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Sep 21, 2021, 04:31 PM
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Discussion

Effects of having three flight planes


I want to build a copy of a Mig prototype, which looks like it is based on the Mig 21: the Ye-8.
-image-

The intake position solves breathing difficulties for the EDF unit.

A 90mm EDF can suck more air than will pass through the normal MIG 21 intake system.

As you can see, the Ye-8 has a forward canard wing as well as an elevator.

1) Can I link elevator and canard in opposite rotation?

2) Can the centre position of the front canard and rear elevators be different?

3) Can the front canard plane alternatively remain fixed at the same pitch as the main wing?

4) does the COG need adjustment to account for the front canard wing?

These Mig 21-type aircraft seem to need the COG well forward of where you would expect.

Possibly the delta main wing has a strong pitch-up tendency?
COG tends to be forward of the main wing AC.

5) Option 1 seems better, but would it be stable?
The rear elevators move as a unit, and have more area and leverage than the front canard.

6) Option 2 could cause the front plane to stall during rotation about the main wing, as the air flow in its location
will have a huge pitch angle.
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Sep 21, 2021, 05:02 PM
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Coupez's Avatar
Quote:
Originally Posted by Owen_bern
4) does the COG need adjustment to account for the front canard wing?
Yes.

The answers to all the other questions depend on what you want the canard to do.
Sep 21, 2021, 08:01 PM
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Quote:
Originally Posted by Coupez
Yes.

The answers to all the other questions depend on what you want the canard to do.
I want the canard to look good for scale effect, but otherwise keep out of the way.

It looks like part of a computer stability control system, which I do not want to get into.

I could just make it flop around in the breeze, maybe with very light spring loading.
an axis slightly ahead of the canard AC should do this?
Sep 21, 2021, 08:10 PM
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Coupez's Avatar
As usual, it looks like you are well into Stage One of the "Six Stages of a Project":

1) Wild Enthusiasm
2) Disillusionment
3) Total Failure
4) Search for the Guilty
5) Punish the Innocent
6) Promote the Uninvolved

The best way to prevent a project from following this typical course is to begin with Stage Zero:

0) Definition of Requirements

What do you want this model airplane to do?

What attracts you to it, other than "it looks cool"?
Sep 21, 2021, 08:56 PM
Registered User
Thread OP
Quote:
Originally Posted by Coupez
As usual, it looks like you are well into Stage One of the "Six Stages of a Project":

1) Wild Enthusiasm
2) Disillusionment
3) Total Failure
4) Search for the Guilty
5) Punish the Innocent
6) Promote the Uninvolved

The best way to prevent a project from following this typical course is to begin with Stage Zero:

0) Definition of Requirements

What do you want this model airplane to do?


What attracts you to it, other than "it looks cool"?
Well , I think the Mig 21 is a good starting point.

1) it is historically significant.

2) It has a single tailpipe, and is about right for a 90mm EDF unit.

3) It has a quaint character, that more modern aircraft are lacking.

Probably the Mig 33 proposal would do the job, if I could get good drawings of it.

4) The Ye-8 is a development of the Mig21, and it has a better air induction system for an EDF model.

5) it would be nice to keep the front plane, if it didn't damage the model behaviour, for the sake of scale looks.
The design I want to use does depart from scale in several other areas, but it would be nice to keep that feature.

6) My absolute ideal would be to have the whole thing be totally VTOL and EDF, but I can't think of a way to do that and also preserve some
semblance of the original.
In that case, I could happily biff the front plane.

A big EDF jet is difficult to land, especially at the proposed wing loading of around 35 oz/sq ft.


7) If I fitted two EDF units, it would get rather heavy. They are about 350g each.
The ones I have are only 2400g thrust each.

I would need to get some 3500g+ units of the same size, maybe 110A at 6S each??
that is about 2400w continuous each?


8) Also, the front UC is well back so the vertical unit would be too far back.

9) Other planes have the UC further forward, and swing forward to stow.
That clashes with my springing scheme.

10) The rear thrust unit would lose a lot of efficiency if I put a thrust diverter behind it,
and two of those units would be unbalanced relative to the cog.

11) It would be unstable in roll when hovering, without separated side vents and extra variable nozzles,
under gyro control.

The harrier gets away with it because of the high wing, and side vents higher than the cog.

12) I don't want it to look like a Harrier , or an F35.

13) adding an extra vertical EDF unit would block the forward air intake.

14) a possibility is to have two EDF units oriented along the fuselage, with center thrust diverters and extra side vents, like the harrier,
- Air inlets would be rather complicated.

15) Another possibility is to have a really powerful EDF well forward, and put the battery towards the rear.
The tailpipe is quite a bit smaller than the fuselage diameter.

Then I could use thrust diverters and swivel nozzles, and conceal them under the mid-wing.
I will hove a look for high-power 90mm units.
Last edited by Owen_bern; Sep 21, 2021 at 09:08 PM.
Sep 21, 2021, 09:17 PM
Registered User
Coupez's Avatar
Quote:
Originally Posted by Owen_bern
6) My absolute ideal would be to have the whole thing be totally VTOL and EDF, but I can't think of a way to do that and also preserve some
semblance of the original.
Perhaps that's because the original wasn't a VTOL?

Form follows function....

Maybe you should start by doing some research on the original Ye-8. Why did it have canards?
Sep 21, 2021, 09:30 PM
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Thread OP
Quote:
Originally Posted by Coupez
Perhaps that's because the original wasn't a VTOL?

Form follows function....

Maybe you should start by doing some research on the original Ye-8. Why did it have canards?
Maybe I should just discard the canards and make my own design that
has a similar look, then revise it for VTOL use.
- better use of resources.
I just want "The Look", not to be true to scale.
Sep 21, 2021, 10:06 PM
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Coupez's Avatar
If you want a realistic VTOL model, maybe start by copying a successful full-scale VTOL design? A Mach 2 jet fighter that didn't even have short field capability (much less VTOL) is unlikely to be a good starting point.

Or take a successful VTOL model airplane design, and "MiG-ify" it in some manner...

But if you simply MUST have a STOL/VTOL jet fighter, you could always design a scale JATO unit...
Sep 21, 2021, 10:30 PM
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Thread OP
Quote:
Originally Posted by Coupez View Post
If you want a realistic VTOL model, maybe start by copying a successful full-scale VTOL design? A Mach 2 jet fighter that didn't even have short field capability (much less VTOL) is unlikely to be a good starting point.

Or take a successful VTOL model airplane design, and "MiG-ify" it in some manner...

But if you simply MUST have a STOL/VTOL jet fighter, you could always design a scale JATO unit...
1) A humungous EDF , well forward mounted, plus harrier-style side/underneath vents.
This could be a good point to start.

The F-35 layout is doubling up on fan units, plus I like the underslung intake rather than side intakes.
The intake could be extended forward a bit, as on the Crusader.


2) some kind of gyro-balance-venting system.

3) -It doesn't matter if it looks like a Mach 2 jet- it will only go about 60mph flat out, anyway.

I need some feedback on 100mm units, compatible motors, that don't cost the earth. $550 US is too expensive! (Hacker).

I can get a 4kgf 6S unit for $122nz or $87 us, so that is my starting benchmark.

I am trying not to use 2x edf units, as I like the narrow single-engine look (or motor, in this case).

This is only a spec-gathering exercise at present, as I have plenty to do already.
Sep 22, 2021, 07:22 AM
AndyKunz's Avatar
There are some excellent YouTube videos of people who have developed EDF VTOL models.

One is a really nice F-35 chassis.

Andy
Sep 22, 2021, 03:27 PM
An itch?. Scratch build.
eflightray's Avatar
Your projects are always way out of any of my concepts, but occasionally fun to read.

My 'jet', I designed and built just to prove to myself I could get it to fly. Twin EDP (Electric Ducted Props), 2.1kg flying, 3s Lipo.

It's totally not what you want, but if only you could finish just one of your many concepts and get it flying, perhaps people may just start posting in your many threads.

I wont bother posting in any of your threads again until I see a video of one of your builds actually flying.

.

Mig Cat Hand (1 min 55 sec)
Sep 22, 2021, 05:20 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by Coupez
............................

1) Wild Enthusiasm
2) Disillusionment
3) Total Failure
4) Search for the Guilty
5) Punish the Innocent
6) Promote the Uninvolved
.............................
I got a laugh out of this! Partly due to it's relevance. I am tempted to print out a copy to remind myself and pin on the wall of my shed..............

Quote:
Originally Posted by eflightray
............................................
............. if only you could finish just one of your many concepts and get it flying, perhaps people may just start posting in your many threads.
I wont bother posting in any of your threads again until I see a video of one of your builds actually flying.
...............................
Sep 22, 2021, 05:55 PM
Registered User
Thread OP
Quote:
Originally Posted by Jim.Thompson
I got a laugh out of this! Partly due to it's relevance. I am tempted to print out a copy to remind myself and pin on the wall of my shed..............



Does my Foamy count?
It is not exactly standard, and it is ready to go.
I just need some good weather.
Sep 22, 2021, 08:31 PM
Registered User
Thread OP
{quote]
Originally Posted by eflightray

if only you could finish just one of your many concepts and get it flying, perhaps people may just start posting in your many threads.
I wont bother posting in any of your threads again until I see a video of one of your builds actually flying.
[/quote]

Is this the opinion of every member of RCGroups?
If this is the case, I may as well stop posting entirely.
I am asking for information that I have not got.

If no-one is going to answer, why should I ask, or say anything at all?

Why should I even bother to post my videos here?

It is difficult to take a video and fly at the same time!

I cannot do that, unless I have some fancy camera setup, or can take a video telemetry feed from a model airplane.
Sep 22, 2021, 09:01 PM
Registered User
Coupez's Avatar
Quote:
Originally Posted by Owen_bern
It is difficult to take a video and fly at the same time!
Here's one I did:

Dr1 Takeoffs Landings (5 min 1 sec)


The camera is on a swiveling mount, controlled by a servo.

You start the camera before takeoff. You shut it off after landing.

To avoid boring people to death, you edit out the parts not relevant to your subject.


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