Is this a totally bonkers idea?

[Bob Moore]

Just wondering if this is feasible. I have an old Stan Yeo Peppi trainer. (That I learned on.) Plus a spare Wot 4 wing. The Peppi has a lot of dihedral and only a 25 engine, plus it weighs a ton so is slow to get off the ground unless there's a good headwind.

The Wot and Peppi wings are both about 700 gms weight, but the Wot wing is about 25% greater surface area, plus no dihedral.

If can mount the Wot wing so that the incidence angles are the same say zero zero. And I get the CoG right is there any reason why this shouldn't fly? I guess it would also be wise to increase the area of the tailplane too. (I've got some corex kicking about.)


Why do I want to do it?

1. I think it will be fun to try it.

and

2. With a bigger wing area it should get off the ground easier.


3 . It might be more fun to fly.


Any advice from home designers/builders most welcome.


Pics. Peppi with Peppi wing. Wot 4 wing. One on top of the other. And side elevation with both.

 

 

 

PS The Wot wing needs a little repair. It was from one that committed suicide. But I still have another lovely electrified one!

Edited By Bob Moore on 24/05/2012 21:46:14

[Allan Bennett]

Oh bother ... why do I lose what I've just written when I go back to check one of the photos before posting?

Anyway, what I was saying is there's no reason why it shouldn't fly, providing you can mount the Wot 4 wing securely and get the c of g right. I've seen one or two frankenstein models at our flying field, and there's no hard-and-fast rules about what connects the flying bits together.

I don't know enough about aerodynamics to advise on whether or not you need to increase the tail size. You've got ailerons, so plenty of control, so I would try it as it is first.

[Peter Miller]

No need to increase the tailplane. Most model have far bigger tails than needed, Some of my aerobatic designs are using tails of 15% of teh wing area. No problems at all.

Set the wing at 0-0, make sure it is firmly attached and you will have a nice model. The extra wing area will reduce the wing loading which can only be good.

[Bob Moore]

Thanks for the responses, very encouraging. I like to experiment a bit.

I think I'll call it Frankenstein too!

[Bob Moore]

Oh well, after all my calcs, and careful mods to fit this wing I test flew the other day. (Well not exactly FLEW.)

After spending ages trying to get the normally reliable SC25 running I screamed (well not exactly screamed) across the strip and it was very reluctant to get off the ground. So much for wing loading calcs and all that stuff!

Might try it with a 40 engine (if I can be bothered.)

[Mark Powell 2]

The two wings will have twice the drag, thus a whole lot, at a high angle of attack, as in 'sat still on the ground' or 'running along with the the tailwheel down'. I hope you got the tail up properly by pushing the stick forward to allow it to accelerate before trying to taking off. Only then pull the stick back.. My underpowered and heavy Auster model is like that, as is a real one! Both will stay on the ground all day if you let them.

Sorry if you know all that, I don't want to teach you to suck eggs. But so many modellers 'heave and hope' because they never have a bloody minded instructor sat next to them to make them do it properly.

[Steve Hargreaves - Moderator]

Might it be a wing incidence issue Bob........? You need to get a certain angle of attack before the wing will generate any lift. With the model sat on the ground is the wing at a positive angle of attack to the oncoming airflow.....if not you will have a heck of a job making it take off.....

[Bob Moore]

Only one wing! Just the Wottie wing is on the model. Pic was intended to show comparative wing areas.

But I think your'e right about the tail dragging. It's always been a problem and I have been advised before that you need to get the tail up and let speed build. Plus on my strip I was slightly up slope.

My other model leccy converted Wot4 and Kerfuffle take off with no probs tail dragging. The Wot has a little wheel though of course.

 

I should give it another chance with a headwind to assist as well. The original Peppi was a pig to get off unless there was a headwind to help.

 

PS The motor is way out front in order to achieve the CoG.

 

Edited By Bob Moore on 16/08/2012 11:59:38

[Bob Moore]

I set the tail and main spar incidence at zero zero, but do you mean angle to the ground? I do think it was question of ground speed. It did begin to lift at one point but it was the end of the strip and I aborted. I think it will go with perserverence!

[Rich too]

I would try hand launching it then. It should fly with the Wot4 wing.

I have an old trainer (20 plus year old Hi Boy) that weighs a ton and I wouldn't expect it to take off from the ground. I always hand launch it and in high winds it flys great.

Go for it!!

Rich

[Bob Moore]

Now that does sound like a good idea.

[Clifford Stone]

The Wot 4 wing is as near as 'dam it' a full cymetrical section, (some say there is a hint of under camber?) needs a bit of angle of attack to get it to lift? I suspect the trainer wing is semi cymetrical at least, what with 'over weight', I think it might be a bit underpowered.

I prefer a 3" wheel on our grass strip to overcome rolling drag too. Full cymetricals need a bit of angle and brut force to get them flying?

More power, bigger prop diamiter, what pitch are you using, fine pitch prop might help, say from 6" down to 5"? But that might present a problem, the weight requires highter flying speed . . . sounds like, round and round and . . . untill you disapear where the sun dont shine?????

A full blown Wot 4 flies OK on a 40, even better on a hot 40 or a sports 60 or 60 four stroke . . . if you get the point?   We might be talking of 4-5lbs here? non lifting section, a 25 motor . . . nah

CJS

Edited By Clifford Stone on 16/08/2012 14:47:06

Edited By Clifford Stone on 16/08/2012 14:53:31

[Bob Moore]

Hi Clifford, you're right, the trainer wing was quite a different profile, as you say a Wottie wing is symetrical. I realise now just a bigger wing area isn't the whole story. Interesting learning experience.

I've got a spare 40 kicking about, I'll bung that on and will have plenty of brute force to get it off the ground! My Wot 4 flew very well on an Irving 40 but I've since converted it to leccy. It will climb vertically with the leccy setup I came up with (and they said it would be underpowered!)

[Aky208]

I wouldn't be worried about the frankenstien thing. i have a model with the rear end of a cessna 172 and the front end of a 109... certainly gets a few looks at the field, especially as i haven't bothered to change the paint job!

Yellow - DPM - Pure White!!!!

It flies though and does well. great for learning those aeros you practiced on the sim for real.

[NigelH]

Posted by Aky208 on 16/08/2012 21:55:39:

I wouldn't be worried about the frankenstien thing. i have a model with the rear end of a cessna 172 and the front end of a 109... certainly gets a few looks at the field, especially as i haven't bothered to change the paint job!

Cool. Makes me think of this

[Biggles' Elder Brother - Moderator]

I think the probelm we have here might be a combination of three things; marginal power, wing section and incidence angle.

The trainer almost certainly has a flat bottom wing section - Clark-Y style. This section will produce lots of lift at zero incidence - in fact it will even produce lift at a small negative incidence! So the trainer set up at 0-0 was fine.

But the WOT4 profile is - as folks have said - damn near symmetrical. This will not produce significant lift unless its at 2-3 degrees incidence.

Now you might get away with it all if you had more power - but even then to be honest its less than ideal. Put a shim between the leading edge and the wing mounting to give it a bit of positive incidence and I think it will be fine.

BEB

[Rich too]

Great video. Do what the boys did and stick some foam packing in there and hand launch the thing!

Rich

[Bob Moore]

It looks to me as though my ARTF Wot 4 is zero zero, but I have taken out packing at the back end of the wing on Frankenstein to give it a 'bit' of positive on the main spar as you suggest BEB. Quite hard to judge really. I put a dowel on the rear, level the model on a work top and try and judge the main spar angle by eye?

As this is a Frankenstein model and the tail is relatively small and close to the main spar I assume incidence will have even more effect?

Anyhow, I'll try again with it like this and the 25, and on a day with a bit of headwind assistance.

Am I right in thinking if you put negative incidence on the main spar then even with up elevator you may not get the nose to come up in flight? Especially when you give even more power? I rebuilt an old Wot 4 that had the fusi smashed in half beneath the main spar and when I maidened it after the rebuild it took off but I couldn't get the nose to come up? It ended up a real bin bag job after that crash! All the electrics were working when I reassembled so it was the only explanation I could think of?

[Clifford Stone]

Bob, the underlying issue might be weight, the Wot 4 wing has no inherent lift without angle of attack, which = drag! It might fly away from a hand launch? but getting it to do anything on a 25, being, as you sugested, a bit weighty??? What does it weigh ready to fly? . . . . . .

CJS

[Bob Moore]

OK, so here's Frankenstein MK2 with mods as suggested.

SC 40 instead of the SC25 that barely dragged it across the strip. Because it's heavier I didn't need the wooden block spacers to push the engine out front to achieve a good CoG.

I have given the main wing a few degs of pos attack. Plus as the tail is quite close to the main wing I've increased the area of the elevator (extended it) by a good 50%. I was worried that with too much AoA if the model climber excessively the elevator might not have enough authority to level the flight. I assume if that is the case, ie excessive climb, reducing power will help? Does that make sense to others with more knowledge please!

It's about 2.4 kgs now.

Anyhow with just a tiny bit of lead n the tail the CoG is perfect and I think it might fly (and be flyable more importantly?)

Any further comments most welcome.

(It will have more bands holding wing of course.)

[Clifford Stone]

Bob, I think its got every chance now, carfull prop choice with a flying weight of 5.25lb -5.5lb dont forget the fuel weighs

CJS

[Bob Moore]

Thanks. I use 10 x 6 on my 40's usually. That's what I have on it at the moment.

[Clifford Stone]

Mmm, thats what I had in mind, fairly standard choice, I might play with props but use the 10x6 as a referance. Been a long time Bob since I did any work with ic so listen to curent advice.

CJS

Edited By Clifford Stone on 24/08/2012 20:15:42

[Bob Moore]

Just wanted to report that I maidened Frankenstein last week and although it struggled to get off on the longish wet grass , it flew very well. I took the advice to add some positive incidence to the main spar but I'm not sure it needed it (or maybe I gave it too much) Initially I had trouble trimming the elevator enough to get it to stop climbing, got there in the end though. Second flight it flew exceedingly well. I've now dropped the incidence angle a bit.

3 dead sticks (cos since almost chopping my thumb off I'm wary of tuning IC) but all of them landed on the strip. Once I'd richened the carb a bit it was great.

Someone described it as stubby looking (short fusi compared to main spar) and with short fusi and the increased size elevator it looped very tightly. Rolled horrible though. It just goes to show you can (if you check a few callcs and CoG) get away with any monstrosity!

Edited By Bob Moore on 29/10/2012 16:10:39