VTOL Jets. Is the Wheesley too underpowered or is it just me?

[ajburges]

I am trying to build a "research jet" for Kerbin. It needs to be able to comfortably complete 2 survey type contracts anywhere and return home. I really like the landing site control VTOLs gave me in .90 so I'm trying to include that to. Atmospheric effects lead mo to believe a cargo/service bay to hold the VTOL jets in flight is an important consideration.

My issue is that the Wheesley engine just doesn't seem to have the thrust needed for (efficient) VTOL. I'm needing near 5:1 Wheesley to Whiplash ratio to get better than unity vertical TWR and that only allows about 550 units of fuel per Whiplash. Those numbers don't seem to work for circumnavigation with scenic detours. At least not without making a monster craft that would be better referred to as a blimp. The Whiplash engine looks to have a better TWR, but it won't fit into a Mk2 cargo bay without clipping out the top and/or bottom.

Anyone have design tips for VTOL that I'm overlooking? I remember a 3:2 Wheesley to Whiplash ratio working in .90. Were the Wheesley engines just nerfed that badly? I'm thinking I may be better off using flaps for STOL for my research jet.

Edit:

Found my answer: PEBKAC

The designs I was exploring had emptied the nacelle tanks as I was exploring fuel loads or CoM migration. Since I had already found a reliable atmospheric setting for TWR in KER I was using that to judge lift thrust, but since KER doesn't properly account for jet fuel routing, it thought they had no fuel! Real hard to get good thrust when you forget to run more than half of your engines.

I should go sit in the corner now.

Edited June 9, 2015 by ajburges

[MarvinKitFox]

Your jet is manned, right?

Simply lug an engineer along, and use parachutes for pinpoint safe landings.

Then uncrate your engineer, repack all the chutes.

Unless the local terrain slope is ludicrous (>30 degrees), you will be able to take-off normally.

I find this to be much more mass and cost effective than lugging engines for true VTOL.

And it uses a lot less fuel.

And yes, the Wheesley basic jet IS too underpowered.

Under the new rules the jet engines are very much weaker at very low speeds.

[NathanKell]

Jet engines were incredibly powerful in .90; this was so they had enough power to overcome the soup. The side effect was it made VTOL kinda trivial. In 1.0, with the soup gone, jets got rebalanced. That makes VTOL hard, although I hasten to point out far from impossible, you just need to build lighter.

[pincushionman]

The behavior of all jets got changed (yes, nerfed, but that's not the whole story) in 1.0. Yes, the Wheasley has a lot less oomph now. And the component CoM is moved too, making things even harder (for vtol, that is).

[WOODY01]

I am guessing that with a VTOL the air flow through the intakes is reduced which reduces the thrust the engine can provide. I could be wrong but this may also be an issue you are facing with the new jet performance changes.

[Coga19000]

Woody makes a good point ;try getting some Intakes facing upwards.

Otherwise, yes, the Jets are nerfed. Well, more balanced than nerfed, but yeah, VTOL is a bit more sensible now.

[ajburges]

I know my way around jet engines mechanics enough to know when intake air is an issue. Did have done fun with asymmetric lift jet flameouts on an early, overly optimistic build earlier though.

Problem is jet thrust is primarily a function of velocity and altitude. Even with unlimited air, the Wheesley simply does not have much power for its weight especially at the low speed VTOL engines normally run at.

Didn't even consider chutes for my jet. It would be lighter, but VTOL gives a touch more control and a bit more style. Flaps and airbrakes can handle any stretch of 500 m.

Maybe I should just start looking at rockets and suicide burns for VTOL performance. I was reluctant to try that before because jet VTOL was so forgiving, but I don't think I can get good VTOL performance in a transcontinental jet.

[Jouni]

Problem is jet thrust is primarily a function of velocity and altitude. Even with unlimited air, the Wheesley simply does not have much power for its weight especially at the low speed VTOL engines normally run at.

Real high-powered jet engines have TWR 7 to 8 with afterburner off. The Wheesley provides a bit over 104 kN for 1.5 tonnes of mass at the launchpad, so it feels about right.

[Wanderfound]

Considered a turbojet tailsitter? They're trickier to build and fly than a conventional cargobay/Wheesley VTOL, but there's a huge saving in dead mass. As well as ditching the cargo bay and surplus jets, the VTOL ability also allows you to get away with minimal wing surface.