-sized equipment. What are the costs of lengthening a nose by two or three inches? Would there be more drag (more sluggish air dumped over the wing center section?) or less yaw stability? Would it still be worth the weight savings?


Thanks for your opinions/advice,
- Chung

maybe go with a v-tail?

xtc

[BMatthews]

Bear in mind that even though you end up using more lead or whatever the overall model weight will still come out to the same amount in the end and it'll fly the way it was originally designed to fly. What you gain in lighter equipment just goes back into the nose and the overall weight remains the same in the end. (actually there would still be a slight reduction as the weight you save in radio can go into the extreme nose where it has better leverage so you would save a 1/2 to 1 ounce or so)

Lengthening the nose certainly IS an option but keep in mind that the overall flying charactaristics will change if you do it by much. The model will be lighter and the penetration ability is going to suffer a little as a result.

[Mark Miller]

Instead of adding weight to the nose concentrate more on making the rear of the plane lighter. Sand until you think it is right and then sand some more. Take it easy with the glue too making that fuselage andtail. It adds up quickly and because of the mechanical advantage of things in the rear 1 oz saved in the rear might save 2 oz's in the nose. Remember that by lengthining any part of an airplane you are increasing the inertia around which that part rotates. Thats why you want to keep those wing tips light. It will produce a good turning plane. Longer or heavier nose or tails will increase pitch and yaw inertia.

As far as the Mirage goes all the ones I have built from the short kit balance well even using smaller radio gear. You can figure about 35 to 37 oz. depending on what you add. My buddy Augie has a Mirage with spoilers and it comes in at 37 oz. no weight needed to balance it either.

BTW...I have just gotten permission and rights to make a full kit of the Mirage. I also just for rights and tooling to the Mark's Models Mini Bird of Time and rights to produce the 2 meter RO-8. This is going to be a fun year.

Mark Miller
Isthmus Model Co.
www.isthmusmodels.com

[fprintf]

Nice to hear you won the rights to the mini BOT - weren't they on ebay for little money earlier this month? Very cool! For me, I'd love a Mirage but it'd have to sit in the basement for a few years until I get really good at building light!

[BMatthews]

Mark, as owner of a RO8 I would like to compliment you on your taste in designs... :D

However I DO hope you can do better than the original kit maker. Not that it would be difficult. The original kit I got was so bad that after reviewing my completed model I realized that I had used only the plans, some strip wood and the trailing edge stock from the original kit. The ribs, spars, fuselage sides and pretty much all the rest was junk of the worst order. Even the plywood sides were so brittle and weak that I broke the first part off one just taking it out of the box. I like the design but I sure didn't like the kit.

[Ollie]

The Mirage was designed for a light wing loading. Three or four ounces if nose weight indicates that the fuselage and tail were not built with the light materials and finish intended by the designer. In that sense it is not a "well built" fuselage. Rather than repairing the fuselage a new fuselage and tail built to the designer's intent to keep the weight down is in order. You can do it with light balsa, light weight linkages, light film covering. There are all sorts of weight saving tricks. Gluing the control horns into slots in the control surfaces saves metal screws and nut plates. Small nylon clevices are plenty strong enough and much lighter than metal. Carbon pushrods in teflon tubes are lighter than almost any other pushrods and housings. Ultra coat light or Micafilm are ligher than most other film coverings and much lighter than painting the fuselage. Reducing the mass of the fuselage will also make it more survivable because less kenetic energy will have to be dissipated in an abrupt arrival. Keeping the extrimities light improves maneuverability and lift signalling a bunch.

[Mark Miller]

Bmatthews,

The new RO-8 kit will be laser and machine cut. None of the original tooling survives so it will have none of the originals problems in that area. Same goes for the Mini Bird of Time. I do have the tooling but it will be laser cut now.

A lot of good designs have been compromised by poor kitting or changes for the sake of easier manufacturing or economy. There is nothing as nice to fly as a good design using the right wood in the right places. Good building practices help a lot too. Ollie has a lot of good points in the above post that will help give you the plane you deserve.

Mark Miller

[markdrela]

The Mirage was designed for a light wing loading. Three or four ounces if nose weight indicates that the fuselage and tail were not built with the light materials and finish intended by the designer. In that sense it is not a "well built" fuselage.

The Mirage that chlee is referring to was built by a friend of mine, from a kit which had rather heavy tail wood. He's a good builder, but was very pressed for time when he built it, and didn't have the time to run out to the hobby shop for light replacement wood. He also used straight Monokote on the tail, since he didn't have any lighter covering.

For the record: The original Mirage kit was of exceptional quality. It was later bought out, and the new manufacturer turned the kit into heavy die-crunched junk.

[rogerflies]

"The model will be lighter and the penetration ability is going to suffer a little as a result."

Why? If the plane weighs less, the drag is reduced because the wing doesn't have to produce as much lift. Flying it at a lighter weight won't be a problem.

Heavy planes fly fast because they have to. Light planes fly fast when you want them to; just put in a little down trim.

I've got a Lovesong which weighs 72 ounces, which is less than most I've seen. With no reflex and no ballast, the speed range was still more than enough for the windiest days. Taking out a few clicks of down trim put it back in the floater category. You can't do that with ballast.

The speed range of a lot of the early models was limited because the structure wasn't rigid enough to prevent flutter. Adding ballast only aggravates that situation.

After I had developed some skill as a pilot and had learned how to build light, the only model I lost downwind was the one that blew up from flutter.

Roger

[chlee]

Thanks for your replies, folks. (Sorry, I was out of action for a while because of exams in school.)

Prof. Drela did warn me last year not to reuse the horizontal stabilizer, because it's heavy. Taking his standards into account, I'd just assumed it was a bit portly but still within a reasonable range for an average builder. But, I just weighed it this morning: 50 grams/1.8 oz. (I should have done this earlier. :p ) For reference, the similar-sized BD stab is listed at 21 grams and is intended for much higher loads. After learning this and the model's full story, I now think it's entirely possible for me to save an ounce in the tail and forgo much of the nose weight in my own build. So indeed, Ollie, Mark Miller, you're right. Even if I still add a bit of noseweight because of the light radio gear as BMatthews says, it won't be as painful as I thought.

This is encouraging. I infer that Monokote isn't necessary for torsional stiffness in the tail. So, I'll try contest-grade balsa and something like Solite or Doculam for the tail.

Mark, I look forward to the release of those kits, as well as the other very interesting projects that you're working on.

Thanks,
- Chung